Acetylsalicylic acid use and development of cardiac allograft vasculopathy: A national prospective study using highly automated 3-D optical coherence tomography analysis

Abstract

Background:

There is conflicting evidence on the role of acetylsalicylic acid (ASA) use in the development of cardiac allograft vasculopathy (CAV).

Methods:

A nationwide prospective two-centre study investigated changes in the coronary artery vasculature by highly automated 3-D optical coherence tomography (OCT) analysis at 1 month and 12 months after heart transplant (HTx). The influence of ASA use on coronary artery microvascular changes was analysed in the overall study cohort and after propensity score matching for selected clinical CAV risk factors.

Results:

In total, 175 patients (mean age 52±12 years, 79% male) were recruited. During the 1-year follow-up, both intimal and media thickness progressed, with ASA having no effect on its progression. However, detailed OCT analysis revealed that ASA use was associated with a lower increase in lipid plaque burden (p=0.013), while it did not affect the other observed pathologies. Propensity score matching of 120 patients (60 patient pairs) showed similar results, with ASA use associated with lower progression of lipid plaques (p=0.002), while having no impact on layered fibrotic plaque (p=0.224), calcification (p=0.231), macrophage infiltration (p=0.197), or the absolute coronary artery risk score (p=0.277). According to Kaplan-Meier analysis, ASA use was not associated with a significant difference in survival (p=0.699)

Conclusion:

This study showed a benefit of early ASA use after HTx on lipid plaque progression. However, ASA use did not have any impact on the progression of other OCT observed pathologies or long-term survival.

Introduction

Cardiac allograft vasculopathy (CAV) remains the leading cause of long-term graft dysfunction and graft loss after heart transplantation (HTx), affecting almost half of patients by 10 years post-transplant.^1–3 Despite a variety of known immune and nonimmune risk factors, preventative strategies and pharmacological treatment are still only partially effective.

Studies evaluating early changes in the coronary artery wall after HTx suggested a significant role of excessive platelet activation and thrombosis in the pathogenesis of CAV.⁴ Some studies suggest that acetylsalicylic acid (ASA) use may improve survival and reduce the risk of CAV.^5,6 The lack of formal recommendations⁷ in the past has led to great variability in ASA use across HTx centers. As the latest ISHLT guidelines⁸ for the first time recommend considering the use of ASA as a prevention of CAV, more data on ASA benefits after HTx is needed to support this. The aim of the present study was to determine the effect of ASA use early after HTx on CAV using serial, highly automated 3-D OCT analysis performed at 1 month and 12 months after HTx.

Methods

Patients

All patients who underwent heart transplantation in the Heart Centre at the Institute of Clinical and Experimental Medicine (IKEM), Prague, and the Centre of Cardiovascular and Transplantation Surgery, Brno, Czech Republic, between October 2014 and January 2018 were evaluated for this study. The study was approved by the respective ethics committees. The above-mentioned centres serve as the only two centres for HTx in the Czech Republic. Patients were included in the study if they survived the first 12 months after HTx, were ≥18 years of age, and were willing to give their informed consent in accordance with the principles of the Declaration of Helsinki. Exclusion criteria included treatment with anti-coagulation therapy or ASA therapy initiation after 4 weeks after HTx. Coronary angiography was performed on 71 donor hearts before HTx. This examination did not influence the initiation of ASA, as its main purpose was to reject inappropriate donors.

Antiplatelet therapy

The present study compared two distinct patient cohorts defined by ASA use during the first year after HTx.

1. In the ASA cohort, oral ASA 100 mg/day was initiated within 4 weeks after HTx and administered throughout the first post-HTx year.

2. In the control cohort, ASA or other antiplatelet or anticoagulant therapy was not administered during the study period.

OCT analysis

As part of routine surveillance cardiac catheterization, coronary OCT imaging was performed 1 month and 12 months after HTx. A commercial intracoronary OCT system (ILUMIEN/DRAGONFLY OPTIS, St. Jude Medical) was used to assess a 54 mm-long segment of the left anterior descending (LAD) artery within a proximal 100 mm segment. The automated pullback technique was employed at 18 mm/sec and 10 frames/mm. In cases where the LAD artery displayed unfavourable anatomical characteristics, the proximal segment of either the left circumflex (LCx) or the right coronary artery (RCA) was imaged instead. The proximal fiduciary point for the left coronary artery was identified as the left main bifurcation, while for the RCA or LCx, it was determined as the first branch or a well-defined calcification. After 12 months, patients underwent repeat cardiac catheterization, and OCT imaging was performed on the same coronary artery. For each frame of all OCT pullbacks, luminal, intimal-layer, and medial-layer surfaces were automatically segmented using highly automated 3-D optical coherence tomography software that was developed at the Iowa Institute for Biomedical Imaging, The University of Iowa, USA.^11,12 This OCT analysis approach was independently validated in an international study on data from the Aarhus University Medical Center¹³ and used for analysis in several other studies.^11,14 (Figure 1). The OCT analysis is comprehensibly described in Supplementary Material (Appendix A).

Figure 1.

Three-dimensional segmentation of luminal (red), intimal (green), and medial (orange) surfaces performed volumetrically in the entire OCT pullback with intimal and medial layer thickness, brightness, and roughness indices calculated in 360 radial directions in each OCT frame.

The observed corresponding segments of the artery were matched between baseline at 1 month and 12 months follow-up; the total number of frames was dependent on the length of the examined artery. Each frame of the coronary artery was evaluated for the presence of four circumferential pathologies¹⁹ (1) lipid plaques (LP) (lipid pools and thin-cap fibroatheromas), (2) layered fibrotic plaques (LFP), (3) calcifications, and (4) macrophage infiltration (bright-spots). Definitions of the pathologies are provided in Supplementary Material (Appendix B). Analysis was then performed by delineating lateral plaque borders and measuring their circumferential angulation. The percentage of total circumference was correlated with the number of analysed frames in each patient (Figure 2).

Figure 2 – OCT analysis with measured angulations as percentage of total circumference.

(A) lipid plaque – angulation 49% (green line), (B) lipid plaque – angulation 57% (green) with focal calcification – angulation 11% (yellow), (C) lipid plaque – angulation 44% (green) with macrophages – angulation 10% (blue), (D) eccentric layered fibrotic plaque (orange), (E) circumferential layered fibrotic plaque, (F) layered fibrotic plaque with intimal neovascularization between 5 o’clock and 7’oclock, (G) subendothelial macrophage infiltration with backscattering, (H) layered fibrotic plaque with macrophage infiltration, (I) lipid plaque with calcification.

To quantify the inherent challenges in manual identification of circumferential pathologies, an intra-observer variability analysis was conducted. A subset of 60 pullbacks was randomly chosen for this purpose, with each pullback averaging 10 randomly identified cross-sectional OCT frames. The same expert (LM) performed blind repeat tracing in all frames. The two tracing sessions were separated in time by several weeks to yield two sets of mutually independent analyses. The re-tracing results were then compared to the original tracings, with angular differences quantified and correlation analysis performed to assess tracing-retracing consistency and reliability.

In the total risk score assessment, each OCT frame was evaluated for the presence of LP, LFP, calcification, macrophages, and neovascularization, with each factor assigned a score of one. Thus, each OCT frame could accumulate a maximum of five points. After evaluating the entire pullback, the scores of all correlated segments were summed and divided by the total number of analysed frames.

Depending on the OCT findings, the vessels were sorted into four phenotypes: 1) normal, 2) lipid phenotype (1 or more areas with LP), 3) thrombofibrotic phenotype (1 or more areas with LFP), and 4) mixed phenotype (lipid + thrombofibrotic phenotype).

Statistical analysis

Data are presented as mean ± standard deviation, median with interquartile ranges [IQRs], or frequency (percent). To compare continuous variables by ASA use in the overall study sample, we used unpaired t-test, Mann-Whitney test, or χ2 test, as appropriate. Propensity score matching was used to account for different risk factors that may influence the progression of coronary artery structural changes. The propensity score for each patient was calculated using a multivariable logistic regression model in which the ASA use was regressed on 9 risk factors: age, gender, donor age, BMI, CMV infection, severe cellular rejection, cold ischemia time, diabetes, and LDL cholesterol. Because groups by ASA use differed at baseline in layered fibrotic plaque extent, matching on this parameter was also used. Subjects were matched on the logit of the propensity score using 1:1 greedy nearest-neighbour matching with a calliper distance of 0.2 times the SD of the logit of the propensity score. MatchIt package version 4.3.4 for R was used. Paired tests were employed to compare differences by matched pairs – related samples Wilcoxon signed rank test, paired t-test, or McNemar’s test, as appropriate. All tests were 2-sided, and p values < 0.05 were considered significant. To evaluate intra-observer variability and assess the consistency of manual tracings, Pearson correlation analysis was employed. Calculations were performed using SPSS version 25.0 (IBM Corporation, Armonk, NY) and R (Vienna, Austria). We could match 60 patients with ASA use with 60 patients without ASA use according to the closest propensity score. Survival data of all patients was collected up to August 15, 2023; these data were subsequently used to construct a Kaplan-Meier curve.

Results

Between October 2014 and January 2018, 189 transplanted patients underwent OCT examinations in 1M and 12M after HTx. In 14 patients, ASA therapy was initiated between 4 weeks and 1 year after HTx and were excluded from this analysis. In total, data from 175 patients was used for this study, with 114 patients on ASA therapy and 61 without ASA use. Altogether, 155 left anterior descending, 11 left circumflex, and 9 right coronary arteries were analysed. At baseline, there were no significant differences in demographics, biochemistry, or medication between the study groups (Table 1).

Table 1.

Patient characteristics by ASA use in the overall study sample.

	Without ASA n=61	With ASA n=114	P
Age, years	51.4±12.4	52±11.8	0.747
Gender (male), n (%)	52 (85.2)	86 (75.4)	0.174
Donor age, years	40.3±12.7	41.7±12.1	0.483
Donor gender (male), n (%)	50 (65.8)	86 (77.5)	0.095
Donor explosive brain death, n (%)	47 (77)	71 (68.3)	0.284
Cold ischemia time, min	138.5 [84–178]	132.7 [91–173]	0.499
Ischemic cardiomyopathy	17 (27.9)	26 (22.8)	0.467
VAD before HTx, n (%)	15 (24.6)	35 (30.7)	0.483
Diabetes, n (%)	23 (37.7)	40 (35.1)	0.744
BMI, kg/m2	25.8±4.6	26.9±4.3	0.108
LV ejection fraction 12M	63.7±4.7	60.4±4.3	<0.001
Laboratory results at 1M/12M
Total cholesterol, mmol/l	4.56±1.13/4.3±1.06	4.82±1.19/4.27±1.17	0.153/0.865
LDL cholesterol, mmol/l	2.39±0.96/2.27±0.83	2.61±0.9/2.29±0.9	0.136/0.855
HDL cholesterol, mmol/l	1.52±0.47/1.26±0.52	1.5±0.4/1.17±0.35	0.782/0.189
Triglycerides, mmol/l	1.43 [1.04–1.78]/ 1.8 [1.08–2.12]	1.55 [1.05–1.91]/ 1.9 [1.22–2.04]	0.216/0.685
HbA1c, mmol/mol	40.6±8.8/45.5±12.9	40.5±7.6/46.6±17.5	0.890/0.687
Haemoglobin, g/l	110±13.6/124±17.1	115±15.5/132.5±15.1	0.083/0.001
Platelet count, 109/l	205±71.3/212±57.5	244±80.5/226±64.9	0.002/0.188
Therapy at 1M/12M
Statin, n (%)	52 (85.2)/ 52 (85.2)	95 (83.3)/102 (89.5)	0.831/0.467
MMF, n (%)	59 (96.7)/ 59 (96.7)	110 (96.5)/110 (96.5)	1.000/1.000
Steroids, n (%)	61 (100)/46 (75.4)	114 (100)/101 (88.6)	1.000/0.030
Tacrolimus, n (%)	59 (96.7)/56 (98.2)	112 (99.1)/113 (100)	0.304/0.335
mTOR inhibitor, n (%)	0/7 (11.5)	0 /11 (9.6)	1.00/0.795
Complications within 12 months after HTx
CMV infection, n (%)	7 (11.5)	12 (10.5)	1.00
Severe cellular rejection, n (%)	3 (4.9)	15 (13.2)	0.118
Humoral rejection, n (%)	1 (1.6)	4 (3.5)	0.034
OCT CAV phenotype 1M/12M
0 (normal)	38 (62.3)/21 (34.4)	60 (52.6)/43 (37.7)	0.077/0.910
1 (lipid)	21 (34.4)/ 19 (31.1)	35 (30.7)/32 (28.1)
2 (thrombofibrotic)	0 (0.0)/ 5 (8.2)	2 (1.8)/7 (6.1)
3 (mixed)	2 (3.3)/16 (26.2)	17 (14.9)/32 (28.1)

Data are presented as mean ± standard deviation, median with interquartile ranges [IQRs], or frequency (percent). ISHLT grade of 2R or higher was considered as severe cellular rejection. Abbreviations: M – month, ASA – acetylsalicylic acid, VAD – ventricular assist device, BMI – body mass index, LV – left ventricle, MMF - mycophenolate mofetil, CMV – cytomegalovirus, OCT – optical coherence tomography, CAV – cardiac allograft vasculopathy

On average, every corresponding part of the OCT pullback had 435 frames per patient, totaling 164,594 frames analyzed. In the intra-observer variability assessment for qualitative OCT analysis, angular differences per frame were reported as follows: −2.3° ± 33.5° for LP, −0.9° ± 43.6° for LFP, 4.0° ± 15.8° for calcifications, and 6.9° ± 20.5° for macrophages. Furthermore, frame-level Pearson correlation analysis revealed correlation coefficients between the retraced and original results to be 0.65 for LP, 0.83 for LFP, 0.78 for calcifications, and 0.65 for macrophages. While there are variations in angular differences attributable to the inherent complexities of frame-level OCT analysis, these findings offer a robust metric for assessing the expert’s (LM) consistency and reliability in identifying specific circumferential pathologies across a large set of randomly selected OCT pullbacks.

At 1 month after HTx, the study groups did not differ in intimal or media thickness, lipid plaque, calcification, or macrophage infiltration burden, while the extent of layered fibrotic plaques was larger in subjects on ASA therapy (p=0.017) (Figure 4).

Figure 4.

Qualitative OCT findings in all patients at baseline (Panel A) and their changes over follow-up period (Panel B)

During the first year after HTx, both intimal (108.4±43.9 vs. 135.8±64.7, p<0.001) and medial thickness (85.2±23.7 vs. 87.4±23.7, p=0.012) progressed, with ASA use having no effect on its progression (Table 2). However, the qualitative OCT analysis demonstrated a reduced extent of lipid plaques in patients with ASA, while there was no effect on other variables (Figure 4).

Table 2.

OCT findings in the overall study sample.

Without ASA (N=61)			With ASA (N=114)		P value
Quantitative OCT measurements 1M/12M
	1M/12M	M12-M1	1M/12M	M12-M1	1M/12M	M12-M1
Mean intimal thickness (μm)	106.4±36.7/138±67.9	31.6±48	109.4±47.3/134.7±63.2	25.3±37.5	0.668/0.745	0.335
Mean medial thickness (μm)	86.0±23.5/89.8±25.0	3.9±11.1	84.8±23.9/86.1±23.0	1.4±12.0	0.746/0.328	0.183
Qualitative OCT measurement – overall burden of observed pathologies per one OCT frame at baseline (1M)
	Without ASA (N=61)		With ASA (N=114)
Lipid plaque	0.00 [0.00–0.87]		0.00 [0.00–2.14]
Layered fibrotic plaque	0.00 [0.00–0.00]		0.00 [0.00–0.00]
Calcification	0.00 [0.00–0.00]		0.00 [0.00–0.00]
Macrophages	0.00 [0.00–0.05]		0.00 [0.00–0.05]
Total risk score	0.00 [0.00–0.05]		0.00 [0.00–0.12]
Qualitative OCT measurement – overall burden of observed pathologies per one OCT frame at follow-up (12M)
Lipid plaque	0.27 [0.00–4.03]		0.36 [0.00–3.65]
Layered fibrotic plaque	0.00 [0.00–0.89]		0.00 [0.00–2.95]
Calcification	0.00 [0.00–0.00]		0.00 [0.00–0.04]
Macrophages	0.02 [0.00–0.43]		0.00 [0.00–0.28]
Total risk score	0.05 [0.01–0.22]		0.07 [0.00–0.34]
Qualitative OCT measurement – overall coronary artery changes per one OCT frame over follow-up period					P value
Lipid plaque	0.21 [0.00–2.73]		0.00 [0.00–0.84]		0.013
Layered fibrotic plaque	0.00 [0.00–0.89]		0.00 [0.00–2.35]		0.631
Calcification	0.00 [0.00–0.00]		0.00 [0.00–0.00]		0.255
Macrophages	0.00 [0.00 −0.24]		0.00 [0.00–0.11]		0.301
Total risk score	0.04 [0.01–0.15]		0.04 [0.00–0.17]		0.818

Data are presented as mean ± standard deviation, median with interquartile ranges [IQRs].

Abbreviations: M – month, ASA – acetylsalicylic acid, OCT – optical coherence tomography

The baseline total risk score represents accumulation of coronary artery wall changes over the course of the donor’s life together with changes that developed within the first month after HTx. The progress of total risk score between 1M and 12M after transplantation was on median higher than the overall baseline risk score (0.0042 [0.0000–0.1611] vs. 0.0039 [0.0000–0.10536]; p=0.011).

Only one episode of significant bleeding (Type 2, menorrhagia not requiring blood transfusion) was observed during the 1-year follow-up (p=1.00). We have observed a higher number of antibody-mediated rejections (p=0.118) and severe cellular rejections (p=0.034) in the ASA group, but the difference between the groups was not significant. Even when the rejections were combined, the difference remained not statistically significant. (p=0.064). Patients were followed from HTx to August 2023, and during this time, ASA usage did not exhibit a significant difference in survival, as evidenced by the Kaplan-Meier curve (p=0.699).(Figure 3).

Figure 3:

Kaplan-Meier survival curve

Propensity score-matched analysis

After propensity score matching, a cohort of 60 paired patients (120 patients in total) divided by ASA use was created. Paired tests confirmed no significant differences in baseline clinical characteristics or OCT measurements (Table 3). However, over the follow-up, ASA use was associated with a significantly reduced extent of lipid plaque burden (p=0.002) (Table 3, Figure 5). The average burden of lipid lesions, relative to 1 frame, remained unchanged in patients using ASA during the follow-up (median 0, IQR 0-0-62), but significantly increased in patients not using ASA (median 0.27, IQR 0–2.66). Baseline LDL cholesterol levels did not correlate with lipid plaque extent changes (p=0.970) or de novo development of lipid plaques (p=0.405). The use of statins also did not alter these changes (p=0.916, p=0.420).

Table 3:

OCT analysis after propensity score matching.

Without ASA (N=60)			With ASA (N=60)		P value
Quantitative OCT measurements 1M/12M
	1M/12M	M12-M1	1M/12M	M12-M1	1M/12M	M12-M1
Mean intimal thickness (μm)	106.7±36.9/138.8±68.2	32.1±48.3	101.5±34.7/124.6±50.7	23.1±30.7	0.413/0.188	0.236
Mean medial thickness (μm)	86.2±23.6/90.2±25.1	3.9±11.2	81.6±21.1/82.4±20.5	0.9±11.4	0.247/0.060	0.179
Qualitative OCT measurements - overall coronary artery change per one OCT frame over follow-up period
OCT baseline	Witdout ASA (n=60)		Witd ASA (n=60)		p-value
Lipid plaque	0.00 [0.00–0.99]		0.00 [0.00–1.23]		0.753
Layered fibrotic plaque	0.00 [0.00–0.00]		0.00 [0.00–0.00]		0.139
Calcification	0.00 [0.00–0.00]		0.00 [0.00–0.00]		0.534
Macrophages	0.00 [0.00–0.06]		0.00 [0.00–0.06]		0.670
Total risk score	0.004 [0.00–0.05]		0.001 [0.00–0.08]		0.958
OCT change during follow-up	Without ASA (n=60)		With ASA (n=60)		p-value
Lipid plaque	0.20 [0.00–2.85]		0.00 [0.00–0.39]		0.002
Layered fibrotic plaque	0.00 [0.00–1.09]		0.00 [0.00–2.09]		0.224
Calcification	0.00 [0.00–0.00]		0.00 [0.00–0.00]		0.231
Macrophages	0.00 [0.00–0.25]		0.00 [0.00–0.09]		0.197
Total risk score	0.04 [0.01–0.15]		0.03 [0.00–0.15]		0.277

Data are presented as mean ± standard deviation, median with interquartile ranges [IQRs].

Abbreviations: M – month, ASA – acetylsalicylic acid, OCT – optical coherence tomography

Figure 5.

OCT findings in matched patients at baseline (Panel A) and their changes over follow-up period (Panel B)

ASA use was not associated with a reduction in the extent of layered fibrotic plaque (p=0.224), calcification (p=0.231) macrophages (p=0.197) or the total risk score (p=0.227).

Discussion

The study presents a 3D OCT evaluation of arterial wall changes and plaque morphology in 175 HTx patients with and without ASA therapy. The main findings can be summed up as follows: (1) We observed significant intimal and medial thickness progression within the first post-transplant year; (2) Early initiation of ASA and its use throughout the first post-HTx year was associated with a significantly lower increase in the extent of lipid plaques progression during the first year after HTx; (3) ASA use did not have any impact on the progression of intimal and medial thickness; (4) There was a significant progression in layered fibrotic plaques burden over the follow-up period, with ASA use having no effect on its development.; (5) The progress of total risk score between 1M and 12M after transplantation was on median higher than the overall baseline risk score.

Despite the existence of many known risk factors, therapeutic options to reduce the burden of CAV remain highly limited. Individual studies have shown that rigorous prevention of CMV infection¹⁵, statin use^16,17, prioritizing everolimus¹⁸ over traditional immunosuppressive therapy, and, more recently, considering antiplatelet therapy can reduce the incidence of CAV. Nevertheless, the association between ASA and CAV development remains unclear due to contradictory and inconsistent findings in reported studies.^5,6,25

Therefore, our study aimed to investigate if early initiation of ASA could influence changes in the coronary artery wall during the first year after HTx and, by doing so, predict its ability to influence the development of CAV. Recent advancements in imaging techniques, particularly OCT, allowed for a closer examination of the arterial wall, revealing a wide range of previously unrecognized abnormalities following HTx^19–20. Using our highly automated 3D quantitative OCT analysis software, we were able to detect small changes in the intimal and medial wall layers of four-fifths of the whole artery length and track them over time. In addition, over 160,000 cross-sectional OCT frames were evaluated in great detail for the presence of the prospectively selected pathologies one by one. The safety of routine low-dose ASA administration was excellent, with only 1 significant (Type 2) bleeding. Kaplan-Meier survival analysis showed that the survival of patients with ASA was not significantly influenced. We have observed a higher number of severe cellular rejections in patients with ASA, yet this difference in groups was not statistically significant. This trend towards a larger rejection risk associated with ASA is discordant with previous studies.^21,22

While the precise role of overt platelet aggregation and platelet thrombi formation²³ requires further investigation, transplantation itself appears to pose a prothrombotic risk. Bjerre et al.²⁴ reported that HTx patients with CAV showed significantly elevated platelet aggregation levels compared to both healthy controls and HTx patients without CAV. Two recent observational retrospective studies have shown that early initiation of ASA after transplantation was associated with reduced CAV development at 5- and 15-year follow-up^5,6. Asleh et al.²⁵ findings agree with the beneficial effect of early ASA use but found that later use of ASA as secondary prevention for patients with established CAV is linked to increased CAV progression and worse overall outcomes.

In our study, we observed a significant increase in intimal and medial thicknesses, while ASA use had no effect on its progression. Another one of the first changes in the arterial wall seen in early CAV seems to be lipid deposition²⁶. Through interaction with endothelial proteoglycans, excessive amounts of lipids are entrapped within the intima and media, both intra and extracellularly²⁷. ASA use was previously demonstrated to reduce the number of foam cells within plaques and increase smooth muscle cell infiltration²⁸. Another way that ASA could affect the stabilization of vulnerable lipid plaques²⁹ is through inhibition of cholesterol crystal formation³⁰, which have been known to induce inflammation³¹ and its ability to perforate the overlying intima layer thanks to its sharp-edged needle-like shape³². Clemmensen, et al. reported that the presence of lipid plaques was a risk factor for CAV, as an increase in their extent correlated with CAV grade²⁷. Results of our detailed 3D OCT analysis documented that early and continuous ASA use in the first post-HTx year significantly reduced the extent of lipid plaque progression. Interestingly, lipid infiltration, thin-cap fibroatheroma, or LP as a part of complex calcified plaque was found in 56% of the ASA group and 45% without ASA at follow-up. Lipid plaques were often found even in vessels, which had a concomitant finding of layered fibrotic plaques, creating the mixed phenotype (34%). To quantify changes of the intimal layer, we introduced the total risk score assessment per each coronary artery, using which each frame was evaluated for the presence of LP, LFP, calcification, macrophages, and neovascularization. We observed a dramatic increase in the total risk score within the first post-HTx year, as the change from 1M to 12M alone was higher than the baseline total risk score. This demonstrates the great burden transplantation poses on coronary arteries. However, ASA use was associated with no beneficial effect on this combined surrogate of coronary artery disease.

Layered fibrotic plaques are thought to be a result of repeated mural thrombosis. Subsequent healing of the thrombosis creates superficial fibrotic layers, characterized by a multi-layered appearance and slightly reduced signal intensity.^4,6 Over time, these thrombi may evolve into a fibrotic stage that can cause severe intimal thickening, luminal narrowing, and the loss of side branches. We have observed LFP both with and without connections to other pathologies. When present, they were usually continuous across a long segment of the artery and became significantly more prevalent over the follow-up period. Despite LFP’s supposed thrombotic origin, ASA usage did not impact its development.

Limitations

This non-randomized observational study presents several limitations:

1. The relatively small sample size of 175 patients may limit generalizability, and the observational design precludes the establishment of causal relationships.

2. The absence of randomization introduced the potential for selection bias, as one of the center’s local protocols initially restricted the initiation of ASA. The decision to administer ASA was left to the discretion of the attending physician, and it was more likely to be administered to patients suspected of having donor-transmitted coronary disease.

3. The first OCT was performed one month after HTx, preventing us from distinguishing between donor-transmitted coronary artery disease and de novo changes resulting from the progression of CAV. To minimize the potential risk of renal function deterioration associated with additional angiographic contrast administration, we limited OCT to one vessel per patient.

4. We attempted to mitigate the influence of confounders through propensity matching and by blinding the OCT assessment to ASA status. Nevertheless, while providing valuable insights, these limitations underscore the need for a cautious interpretation of the study’s conclusions.

Conclusions

In our observational study, we have shown that early initiation and continued use of ASA throughout the first year following HTx is associated with a significantly lower increase in lipid plaque extent at 12-month follow-up. In contrast, ASA did not affect the progression of intimal and medial thickness, lumen area narrowing, or the development of layered fibrotic plaques. These results highlight the potential benefit of ASA in reducing lipid plaque burden, but they also imply that more research (i.e., a randomized blinded study) is necessary to understand how ASA affects other pathological features and the overall prevention of cardiac allograft vasculopathy.

Data statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.