Multicenter assessment of coronary allograft vasculopathy by intravascular ultrasound-derived analysis of plaque composition

The Biological Parallels Between Atherosclerosis and Cardiac Allograft Vasculopathy: Implications for Solid Organ Chronic Rejection

Atherosclerosis and solid organ chronic rejection are pervasive chronic disease states that account for significant morbidity and mortality in developed countries. Recently, a series of shared molecular pathways have emerged, revealing biological parallels from early stages of development up to the advanced forms of pathology. These shared mechanistic processes are inflammatory in nature, reflecting the importance of inflammation in both disorders. Vascular inflammation triggers endothelial dysfunction and disease initiation through aberrant vasomotor control and shared patterns of endothelial activation. Endothelial dysfunction leads to the recruitment of immune cells and the perpetuation of the inflammatory response. This drives lesion formation through the release of key cytokines such as IFN-y, TNF-alpha, and IL-2. Continued interplay between the adaptive and innate immune response (represented by T lymphocytes and macrophages, respectively) promotes lesion instability and thrombotic complications; hallmarks of advanced disease in both atherosclerosis and solid organ chronic rejection. The aim of this study is to identify areas of overlap between atherosclerosis and chronic rejection. We then discuss new approaches to improve current understanding of the pathophysiology of both disorders, and eventually design novel therapeutics.

Analysis of Fibrotic Plaques in Angiographic Manifest Cardiac Allograft Vasculopathy in Long-term Heart Transplanted Patients Using Optical Coherence Tomography

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Background.

The development and progression of cardiac allograft vasculopathy documented by coronary angiography (CAV_angio) after heart transplantation (HTx) has prognostic relevance. Yet there are limited data regarding the role of concomitant intracoronary imaging in the presence CAV_angio. In particular, atherosclerotic plaques might represent a potential target for prevention, but their impact on stenosis is understudied.

Methods.

We used high-resolution intracoronary optical coherence tomography (OCT) to quantify and compare findings of intimal hyperplasia (IH) and plaque morphologies in HTx patients (fibrotic plaque, lipid plaque, and calcified plaque). OCT findings were related to the presence of CAV_angio as well as to the severity of stenosis.

Results.

We included 65 consecutive patients into analysis (66% with CAV_angio, posttransplant interval 9.9 ± 7.6 y). Fibrotic, lipid, and calcified plaques were present in 41 (63.1%), 39 (60%), and 18 (27.7%) patients, respectively. In addition to IH, the presence of fibrotic, lipid, and calcified plaques was found to be associated with CAV_angio. The prevalence of lipid plaque and quantitative measurements of fibrotic plaque increased with stenosis severity (lipid plaque, P < 0.001, maximal and mean fibrotic arc, P = 0.05 and P = 0.001, respectively). Receiver operating characteristic analysis showed that area under the curve of the fibrotic plaque parameter mean fibrotic arc (0.87, 95% confidence interval [0.76-0.99]; P = 0.002) was superior to area under the curve of intima parameters regarding CAV_angio. The effect of mean fibrotic arc (r = 0.52, P < 0.001) was relevant regarding stenosis severity.

Conclusions.

After a longer posttransplant interval, CAV findings in OCT included a combination of IH and atherosclerotic plaques. In addition to IH, the presence of fibrotic, lipid, and calcified plaques is associated with CAV_angio. Further studies are warranted to evaluate if the in vivo screening for plaque progress, particularly of fibrotic plaque, could improve individual secondary prevention and outcome in HTx patients.

Attenuated-Signal Plaque Progression Predicts Long-Term Mortality After Heart Transplantation: IVUS Assessment of Cardiac Allograft Vasculopathy

BACKGROUND

Although cardiac allograft vasculopathy (CAV) is typically characterized by diffuse coronary intimal thickening with pathological vessel remodeling, plaque instability may also play an important role in CAV. Previous studies of native coronary atherosclerosis have demonstrated associations between attenuated-signal plaque (ASP), plaque instability, and adverse clinical events.

OBJECTIVES

This study's aim was to characterize the association between ASP and long-term mortality post-heart transplantation.

METHODS

In 105 heart transplant recipients, serial (baseline and 1-year post-transplant) intravascular ultrasound was performed in the first 50 mm of the left anterior descending artery. The ASP score was calculated by grading the measured angle of attenuation from grades 0 to 4 (specifically, 0°, 1° to 90°, 91° to 180°, 181° to 270°, and >270°) at 1-mm intervals. The primary endpoint was all-cause death or retransplantation.

RESULTS

At 1-year post-transplant, 10.5% of patients demonstrated ASP progression (newly developed or increased ASP). Patients with ASP progression had a higher incidence of acute cellular rejection during the first year (63.6% vs. 22.3%; p = 0.006) and tendency for greater intimal growth (percent intimal volume: 9.2 ± 9.3% vs. 4.4 ± 5.3%; p = 0.07) than those without. Over a median follow-up of 4.6 years, there was a significantly lower event-free survival rate in patients with ASP progression at 1-year post-transplant compared with those without. In contrast, maximum intimal thickness did not predict long-term mortality.

CONCLUSIONS

ASP progression appears to reflect chronic inflammation related to acute cellular rejection and is an independent predictor of long-term mortality after heart transplantation. Serial assessments of plaque instability may enhance identification of high-risk patients who may benefit from closer follow-up and targeted medical therapies.

Multiparametric cardiovascular magnetic resonance assessment of cardiac allograft vasculopathy

OBJECTIVES

This study sought to evaluate the diagnostic performance of multiparametric cardiovascular magnetic resonance (CMR) for detecting cardiac allograft vasculopathy (CAV) using contemporary invasive epicardial artery and microvascular assessment techniques as reference standards, and to compare the performance of CMR with that of angiography.

BACKGROUND

CAV continues to limit the long-term survival of heart transplant recipients. Coronary angiography has a Class I recommendation for CAV surveillance and annual or biannual surveillance angiography is performed routinely in most centers.

METHODS

All transplant recipients referred for surveillance angiography at a single UK center over a 2-year period were prospectively screened for study eligibility. Patients prospectively underwent coronary angiography followed by coronary intravascular ultrasound, fractional flow reserve, and index of microcirculatory resistance. Within 1 month, patients underwent multiparametric CMR, including assessment of regional and global ventricular function, absolute myocardial blood flow quantification, and myocardial tissue characterization. In addition, 10 healthy volunteers underwent CMR.

RESULTS

Forty-eight patients were recruited, median 7.1 years (interquartile range: 4.6 to 10.3 years) since transplantation. The CMR myocardial perfusion reserve was the only independent predictor of both epicardial (β = -0.57, p < 0.001) and microvascular disease (β = -0.60, p < 0.001) on stepwise multivariable regression. The CMR myocardial perfusion reserve significantly outperformed angiography for detecting moderate CAV (area under the curve, 0.89 [95% confidence interval (CI): 0.79 to 1.00] vs. 0.59 [95% CI: 0.42 to 0.77], p = 0.01) and severe CAV (area under the curve, 0.88 [95% CI: 0.78 to 0.98] vs. 0.67 [95% CI: 0.52 to 0.82], p = 0.05).

CONCLUSIONS

CAV, including epicardial and microvascular components, can be detected more accurately using noninvasive CMR-based absolute myocardial blood flow assessment than with invasive coronary angiography, the current clinical surveillance technique.

Attenuation of cardiac allograft vasculopathy by sirolimus: Relationship to time interval after heart transplantation

BACKGROUND

The aim of the study was to assess temporal changes in plaque size and components after heart transplantation (HTx), and to evaluate the differences in treatment effects on plaque progression between sirolimus and calcineurin inhibitors (CNIs).

METHODS

The study comprised 146 HTx recipients who were converted from CNIs to sirolimus as primary immunosuppressant (sirolimus group, n = 61) and those who were maintained on CNIs (CNI group, n = 85). A retrospective compositional analysis of serial virtual histology-intravascular ultrasound was performed.

RESULTS

During a median follow-up of 2.8 years, there was a significant difference in plaque volume in favor of sirolimus between groups (p = 0.004). When subjects were sub-classified according to the time interval between HTx and study inclusion, those in the early group (≤2 years after HTx) had a greater increase in plaque volume (p = 0.006), characterized by a higher progression rate of fibrous plaque volume (p = 0.01). The treatment difference between groups in plaque volume was identified in the early group in favor of sirolimus with attenuating effects on the progression of fibrous plaque component (both p = 0.03 for interaction). By contrast, there were significant differences in necrotic core and dense calcium volume (both p < 0.05 for interaction) in favor of CNIs in the late group (≥6 years after HTx).

CONCLUSIONS

Compared with continued CNI therapy, sirolimus attenuated plaque progression in recipients with early conversion, but contributed to increases in necrotic core and dense calcium volume in those with late conversion. Our study supports the hypothesis that early initiation of sirolimus offers greater benefits in the treatment of CAV.

Four-year clinical outcomes of the OLIVUS-Ex (impact of Olmesartan on progression of coronary atherosclerosis: evaluation by intravascular ultrasound) extension trial

BACKGROUND

The previous OLIVUS trial reported a positive role in achieving a lower rate of coronary atheroma progression through the administration of olmesartan, an angiotension-II receptor blocking agent (ARB), for stable angina pectoris (SAP) patients requiring percutaneous coronary intervention (PCI). However, the benefits between ARB administration on long-term clinical outcomes and serial atheroma changes by IVUS remain unclear. Thus, we examined the 4-year clinical outcomes from OLIVUS according to treatment strategy with olmesartan.

METHODS

Serial volumetric IVUS examinations (baseline and 14 months) were performed in 247 patients with hypertension and SAP. When these patients underwent PCI for culprit lesions, IVUS was performed in their non-culprit vessels. Patients were randomly assigned to receive 20-40mg of olmesartan or control, and treated with a combination of β-blockers, calcium channel blockers, glycemic control agents and/or statins per physician's guidance. Four-year clinical outcomes and annual progression rate of atherosclerosis, assessed by serial IVUS, were compared with major adverse cardio- and cerebrovascular events (MACCE).

RESULTS

Cumulative event-free survival was significantly higher in the olmesartan group than in the control group (p=0.04; log-rank test). By adjusting for validated prognosticators, olmesartan administration was identified as a good predictor of MACCE (p=0.041). On the other hand, patients with adverse events (n=31) had larger annual atheroma progression than the rest of the population (23.8% vs. 2.1%, p<0.001).

CONCLUSIONS

Olmesartan therapy appears to confer improved long-term clinical outcomes. Atheroma volume changes, assessed by IVUS, seem to be a reliable surrogate for future major adverse cardio- and cerebrovascular events in this study cohort.

Extra cellular matrix remodelling after heterotopic rat heart transplantation: gene expression profiling and involvement of ED-A+ fibronectin, alpha-smooth muscle actin and B+ tenascin-C in chronic cardiac allograft rejection

Chronic cardiac rejection is represented by cardiac allograft vasculopathy (CAV) and cardiac interstitial fibrosis (CIF) known to cause severe complications. These processes are accompanied by remarkable changes in the cardiac extra cellular matrix (cECM). The aim of our study was to analyse the cECM remodelling in chronic rejection and to elucidate a potential role of ED-A domain containing fibronectin (ED-A(+) Fn), alpha smooth muscle actin (ASMA) and B domain containing tenascin-C (B(+) Tn-C). A model of chronic rejection after heterotopic rat heart transplantation was used. Allografts, recipient and control hearts were subjected to histological assessment of rejection grade, to real-time PCR based analysis of 84 genes of ECM and adhesion molecules and to immunofluorescence labelling procedures, including ED-A(+) Fn, ASMA and B(+) Tn-C antibodies. Histological analysis revealed different grades of chronic rejection. By gene expression analysis, a relevant up-regulation of the majority of ECM genes in association with chronic rejection could be shown. For 8 genes, there was a relevant up-regulation in allografts as well as in the corresponding recipient hearts. Association of ASMA positive cells with the grade of chronic rejection could be proven. In CAV and also in CIF there were extensive co-depositions of ED-A(+) Fn, ASMA and B(+) Tn-C. In conclusion, chronic cardiac allograft rejection is associated with a cECM remodelling. ASMA protein deposition in CAV, and CIF is a valuable marker to detect chronic rejection. Interactions of VSMCs and Fibro-/Myofibroblasts with ED-A(+) Fn and B(+) Tn-C might functionally contribute to the development of chronic cardiac rejection.