Compensatory enlargement of human coronary arteries during progression of atherosclerosis is unrelated to atheroma burden: serial intravascular ultrasound observations from the REVERSAL trial

Measurement of compensatory arterial remodelling over time with serial coronary computed tomography angiography and 3D metrics

AIMS

The magnitude of alterations in which coronary arteries remodel and narrow over time is not well understood. We aimed to examine changes in coronary arterial remodelling and luminal narrowing by three-dimensional (3D) metrics from serial coronary computed tomography angiography (CCTA).

METHODS AND RESULTS

From a multicentre registry of patients with suspected coronary artery disease who underwent clinically indicated serial CCTA (median interscan interval = 3.3 years), we quantitatively measured coronary plaque, vessel, and lumen volumes on both scans. Primary outcome was the per-segment change in coronary vessel and lumen volume from a change in plaque volume, focusing on arterial remodelling. Multivariate generalized estimating equations including statins were calculated comparing associations between groups of baseline percent atheroma volume (PAV) and location within the coronary artery tree. From 1245 patients (mean age 61 ± 9 years, 39% women), a total of 5721 segments were analysed. For each 1.00 mm3 increase in plaque volume, the vessel volume increased by 0.71 mm3 [95% confidence interval (CI) 0.63 to 0.79 mm3, P < 0.001] with a corresponding reduction in lumen volume by 0.29 mm3 (95% CI -0.37 to -0.21 mm3, P < 0.001). Serial 3D arterial remodelling and luminal narrowing was similar in segments with low and high baseline PAV (P ≥ 0.496). No differences were observed between left main and non-left main segments, proximal and distal segments and side branch and non-side branch segments (P ≥ 0.281).

CONCLUSIONS

Over time, atherosclerotic coronary plaque reveals prominent outward arterial remodelling that co-occurs with modest luminal narrowing. These findings provide additional insight into the compensatory mechanisms involved in the progression of coronary atherosclerosis.

Percent atheroma volume: Optimal variable to report whole-heart atherosclerotic plaque burden with coronary CTA, the PARADIGM study

BACKGROUND AND AIMS

Different methodologies to report whole-heart atherosclerotic plaque on coronary computed tomography angiography (CCTA) have been utilized. We examined which of the three commonly used plaque burden definitions was least affected by differences in body surface area (BSA) and sex.

METHODS

The PARADIGM study includes symptomatic patients with suspected coronary atherosclerosis who underwent serial CCTA >2 years apart. Coronary lumen, vessel, and plaque were quantified from the coronary tree on a 0.5 mm cross-sectional basis by a core-lab, and summed to per-patient. Three quantitative methods of plaque burden were employed: (1) total plaque volume (PV) in mm³, (2) percent atheroma volume (PAV) in % [which equaled: PV/vessel volume * 100%], and (3) normalized total atheroma volume (TAV_norm) in mm³ [which equaled: PV/vessel length * mean population vessel length]. Only data from the baseline CCTA were used. PV, PAV, and TAV_norm were compared between patients in the top quartile of BSA vs the remaining, and between sexes. Associations between vessel volume, BSA, and the three plaque burden methodologies were assessed.

RESULTS

The study population comprised 1479 patients (age 60.7 ± 9.3 years, 58.4% male) who underwent CCTA. A total of 17,649 coronary artery segments were evaluated with a median of 12 (IQR 11-13) segments per-patient (from a 16-segment coronary tree). Patients with a large BSA (top quartile), compared with the remaining patients, had a larger PV and TAV_norm, but similar PAV. The relation between larger BSA and larger absolute plaque volume (PV and TAV_norm) was mediated by the coronary vessel volume. Independent from the atherosclerotic cardiovascular disease risk (ASCVD) score, vessel volume correlated with PV (P < 0.001), and TAV_norm (P = 0.003), but not with PAV (P = 0.201). The three plaque burden methods were equally affected by sex.

CONCLUSIONS

PAV was less affected by patient's body surface area then PV and TAV_norm and may be the preferred method to report coronary atherosclerotic burden.

Relation between baseline plaque features and subsequent coronary artery remodeling determined by optical coherence tomography and intravascular ultrasound

Atherosclerosis often leads to myocardial infarction and stroke. We examined the influence of baseline plaque characteristics on subsequent vascular remodeling in response to changes in plaque size. Using optical coherence tomography (OCT) and intravascular ultrasound (IVUS), we examined 213 plaques from 138 patients with acute coronary syndrome at baseline and repeated IVUS at the 12-month follow-up. The change in external elastic membrane (EEM) area for each 1 mm2 change in plaque area (i.e., the slope of the regression line) was calculated as a measure of vascular remodeling capacity. In plaques with static positive remodeling, the slope was smaller than in plaques without static positive remodeling. In addition, the slope of the regression line for lesions with a large plaque burden was much smaller than that for lesions with a small plaque burden. Multivariate linear regression analysis showed that diabetes, calcification and static positive remodeling were inversely and independently associated with the level of change in EEM area/change in plaque area. Lesions with a large plaque burden, calcifications or static positive remodeling had less remodeling capacity, and calcification and static positive remodeling were independent predictors of reduced subsequent remodeling. Therefore, calcifications and static positive remodeling could be used as morphological biomarkers to predict decreased subsequent arterial remodeling.

A novel model of atherosclerosis in rabbits using injury to arterial walls induced by ferric chloride as evaluated by optical coherence tomography as well as intravascular ultrasound and histology

This study aim was to develop a new model of atherosclerosis by FeCl₃-induced injury to right common carotid arteries (CCAs) of rabbits. Right CCAs were induced in male New Zealand White rabbits (n = 15) by combination of a cholesterol-rich diet and FeCl₃-induced injury to arterial walls. The right and left CCAs were evaluated by histology and in vivo intravascular ultrasound (IVUS) and optical coherence tomography (OCT) examinations of 24 hours (n = 3), 8 weeks (n = 6), and 12 weeks (n = 6) after injury. Each right CCA of the rabbits showed extensive white-yellow plaques. At eight and 12 weeks after injury, IVUS, OCT, and histological findings demonstrated that the right CCAs had evident eccentric plaques. Six plaques (50%) with evident positive remodeling were observed. Marked progression was clearly observed in the same plaque at 12 weeks after injury when it underwent repeat OCT and IVUS. We demonstrated, for the first time, a novel model of atherosclerosis induced by FeCl₃. The model is simple, fast, inexpensive, and reproducible and has a high success rate. The eccentric plaques and remodeling of plaques were common in this model. We successfully carried out IVUS and OCT examinations twice in the same lesion within a relatively long period of time.

An intravascular ultrasound analysis in women experiencing chest pain in the absence of obstructive coronary artery disease: a substudy from the National Heart, Lung and Blood Institute-Sponsored Women's Ischemia Syndrome Evaluation (WISE)

AIMS

Using intravascular ultrasound (IVUS), we sought to characterize coronary morphology in women with chest pain without major epicardial obstructive coronary artery disease (CAD). We have previously observed an unexpectedly high rate of adverse outcomes among women with chest pain and normal or insignificant obstructive CAD. Information about the presence and characteristics of coronary atherosclerosis in these women could provide insight into the mechanisms related to increased risk, as well as improved diagnosis, prevention, and treatment.

METHODS

Women (n = 100) with suspected ischemia without obstructive CAD (>50% stenosis) underwent IVUS of a left coronary segment with measurements by a core lab masked to clinical and angiographic findings.

RESULTS

Angiograhic core lab analysis found 69.6% of patients had no (≤20%) and 30.4% had minimal (20-<50%) CAD. IVUS segmental images were interpretable by the core lab in 92 women, with 19 (21%) having no atherosclerosis (intimal-medial thickness <0.5 mm). In the remaining 73 women (79%), percent atheroma volume was 27 ± 8% and mean maximum plaque thickness was 0.53 ± 0.22 mm. Thirty-eight women with atherosclerosis (53%) had ≥30% of interrogated vessel involved. The average vessel involvement was 40%, and the maximum plaque thickness was 1.27 mm. The number of risk factors strongly correlated with percent atheroma volume (r = 0.53, P < 0.0001) and percent vessel involvement (r = 0.51, P < 0.0001), with the strongest independent predictor of both being age. Remodeling was assessed in 59/73 women (81%), and 73% had evidence of positive remodeling.

CONCLUSIONS

In symptomatic women without significant luminal obstructive CAD, we observed a high prevalence of atherosclerosis with positive remodeling and preserved lumen size. These findings may help explain increased risk and emphasize need for improved diagnostic and treatment options for women with concealed CAD.

Strategies to reverse atherosclerosis: an imaging perspective

Several treatment strategies, including lowering low-density lipoprotein cholesterol with intensive statin therapy, reducing triglycerides with fibrates, and raising high-density lipoprotein cholesterol with nicotinic acid, have the potential to induce atherosclerosis regression. Atherosclerosis imaging techniques including intravascular ultrasound, carotid ultrasound to measure carotid intima-media thickness, and cardiovascular MRI are established modalities for describing longitudinal changes in the quantity and quality of atherosclerotic plaque. An increasing number of clinical trials are using radiologic measures of subclinical atherosclerosis as surrogate end points in lieu of the traditional "hard" end points of myocardial infarction and death. This approach has great appeal, as improvements in atherosclerosis imaging now enable the characterization of early atheromas and positive remodeling within the vessel wall before the plaque becomes obstructive. Additional prospective data correlating these surrogate end points with hard outcomes are needed to determine whether atherosclerosis regression will be the major determinant of future treatment strategies.

Impact of olmesartan on progression of coronary atherosclerosis a serial volumetric intravascular ultrasound analysis from the OLIVUS (impact of OLmesarten on progression of coronary atherosclerosis: evaluation by intravascular ultrasound) trial

OBJECTIVES

The aim of this study was to evaluate the impact of olmesartan on progression of coronary atherosclerosis.

BACKGROUND

Prior intravascular ultrasound (IVUS) trial results suggest slowing of coronary atheroma progression with some medicines but have not shown convincing evidence of regression with angiotension-II receptor blocking agents.

METHODS

A prospective, randomized, multicenter trial-OLIVUS (Impact of OLmesartan on progression of coronary atherosclerosis: evaluation by IntraVascular UltraSound)-was performed in 247 stable angina pectoris patients with native coronary artery disease. When these patients underwent percutaneous coronary intervention for culprit lesions, IVUS was performed in their nonculprit vessels (without angiographically documented coronary stenosis [<50%]). Patients were randomly assigned to receive 10 to 40 mg of olmesartan or control and treated with a combination of beta-blockers, calcium channel blockers, diuretics, nitrates, glycemic control agents, and/or statins per physician's guidance. Serial IVUS examinations (baseline and 14-month follow-up) were performed to assess coronary atheroma volume. Volumetric IVUS analyses included lumen, plaque, vessel volume, percent atheroma volume (PAV), percent change in total atheroma volume (TAV) and PAV.

RESULTS

Patient characteristics and blood pressure control were identical between the 2 groups. However, follow-up IVUS showed significantly decreased TAV and percent change in PAV in the olmesartan group (5.4% vs. 0.6 % for TAV and 3.1% vs. -0.7% for percent change in PAV, control vs. olmesartan, p < 0.05 for all).

CONCLUSIONS

These observations suggest a positive role in a potentially lower rate of coronary atheroma progression through the administration of olmesartan, an angiotension-II receptor blocking agent, for patients with stable angina pectoris.

Progression of Carotid Stenosis Detected by Duplex Ultrasonography Predicts Adverse Outcomes in Cardiovascular High-Risk Patients

BACKGROUND AND PURPOSE

The progression of carotid stenosis reflects the activity of atherosclerotic disease and may indicate a risk for systemic atherothrombotic complications. We investigated whether progressive carotid stenosis determined by duplex ultrasonography predicts adverse outcomes in cardiovascular high-risk patients.

METHODS

We prospectively studied 1065 of 1268 consecutive patients initially asymptomatic with respect to carotid disease. Carotid ultrasound investigations at baseline and after a median of 7.5 months (range, 6 to 9 months) were performed to identify patients with progressive stenosis as defined by Doppler velocity criteria. Patients were then followed up clinically for a median of 3.2 years for the occurrence of major adverse cardiovascular events (composite MACEs: myocardial infarction, percutaneous coronary or peripheral interventions, coronary or vascular surgery, amputation, stroke, and all-cause mortality).

RESULTS

We found progressive carotid stenosis in 93 patients (9%) by ultrasound and thereafter recorded 495 MACEs in 421 patients (40%) during clinical follow-up. Patients with progressive carotid stenosis had a significantly increased risk for cardiovascular events compared with patients with nonprogressive disease: adjusted hazard ratios and confidence intervals were 2.01 for composite MACEs (95% CI, 1.48 to 2.67, P<0.001), 2.38 for myocardial infarction (95% CI, 1.07 to 5.35, P=0.044), 1.59 for any coronary event (95% CI, 1.10 to 2.28, P=0.011), 2.00 for stroke (95% CI, 1.02 to 4.11, P=0.035), 2.42 for any peripheral vascular event (95% CI, 1.61 to 3.62, P<0.001), and 1.75 for cardiovascular death (95% CI, 1.03 to 2.97, P=0.039).

CONCLUSIONS

Progression of carotid stenosis within a 6- to 9-month interval detected by duplex ultrasound predicts midterm clinical adverse events of atherosclerosis in high-risk patients affecting the coronary, cerebrovascular, and peripheral circulations.

Effect of perindopril on coronary remodelling: insights from a multicentre, randomized study

AIMS

This study sought to evaluate the effect of perindopril in coronary remodelling.

METHODS AND RESULTS

In this sub-study of a double-blind, multicentre trial, patients without clinical evidence of heart failure were randomized to perindopril 8 mg/day or placebo for at least 3 years and IVUS investigation was performed at both time-points. Positive and negative remodelling were defined as a relative increase (positive remodelling) or decrease (negative remodelling) of the mean vessel cross-sectional area (CSA)>2 SD of the mean intra-observer difference. A total of 118 matched evaluable IVUS (711 matched 5 mm segments) were available at follow-up. After a median follow-up of 3.0 (inter-quartile range 1.9, 4.1) years, there was no significant difference in the change of plaque CSA between perindopril (360 segments) and placebo (351 segments) groups, P=0.27. Conversely, the change in vessel CSA was significantly different between groups (perindopril -0.18+/-2.4 mm2 vs. placebo 0.19+/-2.4, P = 0.04). Negative remodelling occurred more frequently in the perindopril than in the placebo group (34 vs. 25%, P=0.01). In addition, the placebo group showed a larger, although not significant, mean remodelling index (RI) than the perindopril group (1.03+/-0.2 vs. 1.00+/-0.2, P=0.06). The temporal change in vessel dimensions assessed by the RI was significantly correlated with the change in plaque dimensions (r=0.48, P<0.0001).

CONCLUSION

In this sub-analysis of a multicentre, controlled study, long-term administration of perindopril was associated with a constrictive remodelling pattern without affecting the lumen.

Angiotensin Inhibition Decreases Progression of Advanced Atherosclerosis and Stabilizes Established Atherosclerotic Plaques

Although increased extracellular matrix (ECM) is pathogenic in a variety of chronic tissue injuries, reduced and/or disrupted ECM may be detrimental in atherosclerosis and rather destabilize existing atherosclerotic lesions. This study therefore assessed the effects of angiotensin II (AngII) antagonism on ECM components of advanced atherosclerosis. Twenty-four-week-old apolipoprotein E-deficient mice were treated with the AngII antagonist losartan for 12 wk. Controls received water or hydralazine. AngII antagonism significantly reduced progression of established atherosclerosis, whereas hydralazine showed no benefit despite similar decrease in BP. Although there was no difference in the macrophage component, AngII antagonism increased the relative collagen portion of the lesions; lessened elastin fragmentation, increased the total elastin content of the aorta; and reduced the mRNA and activity/protein of the elastolytic proteases, cathepsin S, and metalloproteinase-9. Extracellular elastin degradation by cultured smooth muscle cells (SMC) was reduced by losartan, as was SMC invasion through an elastin gel barrier. Thus, AngII antagonism lessens progression of atherosclerosis, increases collagen, and preserves elastin components of ECM within the vascular lesions, which, at least in part, is modulated by effects on SMC. These effects not only decrease further expansion of advanced lesions but also stabilize the established atherosclerotic plaques and may underlie the decreased incidence of acute cardiovascular events that are observed in patients in whom AngII antagonism is begun after atherosclerosis is already established.

Is intravascular ultrasound the gold standard surrogate for clinically relevant atherosclerosis progression?

Are progressive changes in intravascular ultrasound (IVUS)-derived indexes of plaque size sufficiently predictive of in-trial or future cardiovascular event risk that IVUS can serve as an efficient surrogate for clinical events in coronary disease trials? This question remains unanswered by clinical trials reported to date. Indeed, the answer may well be "yes." Nevertheless, there are enough concerns about the physical limitations, the fundamental assumptions, and the interpretation of the IVUS measurements that the answer cannot be taken for granted. Here, we review the evidence to date, discuss some of the concerns, and compare IVUS results with those of quantitative arteriography.

Plaque stabilization: Can we turn theory into evidence?

Coronary events often result from thrombi that form because of physical disruption of the atherosclerotic plaque. The dynamic nature of the plaque offers the opportunity to intervene to modify plaque biology with lifestyle changes and, if needed, pharmacologic measures. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) reduce levels of serum cholesterol and decrease the incidence of coronary events, but some of the benefits of statins may not depend on their effects on circulating lipids. Indeed, increasing evidence suggests that statins may also enhance plaque stability. Such evidence includes results of preclinical studies with experimental atherosclerosis as well as imaging data and analyses of proinflammatory and prothrombotic mediators in clinical trials. Currently, however, no studies have demonstrated conclusively the mechanisms underlying the unexpected magnitude and rapidity of statin benefits. This article reviews the evolution of the concept of plaque stabilization and reexamines the evidence for the role of statins in that process.