Prognostic Impact of Microvasculopathy on Survival After Heart Transplantation
Evidence From 9713 Endomyocardial Biopsies
Background— Epicardial vasculopathy has been shown to be associated with poor outcome after heart transplantation. We demonstrate that histologically proven stenotic microvasculopathy is a novel prognostic factor for long-term survival.
Methods and Results— In 9713 biopsies harvested within the first posttransplantation year from 873 patients (83% male; mean age, 49.1±0.6 years), light microscopic evaluations (×200) were performed for microvasculopathy, defined as stenotic endothelial and/or medial disease. Prevalence of severe epicardial vasculopathy was defined by presence of ≥75% luminal stenosis in coronary angiography (available in 611 of 873 patients), which was present in 118 of 611 patients (19%). For Kaplan-Meier analysis, we defined fatal cardiac events as lethal acute myocardial infarction, sudden cardiac death, and graft failure. Stenotic microvasculopathy was present in 379 of 873 patients (43%) and was due to medial (345/379; 91%) rather than endothelial disease (2/379; 1%) or a combination of both (31/379; 8%; P<0.001). Endothelial disease (median [95% CI], 12.07 [10.69 to 13.44] versus 12.73 years [10.16 to 15.30]; P=0.3329) and nonstenotic medial disease (12.44 [11.14 to 13.74] versus 12.43 years [10.51 to 14.35]; P=0.4047) did not decrease overall survival or time to fatal cardiac event. Stenotic microvasculopathy was associated with poor overall survival (10.90 [9.16 to 12.60] versus 13.40 years [11.79 to 15.07]; P=0.0374) and decreased freedom from fatal cardiac events (1, 5, 10 years, 95.6±1.4%, 86.9±2.3%, 75.5±3.1% versus 99.1±0.5%, 96.8±1.0%, 89.8±1.9%; P<0.0001). This finding was independent of epicardial transplant vasculopathy (P=0.0031).
Conclusions— Stenotic microvasculopathy is frequent in routinely processed biopsies and a new prognostic factor for long-term survival after heart transplantation.
Received June 20, 2006; accepted July 3, 2007.
The gradual development of transplant vasculopathy (TVP) is one of the major lethal complications during the long-term course after heart transplantation (HTx).1–3 It is characterized by diffuse atherosclerotic alterations of the transplanted heart.4,5 Progressive myointimal lesions in epicardial blood vessels6,7 and medial thickening7–9 in small, intramyocardial coronary arteries finally result in vascular stenosis, leading to acute or chronic graft failure.
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TVP of the large coronary arteries is of proven prognostic impact.1–3,10 Serial screening for epicardial TVP is established in routine follow-up of cardiac transplant recipients, and diagnosis includes the use of international classifications.11,12 Diagnosis of small-vessel disease by routinely processed right ventricular biopsies has been described previously.8,13,14 However, published data have not ascertained the prognostic relevance of microvasculopathy for graft survival and therefore do not justify serial screening procedures by right ventricular biopsies.1,2 In contrast to these findings in cardiac transplant recipients, nontransplanted patients with microvasculopathy due to diabetes mellitus, amyloidosis, or connective tissue disorders are at increased risk for cardiac-related death.15,16
Therefore, we reevaluated the prognostic value of microvasculopathy for survival after HTx in our single-center experience with 9713 right ventricular biopsies taken during the first year after HTx. We propose a biopsy-derived graduation system of posttransplantation microvascular alterations, which is easy to apply to routinely processed endomyocardial biopsies and which supports evidence for the prognostic value of biopsy screening of cardiac transplant recipients at predefined time intervals.
Between April 1986 and December 2002, 1348 patients underwent primary HTx at our hospital. Of these, we excluded pediatric patients (aged <18 years), patients who died during the first 30 days after transplantation, and those who did not undergo biopsy follow-up within the first posttransplantation year. Eight hundred seventy-three patients were suitable for further analysis. The majority of those patients were male (83%), and the leading indication for HTx was dilated cardiomyopathy (64%). Mean age at HTx was 49.1±0.6 years, and median survival time, including time to cardiac retransplantation (n=16), was 12.4 years (95% CI, 11.4 to 13.5 years).
In these 873 patients, a total of 9713 biopsies were collected (11±1 biopsies per patient) within the first year after HTx and were investigated in the present study. We chose only biopsies harvested during the first posttransplantation year to clarify whether evidence of stenotic microvasculopathy in early biopsy identifies patients at risk for a serious cardiac event in the later follow-up.
Biopsies were subdivided according to the time intervals in which they were taken, ie, ≤30 days, >30 to 90 days, >90 to 180 days, 181 to 270 days, and 271 to 365 days (Table 1). All biopsies harvested from cardiac retransplants were excluded from analyses. All investigations were done retrospectively.
Posttransplantation triple immunosuppression was maintained with cyclosporine A 2 to 4 mg/kg (trough level 250 ng/mL; n=829 [95%]) or tacrolimus (trough level 8 to 10 ng/mL; n=44 [5%]), mycophenolate 30 to 50 mg/kg (target dose 2 to 3 g/d, white blood cell count not ≤3500/μL; n=262 [30%]), or azathioprine 1 to 5 mg/kg (white blood cell count not ≤3500/μL; n=611 [70%]) and prednisolone (target dose 0.15 mg/kg after 2 months). Blood levels of cyclosporine A were measured with the use of an enzyme immune assay. Therapy of acute cellular rejection grades 1A to 217 consisted of an oral steroid regimen for 10 days. All rejection of grade 3A17 or higher or clinically symptomatic rejection was treated with polyclonal antibodies (anti-thymocyte globulin) and steroids for 3 days.
Biopsy Harvest Procedure and Histological Tissue Preparations
The right ventricular biopsies (n=9713) were obtained according to standard procedure through a right ventricular approach from the interventricular septum.18 Histological tissue preparation was performed by hemalum and eosin (H&E) stainings (Mayer’s hemalum and eosin, Merck).
Diagnosis of Microvasculopathy
During routine post–cardiac transplantation biopsy procedure, at least 3 tissue sections are harvested and undergo morphological analysis. If we presuppose a section length of 1.0 to 1.5 mm with a cylindrical form, each section provides an area of 1.5 to 2.5 mm2. With at least 3 tissue samples, the area is 4.5 to 7.5 mm2. If we assume that histological sections are cut at 3 levels, the total area per biopsy is 13.5 to 22.5 mm2. In this endomyocardial tissue, arteriolar vascularization accounts for 103±31 vessels per square millimeter and capillary vascularization for 667±147 vessels per square millimeter.9
Diagnosis of microvasculopathy was done by light microscopy (×200). Pathological findings were classified according to the graduation system given in Figure 1 and Table 2. In microvessels (diameter 10 to 20 μm), both the endothelial layer and the wall (medial) layer were identified. The endothelial layer was defined as the monocell layer at the inner part of the blood vessel wall. It was considered normal when there was a thin layer of cells whose diameter was less than the diameter of the endothelial cell cores (Figure 1A, 1D, and Table 2). Endothelial cells were graded as thickened if the diameter of the cell layer was at least as thick as the endothelial cell cores (Figure 1C and Table 2).
The wall layer (media) was defined as the polycell layer adjacent to the endothelium. The adventitia was not characterized separately. The wall was graded as normal if its diameter was less than the luminal radius (Figure 1A and Table 2). Wall thickening was classified as nonstenotic if the ratio of luminal radius to wall thickness was <3 but ≥1 (Figure 1B and Table 2), and stenotic wall thickening was graded if this ratio was <1 (Figure 1C and 1D and Table 2). This grading system was generated according to a histomorphometric study of large peripheral arteries described by Hieronymi.19 Stenotic microvasculopathy was diagnosed if there was evidence of microvascular stenosis due to either endothelial thickening or wall thickening in at least 1 blood vessel per field of view (Figure 1C and 1D and Table 2).
Independent of microvasculopathy, acute cellular rejection was classified according to the International Society for Heart and Lung Transplantation (ISHLT).17 The investigations were done by 2 pathologists blinded to patient data.
Definition of Epicardial Transplant Vasculopathy
To define the prevalence of epicardial TVP, we evaluated in total 1524 coronary angiographies (9 days to 20.5 years after transplantation) available in 611 patients (70%). Severe epicardial TVP was diagnosed at first presence of ≥75% luminal stenosis.10
Statistics and Definition of End Points for Kaplan-Meier Analyses
SPSS for Windows version 11.01 was used for statistical analysis. Results are given as number (n) and mean±SEM (range), if not otherwise indicated.
Analysis of survival and freedom from end points was performed according to Kaplan-Meier estimation. We assigned 2 combined end points: (1) overall survival, which was defined as time to cardiac retransplantation (n=16) or death from all causes (n=392), ie, coronary artery vasculopathy (including chronic graft failure, acute myocardial infarction, sudden cardiac death), acute cellular rejection, malignancy (including lymphoma), infection (including cytomegalovirus), primary graft failure, multiple organ failure, renal failure, pulmonary causes, cerebrovascular causes, and others3,20; and (2) time to fatal cardiac event,21 ie, time to cardiac retransplantation, chronic graft failure, lethal acute myocardial infarction, or sudden cardiac death (n=94).
Survival in different patient groups was compared with the log-rank test. In Kaplan-Meier analyses, endothelial thickening and nonstenotic and stenotic microvasculopathy were tested separately as determinant factors. Individuals were allocated to (1) patients with evidence of at least 1 diseased biopsy in the 1-year sample volume and compared with patients without evidence of diseased biopsy in the 1-year sample volume. To explore whether the prognostic impact of biopsy screening within the first posttransplantation year is linked to continuous or time-related biopsy follow-ups, we tested (2) in each time interval patients with evidence of at least 1 diseased biopsy and compared them with patients showing no evidence of diseased biopsy in the same time interval. A Cox proportional hazards model was used to investigate possible risk factors for fatal cardiac event or retransplantation. A univariate approach was followed by a multivariate Cox regression with backward elimination procedure. Odds ratio was calculated for evidence of microvasculopathy beyond the first 3 months after transplantation in the case of detection at >30 to 90 days after HTx. Univariate and multivariate (backward elimination procedure) logistic regression analysis was performed to identify risk factors for stenotic microvasculopathy. P<0.05 was considered statistically significant.
The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
Prevalence of Microvasculopathy and Severe Epicardial Vasculopathy
Stenotic microvasculopathy was present in 379 of 873 patients (43%) and was due to concentric medial disease (345/379; 91%) rather than concentric endothelial disease (2/379; 1%) or a combination of both (31/379; 8%; χ2=519.884, P<0.001). Once developed, stenotic microvasculopathy correlated significantly with subsequent evidence of stenotic microvasculopathy in biopsy (odds ratio, 2.77; 95% CI, 1.90 to 4.04; P<0.001). Severe epicardial TVP was recorded in 118 of 612 patients (19%) at a mean time of 5.7±0.2 years after transplantation. Single-vessel disease was found in 50 cases (42%), double-vessel disease in 31 cases (26%), and triple-vessel disease in 37 cases (34%).
Freedom From Stenotic Microvasculopathy and Severe Epicardial Vasculopathy
Freedom from microvasculopathy at 3, 6, 9, and 12 months after transplantation was 64±3%, 44±3%, 35±3%, and 32±3%, respectively. In 611 patients who underwent coronary angiographic investigations, freedom from severe epicardial TVP at 1, 3, 5, and 10 years after transplantation was 98.8±0.5%, 96.9±0.8%, 91.6±1.4%, and 75.0±2.7%, respectively.
Microvasculopathy and Overall Survival
The overall survival (median time to death or cardiac retransplantation) of our population was 12.43 years (95% CI, 11.41 to 13.45 years).
In analysis of the 1-year sample volume of biopsies, neither endothelial thickening (median [95% CI], 12.07 years [10.69 to 13.44] versus 12.73 years [10.16 to 15.30]; P=0.3329) nor nonstenotic wall thickening (12.44 [11.14 to 13.74] versus 12.43 years [10.51 to 14.35]; P=0.4047) was associated with decreased survival. In addition, the time point of biopsy harvest indicating endothelial thickening or nonstenotic wall thickening was not correlated with poor survival.
Stenotic microvasculopathy evidenced by stenotic medial disease, however, was associated with poor overall survival (10.90 years [9.16 to 12.60] versus 13.40 years [11.79 to 15.07]; P=0.0374; Figure 2). Decreased survival was also found if microvasculopathy was evident in biopsies obtained during days >270 to 365 (8.06 years [2.82 to 13.29] versus 13.35 years [11.91 to 14.79]; P=0.0183) but not if evident in biopsies harvested during days ≤30 (10.11 years [7.38 to 12.83] versus 12.25 years [1.11 to 13.39]; P=0.1966), days >30 to 90 (11.43 years [7.55 to 15.31] versus 12.07 years [10.74 to 13.59]; P=0.5191), days >90 to 180 (11.17 years [7.74 to 14.59] versus 12.53 years [11.11 to 13.95]; P=0.1287), or days >180 to 270 after transplantation (12.25 years [9.04 to 15.47] versus 12.53 years [11.18 to 13.89]; P=0.8407).
Microvasculopathy and Fatal Cardiac Events
Freedom from serious cardiac event or cardiac retransplantation (n=552) at 1, 5, and 10 years after transplantation was 97.6±0.7%, 92.6±1.1%, and 83.6±1.8%, respectively.
When the 1-year biopsy sample volume was analyzed, freedom from fatal cardiac event was not decreased in the presence of endothelial thickening or nonstenotic wall thickening. In addition, the time point of biopsy harvest indicating endothelial thickening or nonstenotic wall thickening was not correlated with decreased freedom from fatal cardiac events.
Stenotic microvasculopathy evidenced by stenotic wall thickening was the only parameter that decreased freedom from fatal cardiac events (Figure 3), and this effect was independent of epicardial TVP. Further analyses of time points of biopsy harvest procedures within the first posttransplant year showed that stenotic microvasculopathy evidenced at >30 to 90 days and >270 to 365 posttransplant days was associated with high rates of fatal cardiac events, whereas no correlation was found with stenotic microvasculopathy evidenced at ≤30 days, >90 to 180 days, and >180 to 270 days (Figure 4).
Cox proportional hazards analyses for fatal cardiac events, ie, cardiac-related death (excluding acute cellular rejection) and cardiac retransplantation, are presented in Table 3. In univariate regression analyses, we found stenotic microvasculopathy evident in at least 1 biopsy of the 1-year sample volume, in at least 1 biopsy harvested at days >30 to 90 or at days >270 to 365, or in at least 1 of both time intervals; nonstenotic microvasculopathy or endothelial thickening evident in at least 1 biopsy of the 1-year sample volume; the number and grade of acute cellular rejection episodes; the pretransplant conditions of recipient cytomegalovirus positive at HTx, donor age, and transplant year before 1992; and the clinical parameters of treated diabetes mellitus and epicardial vasculopathy to be associated with fatal cardiac events, whereas treated arterial hypertension, female recipient gender, and dilated cardiomyopathy before HTx were inversely correlated with fatal cardiac events.
However, in multivariate regression analysis (Table 3), we found only stenotic microvasculopathy evidenced in at least 1 biopsy harvested at days >30 to 90 or at days >270 to 365 (risk ratio [95% CI], 2.02 [1.27 to 3.24]; P=0.003), treated diabetes mellitus (1.77 [1.09 to 2.68]; P=0.020), and epicardial vasculopathy (2.58 [1.61 to 4.14]; P<0.0001) to be associated with fatal cardiac events.
Correlation of Stenotic Microvasculopathy in Biopsy and Severe Epicardial Vasculopathy in Angiography
Freedom from epicardial TVP in patients without stenotic microvasculopathy at 1, 3, 5, 7, 10, and 15 years was 100%, 98±2%, 98±2%, 96±3%, 93±4%, and 80±7%, respectively, and in patients with microvasculopathy at the same intervals was 99±1%, 98±1%, 95±2%, 94±2%, 87±3%, and 81±4%, respectively (P=0.4510).
Because, except for 1 patient, all cases of stenotic epicardial TVP were diagnosed beyond the first year, we tested the correlation of stenotic microvasculopathy evident within the first posttransplantation year with later evidence of epicardial TVP. Here we found only patients with stenotic microvasculopathy at >270 to 365 days after transplantation to be at higher risk of later developing stenotic 3-vessel disease in coronary angiography (odds ratio, 3.28 [95% CI, 1.16 to 9.27]; P=0.025) with involvement of the left coronary artery (2.56 [1.24 to 5.30]; P=0.011).
Risk Factors for Stenotic Microvasculopathy
At all time points of biopsy harvest, we found a correlation between endothelial thickening and stenotic microvasculopathy, ie, at days >30 to 90 (Pearson correlation coefficient r=0.220; P=0.001), >90 to 180 (r=0.193; P=0.003), >180 to 270 (r=0.308; P<0.0001), and >270 to 360 (r=0.241; P<0.0001) after transplantation.
In univariate regression analyses for stenotic microvasculopathy in at least 1 biopsy of the 1-year sample volume (Table 4), the following were identified as significant risk factors: at least 1 biopsy with nonstenotic microvasculopathy within the first 90 days, at least 1 biopsy with endothelial thickening within the first 270 days, acute cellular rejection of any grade (overall prevalence of ISHLT grades 1A to 2 in 40% [3864/9713] and ISHLT grades 3A to 4 in 9% [864/9713] of biopsies), coronary heart disease as diagnosis leading to HTx, and transplant years before 1992. Ischemic and reperfusion times, donor age, assist device before HTx, positive cytomegalovirus status at HTx, at least 1 episode of treated cytomegalovirus infection after transplantation, renal insufficiency (serum creatinine >1.6 mg/dL), and treated hyperlipidemia were correlated with lower evidence of stenotic microvasculopathy. However, the majority of patients with renal insufficiency (70%; 535/761) were treated additionally for hyperlipidemia (P<0.0001).
Multivariate regression analysis (Table 4) confirmed only endothelial disease in at least 1 biopsy during posttransplantation days >30 to 90 (odds ratio, 1.96 [95% CI, 1.38 to 2.78]; P<0.0001) and the number of 1-year acute cellular rejection ISHLT grades ≤2 (odds ratio, 1.17 [95% CI, 1.12 to 1.22]; P<0.0001) as significant risk factors, whereas treated hyperlipidemia was associated with lower evidence of stenotic microvasculopathy in at least 1 biopsy of the 1-year sample volume (odds ratio, 0.68 [95% CI, 0.47 to 0.96]; P=0.029).
In the present study we describe in a representative cohort of 873 HTx patients the prevalence and prognostic impact of early microvasculopathy in routinely processed endomyocardial biopsies. We found that stenotic microvasculopathy after HTx is a medial disease that affects >40% of cardiac transplant recipients within the first posttransplantation year. It is associated with both poor overall survival and reduced freedom from fatal cardiac events if evident in at least 1 biopsy harvested within the first posttransplantation year, independently of epicardial TVP.
We chose the intimal and medial layers as target parameters for small-vessel disease in biopsy because both endothelial cells and smooth muscle cells play a central role in the development of TVP.21,22 In support of data published by ourselves and others,7–9,23 we found stenotic microvasculopathy as a consequence of medial disease but without intimal thickening, which has been identified as a major pathological finding in epicardial TVP.6,7 Thus, TVP after HTx presents itself as concentric medial disease in the microvasculature and as intimal disease in epicardial coronary arteries.6,7
Our finding that evidence of stenotic microvasculopathy in biopsy as early as within the first postoperative year is relevant for long-term prognosis after HTx has been suggested previously.13 However, we present longitudinal data from a large cohort of patients and investigated the impact on clinical outcomes, which has not been reported earlier. We proved the prognostic impact of stenotic microvasculopathy in at least 1 biopsy of the total sample volume for the development of fatal cardiac events. According to the multivariate Cox proportional hazards model, we also showed evidence of stenotic microvasculopathy in at least 1 biopsy at posttransplantation days >30 to 90 and >270 to 365 together with severe epicardial vasculopathy and diabetes mellitus to be relevant for risk estimation of fatal cardiac events.
However, we also identified “intermediate” lesions that were nonstenotic and not associated with poor survival or fatal cardiac events. According to Armstrong and colleagues23 and our previous observations,9 these findings might represent microvascular remodeling after HTx, characterized by an increase of vascular smooth muscle α-actin over time. Thus, posttransplantation microvascular alterations might not be graded primarily as disease24 but rather as a transplant-related, “physiological” process. Follow-up data in this field are mandatory and may provide evidence for the impact of this microvascular remodeling on the later development of stenotic microvasculopathy.
Endothelial cell swelling has been characterized before in terms of antibody-mediated rejection.25 We did not investigate vascular deposition of immunoglobulin and complement because our primary target was to establish morphological criteria for microvascular disease in routinely processed biopsies with impact on survival. We proved that endothelial thickening alone was not correlated with poor survival, but it was significantly associated with evidence of stenotic microvasculopathy. Endothelial cells play a central role in the development of epicardial TVP21 and have been suggested as “key operators” in the “response to injury model,” finally leading to obstructive coronary lesions in the transplanted heart.26 Although we could not determine the origin of endothelial thickening, we suggest a change in the endothelial cell surface as initiating the development of microvasculopathy.26 We demonstrated acute cellular rejections of ISHLT grades ≤217 as risk factors for the development of stenotic microvasculopathy, which supports our hypothesis that microvasculopathy is an immune-mediated phenomenon, similar to epicardial TVP.21 Furthermore, this finding supports our own strategy of treating even low-grade acute cellular rejection with increased immunosuppression.
Stenotic microvasculopathy in biopsy seems to be a de novo process in the transplanted heart rather than an effect due to imported lesions because we found a correlation with younger donor age. Furthermore, coronary heart disease as a primary cause of HTx was not confirmed as a risk factor in multivariate regression analysis, suggesting only weak effects of classic cardiovascular risk factors in the development of stenotic microvasculopathy, which has also been demonstrated for epicardial TVP.21 Proliferation of vascular smooth muscle cells has been demonstrated in the development of stenotic microvasculopathy; however, this process was discontinued beyond the first 3 posttransplantation months.9 Thus, mechanisms other than microvascular stenosis itself may play a role in microvasculopathy at the end of the first posttransplantation year and its effects on serious cardiac events in further follow-up. Because we found a strong correlation between endothelial disease and stenotic microvasculopathy at any time after HTx, we suggest a shift from an early immunogenic to a later prothrombotic endothelium phenotype to be causal for poor prognosis of stenotic microvasculopathy at the end of the first year. Enhanced platelet activation has been described in the development and progression of epicardial vasculopathy27 and might be involved in our finding of lower risk for microvasculopathy in patients on assist device before transplantation, who are usually on antiplatelet therapy. Clopidogrel is known to have antithrombotic and antagonistic effects on smooth muscle cell proliferation,28 and we suggest that it may be a novel approach in prevention and treatment of transplant vasculopathy in epicardial and small intramyocardial blood vessels. Our study also supports a known prophylactic approach to transplant vasculopathy, which is the use of statins.29 We suggest beneficial effects of early statin treatment on the epicardial29 and microvascular level because we demonstrated patients with treated hyperlipidemia to be at low risk for stenotic microvasculopathy within the first posttransplantation year. Although we found, as for epicardial TVP, an era effect,3 which might be due to different strategies in the posttransplantation management of comorbidities, we failed to demonstrate as risk factors for microvasculopathy greater age of recipients or donor grafts, female gender, or cytomegalovirus, which have been shown to have an impact on the development of epicardial TVP.21,30,31 This might be due, at least in part, to different etiopathogenetic pathways for intima-related epicardial and media-related microvascular manifestation of this disease. In support of this partial overlap hypothesis, evidence of stenotic microvasculopathy at >270 to 365 days after transplantation identified patients with higher risk for the development of stenotic epicardial TVP in further follow-up and may be useful as a surrogate marker for subsequent severe epicardial TVP.
We did not analyze the impact of different immunosuppressive regimens on the development of microvasculopathy in biopsy because the number of patients on tacrolimus or mycophenolate was low. Thus far, published treatments focus exclusively on preventive and therapeutic strategies for epicardial vasculopathy20,29; however, our data demonstrate the need to include stenotic microvasculopathy in biopsy as a novel target lesion in future clinical trials.
The histomorphometric evaluation of biopsies was performed retrospectively; therefore, we have initiated a prospective clinical trial to confirm our results in a longitudinal observational study protocol. The tissue sections investigated here were restricted to right ventricular endomyocardium, and a sampling bias cannot be excluded. No functional tests were performed to evaluate the hemodynamic significance of microvasculopathy. This was due to the retrospective design of the study and was why we chose overall survival and fatal cardiac events as reliable end points.
Pathological features of the microvascular endothelial and wall layer in routinely processed posttransplantation biopsies are frequent and not necessarily associated with poor outcome. Evidence of stenotic microvasculopathy in biopsy, however, has a prognostic impact on survival after HTx and is associated with fatal cardiac events independently of epicardial vasculopathy. The graduation of microvascular findings proposed here is easy to apply in routinely processed endomyocardial tissue sections. It provides evidence for the prognostic value of time-dependent biopsy screening of cardiac transplant recipients for microvasculopathy, and closer attention should be given to stenotic microvasculopathy evident in biopsies harvested within the first and the last 3 months of the first year after HTx. Patients with stenotic microvasculopathy are at increased risk of developing stenotic epicardial disease and should undergo angiographic follow-up to identify potential epicardial target lesions. Early statin therapy and aggressive treatment of acute cellular rejection within the first posttransplantation year independent of grade may prove to be promising preventive strategies for microvasculopathy and deserve further study.
Ther authors thank Wolf Rafflenbeul, MD, PhD; Martina de la Chevallerie, MD; and Duska Dragun, MD, PhD, for their valuable comments on this manuscript. We are grateful for editorial assistance from Anne Gale, ELS.
Source of Funding
Our prospective study, in which we validate the graduation of microvasculopathy presented here, was supported by the German Research Foundation (trial registration No. He 1669/13-1).
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Transplant vasculopathy is one of the major complications threatening long-term survival in cardiac transplant recipients. Epicardial vasculopathy indicates poor clinical course, but prognostic relevance of microvasculopathy for graft survival has not yet been established. We demonstrate in 9713 biopsies harvested from 873 patients that histologically proven stenotic microvasculopathy within the first posttransplantation year is a novel prognostic factor for long-term survival. Stenotic microvasculopathy affected 43% of our patients and was associated with poor overall survival (P=0.0374) and decreased freedom from fatal cardiac events, ie, cardiac retransplantation, lethal acute myocardial infarction, sudden cardiac death, and graft failure (P<0.0001), independently of epicardial transplant vasculopathy (P=0.0031). Stenotic microvasculopathy was associated with prevalence and severity of acute cellular rejection and was decreased in the presence of statin therapy. Patients with microvasculopathy in biopsy were at higher risk of developing stenotic epicardial vasculopathy in further follow-up. Protective effects of statins have been proven in epicardial vasculopathy, and acute cellular rejection has been suggested as a risk factor in this field. To prevent both the epicardial and microvascular phenotype, we recommend statin use in all cardiac transplant recipients and aggressive treatment of acute cellular rejection independently of severity. We suggest yearly angiographic follow-up examinations to identify patients in whom beneficial effects of interventional treatment can be expected. Biopsy screening at 30 to 90 days and 270 to 365 days after heart transplantation is recommended to characterize patients at high risk for a lethal clinical course because of stenotic microvasculopathy in the long-term follow-up.