- Email: [email protected]
Is all intimal proliferation created equal in cardiac allograft vasculopathy? The quantity–quality paradox
ALLOGRAFT VASCULOPATHY
Is All Intimal Proliferation Created Equal in Cardiac Allograft Vasculopathy? The Quantity–Quality Paradox Mandeep R. Mehra, MD, Hector O. Ventura, MD, Patricia A. Uber, PharmD, Robert L. Scott, MD, and Myung H. Park, MD Background: Pre-angiographic detection of intimal proliferation using intravascular ultrasound in heart transplant recipients has focused investigators’ attention on the prognostic utility of such early information. Not all heart transplant recipients who exhibit a “prognostically relevant” threshold of severe (⬎0.5 mm) intimal thickening experience cardiac events. We sought to contrast clinical characteristics of heart transplant recipients who have prognostically relevant, severe intimal proliferation and who experience cardiac events with those who remain event free. Methods: We prospectively followed an inception cohort of 54 consecutive heart transplant recipients with severe intimal proliferation (intimal thickness ⬎0.5mm) of the coronary arteries after index intravascular ultrasound examination to assess the development of cardiac events (sudden cardiac death, myocardial infarction) and/or the necessity for coronary revascularization with percutaneous techniques (angioplasty, atherectomy, stent implantation) or surgical bypass. Results: Based on the occurrence of adverse cardiac events during the subsequent 24 months, we divided the study cohort into 2 groups: Group 1 (no event, n ⫽ 33) and Group 2 (cardiac event, n ⫽ 21). Both groups demonstrated similar intimal thickness at the index ultrasound (Group 1, 0.89 ⫾ 0.27 mm, vs Group 2, 0.94 ⫾ 0.36 mm; p ⫽ not significant). Those with cardiac events were more likely than those without events to have hyperlipidemia, to have greater exposure to cumulative and average daily prednisone, and to exhibit greater average biopsy rejection scores at follow-up. Conclusions: These observations underscore the importance of the quality and not merely the quantity of intimal proliferation in determining occurrence of morbid cardiac events and further emphasize the interaction of immunologic and nonimmunologic factors in determining event vulnerability in cardiac allograft vasculopathy. J Heart Lung Transplant 2003;22:118 –123.
I
ntravascular ultrasound technology has allowed delineation of the unique morphologic features of From the Ochsner Cardiomyopathy and Heart Transplantation Center, Ochsner Clinic Foundation, New Orleans, Louisiana. Submitted June 28, 2001; revised September 26, 2001; accepted April 24, 2002. Reprint requests: Dr. Mandeep R. Mehra, 1514 Jefferson Highway, New Orleans, Louisiana 70121. Telephone: 504-842-5630.
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cardiac allograft vasculopathy.1 Rapid advances in characterizing the natural history of cardiac allograft vasculopathy with pre-angiographic detection Fax: 504-842-4184. E-mail: [email protected] Copyright © 2003 by the International Society for Heart and Lung Transplantation. 1053-2498/03/$–see front matter PII S1053-2498(02)00492-8
The Journal of Heart and Lung Transplantation Volume 22, Number 2
of intimal proliferation have focused investigator’s attention on the prognostic utility of such early information.2,3 Indeed, studies by our group and others seeking to define the ramifications of intravascular ultrasound– detected intimal proliferation have established a prognostically relevant severity threshold of ⬎0.5 mm, which reliably correlates with the occurrence of adverse clinical events in heart transplant recipients, even in the absence of angiographically evident disease.3,4 Even though identifying a prognostically relevant threshold of intravascular ultrasound– derived intimal proliferation is a major accomplishment, not all heart transplant recipients who exhibit this finding experience morbid events. Several questions can be raised regarding this issue: Do particular factors distinguish heart transplant recipients with prognostically relevant intimal proliferation who go on to experience morbid clinical events from those who do not? Is the further magnitude of intimal proliferation or the duration of survival a major determinant of clinical events, or are other clinical factors ultimately responsible for clinical vulnerability to adverse events? Therefore, our purpose in this investigation was 2-fold: (1) to compare similarities and differences that characterize heart transplant recipients with prognostically relevant, severe intimal proliferation who experience cardiac events with those who remain event free; and (2) to describe the importance of clinical and laboratory factors in determining the vulnerability of intimal proliferation to cardiac events.
METHODS Patient Population The study population consisted of an inception cohort of 54 consecutive heart transplant recipients with evidence of prognostically relevant severe intimal proliferation (intimal thickness, ⬎0.5 mm), determined by intravascular ultrasound examination of the coronary arteries between 1994 to 1995. These patients were then prospectively followed after index intravascular ultrasound examination and to assess the development of cardiac events. All study participants provided informed consent and the institutional review board approved the study.
Data Collection Non-immunologic risk factors In all cardiac transplant recipients, we assessed fasting lipid profile (triglyceride, total cholesterol, low-density lipoprotein cholesterol, and high-den-
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sity lipoprotein cholesterol levels) at the time of ultrasound examination, obesity (percentage weight gain, body mass index), hypertension (defined according to the Joint National Committee on Prevention, Detection, and Treatment of High Blood Pressure [JNC-VI] criteria), diabetes mellitus, donor age and gender, ischemic time, time since transplantation, and cytomegalovirus infection (defined as a clinical syndrome in association with either new seroconversion, positive blood cultures, or evidence of tissue invasion) that required therapeutic intervention with intravenous ganciclovir. Immunologic risk factors Rejection surveillance during the first year consisted of weekly endomyocardial biopsies for the first month after transplantation, biweekly until the third month, monthly until the sixth month, and bimonthly thereafter until completion of the first year. Thus, the routine protocol mandates 14 biopsies during the first year. All biopsy specimens were graded using the International Society for Heart and Lung Transplantation (ISHLT) grading scheme. The criteria for treating cellular rejection included the finding of a 3A or greater biopsy grade. If treatment was initiated for a lower biopsy grade, it was done only in the presence of hemodynamic compromise as evidenced by 1 or more of the following: a 20% decrease in ventricular ejection fraction, an increase in pulmonary capillary wedge pressure ⬎25%, and a decrease by 25% in the cardiac index or an absolute value of ⬍2.0 liter/min/ m2. Furthermore, episodes of treated rejection mandated follow-up biopsy within 1 to 2 weeks to document resolution or regression to a lower rejection grade. Additionally, a first-year mean biopsy rejection score, as previously described, was determined for all patients. We adapted this from the standardized ISHLT criteria and assigned individual scores to each defined biopsy grade as follows: ISHLT Grade 0 ⫽ 0, Grade IA ⫽ 1, Grade IB ⫽ 2, Grade 2 ⫽ 3, Grade 3A ⫽ 4, Grade 3B ⫽ 5, and Grade 4 ⫽ 6. We computed the mean biopsy score as the average of all biopsy scores during the first year after transplantation. In addition, we assessed in all patients episodes of vascular (humoral) rejection and the number of HLA-A, -B, or -DR matches between the donor and recipient. Acute vascular rejection was defined by the presence of hemodynamic compromise along with histologic evidence of endothelial cell activation and positive immunofluorescence in biopsy
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specimens. More importantly, we also assessed immunosuppression regimens in all patients and calculated the cumulative prednisone dose (total amount of intravenous and oral prednisone consumed in grams), average daily prednisone dose (mg/kg/day), mean cyclosporine dose (mg/kg/day), mean cyclosporine levels (pg/ml), and mean azathioprine dose (mg/kg/day). We also assessed the use of cytolytic therapy (OKT3 or anti-thymocyte globulin) and methotrexate for each study patient.
Intravascular Ultrasound Coronary ultrasound procedure Coronary ultrasound was performed as we have previously reported.3 After administration of 200 g intracoronary nitroglycerin, the ultrasound catheter was positioned in the distal segment of the target vessel over a 0.014-inch (0.036-cm) guide wire. The target vessel was selected by the presence of at least 3 easily definable and reproducible branch points to assist in the accurate and serial assessment of 3 regions of interest. The guide wire was removed, and the ultrasound catheter was advanced to the distal end of the ultrasound sheath under fluoroscopic guidance. The drive module was then engaged, and continuous images of the coronary artery were obtained as the ultrasound transducer was slowly withdrawn. Additionally, fluoroscopic pictures and audio annotations were used to ensure the correct localization of the artery segment for subsequent off-line analysis. Guiding catheter pressure, ST-segment changes, and cardiac rhythm were continuously monitored during the procedure. After ultrasound images were obtained, both the transducer and sheath were removed, and a final angiogram was obtained to confirm the patency of the coronary vessel. No complications were encountered except for coronary artery vasospasm, readily reversed by intracoronary infusion of nitrates or verapamil. Coronary ultrasound assessment One of the investigators, who had no knowledge of the prior assessment of risk factors, performed the intravascular ultrasound measurements. Three coronary sites per vessel (proximal, mid, and distal), for a total of 162 coronary artery segments, were evaluated. The left anterior descending artery was examined in 48 patients, the circumflex artery was examined in 2, and the right coronary artery was examined in the remaining 4 subjects. Maximal intimal thickness and intimal area were obtained by tracing the lumen vessel wall interface and the
The Journal of Heart and Lung Transplantation February 2003
external border of the intimal layer. Intimal index was calculated as the ratio of intimal area to the total vessel area. The definition of severe intimal thickness was based on the scheme previously described by St. Goar et al,5 wherein severe intimal thickening is ⬎0.5 mm of intimal proliferation involving ⬎180° of the vessel circumference, or any intimal layer ⬎1.0 mm in any one area of the vessel circumference. This threshold of severity denotes the unequivocal presence of intimal thickening and is beyond the 98th percentile of any published normal values. Moreover, we have demonstrated previously that this threshold of severe intimal proliferation evidenced by intravascular ultrasound is predictive of cardiac events even in the absence of angiographic abnormalities, and therefore denotes a prognostically relevant threshold of abnormality.2
Cardiac Events We defined cardiac events as the occurrence of sudden cardiac death, myocardial infarction, or the necessity for coronary revascularization with percutaneous techniques (angioplasty, atherectomy, stent implantation) or surgical bypass.
Statistical Methods Normally distributed data are reported as mean ⫾ standard deviation. Differences among categorical variables were assessed using chi-square or Fisher’s exact test. We used the unpaired Student’s t-test to define differences among continuous variables in sub-groups. Kaplan Meier actuarial analysis was used to assess event-free survival for the study cohort. All analyses were performed using Statview 4.5 (Abacus concepts Inc., Berkeley, CA) statistical software, and statistical significance was set at a p ⬍ 0.05.
RESULTS Clinical Characteristics The study population included 54 consecutive heart transplant recipients (50 men and 4 women) with a mean age of 53 ⫾ 8 years (range, 22 to 68 years) who were prospectively followed for 24 months after index ultrasound examination that detected prognostically relevant intimal proliferation (⬎0.5mm). Based on the occurrence of adverse cardiac events, we divided the study cohort into 2 groups: Group 1 (no event, n ⫽ 33) and Group 2 (cardiac event, n ⫽ 21). All subsequent results compare clinical characteristics, non-immunologic, and immunologic risk factors between these 2 groups of patients.
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TABLE I Non-immunologic factors
Recipient age (years) Donor age (years) Recipient sex Donor sex Ischemic time (minutes) Diabetes mellitus Weight gain CMV infection % Post-transplant survival (years) Total cholesterol (mg/dl) LDL (mg/dl) HDL (mg/dl) Triglycerides (mg/dl) Lipid therapy
Event-free group (n ⴝ 33)
Cardiac event group (n ⴝ 21)
52 ⫾ 10 32 ⫾ 11 32 male (97%) 19 male (58%) 177 ⫾ 65 37% 14.2 ⫾ 9.5 12.9% 2.8 ⫾ 1.6 209 ⫾ 23 139 ⫾ 23 27 ⫾ 9 167 ⫾ 55 45%
54 ⫾ 6 30 ⫾ 10 18 male (86%) 12 male (57%) 179 ⫾ 33 32% 10.3 ⫾ 7.2 11% 3.1 ⫾ 1.8 257 ⫾ 32# 176 ⫾ 36## 29 ⫾ 11 215 ⫾ 84* 57%
#
p ⬍ 0.001, ##p ⫽ 0.005, *p ⫽ 0.01. CMV, cytomegalovirus; HDL, high-density lipoprotein; LDL, low-density lipoprotein.
Cardiac Event Analysis
Differences in Non-immunologic Factors
We noted 21 adverse clinical events. Of these, 15 were cardiac deaths, 2 were myocardial infarctions, and 4 were percutaneous revascularizations (3 arthrectomies and 1 coronary stent implantation). Twenty-five percent of the patients with cardiac events demonstrated rapid progression of disease, as seen by angiography performed because of myocardial infarction or revascularization procedures; 2 patients who experienced sudden death demonstrated severe 3-vessel coronary artery disease on necropsy. The remaining 33 heart transplant recipients remained event free (Figure 1).
Table I lists comparative non-immunologic characteristics of the no-event (Group 1) and cardiac event (Group 2) cohorts with regard to recipient and donor age, recipient and donor sex, cold ischemic time, lipid characteristics, weight gain, cytomegalovirus infection, and diabetes mellitus. Specifically, we observed no significant clinical differences between the 2 groups with reference to any of these non-immunologic factors except for increased levels of lipids (total cholesterol, low-density lipoprotein cholesterol, and triglycerides) in those with cardiac events despite lipid-decreasing therapy (all p ⬍ 0.01).
Differences in Immunologic Factors Table II lists a comparison of immunologic risk factors including episodes of allograft rejection, the number of HLA matches, and the mean first-year biopsy rejection score. Although we observed no significant differences among clinical episodes of
TABLE II Immunologic variables Event-free group (n ⴝ 33)
FIGURE Actuarial-survival curve of patients with events depicting number of events over time after the index intravascular ultrasound detected severe intimal thickening (⬎0.5 mm).
Cardiac event group (n ⴝ 21)
Number of HLA matches 1.0 ⫾ 1.1 0.6 ⫾ 0.7 Treated rejection episodes 40% 38% Average biopsy rejection score 0.86 ⫾ 0.35 1.1 ⫾ 0.36# #
p ⫽ 0.05
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TABLE III Immunosuppressive regimens
Cumulative prednisone (g) Average prednisone (mg/kg/day) Average cyclosporine (mg/kg/day) Mean cyclosporine level (pg/ml) Average azathioprine (mg/kg/day)
Intravascular Ultrasound Analysis
Event-free group (n ⴝ 33)
Cardiac event group (n ⴝ 21)
10.6 ⫾ 4.8 0.09 ⫾ 0.04
15.6 ⫾ 6.9* 0.13 ⫾ 0.06**
3.9 ⫾ 1.0
3.6 ⫾ 1.6
170 ⫾ 34
167 ⫾ 32
1.4 ⫾ 0.5
1.3 ⫾ 0.7
*p ⫽ 0.005, **p ⫽ 0.06.
We found no significant differences with regard to magnitude of intimal proliferation in the group with cardiac events (Group 2) compared with the group without events (Group 1) (intimal thickness, 0.94 ⫾ 0.36 mm vs 0.89 ⫾ 0.27 mm; p ⫽ 0.21). We further assessed lesions for plaque location, morphology, and eccentricity. The predominant morphologic characteristics of the vessels studied revealed diffuse and concentric lesions (at least 2 of 3 segments) in 82%, whereas only 18% of vessels studied revealed proximal, focal, and eccentric lesions. The intraobserver (4.1%) and interobserver (5.4%) variability was assessed as previously reported and demonstrated good test reproducibility.3
Survival Analysis allograft rejection or the number of HLA matches, heart transplant recipients with cardiac events had higher average biopsy rejection scores (Group 2, 1.1 ⫾ 0.31, vs Group 1, 0.81 ⫾ 0.24; p ⬍ 0.05).
Differences in Immunosuppression Regimens Table III compares immunosuppression exposure between the patients with cardiac events and those without clinical events. We found significant differences in relation to cumulative prednisone dose (Group 1, 10.6 ⫾ 4.7 g, vs Group 2, 15.6 ⫾ 6.9 g; p ⫽ 0.005), and average prednisone dose (Group 1, 0.09 ⫾ 0.04 mg/kg/day, vs Group 2, 0.13 ⫾ 0.05 mg/kg/day; p ⫽ 0.05). We observed no significant differences in cyclosporine, azathioprine, and cytolytic antibody exposure during the transplant duration. Multiple regression analysis of variables associated with greater cumulative prednisone dose included time after transplantation; cholesterol, triglycerides, and high-density lipoprotein cholesterol concentrations; and weight gain after transplantation (Table IV).
TABLE IV Factors associated with cumulative prednisone exposure: multiple regression analysis Post-transplant survival Total cholesterol (mg/dl) HDL cholesterol Triglycerides % Weight gain HDL, high-density lipoprotein.
r value
p value
0.56 0.35 0.34 0.24 0.39
⬍0.0001 0.01 0.007 0.05 0.006
We found no significant difference in time from transplantation to index ultrasound between the 2 groups (Group 1, 32.4 ⫾ 3.3 months, vs Group 2, 38.3 ⫾ 4.9 months; p ⫽ 0.31). Additionally, the 2 groups did not differ with regard to follow-up time after index intravascular ultrasound examination detected the presence of severe intimal proliferation (Group 1, 26.6 ⫾ 1.9 months, vs Group 2, 24.3 ⫾ 3.1 months; p ⫽ 0.49).
DISCUSSION The findings of this investigation demonstrate that factors independent of survival time and magnitude of intimal thickness determine the expression of clinical events in patients with cardiac allograft vasculopathy manifested with prognostically relevant intimal proliferation detected by intravascular ultrasound.3 Thus, heart transplant recipients with significant cardiac allograft vasculopathy who were exposed to greater cumulative prednisone consumption (a surrogate marker for worse hyperlipidemia, excess weight gain, and alloreactivity) had more severe hyperlipidemia and higher rejection scores and were most likely to experience deleterious cardiac events despite similar degrees of intimal thickness and survival times. Intravascular ultrasound detection of severe, prognostically relevant intimal thickening again confirmed this as a dreaded development because 39% of the study cohort experienced cardiac events within 3 years of index ultrasound. Yet, despite the quantitative similarities in intimal thickening in the 2 groups, clinical characteristics that display interactive behavior between the immunologic and nonimmunologic milieu were more predictive of event
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predilection. These data suggest that the “quantitative” mind-set extolled from investigations using ultrasound may be operative only to a relevant threshold whereas the dynamic “qualitative” aspects of the plaque predominate when a certain burden is achieved. Early investigations of endothelial dysfunction suggest the dynamic nature of cardiac allograft vasculopathy; the finding of specific immunologic and hematologic markers of inflammation and thrombosis predict the angiographic development of disease or graft failure.6 – 8 Drawing parallels from investigations in native coronary disease, event predilection in cardiac allograft vasculopathy may result from plaque rupture, erosion, or diffuse ischemic arrhythmic complications. Therefore, heterogeneously distributed forms of cardiac allograft vasculopathy that bear close resemblance to native atherosclerosis are probably prone to plaque disturbance and eventual clinical events.9 In this regard, Costanzo et al10 demonstrated that angiographically evident disease is highly predictive of future cardiac events. However, Julius et al11 used intravascular ultrasound to study 30 cardiac allograft recipients and demonstrated an increased incidence of intimal thickening. More striking, they observed that intimal thickening that occurred 3 months after transplantation did not necessarily predict the future development of angiographic disease at 1 and 2 years, suggesting that qualitative factors may be seminally operative in determining progression of disease, as we have alluded. One important limitation of this investigation requires mention. This study used an inception cohort derived from heart transplant recipients at various time points in their disease process. However, the demonstration of similar post-transplant times to index ultrasound in both groups somewhat obviates this limitation and thus represents the best clinical control possible.
CONCLUSIONS The results of our study provide important support for the presence of a prognostically relevant
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threshold for intimal thickening but challenges the notion of cardiac allograft vasculopathy as a quantitative disease process. Furthermore, it describes putative qualitative interactions between non-immunologic and immunologic events that mediate event predilection. REFERENCES 1. Mehra MR. Crossing the vasculopathy bridge from morphology to therapy: a single center experience. J Heart Lung Transplant 2000;19(6):522–8. 2. Mehra MR, Ventura HO, Chambers R, et al. Predictive model to assess risk for cardiac allograft vasculopathy: an intravascular ultrasound study. J Am Coll Cardiol 1995;26(6):1537–44. 3. Mehra MR, Ventura HO, Stapleton DD, et al. Presence of severe intimal thickening by intravascular ultrasonography predicts cardiac events in cardiac allograft vasculopathy. J Heart Lung Transplant 1995;14(4):632–9. 4. Rickenbacher PR, Pinto FJ, Lewis NP, et al. Prognostic importance of intimal thickness as measured by intracoronary ultrasound after cardiac transplantation. Circulation 1995;92(12): 3445–52. 5. St Goar FG, Pinto FJ, Alderman EL, et al. Intracoronary ultrasound in cardiac transplant recipients. In vivo evidence of “angiographically silent” intimal thickening. Circulation 1992; 85(3):979–87. 6. Davis SF, Yeung AC, Meredith IT, et al. Early endothelial dysfunction predicts the development of transplant coronary artery disease at 1 year posttransplant. Circulation 1996;93(3): 457–62. 7. Labarrere CA, Pitts D, Nelson DR, Faulk WP. Vascular tissue plasminogen activator and the development of coronary artery disease in heart-transplant recipients. N Engl J Med 1995;333: 1111–6. 8. Labarrere CA, Nelson DR, Cox CJ, et al. Cardiac-specific troponin I levels and risk of coronary artery disease and graft failure following heart transplantation. JAMA 2000;284:457– 464. 9. Libby P. Coronary artery injury and the biology of atherosclerosis: inflammation, thrombosis, and stabilization. Am J Cardiol 2000;86(suppl 2):3–8. 10. Costanzo MR, Naftel DC, Pritzker MR, et al. Heart transplant coronary artery disease detected by coronary angiography: a multiinstitutional study of preoperative donor and recipient risk factors. Cardiac Transplant Research Database. J Heart Lung Transplant 1998;17(8):744–53. 11. Julius BK, Attenhofer Jost CH, et al. Incidence, progression and functional significance of cardiac allograft vasculopathy after heart transplantation. Transplantation 2000; 69(5):847–53.
Is All Intimal Proliferation Created Equal in Cardiac Allograft Vasculopathy? The Quantity–Quality Paradox Mandeep R. Mehra, MD, Hector O. Ventura, MD, Patricia A. Uber, PharmD, Robert L. Scott, MD, and Myung H. Park, MD Background: Pre-angiographic detection of intimal proliferation using intravascular ultrasound in heart transplant recipients has focused investigators’ attention on the prognostic utility of such early information. Not all heart transplant recipients who exhibit a “prognostically relevant” threshold of severe (⬎0.5 mm) intimal thickening experience cardiac events. We sought to contrast clinical characteristics of heart transplant recipients who have prognostically relevant, severe intimal proliferation and who experience cardiac events with those who remain event free. Methods: We prospectively followed an inception cohort of 54 consecutive heart transplant recipients with severe intimal proliferation (intimal thickness ⬎0.5mm) of the coronary arteries after index intravascular ultrasound examination to assess the development of cardiac events (sudden cardiac death, myocardial infarction) and/or the necessity for coronary revascularization with percutaneous techniques (angioplasty, atherectomy, stent implantation) or surgical bypass. Results: Based on the occurrence of adverse cardiac events during the subsequent 24 months, we divided the study cohort into 2 groups: Group 1 (no event, n ⫽ 33) and Group 2 (cardiac event, n ⫽ 21). Both groups demonstrated similar intimal thickness at the index ultrasound (Group 1, 0.89 ⫾ 0.27 mm, vs Group 2, 0.94 ⫾ 0.36 mm; p ⫽ not significant). Those with cardiac events were more likely than those without events to have hyperlipidemia, to have greater exposure to cumulative and average daily prednisone, and to exhibit greater average biopsy rejection scores at follow-up. Conclusions: These observations underscore the importance of the quality and not merely the quantity of intimal proliferation in determining occurrence of morbid cardiac events and further emphasize the interaction of immunologic and nonimmunologic factors in determining event vulnerability in cardiac allograft vasculopathy. J Heart Lung Transplant 2003;22:118 –123.
I
ntravascular ultrasound technology has allowed delineation of the unique morphologic features of From the Ochsner Cardiomyopathy and Heart Transplantation Center, Ochsner Clinic Foundation, New Orleans, Louisiana. Submitted June 28, 2001; revised September 26, 2001; accepted April 24, 2002. Reprint requests: Dr. Mandeep R. Mehra, 1514 Jefferson Highway, New Orleans, Louisiana 70121. Telephone: 504-842-5630.
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cardiac allograft vasculopathy.1 Rapid advances in characterizing the natural history of cardiac allograft vasculopathy with pre-angiographic detection Fax: 504-842-4184. E-mail: [email protected] Copyright © 2003 by the International Society for Heart and Lung Transplantation. 1053-2498/03/$–see front matter PII S1053-2498(02)00492-8
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of intimal proliferation have focused investigator’s attention on the prognostic utility of such early information.2,3 Indeed, studies by our group and others seeking to define the ramifications of intravascular ultrasound– detected intimal proliferation have established a prognostically relevant severity threshold of ⬎0.5 mm, which reliably correlates with the occurrence of adverse clinical events in heart transplant recipients, even in the absence of angiographically evident disease.3,4 Even though identifying a prognostically relevant threshold of intravascular ultrasound– derived intimal proliferation is a major accomplishment, not all heart transplant recipients who exhibit this finding experience morbid events. Several questions can be raised regarding this issue: Do particular factors distinguish heart transplant recipients with prognostically relevant intimal proliferation who go on to experience morbid clinical events from those who do not? Is the further magnitude of intimal proliferation or the duration of survival a major determinant of clinical events, or are other clinical factors ultimately responsible for clinical vulnerability to adverse events? Therefore, our purpose in this investigation was 2-fold: (1) to compare similarities and differences that characterize heart transplant recipients with prognostically relevant, severe intimal proliferation who experience cardiac events with those who remain event free; and (2) to describe the importance of clinical and laboratory factors in determining the vulnerability of intimal proliferation to cardiac events.
METHODS Patient Population The study population consisted of an inception cohort of 54 consecutive heart transplant recipients with evidence of prognostically relevant severe intimal proliferation (intimal thickness, ⬎0.5 mm), determined by intravascular ultrasound examination of the coronary arteries between 1994 to 1995. These patients were then prospectively followed after index intravascular ultrasound examination and to assess the development of cardiac events. All study participants provided informed consent and the institutional review board approved the study.
Data Collection Non-immunologic risk factors In all cardiac transplant recipients, we assessed fasting lipid profile (triglyceride, total cholesterol, low-density lipoprotein cholesterol, and high-den-
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sity lipoprotein cholesterol levels) at the time of ultrasound examination, obesity (percentage weight gain, body mass index), hypertension (defined according to the Joint National Committee on Prevention, Detection, and Treatment of High Blood Pressure [JNC-VI] criteria), diabetes mellitus, donor age and gender, ischemic time, time since transplantation, and cytomegalovirus infection (defined as a clinical syndrome in association with either new seroconversion, positive blood cultures, or evidence of tissue invasion) that required therapeutic intervention with intravenous ganciclovir. Immunologic risk factors Rejection surveillance during the first year consisted of weekly endomyocardial biopsies for the first month after transplantation, biweekly until the third month, monthly until the sixth month, and bimonthly thereafter until completion of the first year. Thus, the routine protocol mandates 14 biopsies during the first year. All biopsy specimens were graded using the International Society for Heart and Lung Transplantation (ISHLT) grading scheme. The criteria for treating cellular rejection included the finding of a 3A or greater biopsy grade. If treatment was initiated for a lower biopsy grade, it was done only in the presence of hemodynamic compromise as evidenced by 1 or more of the following: a 20% decrease in ventricular ejection fraction, an increase in pulmonary capillary wedge pressure ⬎25%, and a decrease by 25% in the cardiac index or an absolute value of ⬍2.0 liter/min/ m2. Furthermore, episodes of treated rejection mandated follow-up biopsy within 1 to 2 weeks to document resolution or regression to a lower rejection grade. Additionally, a first-year mean biopsy rejection score, as previously described, was determined for all patients. We adapted this from the standardized ISHLT criteria and assigned individual scores to each defined biopsy grade as follows: ISHLT Grade 0 ⫽ 0, Grade IA ⫽ 1, Grade IB ⫽ 2, Grade 2 ⫽ 3, Grade 3A ⫽ 4, Grade 3B ⫽ 5, and Grade 4 ⫽ 6. We computed the mean biopsy score as the average of all biopsy scores during the first year after transplantation. In addition, we assessed in all patients episodes of vascular (humoral) rejection and the number of HLA-A, -B, or -DR matches between the donor and recipient. Acute vascular rejection was defined by the presence of hemodynamic compromise along with histologic evidence of endothelial cell activation and positive immunofluorescence in biopsy
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specimens. More importantly, we also assessed immunosuppression regimens in all patients and calculated the cumulative prednisone dose (total amount of intravenous and oral prednisone consumed in grams), average daily prednisone dose (mg/kg/day), mean cyclosporine dose (mg/kg/day), mean cyclosporine levels (pg/ml), and mean azathioprine dose (mg/kg/day). We also assessed the use of cytolytic therapy (OKT3 or anti-thymocyte globulin) and methotrexate for each study patient.
Intravascular Ultrasound Coronary ultrasound procedure Coronary ultrasound was performed as we have previously reported.3 After administration of 200 g intracoronary nitroglycerin, the ultrasound catheter was positioned in the distal segment of the target vessel over a 0.014-inch (0.036-cm) guide wire. The target vessel was selected by the presence of at least 3 easily definable and reproducible branch points to assist in the accurate and serial assessment of 3 regions of interest. The guide wire was removed, and the ultrasound catheter was advanced to the distal end of the ultrasound sheath under fluoroscopic guidance. The drive module was then engaged, and continuous images of the coronary artery were obtained as the ultrasound transducer was slowly withdrawn. Additionally, fluoroscopic pictures and audio annotations were used to ensure the correct localization of the artery segment for subsequent off-line analysis. Guiding catheter pressure, ST-segment changes, and cardiac rhythm were continuously monitored during the procedure. After ultrasound images were obtained, both the transducer and sheath were removed, and a final angiogram was obtained to confirm the patency of the coronary vessel. No complications were encountered except for coronary artery vasospasm, readily reversed by intracoronary infusion of nitrates or verapamil. Coronary ultrasound assessment One of the investigators, who had no knowledge of the prior assessment of risk factors, performed the intravascular ultrasound measurements. Three coronary sites per vessel (proximal, mid, and distal), for a total of 162 coronary artery segments, were evaluated. The left anterior descending artery was examined in 48 patients, the circumflex artery was examined in 2, and the right coronary artery was examined in the remaining 4 subjects. Maximal intimal thickness and intimal area were obtained by tracing the lumen vessel wall interface and the
The Journal of Heart and Lung Transplantation February 2003
external border of the intimal layer. Intimal index was calculated as the ratio of intimal area to the total vessel area. The definition of severe intimal thickness was based on the scheme previously described by St. Goar et al,5 wherein severe intimal thickening is ⬎0.5 mm of intimal proliferation involving ⬎180° of the vessel circumference, or any intimal layer ⬎1.0 mm in any one area of the vessel circumference. This threshold of severity denotes the unequivocal presence of intimal thickening and is beyond the 98th percentile of any published normal values. Moreover, we have demonstrated previously that this threshold of severe intimal proliferation evidenced by intravascular ultrasound is predictive of cardiac events even in the absence of angiographic abnormalities, and therefore denotes a prognostically relevant threshold of abnormality.2
Cardiac Events We defined cardiac events as the occurrence of sudden cardiac death, myocardial infarction, or the necessity for coronary revascularization with percutaneous techniques (angioplasty, atherectomy, stent implantation) or surgical bypass.
Statistical Methods Normally distributed data are reported as mean ⫾ standard deviation. Differences among categorical variables were assessed using chi-square or Fisher’s exact test. We used the unpaired Student’s t-test to define differences among continuous variables in sub-groups. Kaplan Meier actuarial analysis was used to assess event-free survival for the study cohort. All analyses were performed using Statview 4.5 (Abacus concepts Inc., Berkeley, CA) statistical software, and statistical significance was set at a p ⬍ 0.05.
RESULTS Clinical Characteristics The study population included 54 consecutive heart transplant recipients (50 men and 4 women) with a mean age of 53 ⫾ 8 years (range, 22 to 68 years) who were prospectively followed for 24 months after index ultrasound examination that detected prognostically relevant intimal proliferation (⬎0.5mm). Based on the occurrence of adverse cardiac events, we divided the study cohort into 2 groups: Group 1 (no event, n ⫽ 33) and Group 2 (cardiac event, n ⫽ 21). All subsequent results compare clinical characteristics, non-immunologic, and immunologic risk factors between these 2 groups of patients.
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TABLE I Non-immunologic factors
Recipient age (years) Donor age (years) Recipient sex Donor sex Ischemic time (minutes) Diabetes mellitus Weight gain CMV infection % Post-transplant survival (years) Total cholesterol (mg/dl) LDL (mg/dl) HDL (mg/dl) Triglycerides (mg/dl) Lipid therapy
Event-free group (n ⴝ 33)
Cardiac event group (n ⴝ 21)
52 ⫾ 10 32 ⫾ 11 32 male (97%) 19 male (58%) 177 ⫾ 65 37% 14.2 ⫾ 9.5 12.9% 2.8 ⫾ 1.6 209 ⫾ 23 139 ⫾ 23 27 ⫾ 9 167 ⫾ 55 45%
54 ⫾ 6 30 ⫾ 10 18 male (86%) 12 male (57%) 179 ⫾ 33 32% 10.3 ⫾ 7.2 11% 3.1 ⫾ 1.8 257 ⫾ 32# 176 ⫾ 36## 29 ⫾ 11 215 ⫾ 84* 57%
#
p ⬍ 0.001, ##p ⫽ 0.005, *p ⫽ 0.01. CMV, cytomegalovirus; HDL, high-density lipoprotein; LDL, low-density lipoprotein.
Cardiac Event Analysis
Differences in Non-immunologic Factors
We noted 21 adverse clinical events. Of these, 15 were cardiac deaths, 2 were myocardial infarctions, and 4 were percutaneous revascularizations (3 arthrectomies and 1 coronary stent implantation). Twenty-five percent of the patients with cardiac events demonstrated rapid progression of disease, as seen by angiography performed because of myocardial infarction or revascularization procedures; 2 patients who experienced sudden death demonstrated severe 3-vessel coronary artery disease on necropsy. The remaining 33 heart transplant recipients remained event free (Figure 1).
Table I lists comparative non-immunologic characteristics of the no-event (Group 1) and cardiac event (Group 2) cohorts with regard to recipient and donor age, recipient and donor sex, cold ischemic time, lipid characteristics, weight gain, cytomegalovirus infection, and diabetes mellitus. Specifically, we observed no significant clinical differences between the 2 groups with reference to any of these non-immunologic factors except for increased levels of lipids (total cholesterol, low-density lipoprotein cholesterol, and triglycerides) in those with cardiac events despite lipid-decreasing therapy (all p ⬍ 0.01).
Differences in Immunologic Factors Table II lists a comparison of immunologic risk factors including episodes of allograft rejection, the number of HLA matches, and the mean first-year biopsy rejection score. Although we observed no significant differences among clinical episodes of
TABLE II Immunologic variables Event-free group (n ⴝ 33)
FIGURE Actuarial-survival curve of patients with events depicting number of events over time after the index intravascular ultrasound detected severe intimal thickening (⬎0.5 mm).
Cardiac event group (n ⴝ 21)
Number of HLA matches 1.0 ⫾ 1.1 0.6 ⫾ 0.7 Treated rejection episodes 40% 38% Average biopsy rejection score 0.86 ⫾ 0.35 1.1 ⫾ 0.36# #
p ⫽ 0.05
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TABLE III Immunosuppressive regimens
Cumulative prednisone (g) Average prednisone (mg/kg/day) Average cyclosporine (mg/kg/day) Mean cyclosporine level (pg/ml) Average azathioprine (mg/kg/day)
Intravascular Ultrasound Analysis
Event-free group (n ⴝ 33)
Cardiac event group (n ⴝ 21)
10.6 ⫾ 4.8 0.09 ⫾ 0.04
15.6 ⫾ 6.9* 0.13 ⫾ 0.06**
3.9 ⫾ 1.0
3.6 ⫾ 1.6
170 ⫾ 34
167 ⫾ 32
1.4 ⫾ 0.5
1.3 ⫾ 0.7
*p ⫽ 0.005, **p ⫽ 0.06.
We found no significant differences with regard to magnitude of intimal proliferation in the group with cardiac events (Group 2) compared with the group without events (Group 1) (intimal thickness, 0.94 ⫾ 0.36 mm vs 0.89 ⫾ 0.27 mm; p ⫽ 0.21). We further assessed lesions for plaque location, morphology, and eccentricity. The predominant morphologic characteristics of the vessels studied revealed diffuse and concentric lesions (at least 2 of 3 segments) in 82%, whereas only 18% of vessels studied revealed proximal, focal, and eccentric lesions. The intraobserver (4.1%) and interobserver (5.4%) variability was assessed as previously reported and demonstrated good test reproducibility.3
Survival Analysis allograft rejection or the number of HLA matches, heart transplant recipients with cardiac events had higher average biopsy rejection scores (Group 2, 1.1 ⫾ 0.31, vs Group 1, 0.81 ⫾ 0.24; p ⬍ 0.05).
Differences in Immunosuppression Regimens Table III compares immunosuppression exposure between the patients with cardiac events and those without clinical events. We found significant differences in relation to cumulative prednisone dose (Group 1, 10.6 ⫾ 4.7 g, vs Group 2, 15.6 ⫾ 6.9 g; p ⫽ 0.005), and average prednisone dose (Group 1, 0.09 ⫾ 0.04 mg/kg/day, vs Group 2, 0.13 ⫾ 0.05 mg/kg/day; p ⫽ 0.05). We observed no significant differences in cyclosporine, azathioprine, and cytolytic antibody exposure during the transplant duration. Multiple regression analysis of variables associated with greater cumulative prednisone dose included time after transplantation; cholesterol, triglycerides, and high-density lipoprotein cholesterol concentrations; and weight gain after transplantation (Table IV).
TABLE IV Factors associated with cumulative prednisone exposure: multiple regression analysis Post-transplant survival Total cholesterol (mg/dl) HDL cholesterol Triglycerides % Weight gain HDL, high-density lipoprotein.
r value
p value
0.56 0.35 0.34 0.24 0.39
⬍0.0001 0.01 0.007 0.05 0.006
We found no significant difference in time from transplantation to index ultrasound between the 2 groups (Group 1, 32.4 ⫾ 3.3 months, vs Group 2, 38.3 ⫾ 4.9 months; p ⫽ 0.31). Additionally, the 2 groups did not differ with regard to follow-up time after index intravascular ultrasound examination detected the presence of severe intimal proliferation (Group 1, 26.6 ⫾ 1.9 months, vs Group 2, 24.3 ⫾ 3.1 months; p ⫽ 0.49).
DISCUSSION The findings of this investigation demonstrate that factors independent of survival time and magnitude of intimal thickness determine the expression of clinical events in patients with cardiac allograft vasculopathy manifested with prognostically relevant intimal proliferation detected by intravascular ultrasound.3 Thus, heart transplant recipients with significant cardiac allograft vasculopathy who were exposed to greater cumulative prednisone consumption (a surrogate marker for worse hyperlipidemia, excess weight gain, and alloreactivity) had more severe hyperlipidemia and higher rejection scores and were most likely to experience deleterious cardiac events despite similar degrees of intimal thickness and survival times. Intravascular ultrasound detection of severe, prognostically relevant intimal thickening again confirmed this as a dreaded development because 39% of the study cohort experienced cardiac events within 3 years of index ultrasound. Yet, despite the quantitative similarities in intimal thickening in the 2 groups, clinical characteristics that display interactive behavior between the immunologic and nonimmunologic milieu were more predictive of event
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predilection. These data suggest that the “quantitative” mind-set extolled from investigations using ultrasound may be operative only to a relevant threshold whereas the dynamic “qualitative” aspects of the plaque predominate when a certain burden is achieved. Early investigations of endothelial dysfunction suggest the dynamic nature of cardiac allograft vasculopathy; the finding of specific immunologic and hematologic markers of inflammation and thrombosis predict the angiographic development of disease or graft failure.6 – 8 Drawing parallels from investigations in native coronary disease, event predilection in cardiac allograft vasculopathy may result from plaque rupture, erosion, or diffuse ischemic arrhythmic complications. Therefore, heterogeneously distributed forms of cardiac allograft vasculopathy that bear close resemblance to native atherosclerosis are probably prone to plaque disturbance and eventual clinical events.9 In this regard, Costanzo et al10 demonstrated that angiographically evident disease is highly predictive of future cardiac events. However, Julius et al11 used intravascular ultrasound to study 30 cardiac allograft recipients and demonstrated an increased incidence of intimal thickening. More striking, they observed that intimal thickening that occurred 3 months after transplantation did not necessarily predict the future development of angiographic disease at 1 and 2 years, suggesting that qualitative factors may be seminally operative in determining progression of disease, as we have alluded. One important limitation of this investigation requires mention. This study used an inception cohort derived from heart transplant recipients at various time points in their disease process. However, the demonstration of similar post-transplant times to index ultrasound in both groups somewhat obviates this limitation and thus represents the best clinical control possible.
CONCLUSIONS The results of our study provide important support for the presence of a prognostically relevant
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threshold for intimal thickening but challenges the notion of cardiac allograft vasculopathy as a quantitative disease process. Furthermore, it describes putative qualitative interactions between non-immunologic and immunologic events that mediate event predilection. REFERENCES 1. Mehra MR. Crossing the vasculopathy bridge from morphology to therapy: a single center experience. J Heart Lung Transplant 2000;19(6):522–8. 2. Mehra MR, Ventura HO, Chambers R, et al. Predictive model to assess risk for cardiac allograft vasculopathy: an intravascular ultrasound study. J Am Coll Cardiol 1995;26(6):1537–44. 3. Mehra MR, Ventura HO, Stapleton DD, et al. Presence of severe intimal thickening by intravascular ultrasonography predicts cardiac events in cardiac allograft vasculopathy. J Heart Lung Transplant 1995;14(4):632–9. 4. Rickenbacher PR, Pinto FJ, Lewis NP, et al. Prognostic importance of intimal thickness as measured by intracoronary ultrasound after cardiac transplantation. Circulation 1995;92(12): 3445–52. 5. St Goar FG, Pinto FJ, Alderman EL, et al. Intracoronary ultrasound in cardiac transplant recipients. In vivo evidence of “angiographically silent” intimal thickening. Circulation 1992; 85(3):979–87. 6. Davis SF, Yeung AC, Meredith IT, et al. Early endothelial dysfunction predicts the development of transplant coronary artery disease at 1 year posttransplant. Circulation 1996;93(3): 457–62. 7. Labarrere CA, Pitts D, Nelson DR, Faulk WP. Vascular tissue plasminogen activator and the development of coronary artery disease in heart-transplant recipients. N Engl J Med 1995;333: 1111–6. 8. Labarrere CA, Nelson DR, Cox CJ, et al. Cardiac-specific troponin I levels and risk of coronary artery disease and graft failure following heart transplantation. JAMA 2000;284:457– 464. 9. Libby P. Coronary artery injury and the biology of atherosclerosis: inflammation, thrombosis, and stabilization. Am J Cardiol 2000;86(suppl 2):3–8. 10. Costanzo MR, Naftel DC, Pritzker MR, et al. Heart transplant coronary artery disease detected by coronary angiography: a multiinstitutional study of preoperative donor and recipient risk factors. Cardiac Transplant Research Database. J Heart Lung Transplant 1998;17(8):744–53. 11. Julius BK, Attenhofer Jost CH, et al. Incidence, progression and functional significance of cardiac allograft vasculopathy after heart transplantation. Transplantation 2000; 69(5):847–53.