Abstract<\/h3>\n
Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of mortality worldwide, and its clinical manifestations represent the late-stage culmination of a biological trajectory that begins decades earlier \u2014 often in fetal life and certainly by the second decade. This review integrates structural vascular biology, hemodynamics, lipid causality, inflammation, sex-specific phenotypes, neurodegeneration, and lifestyle reversibility into a unified framework for understanding subclinical atherosclerosis as an active, progressive, and modifiable disease. We examine regional heterogeneity in arterial wall architecture and the role of vasa vasorum, the divergence of large-artery atherosclerosis from cerebral small vessel disease, the hemodynamic determinants of plaque localization, and the longitudinal evidence from PDAY, Bogalusa, CARDIA, MESA, and the FELIC fetal series that anchor disease initiation in early life. We synthesize Mendelian-randomization, population-genetic, and intervention-trial evidence establishing apolipoprotein B\u2013containing lipoproteins as the necessary causal driver of atherogenesis, and we situate Lp(a), inflammation, clonal hematopoiesis, endothelial dysfunction, microvascular rarefaction, and arterial stiffening within this framework. We close with the imaging and biomarker tools that allow detection during the long pre-clinical window, the sex-specific phenotypes that have historically been under-recognized, and the trial evidence \u2014 most prominently the Lifestyle Heart Trial, the Esselstyn case series, STARS, and the IVUS-documented statin and PCSK9-inhibitor regression trials (REVERSAL, ASTEROID, SATURN, GLAGOV, PACMAN-AMI, HUYGENS) \u2014 supporting the conclusion that subclinical atherosclerosis is, when addressed early and aggressively, a reversible disease.<\/p>\n
Keywords<\/h4>\n
Subclinical atherosclerosis; apolipoprotein B; lipoprotein(a); endothelial dysfunction; vasa vasorum; cerebral small vessel disease; coronary artery calcium; pulse wave velocity; plaque regression; whole-food plant-based diet.<\/p>\n
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1. Introduction<\/h3>\n
The emergence of clinical ASCVD is the culmination of a silent, multi-decadal biological trajectory that often begins in the second decade of life \u2014 and in the case of fetuses exposed to maternal hypercholesterolemia, even before birth. Subclinical atherosclerosis refers to the presence of structural arterial wall alterations \u2014 including intimal thickening, lipoprotein retention, foam-cell accumulation, and early plaque formation \u2014 that precede overt symptomatic manifestations such as angina, myocardial infarction, ischemic stroke, peripheral claudication, or vascular dementia. This silent progression is governed by a tightly coupled interplay between hemodynamic forces, structural variations in the arterial wall, lipoprotein flux, immune activation, and metabolic stress.<\/p>\n
Although traditionally framed as a disease of senescence, longitudinal cohort studies and autopsy data have fundamentally shifted the focus toward young adults and adolescents, revealing that subtle everyday functional deficits \u2014 ranging from diminished cognitive processing speed to impaired renal and erectile reserve \u2014 emerge long before the traditional clinical thresholds for diagnosis are met. The most rigorous formulation of this life-course concept is the cumulative-exposure or \u201ccholesterol-years\u201d model, in which the integral of plasma apoB-particle concentration over time predicts both the timing and severity of clinical events [7], [9].<\/p>\n
This review provides a comprehensive synthesis of the pathophysiology, anatomical distribution, and functional consequences of subclinical vascular disease across the human arterial tree, with particular attention to (i) the divergent biology of large-artery atherosclerosis and cerebral small vessel disease; (ii) the causal centrality of apoB-containing lipoproteins and the contribution of Lp(a), inflammation, and clonal hematopoiesis; (iii) sex-specific phenotypes; (iv) emerging detection modalities; and (v) the trial-based evidence that subclinical disease is reversible when addressed early and aggressively.<\/p>\n
2. Apolipoprotein B\u2013Containing Lipoproteins as the Necessary Causal Driver<\/h3>\n2.1 The Mendelian-Randomization Synthesis<\/h4>\n
Mendelian randomization (MR) provides one of the most rigorous forms of causal inference available outside randomized controlled trials. By exploiting the random allocation of alleles at conception, MR studies estimate the lifelong effect of a genetically determined exposure unconfounded by reverse causation, lifestyle covariates, or measurement error. Ference and colleagues analyzed 50 polymorphisms across nine LDL-related genes in 312,321 participants and established that each 1 mmol\/L (\u224838.7 mg\/dL) genetically lower LDL-C confers a relative risk reduction of approximately 54.5 percent for coronary heart disease \u2014 an effect roughly three times larger per unit LDL than that of statins initiated in mid-life [1].<\/p>\n
The dose-response relationship is log-linear with no detectable threshold, supporting a cumulative-exposure model. A second MR study using polymorphisms in PCSK9, HMGCR, and NPC1L1 demonstrated that risk reduction tracks closely with the magnitude and duration of LDL-C lowering, supporting the conclusion that integrated lifetime exposure to apoB-containing lipoproteins is a central determinant of atherogenesis, while the specific molecular pathway through which LDL-C is lowered is less important for ASCVD risk reduction [3]. A 2017 European Atherosclerosis Society Consensus Statement reviewed more than 200 genetic, prospective epidemiologic, and randomized intervention studies and concluded that LDL fulfills the Bradford Hill criteria for causality in ASCVD [4], and the 2020 EAS update extended this conclusion to apoB-containing lipoproteins generally [19].<\/p>\n
2.2 ApoB as the Unifying Particle<\/h4>\n
Each major atherogenic lipoprotein particle \u2014 VLDL, IDL, LDL, Lp(a), and chylomicron remnants \u2014 carries a single apolipoprotein B molecule: apoB-100 for hepatically derived particles and apoB-48 for intestinal remnants. ApoB therefore counts atherogenic particles, whereas LDL-C measures a cargo whose ratio to the carrier varies with metabolic state. In the UK Biobank analysis of 389,529 participants, apoB was the dominant predictor of myocardial infarction; LDL-C and non-HDL-C lost statistical significance after adjustment for apoB [5]. In states of discordance \u2014 where LDL-C is normal but particle number is high, as in metabolic syndrome and insulin resistance \u2014 apoB unmasks substantial atherogenic risk that an LDL-C-only strategy would miss [6].<\/p>\n
2.3 Cumulative Exposure and the \u201cCholesterol-Years\u201d Concept<\/h4>\n
The cumulative-exposure model treats ASCVD risk as a function of the integral of plasma LDL-C concentration over time, analogous to \u201cpack-years\u201d for tobacco. Several analyses support a dose\u2013time relationship between LDL-C exposure and ASCVD events. The \u201cthreshold\u201d for clinically apparent disease in men has been described in some analyses as approximately 5,000 mg\/dL\u00b7years \u2014 for example, LDL 125 mg\/dL \u00d7 40 years, corresponding to age ~50 in modern Western populations \u2014 but the exact LDL-year value at which clinical disease emerges is model-dependent and should be presented as illustrative rather than as a universal biological cutoff [7], [9].<\/p>\n
The \u201cLDL plaque-years\u201d framework reframes prevention quantitatively around cumulative burden. For example, lifelong LDL of 70 mg\/dL \u00d7 80 years yields \u22485,600 mg\/dL\u00b7years; LDL 130 mg\/dL \u00d7 50 years yields \u22486,500 mg\/dL\u00b7years; and untreated heterozygous familial hypercholesterolemia patients with LDL of 250 mg\/dL exceed common illustrative thresholds by their early thirties. These calculations are useful for communicating dose\u2013time biology and for explaining why untreated heterozygous FH carries a high lifetime CHD risk, but they should not be presented as validated individual-risk thresholds [7], [8], [9].<\/p>\n
Category<\/strong><\/td>\n| Cumulative LDL exposure<\/strong><\/td>\n | Approximate trajectory<\/strong><\/td>\n | Illustrative lifetime CHD risk<\/strong><\/td>\n<\/tr>\n<\/thead>\n\n | Low<\/td>\n | <5,000 mg\/dL\u00b7yr<\/td>\n | LDL 70 \u00d7 70 yr<\/td>\n | <5%<\/td>\n<\/tr>\n | Intermediate<\/td>\n | 5,000\u20138,000 mg\/dL\u00b7yr<\/td>\n | LDL 100 \u00d7 60 yr<\/td>\n | 10\u201320%<\/td>\n<\/tr>\n | High<\/td>\n | 8,000\u201312,000 mg\/dL\u00b7yr<\/td>\n | LDL 130 \u00d7 65 yr<\/td>\n | 30\u201350%<\/td>\n<\/tr>\n | Very high<\/td>\n | >12,000 mg\/dL\u00b7yr<\/td>\n | LDL 190 \u00d7 65 yr (HeFH)<\/td>\n | >50% by age 60<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n | Table 1.<\/em><\/strong> Illustrative cumulative LDL-cholesterol exposure categories and approximate lifetime coronary heart disease risk. Adapted from Ference et al. and Domanski et al. [7], [8], [9]. These categories are illustrative communication aids, not guideline-validated individual-risk thresholds.<\/em><\/p>\n Kaplan and colleagues examined CAC scores in 705 Tsimane forager-horticulturalists of the Bolivian Amazon aged 40 to 94. The mean LDL-C was 91 mg\/dL, and 85 percent of adults aged 40 and older had a CAC of zero, compared with approximately 50 percent of US adults of similar age in MESA. Sixty-five percent of those over 75 had a CAC of zero \u2014 the lowest level of coronary atherosclerosis ever measured in any population \u2014 and only 8 percent had a CAC \u2265100, versus more than 50 percent in age-matched US populations [10].<\/p>\n This natural experiment supports the conclusion that maintaining relatively low LDL-C across the life course, combined with high physical activity and minimal smoking, is associated with very low prevalence of coronary calcification. It should not be framed as proving that LDL-C \u226490 mg\/dL virtually eliminates coronary atherosclerosis, because the Tsimane phenotype reflects multiple lifelong exposures and not LDL-C in isolation. The Hadza of Tanzania have been described as a physically active hunter-gatherer population with favorable cardiometabolic features in available studies, but direct CAC imaging has not been performed in this group; conclusions about the absence of clinical coronary disease in the Hadza are therefore inferential rather than direct [11].<\/p>\n Cohen and colleagues identified naturally occurring loss-of-function mutations in PCSK9 (R46L, Y142X, C679X) that lower LDL by 15\u201340 percent across the life course. Carriers of selected variants exhibited large reductions in CHD events, with the most striking estimates \u2014 including reductions approaching 88 percent for some variants \u2014 reflecting effect sizes that vary by variant and ancestry [12]. Such effect sizes far exceed what any pharmacologic intervention initiated in mid-life can achieve. Similarly, homozygous loss-of-function variants in ANGPTL3 produce hypobetalipoproteinemia with very low LDL and triglycerides; epidemiologic series describe markedly reduced ASCVD risk and favorable lipid profiles in such carriers, although event rates have not been quantified in randomized cohorts [13].<\/p>\n These genetic experiments establish a useful boundary condition: when lifelong apoB-particle burden is genetically low, atherosclerosis appears markedly suppressed even without pharmacologic intervention. Pharmacologic mimicry of these phenotypes \u2014 through PCSK9 monoclonal antibodies, siRNA agents, and ANGPTL3 inhibitors \u2014 has demonstrated additive event reduction on top of statin therapy. Analyses of FOURIER and the FOURIER open-label extension support progressively lower event rates among patients achieving very low LDL, including LDL <20 mg\/dL, without an excess safety signal over available follow-up [18].<\/p>\n Endothelial transcytosis of LDL into the intima is concentration-dependent, and proteoglycan-mediated retention \u2014 the response-to-retention paradigm of Tabas, Williams, and Bor\u00e9n \u2014 becomes less likely as apoB-particle flux falls [83]. Newborns have LDL-C \u224830 mg\/dL, and atherosclerotic lesions are not typically detected at this stage; this should be interpreted as evidence that very low lifelong LDL-C is incompatible with the early steps of atherogenesis on a population scale, rather than as a claim that atherosclerosis is biologically impossible at any single LDL-C value. Cohorts with lifelong LDL <70 mg\/dL (PCSK9 LOF, ANGPTL3 LOF, treated FH) demonstrate marked reductions in event rates, with IVUS-documented plaque regression at on-treatment LDL <60 mg\/dL across the REVERSAL, ASTEROID, SATURN, and GLAGOV trials [14], [15], [16], [17].<\/p>\n FOURIER-OLE extended evolocumab follow-up for a median of approximately 5 years and reported continued event reduction at on-treatment LDL <20 mg\/dL with no excess safety signal over available follow-up [18]. A formal demonstration of dose-response without plateau at these very low LDL levels has not been firmly established, but available data are consistent with continued benefit and no offsetting toxicity through the lowest LDL achieved in trial populations to date.<\/p>\n A small group of authors \u2014 most prominently Ravnskov, Diamond, and Kendrick \u2014 have argued that LDL is non-causal, citing observational studies in elderly populations in which LDL appears non-predictive (the so-called \u201clipid paradox\u201d). The standard rebuttals are well established. First, reverse causality dominates in late life: chronic illness, malabsorption, and frailty lower LDL, biasing the LDL\u2013mortality association in cross-sectional analyses. Second, survivor bias selects for genetically protected individuals among those reaching age 80 with high LDL. Third, attenuation of relative risk with age does not imply attenuation of absolute risk; the absolute event rate increases dramatically with age. Fourth, the genetic and pharmacologic evidence is mutually corroborative across approximately twenty independent lines of investigation, satisfying triangulation criteria for causality [4], [6], [19]. The skeptic position rests almost entirely on observational data while ignoring the convergent genetic and randomized-trial evidence.<\/p>\n In large-caliber systemic arteries, the metabolic demands of the thick wall exceed the capacity for simple oxygen diffusion from the lumen. The \u201ccritical depth\u201d is defined as the physiological limit of oxygen and nutrient diffusion from luminal blood, established by Geiringer at approximately 0.5 mm (\u2248500 \u03bcm), or roughly 29\u201330 lamellar units of the medial wall [78], [79]. Each lamellar unit consists of an elastic lamina and its associated layer of smooth-muscle cells and extracellular matrix, approximately 15 \u03bcm thick. Wall segments thicker than this threshold require an intrinsic microvascular network \u2014 the vasa vasorum \u2014 to maintain viability of the outer media and adventitia.<\/p>\n Vasa vasorum are categorized into vasa vasorum interna, which arise directly from the arterial lumen, and vasa vasorum externa, which originate from remote branches and penetrate the adventitia. Geiringer\u2019s investigations established that vasa vasorum are abundant in the adventitia and outer third of the media, while the inner \u22480.5 mm (\u224830 lamellar units) of the wall remains avascular and is supplied solely by luminal diffusion [79]. When the wall thickens because of atherosclerotic plaque or hypertensive hyperplasia, the diffusion distance increases, generating a hypoxic environment in the deeper layers. Hypoxia triggers HIF-1\u03b1\u2013dependent angiogenic signaling, leading to proliferation of vasa vasorum that can penetrate the internal elastic lamina and enter the plaque itself, where they serve both as conduits for inflammatory cells and as fragile sources of intraplaque hemorrhage.<\/p>\n The intracranial vasculature presents a unique architectural profile compared with the systemic circulation. Healthy intracranial arteries are characterized by a thinner tunica media, less abundant adventitia, and a relative paucity of elastic fibers; many lack a well-defined external elastic lamina. A primary distinguishing feature is that intracranial vessels are bathed in nutrient-rich cerebrospinal fluid, which provides metabolic support through external diffusion and partly compensates for the relative absence of vasa vasorum early in life.<\/p>\n Modern autopsy and imaging studies have refined the historical view that vasa vasorum are absent in the brain. In one autopsy series of 50 cases, vasa vasorum were identified in 72 percent of patients, localized primarily in the tunica adventitia. Their distribution is markedly non-uniform: vasa vasorum are more frequently found in proximal segments \u2014 the vertebral arteries, basilar artery, and intracranial portion of the internal carotid artery \u2014 than in distal segments such as the middle cerebral or anterior cerebral arteries. Although atherosclerosis can occur in the absence of vasa vasorum, their development is strongly associated with the progression of intracranial disease: in the intracranial vertebral artery, the presence of adventitial vasa vasorum correlates with greater plaque load, denser intraplaque calcification, and more severe luminal stenosis.<\/p>\n Table 2.<\/em><\/strong> Comparative architecture of arterial wall thickness, vasa vasorum density, and nutritional source across the systemic and cerebral circulations. EEL, external elastic lamina; ICA, internal carotid artery; VA, vertebral artery; MCA, middle cerebral artery; ACA, anterior cerebral artery; VV, vasa vasorum; CSF, cerebrospinal fluid.<\/em><\/p>\n The focal nature of atherosclerosis is dictated by the interaction between blood flow and arterial geometry. The endothelium serves as a mechanosensor, translating physical stress into biological signaling through primary cilia, integrins, glycocalyx-mediated mechanotransduction, and ion channels (notably Piezo1 and TRPV4). In straight arterial segments, flow is laminar, generating high, unidirectional wall shear stress (typically 1\u20137 Pa, or 10\u201370 dyn\/cm\u00b2). This environment maintains an atheroresistant endothelial phenotype characterized by sustained activation of endothelial nitric oxide synthase (eNOS), phosphorylation of KLF2 and KLF4 transcription factors, and suppression of NF-\u03baB signaling, with the result that nitric oxide production is high, leukocyte adhesion is suppressed, and intimal permeability remains low [85].<\/p>\n In contrast, at branch points, bifurcations, and areas of high curvature, flow becomes \u201cdisturbed.\u201d These atheroprone zones experience low time-averaged wall shear stress (often <0.4 Pa) and high oscillatory shear index, with the direction of frictional force reversing during the cardiac cycle. In disturbed-flow regions, the endothelium undergoes a phenotypic switch: tight junctions loosen, allowing increased transcytosis of LDL into the intima; expression of VCAM-1, ICAM-1, E-selectin, and MCP-1 captures circulating monocytes and T-cells; reactive oxygen species generation rises through NADPH oxidase activation; and the protective KLF2\/eNOS axis is suppressed.<\/p>\n The seminal computational fluid dynamic study by Ku and colleagues at the human carotid bifurcation demonstrated tight spatial concordance between low-shear regions and intimal thickening \u2014 the founding empirical study of the hemodynamic theory of atherogenesis [71]. This pattern recurs at every branching point of the arterial tree: the proximal segments of the LAD and LCx, the carotid bulb, the abdominal aortic bifurcation, and the renal artery ostia all exhibit this geometry-dependent vulnerability.<\/p>\n Once retained in the intima, LDL undergoes oxidative modification by myeloperoxidase, lipoxygenase, and reactive oxygen species. Oxidized LDL is recognized by scavenger receptors (CD36, SR-A) on resident and newly recruited macrophages, which internalize it and become foam cells. In early subclinical lesions, foam-cell death is balanced by efferocytosis \u2014 the clearance of apoptotic cells by neighboring macrophages \u2014 but as the microenvironment becomes increasingly toxic, efferocytosis fails, apoptotic and necrotic debris accumulates, and a necrotic core forms. Vascular smooth-muscle cells (VSMCs) simultaneously switch from a contractile to a synthetic phenotype, migrating from the media into the intima where they secrete a collagen-rich fibrous cap that initially stabilizes the lesion. The balance between cap-thickening repair and core-expanding inflammation defines whether a plaque remains stable or progresses to vulnerability [82], [83], [84].<\/p>\n Endothelial dysfunction precedes any structural lesion detectable by carotid intima-media thickness (CIMT), coronary artery calcium scoring, or angiography. It is functional, dynamic, and partially reversible \u2014 and therefore represents the earliest practical window for primordial intervention.<\/p>\n Brachial flow-mediated dilation (FMD), measured by ultrasound after a 5-minute forearm cuff occlusion, quantifies endothelium-dependent (largely nitric-oxide-mediated) vasodilation. Lower FMD is associated with increased cardiovascular risk, but FMD is protocol-dependent and no single universal cutoff applies across laboratories; values below approximately 5\u20137 percent are commonly treated as abnormal in research contexts. In the Multi-Ethnic Study of Atherosclerosis, FMD added independent prognostic information beyond Framingham risk and CIMT [33]. FMD is impaired in subjects with even mildly elevated LDL, insulin resistance, untreated hypertension, or chronic exposure to particulate air pollution.<\/p>\n The reactive hyperemia index (RHI), measured non-invasively by digital plethysmography (EndoPAT), reflects microvascular endothelial function in the fingertip after reactive hyperemia. An RHI threshold around 1.67 has been used to identify coronary endothelial dysfunction or early coronary atherosclerosis in selected cohorts; sensitivity and specificity depend on the population and the reference standard [34]. RHI is operator-independent, has good reproducibility, and has been used as an outcome in lifestyle and pharmacologic intervention trials.<\/p>\n The endothelial glycocalyx is a 0.5\u20133 \u03bcm gel-like surface layer composed of proteoglycans (heparan sulfate, chondroitin sulfate), glycoproteins (syndecan-1), and adsorbed plasma proteins. It modulates LDL transcytosis, leukocyte rolling, and shear-stress mechanotransduction. Glycocalyx degradation \u2014 driven by oxidized LDL, hyperglycemia, TNF-\u03b1, and reactive oxygen species \u2014 exposes adhesion molecules and increases intimal lipoprotein flux. Glycocalyx thinning, detectable by sublingual sidestream dark-field imaging and by elevated plasma syndecan-1 and hyaluronan, occurs before measurable FMD impairment and is among the earliest detectable abnormalities in subclinical disease [35], [36].<\/p>\n Coronary flow reserve (CFR) below 2.0 by positron emission tomography, below 2.5 by transthoracic Doppler, or below 2.0 by cardiac magnetic resonance is independently predictive of cardiovascular events even in the absence of obstructive epicardial disease. Microvascular endothelial dysfunction can occur with normal coronary angiograms, providing the substrate for the syndrome of ischemia with non-obstructive coronary arteries (INOCA), discussed in Section 8 [37].<\/p>\n Atherosclerosis is a systemic but non-uniform disease, favoring specific anatomical sites characterized by complex geometry and disturbed flow. Precise mapping across vascular beds reveals the predictable, geometry-dependent pattern of plaque localization.<\/p>\n In the neck, the carotid bifurcation and the proximal internal carotid artery are the primary sites for early plaque development, owing to flow separation, recirculation, and low oscillatory shear at the carotid bulb. Within the cranium, disease is most frequently observed in the intracranial ICA (carotid siphon) and the proximal segments of the major branches of the circle of Willis. Autopsy series indicate that intracranial atherosclerosis lags extracranial disease by approximately 15 to 20 years; stable lesions are more common in the ICA, while more dynamic, progressive lesions are found in the MCA, ACA, and posterior cerebral arteries.<\/p>\n Importantly, intracranial atherosclerotic disease (ICAD) accounts for approximately 9 percent of strokes in white populations but 30 to 50 percent of strokes in East Asian, Black, and Hispanic populations [73], [74]. This racial disparity persists after adjustment for traditional risk factors, suggesting underlying genetic and structural contributions. The SAMMPRIS trial established medical management as superior to stenting for symptomatic ICAD with \u226570 percent stenosis [73].<\/p>\n Coronary atherosclerosis typically initiates in the proximal segments of the epicardial arteries, with the proximal LAD showing the highest plaque prevalence \u2014 particularly within the first 40 mm \u2014 owing to its acute take-off angle and the high flow disturbance generated at the bifurcations of diagonal and septal branches. Bifurcations of the LAD with diagonals, the LCx with obtuse marginals, and the RCA with the posterior descending artery all show predilection at the lateral, low-shear walls of the side branches.<\/p>\n The Pathobiological Determinants of Atherosclerosis in Youth (PDAY) study confirmed that fatty streaks and raised lesions are present in the coronaries of individuals as young as 15\u201334 years. In the aorta, a clear gradient of susceptibility exists: the abdominal aorta is more severely affected than the thoracic aorta, with the highest concentration of plaques occurring in the distal abdominal aorta and at the aortic bifurcation.<\/p>\n Atherosclerotic renal artery stenosis (ARAS) accounts for approximately 90 percent of renal artery stenosis cases and primarily involves the renal artery ostia and the proximal 2 cm of the main renal artery. By contrast, fibromuscular dysplasia, which accounts for the remaining \u224810 percent, typically affects the middle and distal segments or intrarenal branches. Mesenteric artery disease \u2014 involving the celiac trunk and the superior and inferior mesenteric arteries \u2014 also occurs most often at the aortic origins, where flow turbulence is greatest.<\/p>\n Peripheral arterial disease follows a predictable progression from elastic to muscular arteries. Atherosclerosis typically appears first in the suprainguinal elastic arteries (aorta and iliacs) before progressing to the infrainguinal muscular arteries (femoral, popliteal, and tibial). Pelvic vascular disease frequently involves the internal pudendal artery (IPA), where significant stenosis or occlusion has been documented in approximately 54 percent of men screened for coronary artery disease \u2014 an extraordinary prevalence reflecting the small caliber and shared risk-factor exposure of these vessels. The distal branches of the IPA, including the cavernosal arteries, are uniquely susceptible because of their small diameter (0.5\u20131 mm), as discussed in Section 9.<\/p>\n The distinction between classic atherosclerosis and cerebral small vessel disease (cSVD) is fundamental to understanding the divergent mechanisms of vascular injury across the human body.<\/p>\n The penetrating arterioles (40\u2013200 \u03bcm in diameter) that supply the deep brain \u2014 basal ganglia, thalamus, internal capsule, and periventricular white matter \u2014 do not exhibit the eccentric, lipid-rich plaques typical of large-vessel atherosclerosis. Three structural and biological factors explain this divergence:<\/p>\n First, structural simplicity: these vessels lack the multi-layered lamellar structure and the well-defined internal and external elastic laminae that support classic plaque architecture. Second, blood\u2013brain barrier specialization: the endothelial cells of these vessels are specialized components of the neurovascular unit, with tight junctions formed by claudin-5, occludin, and ZO-1, supported by pericytes, astrocyte end-feet, and a unique metabolic environment that differs fundamentally from systemic vessels. Third, the absence of vasa vasorum: these vessels rely entirely on luminal and external diffusion and do not possess the intrinsic microvascular network that can be co-opted for plaque nourishment in larger arteries.<\/p>\n Instead of classic atherosclerosis, penetrating arterioles develop a distinct set of pathologies collectively termed cerebral small vessel disease. Lipohyalinosis, originally characterized by C. Miller Fisher as \u201csegmental arteriolar wall disorganization,\u201d involves accumulation of waxy, glassy lipid and protein aggregates within the vessel wall, fibrinoid necrosis of medial smooth-muscle cells, and luminal narrowing. It is driven primarily by chronic hypertension and is the principal substrate of lacunar infarcts in the lenticulostriate, thalamoperforating, and pontine penetrating arterioles.<\/p>\n Hyperplastic arteriolosclerosis involves concentric \u201conion-skin\u201d thickening of the wall due to smooth-muscle proliferation and basement-membrane duplication and is more characteristic of malignant or accelerated hypertension. Microatheroma refers to occlusive lesions in larger penetrating vessels (200\u2013800 \u03bcm); these share some features with atherosclerosis (foam cells, lipid retention) but typically occur at the proximal origin of the perforator and reflect the spillover of large-artery disease into branches.<\/p>\n Cerebral amyloid angiopathy (CAA) involves progressive deposition of \u03b2-amyloid (A\u03b2) \u2014 predominantly A\u03b240 and to a lesser extent A\u03b242 \u2014 in the media and adventitia of cortical and leptomeningeal arterioles (typically <2 mm in caliber). CAA is independent of hypertension and is a major contributor to lobar microbleeds, superficial siderosis, and convexity subarachnoid hemorrhage [23], [24]. Pathologically advanced cSVD frequently shows a transition from endothelial dysfunction to BBB disruption: failure of the BBB allows toxic serum components \u2014 fibrinogen, IgG, complement \u2014 to extravasate into the brain, triggering perivascular inflammation, \u201cforced dilatation,\u201d and connective-tissue accumulation that leaves downstream vessels vulnerable to high-pressure damage.<\/p>\n The earliest documented atherosclerotic lesion in humans is fetal. Napoli and colleagues, in the FELIC (Fate of Early Lesions in Children) study, demonstrated that fatty streaks form in the aortic intima of fetuses, with intimal accumulation of LDL and its oxidation preceding monocyte recruitment. Fetal fatty-streak formation was greatly enhanced by maternal hypercholesterolemia during pregnancy, suggesting that the maternal lipid environment programs offspring vascular vulnerability decades before clinical disease [52].<\/p>\n These observations transformed the conception of atherosclerosis from a disease of mid-life to a life-course disease initiated in utero, with the prenatal environment establishing the trajectory of subsequent intimal LDL accumulation.<\/p>\n The PDAY study performed standardized autopsies on more than 3,000 individuals aged 15\u201334 who died of trauma, cataloguing the prevalence and extent of fatty streaks and raised lesions in the coronary arteries and aorta. Fatty streaks were present in essentially all aortas and in the coronaries of a majority by the late twenties; raised lesions appeared in approximately 20 percent of men aged 30\u201334. The study developed the PDAY risk score, which demonstrated that smoking, non-HDL cholesterol, and hypertension in youth are strong predictors of advanced calcification decades later.<\/p>\n The Bogalusa Heart Study extended these observations to a longitudinal community-based cohort, demonstrating that risk factors measured at ages 5\u201317 predict subclinical morbidity in adulthood. Berenson and colleagues, in autopsy data from 204 youths aged 2\u201339 who died of trauma, documented aortic fatty streaks in approximately half of children aged 2\u201315, rising to nearly 100 percent by age 21; coronary fatty streaks in 8 percent of children aged 2\u201315 and 69 percent of those aged 26\u201339; and coronary raised lesions in 3 percent of those aged 6\u201315 and 30 percent of those aged 26\u201339. The number of cardiovascular risk factors directly correlated with the extent of both fatty streaks and fibrous plaques [53].<\/p>\n The Coronary Artery Risk Development in Young Adults (CARDIA) study followed 5,115 participants from ages 18\u201330 across more than 35 years of follow-up. Several findings have shaped contemporary preventive cardiology. First, sustained exposure to even modestly elevated LDL-C and blood pressure during the twenties and thirties contributes to ASCVD risk independently of risk levels later in life. Second, by Year 25 (mean age 50), approximately 27.7 percent of participants had detectable coronary artery calcium and approximately 53 percent had abdominal aortic calcium. Third, participants who adopted healthy habits \u2014 diet, exercise, smoking cessation, weight maintenance \u2014 during young adulthood had significantly less subclinical disease in middle age, with absolute reductions in event risk substantially larger than what mid-life intervention can achieve.<\/p>\n Heterozygous familial hypercholesterolemia (HeFH; prevalence \u22481:250) presents with LDL-C of 190\u2013400 mg\/dL from birth, the result of pathogenic variants in LDLR, APOB, or rarely PCSK9. Untreated, HeFH carries an approximately 50 percent CHD risk by age 50 in men. CIMT is significantly elevated in HeFH children by age 8\u201310. The landmark trial by Wiegman and colleagues demonstrated that statin initiation between ages 8 and 18 normalized CIMT progression compared with peers [54]. The 20-year follow-up of that cohort (Luirink and colleagues) showed that early statin treatment reduced MI risk by approximately 75 percent compared with untreated parents \u2014 among the strongest demonstrations in any field of medicine that early, sustained intervention can fundamentally alter a genetically determined disease trajectory [55].<\/p>\n Subclinical atherosclerosis is often described as \u201csilent,\u201d yet rigorous research demonstrates measurable functional deficits well before traditional clinical thresholds are reached.<\/p>\n In the CARDIA cohort, higher levels of CAC and abdominal aortic calcium at ages 43\u201355 were significantly associated with worse scores on tests of psychomotor speed (Digit Symbol Substitution Test), sustained attention, and verbal memory. This relationship persists after adjustment for age, sex, education, and traditional risk factors, suggesting that advanced calcified lesions in mid-life reflect a lifetime of vascular stress that also affects the brain microvasculature and white-matter integrity. Intelligence at age 19 has been found to inversely correlate with carotid plaque status at age 60, an association likely mediated by the long-term influence of cognitive ability on socioeconomic status, healthcare access, and adherence to healthy lifestyles.<\/p>\n The relationship between physical activity and subclinical disease is bidirectional. High cardiorespiratory fitness in young adulthood protects against the development of CAC and increased CIMT 15 to 25 years later. Conversely, the presence of subclinical atherosclerosis subtly impairs exercise tolerance: subclinical disease reduces vascular reserve \u2014 the ability of arteries to dilate and increase flow during peak exertion \u2014 contributing to earlier fatigue and reduced V\u0307O\u2082 peak. Individuals with low cardiorespiratory fitness are two to three times more likely to die prematurely from ASCVD even when matched for traditional risk factors.<\/p>\n Extreme sleep durations (<6 or >8 hours) and poor subjective sleep quality are associated with increased CAC prevalence and higher pulse-wave velocity. Sleep-duration irregularity \u2014 variation greater than 120 minutes across a week \u2014 is linked to a 33 percent higher prevalence of high CAC burden. Circadian misalignment drives chronic low-grade inflammation and sympathetic nervous system activation, predisposing individuals to subclinical atherosclerosis. Although direct causal links to mood disorders are still emerging, the combination of vascular-driven fatigue, impaired sleep, and chronic inflammation contributes to reduced quality of life.<\/p>\n Erectile dysfunction (ED) is often the first clinical manifestation of systemic vascular disease. The internal pudendal artery (1\u20132 mm) and its cavernosal branches (0.5\u20131 mm) are markedly smaller than the proximal coronary arteries (3\u20134 mm), the internal carotid (5\u20137 mm), or the femoral artery (6\u20138 mm). According to the artery-size hypothesis articulated by Montorsi and colleagues, equivalent atherosclerotic plaque burden produces hemodynamically significant stenosis in small vessels first, so the cavernosal circulation reaches the threshold for symptomatic compromise years before the coronary circulation does [80].<\/p>\n Men with vascular ED have a markedly higher prevalence of subclinical CAD; the COBRA trial reported that vasculogenic ED preceded the symptomatic onset of CAD by a mean of approximately 3 years (range 2 to 5 years) [80]. This temporal relationship makes ED a clinically actionable sentinel: every man presenting with vasculogenic ED warrants formal cardiovascular risk assessment, often including CAC scoring, lipid profiling with apoB and Lp(a), and consideration of antiplatelet and lipid-lowering therapy.<\/p>\n In young, non-hypertensive adults, renal function (estimated glomerular filtration rate, eGFR) is independently associated with arterial stiffness measured by brachial-ankle pulse wave velocity (baPWV). Mediation analysis indicates that eGFR mediates the relationship between both systolic and diastolic blood pressure and subclinical atherosclerosis, particularly in males, suggesting that elevated blood pressure influences cardiovascular health partly through early reduction in renal reserve, with secondary endocrine and oxidative changes that accelerate atherosclerotic progression.<\/p>\n Cardiovascular disease has historically been studied in male-predominant cohorts, and the recognition of distinct female phenotypes has lagged the corresponding biology by decades. Several mechanisms produce sex-specific differences in subclinical disease.<\/p>\n Women are disproportionately affected by coronary microvascular dysfunction (CMD), which is the dominant mechanism of ischemia in 50\u201360 percent of women with angina and non-obstructive coronary arteries. The Women\u2019s Ischemia Syndrome Evaluation (WISE) study established CMD as a major sex-specific subclinical phenotype with prognostic implications equivalent to obstructive CAD [38].<\/p>\n Ischemia with non-obstructive coronary arteries (INOCA) refers to symptomatic ischemia in the presence of <50 percent coronary stenosis; approximately 70 percent of patients are women. MI with non-obstructive coronary arteries (MINOCA) refers to MI with <50 percent stenosis, accounts for 5\u201315 percent of all MIs, and is two to three times more common in women than men. Mechanisms include microvascular dysfunction, plaque erosion (rather than rupture), epicardial vasospasm, and spontaneous coronary artery dissection. Diagnosis requires invasive coronary functional testing \u2014 acetylcholine provocation, adenosine-induced flow reserve, and intravascular imaging \u2014 modalities still inconsistently available outside specialized centers [39].<\/p>\n Adverse pregnancy outcomes \u2014 preeclampsia, gestational hypertension, gestational diabetes, preterm delivery \u2014 confer a 2- to 4-fold lifetime increase in cardiovascular events. Pregnancy is now recognized as a \u201cphysiological stress test\u201d that exposes latent vascular and metabolic dysfunction; preeclampsia in particular is associated with elevated CIMT, increased PWV, and altered endothelial function years to decades after the index pregnancy [40]. A 2020 American Heart Association scientific statement recommends incorporating pregnancy history into routine cardiovascular risk assessment for women.<\/p>\n The Study of Women\u2019s Health Across the Nation (SWAN) demonstrated accelerated CIMT progression and arterial stiffening across the late perimenopause and early postmenopause, with median CIMT progression approximately doubling in the year before to year after the final menstrual period. Estrogen withdrawal removes its tonic effects on lipid metabolism, endothelial function, and vascular smooth-muscle phenotype. The SWAN findings have driven the recognition that the menopause transition is a vulnerable window for primary prevention rather than a static post-event endpoint [41].<\/p>\n Spontaneous coronary artery dissection (SCAD) is responsible for a disproportionate share of acute coronary syndromes in young women: more than 90 percent of SCAD cases occur in women, particularly in the peripartum period and in those aged 40\u201355. Approximately half of SCAD patients have coexisting fibromuscular dysplasia. SCAD is non-atherosclerotic, but its identification has reshaped the differential diagnosis of MI in young women [42].<\/p>\n Table 3.<\/em><\/strong> Female-predominant subclinical and clinical phenotypes of cardiovascular disease. CFR, coronary flow reserve; OCT, optical coherence tomography; IVUS, intravascular ultrasound; SCAD, spontaneous coronary artery dissection; CIMT, carotid intima-media thickness; PWV, pulse wave velocity.<\/em><\/p>\n The historical binary distinction between vascular dementia and Alzheimer\u2019s disease (AD) is increasingly untenable. Vascular factors \u2014 both large-vessel atherosclerosis and small vessel disease \u2014 are now recognized as central contributors to the development and trajectory of AD pathology, and a substantial fraction of clinically diagnosed AD has mixed vascular and neurodegenerative pathology at autopsy.<\/p>\n Severe atherosclerosis of the circle of Willis is significantly more prevalent in AD brains than in age-matched controls. Reduced cerebral perfusion \u2014 \u201coligemia\u201d rather than frank ischemia \u2014 facilitates accumulation of \u03b2-amyloid (A\u03b2) by both increasing its production and impairing its clearance through perivascular and glymphatic pathways. A\u03b2 itself is vasoactive, producing constriction of cerebral arteries and further aggravating the oligemic state in a self-reinforcing cycle of neurovascular decay.<\/p>\n Recent work has documented that systemic atherosclerosis is associated with amyloid and tau pathology mediated by BBB dysfunction in the hippocampus [23]. Vascular damage produces endothelial and smooth-muscle apoptosis, exacerbating cerebral amyloid angiopathy and promoting perivascular tau accumulation. Macrophages within atherosclerotic plaques can process platelet-derived amyloid precursor protein into A\u03b240 and A\u03b242, providing a direct biological link between systemic ApoB-driven atherosclerosis and neurodegenerative disease.<\/p>\n High-sensitivity C-reactive protein (hs-CRP) integrates upstream interleukin-6 signaling and has been validated as an independent predictor of vascular events in JUPITER and multiple subsequent trials [28]. In statin-treated patients, \u201cresidual inflammatory risk\u201d \u2014 defined as hs-CRP \u22652 mg\/L despite LDL <70 mg\/dL \u2014 remains a powerful predictor of recurrent events; in many secondary-prevention cohorts, residual inflammatory risk now exceeds residual cholesterol risk in magnitude [29].<\/p>\n The Canakinumab Anti-Inflammatory Thrombosis Outcome Study (CANTOS) provided randomized evidence that targeting inflammation in the absence of any LDL-lowering effect can reduce cardiovascular events. Canakinumab \u2014 a monoclonal antibody against IL-1\u03b2 \u2014 reduced the primary major adverse cardiovascular events (MACE) endpoint by approximately 15 percent at the 150 mg dose without lowering LDL-C, with the greatest benefit in those with the largest reduction in IL-6 [30]. The trial supports the conclusion that inflammatory signaling contributes to recurrent events through mechanisms not fully captured by LDL-C reduction alone, and it identifies the NLRP3 inflammasome \u2192 IL-1\u03b2 \u2192 IL-6 \u2192 CRP axis as a clinically tractable therapeutic target. Atherosclerosis is now best framed as a disease driven by parallel and partially independent processes \u2014 apoB-particle retention and innate immune activation \u2014 both of which can be addressed for optimal event reduction.<\/p>\n Clonal hematopoiesis of indeterminate potential (CHIP) refers to the presence of acquired somatic mutations in hematopoietic stem cells \u2014 most commonly in DNMT3A, TET2, ASXL1, and JAK2 \u2014 without overt hematologic malignancy. CHIP is detectable in fewer than 1 percent of young adults but in approximately 10 percent of individuals over age 70. Jaiswal and colleagues demonstrated that CHIP carriers have approximately 2-fold increased risk of coronary heart disease and earlier MI (by 5\u201310 years) [31]. Mechanistically, mutant myeloid cells secrete excess IL-1\u03b2 and IL-6, accelerating vascular inflammation; consistent with this, several studies have reported greater subclinical atherosclerotic burden or progression in CHIP carriers, although effect sizes vary by mutation, cohort, and imaging endpoint. CHIP represents a major emerging axis of cardiovascular risk that is not detected by traditional risk-factor measurement.<\/p>\n The neutrophil-to-lymphocyte ratio (NLR), readily computable from any complete blood count, is an inexpensive marker of systemic inflammation. Reviews and meta-analyses associate higher NLR with increased cardiovascular risk and accelerated subclinical atherosclerosis, but cutoffs vary by population and clinical setting; the commonly cited NLR threshold of >3.0 is best presented as a research-context cutoff rather than as a guideline-endorsed diagnostic threshold [32].<\/p>\n Lipoprotein(a) [Lp(a)] is predominantly genetically determined by variation at the LPA locus on chromosome 6q26-q27. The Copenhagen General Population Study demonstrated a stepwise dose-response relationship between LPA kringle IV-2 copy-number variation and myocardial infarction risk; Mendelian-randomization studies have confirmed causality with effect sizes greater per unit than those of LDL-C [20], [21], [27].<\/p>\n Lp(a) consists of an LDL-like particle (one apoB-100 molecule, cholesterol, phospholipids) covalently linked via a single disulfide bond between Cys4326 of apoB and Cys4057 of apolipoprotein(a) [apo(a)]. Apo(a) is structurally homologous to plasminogen, possessing 10 kringle IV repeats and a single kringle V domain, but lacks proteolytic activity. Multiple mechanisms of pathogenicity converge:<\/p>\n First, Lp(a) is the principal carrier of oxidized phospholipids on apoB lipoproteins; approximately 85 percent of plasma OxPL associated with apoB are bound to Lp(a). OxPL activate endothelial cells, monocytes, and platelets [22]. Second, the kringle IV-10 lysine-binding site of apo(a) competes with plasminogen for fibrin, impairing fibrinolysis and rendering Lp(a) prothrombotic [23]. Third, Lp(a) induces IL-6, IL-8, and MCP-1 expression in vascular cells, contributing to the pro-inflammatory phenotype. Fourth, Lp(a) is associated with calcific aortic valve stenosis, with Mendelian-randomization data establishing a causal link [24].<\/p>\n Approximately 20 percent of the global population has Lp(a) >50 mg\/dL (>125 nmol\/L), the threshold above which cardiovascular risk is materially elevated; approximately 1 in 5 individuals with premature MI have elevated Lp(a) [25], [26]. Distribution differs by ancestry: highest in West Africans, intermediate in Europeans, and lowest in East Asians.<\/p>\n Elevated Lp(a) should be treated as an independent causal risk factor that can coexist with absent, mild, or advanced coronary artery calcium. In MESA and the Dallas Heart Study, elevated Lp(a) and CAC were each independently associated with ASCVD risk, and participants with both elevated Lp(a) and CAC \u2265100 had the highest observed risk [87]. Once-in-a-lifetime Lp(a) measurement is now supported by contemporary EAS\/ESC guidance and by the 2024 National Lipid Association focused update on Lp(a) in clinical practice [25], [86]. Subclinical disease evaluation should include consideration of Lp(a)-driven phenotypes when CAC, plaque burden, aortic valve calcification, or events occur out of proportion to traditional risk factors. Emerging therapeutics \u2014 antisense oligonucleotides (pelacarsen) and siRNA agents targeting LPA mRNA \u2014 can lower Lp(a) by 80\u201398 percent and are currently in phase 3 cardiovascular outcome trials.<\/p>\n Capillary rarefaction \u2014 a reduction in the number of perfused capillaries per unit tissue volume \u2014 is a hallmark of essential hypertension and precedes the development of fixed BP elevation. Antonios and colleagues demonstrated approximately 14 percent reduction in dorsal-finger capillary density in hypertensives versus normotensives [56]. Rarefaction increases peripheral vascular resistance and contributes to organ dysfunction across the kidneys, retina, and heart.<\/p>\n Coronary microvascular dysfunction (CMD) affects approximately half of women with chest pain and a quarter of men. Diagnosis is based on PET-derived coronary flow reserve <2.0 or invasively measured index of microcirculatory resistance (IMR) >25. The long-term prognosis is sobering: even in the absence of obstructive epicardial disease, CMD doubles the risk of MACE. The ISCHEMIA trial substudy and the WISE-CVD continuation studies have established CMD as a clinically important entity [37], [38].<\/p>\n Retinal arteriolar narrowing \u2014 quantified by lower arteriole-to-venule ratio on fundoscopy or by optical coherence tomography angiography \u2014 predicts cardiovascular events independently of traditional risk factors. The retina is the only vascular bed directly visualizable in vivo and provides a non-invasive read-out of systemic microvascular health [57].<\/p>\n Glagov and colleagues, in 1987, demonstrated that human coronary arteries undergo a two-stage remodeling process in response to plaque accumulation. In the compensatory phase, while plaque area remains less than approximately 40 percent of the area bounded by the internal elastic lamina, the total vessel area increases such that the lumen area remains approximately constant or even slightly increases [77]. This outward remodeling allows substantial plaque burden to coexist with no restriction of resting blood flow \u2014 and thus no symptoms and no abnormality on standard luminography. Only in the encroachment phase, when plaque area exceeds \u224840 percent of the IEL area, does the vessel become unable to expand further, and the lumen begins to narrow rapidly. This biology explains why coronary angiography systematically underestimates plaque burden and why a single negative coronary angiogram does not exclude clinically meaningful subclinical disease.<\/p>\n The cardiovascular system possesses substantial functional reserve. In the coronary and renal beds, resting blood flow is typically maintained until stenosis exceeds 60\u201370 percent of luminal diameter; in skeletal-muscle beds, flow reserves are even higher. Slow progression of subclinical disease often allows the development of collateral circulation \u2014 alternative vascular pathways that bypass obstructive lesions \u2014 further masking the primary disease and contributing to the asymptomatic course.<\/p>\n Not all plaques are equally dangerous. The Virmani\u2013Stary classification defined the \u201cthin-cap fibroatheroma\u201d (TCFA) as a plaque with a fibrous cap thinner than 65 \u03bcm overlying a large lipid-rich necrotic core (>10 percent of plaque volume), with macrophage infiltration of the cap, intraplaque hemorrhage, and positive (outward) remodeling [81], [82]. The PROSPECT trial used three-vessel intravascular ultrasound with virtual histology to characterize 697 patients with acute coronary syndromes and showed that culprit lesions of subsequent events were predominantly TCFAs with plaque burden \u226570 percent and minimum lumen area \u22644.0 mm\u00b2 [72].<\/p>\n Table 4.<\/em><\/strong> Vulnerable-plaque features and approximate hazard ratios for major adverse cardiovascular events. Ranges synthesized from PROSPECT, ICONIC, SCOT-HEART, and CRISP-CT data [63], [64], [65], [67], [72].<\/em><\/p>\n Vascular calcification is not monolithic. Two distinct phenotypes coexist with different mechanisms, prognoses, and therapeutic implications. Intimal calcification occurs within lipid-rich atherosclerotic plaques and is the substrate quantified by the Agatston-method coronary artery calcium score; it is apoB-driven and predicts events. Medial calcification, classically described by M\u00f6nckeberg, occurs within the tunica media independently of lipids and is driven by osteogenic transdifferentiation of vascular smooth-muscle cells; it is most prominent in chronic kidney disease, type 2 diabetes, and aging [58].<\/p>\n Aortic elastin has a half-life of approximately 70 years and is essentially non-renewable in the adult vasculature. Cyclic mechanical stress, MMP-2\/MMP-9 activity, and elastolytic enzymes such as cathepsins S and K cause elastin fragmentation that directly increases pulse wave velocity. Loss of elastin recoil shifts mechanical load to collagen \u2014 a fiber 100 to 1000 times stiffer than elastin \u2014 producing the progressive aortic stiffening characteristic of vascular aging.<\/p>\n In CKD, hyperphosphatemia drives VSMC apoptosis and matrix-vesicle release, which nucleate hydroxyapatite crystals. Pyrophosphate, fetuin-A, and matrix Gla protein are physiological inhibitors that decline with age and CKD. Klotho \u2014 a transmembrane and circulating protein expressed in kidney that serves as co-receptor for FGF23 \u2014 declines with age, and klotho deficiency directly accelerates vascular calcification. FGF23 itself is independently associated with left ventricular hypertrophy, vascular calcification, and cardiovascular mortality [58], [59].<\/p>\n Pulse wave velocity, the gold-standard non-invasive measure of arterial stiffness, has well-established prognostic thresholds. Carotid\u2013femoral PWV (cfPWV) is the gold standard; the European Society of Hypertension\/European Society of Cardiology consensus document established >10 m\/s as the threshold for elevated cardiovascular risk after correction for the actual travel path of the pulse wave [60]. Brachial\u2013ankle PWV (baPWV), used predominantly in East Asian populations, has a commonly applied threshold of >14 m\/s for elevated risk and >18 m\/s for severe arterial stiffening [61].<\/p>\n Augmentation index (AIx@75), derived from pulse wave analysis, reflects wave reflection from the periphery and is elevated in arterial stiffening; thresholds >25 percent are associated with elevated risk [60]. The cardio-ankle vascular index (CAVI) is a BP-independent measure of arterial stiffness, with values >9 indicating elevated risk [62].<\/p>\n Non-contrast CT scanning of the heart with computation of the Agatston score remains the most widely validated single test for subclinical coronary disease. CAC of zero in asymptomatic adults confers a very low 10-year MACE risk, and CAC is incorporated as a risk-decision tool in the 2018 AHA\/ACC cholesterol guidelines and the 2019 ESC\/EAS dyslipidemia guidelines. The radiation dose is approximately 1 mSv, comparable to natural background exposure for several months.<\/p>\n Coronary CT angiography (CCTA) provides whole-vessel morphology and the ability to identify high-risk plaque features that are not captured by Agatston scoring alone. These features include low-attenuation plaque (<30 HU within plaque, indicating lipid-rich necrotic core; HR for MACE \u22482.5\u20133.0); positive remodeling (remodeling index \u22651.10); spotty calcification; and the napkin-ring sign (central low attenuation surrounded by a rim of higher attenuation; HR \u22485) [63], [64].<\/p>\n The five-year SCOT-HEART analysis demonstrated that CCTA-guided management reduced fatal and non-fatal MI by 41 percent compared with standard care in symptomatic patients [65]. The PROMISE and CONFIRM2 registries have provided further prognostic validation.<\/p>\n Pericoronary fat attenuation index (FAI), introduced by Antonopoulos and colleagues, quantifies CT attenuation of pericoronary adipose tissue within a defined radial zone. Inflamed coronary segments shift the local adipose attenuation toward less negative HU values (less lipid, more aqueous), reflecting paracrine inflammatory signaling between coronary plaque and surrounding fat [66]. The CRISP-CT study demonstrated that elevated perivascular FAI predicts cardiac mortality independently of plaque burden, with the strongest signal observed for high FAI around the proximal right coronary artery [67]. FAI-derived metrics are now incorporated into commercial post-processing platforms; U.S. FDA clearance has been reported for some products in this family (e.g., CaRi-Plaque), while CaRi-Heart\/FAI-Score has regulatory clearance in selected non-U.S. markets and remains in evolving regulatory status in the United States, so specific labeling claims should be verified by product and date.<\/p>\n AI-enhanced and deep-learning quantitative coronary CT angiography (AI-QCT) \u2014 exemplified by the Cleerly and HeartFlow Plaque Analysis platforms \u2014 automates segmentation of total plaque volume; calcified, non-calcified, and low-attenuation components; remodeling indices; and pericoronary fat attenuation. A 2022 international multicenter study by Lin and colleagues validated a deep-learning CCTA pipeline against expert readers and demonstrated favorable reproducibility and prognostic performance for plaque, stenosis, and risk prediction [88]. AI-QCT methods are increasingly used clinically, but specific platform claims should be matched to platform-specific validation data.<\/p>\n High-resolution 3-Tesla vessel-wall MRI with black-blood sequences (DANTE-prepared T1, SPACE, MERGE) directly images the arterial wall, allowing differentiation of intracranial atherosclerosis (eccentric, peripheral enhancement) from vasculitis (concentric enhancement) and dissection (intramural hematoma). VW-MRI detects plaque before luminal narrowing and is particularly valuable in evaluating intracranial atherosclerotic disease [69].<\/p>\n Intravascular optical coherence tomography (OCT) provides 10-\u03bcm-resolution cross-sectional imaging of coronary plaques, capable of measuring fibrous cap thickness directly and identifying microcalcifications, plaque erosion, and intracoronary thrombus. OCT is the imaging modality of choice when characterizing plaque morphology in MINOCA and SCAD.<\/p>\n Contrast-enhanced ultrasound and super-resolution ultrasound localization microscopy (ULM) image vasa vasorum neovascularization within carotid plaques and detect microvascular rarefaction at micron-scale resolution, providing a functional read-out of plaque inflammation and tissue microcirculation [70].<\/p>\n Carotid intima-media thickness >0.9 mm (and focal IMT >1.5 mm defining plaque) on high-resolution B-mode ultrasound predicts cardiovascular events and is widely used in pediatric and FH research. Ankle-brachial index <0.9 indicates significant peripheral arterial disease and confers elevated cardiovascular risk irrespective of symptoms. Renal Doppler with peak systolic velocity >180\u2013200 cm\/s at the renal ostium and renal-aortic ratio >3.5 is the screening test of choice for renal artery stenosis.<\/p>\n Table 5.<\/em><\/strong> Preferred imaging and physiological modalities for detection of subclinical vascular disease across the arterial tree. CAC, coronary artery calcium; CCTA, coronary CT angiography; LAP, low-attenuation plaque; NRS, napkin-ring sign; PR, positive remodeling; FAI, pericoronary fat attenuation index; AI-QCT, AI-quantitative coronary CT; CIMT, carotid intima-media thickness; PWV, pulse wave velocity; FMD, flow-mediated dilation; RHI, reactive hyperemia index.<\/em><\/p>\n The chromosome 9p21.3 locus was identified by genome-wide association in 2007 as the first robustly replicated CHD susceptibility region. Each risk allele confers approximately 25 percent increased CHD risk, independent of all known traditional risk factors. The locus contains the long non-coding RNA ANRIL and lies adjacent to the CDKN2A\/CDKN2B tumor-suppressor genes; the proposed mechanism involves dysregulation of vascular smooth-muscle proliferation and senescence [75].<\/p>\n Familial hypercholesterolemia is caused by pathogenic variants in LDLR (>2,000 mutations described), APOB (R3500Q the canonical variant of familial defective apoB), or, rarely, gain-of-function variants in PCSK9. The prevalence of heterozygous FH is approximately 1 in 250 in most populations; homozygous FH is roughly 1 in 300,000. Loss-of-function variants in PCSK9 (R46L, Y142X, C679X) reduce LDL across the life course and confer 30\u201388 percent reductions in CHD [12].<\/p>\n Khera and colleagues constructed a polygenic risk score comprising 6.6 million variants and demonstrated that the top 8 percent of the population have a 3-fold increased CHD risk \u2014 an effect equivalent in magnitude to monogenic FH. Polygenic scores add incremental prognostic information beyond traditional risk factors and Mendelian variants and are increasingly being incorporated into multi-layered risk-stratification models [76].<\/p>\n A central question for the practicing clinician is whether subclinical atherosclerosis can be reversed once established. The available imaging-based randomized and case-series evidence supports the conclusion that, with sufficient reduction in apoB-particle exposure and inflammation, both functional and structural plaque regression is achievable.<\/p>\n The Lifestyle Heart Trial randomized 48 patients with angiographically documented CAD to a comprehensive lifestyle intervention or usual care. The intervention combined a whole-food plant-based (WFPB) diet (\u224810 percent of calories from fat), aerobic exercise, stress management with yoga and meditation, group support, and smoking cessation. Quantitative coronary angiography at 1 year showed mean percent diameter stenosis decreased from 40.0 percent to 37.8 percent in the experimental group versus an increase from 42.7 percent to 46.1 percent in controls (between-group p<0.001) [43]. At 5-year follow-up, the experimental group showed continued regression to 37.3 percent versus control progression to 51.9 percent, with approximately 2.5-fold fewer cardiac events in the intervention group [44]. The Lifestyle Heart Trial is among the best-known randomized lifestyle interventions to demonstrate angiographic regression of coronary atherosclerosis.<\/p>\n Esselstyn and colleagues prospectively followed 198 consecutive self-selected patients with established CAD who adopted an oil-free WFPB diet. Of these, 177 (89.4 percent) were adherent over a mean 3.7 years of follow-up. Adherent patients experienced a 0.6 percent recurrent event rate, while non-adherent patients experienced a 62 percent event rate, and several patients showed angiographically documented coronary regression. The principal limitations are well recognized: the absence of a concurrent control group, self-selected participants, adherence-related selection effects, and reliance on chart-based outcome ascertainment. The findings are best presented as supportive and hypothesis-generating, consistent with the intensive lifestyle-trial evidence above, rather than as proof that WFPB intervention is uniquely effective [45].<\/p>\n The St Thomas\u2019 Atherosclerosis Regression Study (STARS) randomized 90 men with CAD to usual care, a lipid-lowering diet, or diet plus cholestyramine. Quantitative angiography at 39 months showed regression in 38 percent of the diet group, 33 percent of the diet + drug group, and only 4 percent of usual-care patients, with progression in 15 percent, 12 percent, and 46 percent respectively [46]. The Heidelberg Trial (Schuler and colleagues) demonstrated, with a multifactorial intervention combining a low-fat diet and structured exercise, reduced angiographic progression and modest regression at 1 year [47].<\/p>\n Beginning with REVERSAL in 2004, intravascular ultrasound has provided high-resolution quantification of changes in percent atheroma volume (PAV) and total atheroma volume (TAV) in response to lipid-lowering therapy. The cumulative dataset establishes a clear dose\u2013response: progressively lower on-treatment LDL produces progressively greater plaque regression.<\/p>\n Table 6.<\/em><\/strong> Imaging-verified plaque regression trials, organized by intervention intensity and on-treatment LDL-C. PAV, percent atheroma volume; TAV, total atheroma volume; WFPB, whole-food plant-based [14], [15], [16], [17], [43], [44], [45], [46], [48], [49].<\/em><\/p>\n REVERSAL demonstrated essentially halted progression at LDL \u224879 mg\/dL with high-dose statin therapy [14]. ASTEROID was the first trial to demonstrate clear regression \u2014 PAV reduced by 0.98 percent and TAV reduced by 6.8 percent \u2014 at on-treatment LDL of 60.8 mg\/dL with rosuvastatin 40 mg [15]. SATURN extended the comparison to include atorvastatin 80 mg [16]. GLAGOV randomized 968 patients on optimized statin therapy to evolocumab or placebo and demonstrated PAV regression of 0.95 percent in the evolocumab arm at on-treatment LDL of 36.6 mg\/dL [17]. PACMAN-AMI, in patients post-acute MI, demonstrated PAV reduction of 2.13 percent and concurrent stabilization of plaque morphology \u2014 increased fibrous cap thickness, decreased lipid pool \u2014 at on-treatment LDL of 23.5 mg\/dL with alirocumab on top of high-intensity statin [48]. HUYGENS, using OCT to measure fibrous-cap thickness directly, demonstrated an increase of 42.7 \u03bcm at on-treatment LDL of 28.1 mg\/dL \u2014 converting many plaques from the TCFA to the thick-cap fibroatheroma classification [49].<\/p>\n The combined message of these trials is that plaque regression and stabilization have been repeatedly observed with intensive LDL-C lowering, especially when achieved LDL-C is well below 70 mg\/dL; the magnitude of regression varies by baseline plaque burden, imaging modality, achieved apoB\/LDL-C, and background therapy.<\/p>\n Once a vulnerable plaque has formed \u2014 with its necrotic core, thin fibrous cap, and positive remodeling \u2014 even aggressive therapy can reduce and stabilize risk but does not eliminate all residual events, even at very low achieved LDL-C [18]. Conversely, primordial prevention \u2014 preventing the first transcytosis\u2013retention event by maintaining low apoB exposure across the life course \u2014 more closely approximates the large lifetime benefit observed in genetically lower-LDL states. The operational implication is direct: start early, lower sufficiently, and sustain risk-factor control indefinitely.<\/p>\n Statin therapy has been observed to increase the volume of coronary calcium even while reducing event rates. This does not necessarily indicate harmful progression: statins can increase plaque calcium density (a marker associated with healing and stabilization) while reducing the lipid-rich, vulnerable component of plaque. Because the Agatston score weights calcium density (assigning higher scores to denser calcium), a stabilizing lesion may yield a higher Agatston score even as event risk falls. The CAC density and volume score, developed by Criqui and colleagues, addresses this paradox by demonstrating that, at any given total Agatston score, higher CAC density predicts fewer events [50], [51]. The clinical implication is that serial CAC scoring during statin therapy must be interpreted with reference to density and morphology, not the Agatston number alone.<\/p>\n Subclinical atherosclerosis is not a passive state of aging but an active, progressive biological syndrome with measurable consequences in early adulthood \u2014 and, increasingly, in childhood and even in utero. The body of evidence reviewed here supports several integrated conclusions.<\/p>\n First, atherogenesis is causally driven by apoB-containing lipoproteins. The convergence of Mendelian-randomization, familial-genetic, and randomized-trial evidence across approximately twenty independent lines of investigation establishes apoB causality with rigor unmatched in most areas of medicine. Risk is proportional to the integral of apoB-particle exposure over time. The corollary is that primordial prevention \u2014 maintaining low apoB across the life course \u2014 yields the largest possible event reduction.<\/p>\n Second, parallel non-lipid pathways amplify or modulate apoB-driven atherogenesis. Lp(a), inflammation (NLRP3 \u2192 IL-1\u03b2 \u2192 IL-6 \u2192 CRP), clonal hematopoiesis, hypertension, glycemic dysregulation, and arterial stiffening each contribute mechanistically distinct components of risk. Comprehensive prevention addresses all of these axes, not LDL alone.<\/p>\n Third, the divergence between large-artery atherosclerosis and cerebral small vessel disease reflects a fundamental structural and hemodynamic threshold. Vessel-wall complexity and the presence of vasa vasorum permit lipid-core plaque formation; the simpler architecture of penetrating arterioles favors lipohyalinosis, microatheroma, and amyloid angiopathy instead. Each pathology has its own risk-factor profile and optimal therapeutic approach.<\/p>\n Fourth, the \u201cclinical silence\u201d of subclinical disease is maintained by adaptive remodeling \u2014 the Glagov phenomenon \u2014 and by physiological reserve in flow capacity. This silence is regularly punctured by subtle functional decays in cognitive processing speed, sleep regularity, exercise tolerance, and erectile function. These functional signals, properly recognized, provide a clinically actionable window for intervention years before the first overt event.<\/p>\n Fifth, sex-specific phenotypes \u2014 INOCA, MINOCA, SCAD, preeclampsia legacy effects, menopause-accelerated CIMT progression \u2014 have historically been under-diagnosed and require dedicated clinical pathways.<\/p>\n Sixth, the trial evidence \u2014 from the Lifestyle Heart Trial through the modern IVUS regression trials with PCSK9 inhibitors \u2014 supports the conclusion that subclinical atherosclerosis is, when addressed early and aggressively, partially reversible. Plaque can be stabilized, fibrous caps thickened, and event rates reduced. Whole-food plant-based dietary patterns and pharmacologic LDL-lowering both produce regression in their respective trial contexts; comprehensive lifestyle intervention complements rather than replaces appropriate pharmacologic therapy.<\/p>\n The life-course perspective provided by Napoli\/FELIC, Bogalusa, PDAY, CARDIA, MESA, and the Tsimane natural experiment carries one practical message: the vascular integrity of late life is built on the risk exposures of youth. Early detection through CAC scoring, pulse wave velocity, vessel-wall MRI, FAI, and emerging AI-augmented imaging, combined with aggressive risk-factor management addressing apoB, Lp(a), inflammation, blood pressure, glycemia, sleep, fitness, and tobacco exposure, offers the realistic possibility of compressing cardiovascular morbidity to the very end of life. The goal of preventive cardiology is no longer the deferral of the first event by a decade; it is the elimination of clinical atherosclerotic disease as a routine cause of human suffering.<\/p>\n |