Relationship between coronary function by positron emission tomography and temporal changes in morphology by intravascular ultrasound (IVUS) in transplant recipients

Relationship Between Coronary Function by Positron Emission Tomography and Temporal Changes in Morphology by Intravascular Ultrasound (IVUS) in Transplant Recipients Martin Allen-Auerbach, MD, Heiko Scho ¨der, MD, Jay Johnson, MD, Klaus Kofoed, MD, Kim Einhorn, BA, Michael E. Phelps, PhD, Jon Kobashigawa, MD, and Johannes Czernin, MD Background: Transplant coronary vasculopathy is one of the major causes of graft failure and death in cardiac transplant recipients. A non-invasive test of coronary function to predict the course of this disease would be desirable. Methods: To determine whether the degree of abnormalities in endothelial dependent coronary vasomotion (cold pressor testing) or endothelial independent vasodilatory capacity (intravenous dipyridamole) as determined by positron emission tomography (PET) one to two years after heart transplantation is correlated with the course of transplant vasculopathy. Nineteen patients had baseline PET and intravascular ultrasound studies (IVUS) at 18 6 6 months after cardiac transplantation and a follow up IVUS study 15 6 5 months later. Results: Myocardial blood flow was higher in patients than in healthy controls (p , 0.002) but increased during cold pressor testing only in controls (p , 0.005). Myocardial blood flow normalized to the rate pressure product declined in patients (p , 0.001). Dipyridamole-induced hyperemic blood flow and the flow reserve normalized to the resting rate pressure product were lower in patients than in controls (p , 0.001 and p , 0.01). The normalized flow reserve was correlated with changes in total vessel area (r 5 0.55; p 5 0.02) and lumen diameter (r 5 0.52; p , 0.05). Conclusion: These findings suggest that the degree of abnormalities in endothelial independent myocardial flow as detected by PET one to two years after transplantation is associated with morphological indices of disease progression by IVUS. J Heart Lung Transplant 1999;18:211–219.

From Ahmanson Biological Imaging Clinic/Nuclear Medicine, Department of Molecular and Medical Pharmacology, UCLA School of Medicine, Los Angeles, California. Submitted May 28, 1998; accepted September 21, 1998. This work was supported in part by the Director of the Office of Energy Research, Office of Health and Environmental Research, Washington, DC, by Research Grant #HL 33177, National Institutes of Health, Bethesda, MD and by an Investigative Group Award by the Greater Los Angeles Affiliate of the American Heart Association, Los Angeles, CA. Johannes

Czernin is the recipient of a clinician-scientist award from the American Heart Association. Reprint requests: Johannes Czernin, MD, Ahmanson Biological Imaging Clinic/Nuclear Medicine, Department of Molecular and Medical Pharmacology, UCLA, School of Medicine, AR259 CHS, Los Angeles, CA 90095-6948. Copyright © 1999 by the International Society for Heart and Lung Transplantation. 1053-2498/99/$–see front matter PII S1053-2498(98)00037-0

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ransplant coronary vasculopathy is one of the major causes of graft failure and death in cardiac transplant recipients.1 Conservative estimates derived from coronary angiographic studies suggest a 40 –50% incidence of disease 5 years after transplantation.2,3 Transplant vasculopathy is associated with abnormalities in endothelial-dependent and -independent coronary function.4,5 While endothelial cell dysfunction has previously been reported to be unrelated to the degree of intimal thickening by intravascular ultrasound (IVUS),6 Kofoed et al recently demonstrated that the endothelial independent hyperemic blood flow response to dipyridamole is inversely correlated with the degree of coronary intimal thickness in transplant recipients.5 A non-invasive test of coronary function for predicting the course of transplant vasculopathy would be desirable. However, it is still unknown whether the degree of impairment in endothelial dependent and independent coronary vasomotion at any time after surgery predicts the subsequent course of the disease.7,8 Dynamic PET imaging using N-13 ammonia and a validated two-compartment model allows the quantification of myocardial blood flow in units of ml/g/ min. Such measurements performed, for instance, during cold pressor testing and intravenous dipyridamole provide indices of endothelial dependent and independent coronary function.5 Thus, other than Doppler flow velocity measurements, PET is capable of non-invasively determining regional and global endothelial-dependent and -independent myocardial blood flow in transplant recipients. These findings can then be related to the subsequent course of transplant vasculopathy as determined by serial measurements of coronary morphology with IVUS. Through this longitudinal study we sought to resolve whether the degree of abnormalities in coronary vasomotion (cold pressor testing) or vasodilatory capacity (dipyridamole) as determined by PET one to two years after heart transplantation were associated with morphological changes of the coronary vasculature as determined by serial quantitative IVUS-measurements.

STUDY POPULATION Nineteen of 31 patients who were enrolled in a previously published study5 (16 males, 3 females, mean age 54 6 7 years) had baseline PET and IVUS studies at 18 6 6 months after cardiac transplantation. A follow-up IVUS study was performed in all

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patients at 15 6 5 months after the baseline study. All had myocardial blood flow studies at rest and during cold pressor testing. Seventeen of the 19 patients underwent hyperemic blood flow studies during intravenous dipyridamole (2 of the 19 patients refused to undergo pharmacological stress). Thus, 17 of the 19 patients underwent the complete study protocol. Indications for heart transplantation were cardiomyopathies of various etiologies (ischemic cardiomyopathy; n 5 10, idiopathic cardiomyopathy; n 5 7, valvular heart disease; n 5 1, retransplantation because of progressive cardiac allograft vasculopathy; n 5 1). The mean age of the donor hearts was 31 6 14 years. All patients had bioptic evidence of mild rejection at some point between the time of the transplantation and the follow up IVUS. The severity of past rejections by myocardial biopsy ranged from 1A (all patients) to 3A (6 patients) by ISHT classification.9 At the time of PET, 8 patients were treated with triple-drug (cyclosporine, azathioprine and prednisone) and 11 with double-drug (azathioprine and cyclosporine) immunsuppression. Seventeen patients received the HMG-CoA reductase inhibitor pravastatin. Other medications included ACE inhibitors, calcium channel blockers, diuretics, and acetylsalicylic acid. Two previously established control groups5 consisted of a total of 20 healthy volunteers, matched in age and gender to the heart donors. Subgroup I (n 5 10; age, 35 6 18 years) was studied with PET at rest and during cold pressor testing. Subgroup II (n 5 10; age, 35 6 13 years) was examined at rest and during dipyridamole-induced hyperemia. All participants signed an informed consent form approved by the UCLA Human Subject Protection Committee.

STUDY PROTOCOL IVUS and coronary angiography The angiographic extent and severity of coronary artery disease were assessed visually from standard views at 1 6 9 weeks prior to the PET study. A commercially available IVUS system (Cardiovascular Imaging Systems, Sunnyvale California) was used to determine the degree of vasculopathy in the left anterior descending coronary artery as described previously. Because the ultrasonographic assessment of all three coronary arteries is not feasible and because transplant vasculopathy is a symmetric process involving all three vascular territories to a similar degree10 only the LAD was examined. After

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intracoronary administration of nitroglycerin, a 0.018-inch guide-wire was introduced into the LAD. A 4.3 French, 30 MHz IVUS catheter was advanced over the guide wire to a distal site of the LAD. Images were recorded continuously via super VHS videotape during a 30 second pullback period. From the video recording ten evenly spread end-diastolic images were converted into a 640 3 480 pixel image matrix, that were then analyzed with the use of computerized morphometric analysis. The circumferences of the lumen border, internal elastic lamina, intima and the maximal intimal thickness were manually traced.11,12 Total vessel area (mm2), lumen diameter (mm), maximal intimal thickness (mm), lumen area (mm2) and intimal area (mm2) were computed. The intimal index was calculated as (intimal area/total vessel area). Estimates of total “plaque burden” were calculated in each patient as average maximal intimal thickness and intimal index of the 10 vascular sites. A morphometric site by site analysis of the baseline and follow-up IVUS study was used to calculate differences in these parameters.

Myocardial biopsy Four endomyocardial biopsies from the inter-ventricular septum obtained during baseline and follow up IVUS and angiographic studies were graded according to the International Society of Heart Transplantation classification system (ISHT).9

Positron emission tomography Myocardial blood flow was quantified at rest (n 5 19), during cold pressor testing (n 5 19) and during dipyridamole induced hyperemia (n 5 17) as described previously.5,13 The Siemens/CTI 931/08-12 positron tomograph, which acquires 15 transaxial images simultaneously, was used.14 All patients refrained from caffeinecontaining food and beverages for 24 hours prior to the PET study.15 A 20 minute transmission scan was acquired first to correct for photon attenuation. This was followed by the intravenous injection of 740 MBq of N-13 ammonia while simultaneously starting the dynamic imaging sequence. The myocardial blood flow response to cold as an index of endothelial dependent coronary function was evaluated by immersing the patient’s left hand in ice water slush for 105 seconds (cold pressor test). At 45 seconds after the start of the cold pressor test, 740 MBq of N-13 ammonia were injected and the dynamic imaging sequence started. Intravenous dipyridamole (0.56 mg/kg over 4 minutes) was used to induce

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coronary hyperemia. Four minutes after the end of the infusion 740 MBq of N-13 ammonia were injected and the serial image acquisition (12 frames of 10 sec each, two frames of 30 sec each, one frame of 60 sec and one frame of 15 minutes) begun. Heart rate and blood pressure were measured in minute intervals during the dynamic image acquisition. The rate pressure product and mean arterial blood pressure were calculated from the two measurements obtained during the first two minutes of the dynamic image acquisition.

Quantification of blood flow Myocardial blood flow was quantified in the territories of the LAD, the LCX and the RCA.13 Regions of interest were approximated to the 3 vascular territories on three short axis images (one basilar, one mid-ventricular and one apical image) as described previously. A small region of interest was centered in the left ventricular blood pool to derive the arterial input function.16 The regions were copied to the first 120 seconds of the dynamic imaging sequence to obtain tissue time activity curves. For each of the vascular territories the three tissue curves (basilar, mid-ventricular and apical) were averaged and corrected for partial volume effects and physical decay17 and were fitted with a previously validated two compartment model for N-13 ammonia correcting for spill over of activity from blood pool into the left ventricular myocardium.18 Transplant vasculopathy is a symmetric process involving all three major coronary arteries to a similar degree.10 Because no significant differences in myocardial blood flow between coronary territories of the LAD, LCX and RCA at rest, during cold pressor testing and during dipyridamole induced hyperemia were observed the territorial blood flow values were averaged and a mean myocardial blood flow value was obtained for each patient. The myocardial flow reserve was defined as the ratio of hyperemic to resting blood flow. To account for individual differences in resting cardiac work, myocardial blood flow at rest and during cold pressor testing were normalized to the rate pressure product as an index of cardiac work.13 For the same reason, the myocardial flow reserve was normalized to the resting rate pressure product.

Statistical analysis Mean values are given with standard deviations. The paired t-test was used for comparison within individuals. The unpaired t-test was used to assess differences between groups. Correlations were

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sought using least square regression analysis. Probability levels of less than 0.05 were considered statistically significant.

RESULTS Coronary angiography One patient had a 60% ostial stenosis of the LCX. Semiquantitative polar map analysis revealed a defect at the interface between RCA and LCX territory. Two other patients had evidence of mild coronary artery disease in the territories of the LAD and RCA with none of the stenoses exceeding 40%. These stenoses remained undetected by polar map analysis. The remaining patients had no angiographic evidence for epicardial coronary artery disease.

IVUS Average maximal intimal thickness and intimal index of the 10 vascular sites decreased by 0.09 6 0.14 mm (p 5 0.008) and 0.03 6 0.05 (p 5 0.01) from the baseline to the follow up IVUS study. The total vessel area decreased by 1.5 6 2.5 mm2 (p 5 0.02). The coronary lumen diameter tended to decrease from baseline to follow up (0.16 6 0.35 mm; p 5 0.066).

Endomyocardial biopsy From the time of transplantation until the IVUS follow up, all patients experienced episodes of grade 1A rejections. Fifteen patients demonstrated additional grade 1B and 6 patients additional grade 3A rejections at some point during this observation period. Only two patients had rejection episodes within 8 weeks of the PET study. Their rejections, however, did not exceed grade 1B.

FIGURE 1 Differences in total vessel area (y-axis) as a function of normalized myocardial flow reserve (x-axis) defined as ratio of myocardial blood flow during dipyridamole to myocardial blood flow at rest normalized to the rate pressure product. A lower normalized myocardial flow reserve at baseline was correlated with a decrease in total vessel area by y 5 2.306*x 2 5.586; r 5 0.55; p 5 0.02.

9615 6 2885; p , 0.0004). During intravenous dipyridamole the heart rate increased less in the transplant recipients than in controls (14 6 8% vs 44 6 27% p 5 NS). Systolic blood pressure increased only in controls (9 6 9%; p , 0.005). Diastolic blood pressure remained unchanged in both groups. Mean aortic blood pressure was similar in patients and controls (92 6 12 vs 90 6 12 mmHg; p 5 NS). Semiquantitative polar map analysis: Three of the 19 patients demonstrated abnormalities in the rela-

Positron emission tomography Hemodynamic findings: Heart rate (83 6 9 vs 66 6 13 beats/min; p , 0.001), systolic blood pressure (127 6 18 vs 114 6 12 mmHg; p , 0.01), diastolic blood pressure (80 6 11 vs 68 6 10 mmHg; p , 0.006) and rate pressure product (10497 6 1906 vs 7424 6 1353; p , 0.0001) at rest were higher in patients than in controls. The response to cold did not differ between the two groups. Heart rate, systolic blood pressure, diastolic blood pressure and rate pressure product increased to a similar degree in patients and in control subjects (7 6 6%, 21 6 10%, 17 6 12%, 30 6 13%, and 17 6 12%, 18 6 15%, 27 6 13%, 35 6 34%; all p 5 NS). The rate-pressure product during cold was higher in patients than in control subjects (13488 6 2172 vs

FIGURE 2 Differences in lumen diameter (y-axis) as a

function of normalized myocardial flow reserve (x-axis). A lower flow reserve at baseline was associated with a subsequent decrease in lumen diameter by IVUS. These parameters were correlated by y 5 0.303x 2 0.694; r 5 0.52; p 5 0.034.

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tive N-13 ammonia activity distribution at rest, during cold pressor testing and during dipyridamole induced hyperemia. In all three of these patients, these defects were fixed and located at the interface of the left circumflex and the right coronary artery territory. One of these patients had angiographic evidence of a 60% stenosis of the left circumflex coronary artery, while the two remaining patients had no angiographic evidence for coronary artery disease. Myocardial blood flow at rest: Regional myocardial blood flows at rest in the territories of the LAD, LCX and RCA averaged 0.88 6 0.19, 0.78 6 0.21, and 0.91 6 0.23 ml/g/min (p 5 NS). Similarly, no differences in regional blood flow were noted during cold pressor testing (0.91 6 0.33, 0.84 6 0.3, and 0.87 6 0.41 ml/g/min; p 5 NS) or dipyridamole (1.52 6 0.69, 1.36 6 0.65, and 1.49 6 0.74 ml/g/min; p 5 NS). Because no regional differences were observed a single average blood flow value was calculated for each patient. Mean resting myocardial blood flow was higher in patients than in controls (0.85 6 0.17 vs 0.68 6 0.16 ml/g/min; p , 0.002) and was correlated linearly with the rate pressure product in both groups (r 5 0.48, p , 0.04 and r 5 0.60, p , 0.01). Because of this significant relationship, resting myocardial blood flow was normalized to the rate pressure product as an index of cardiac work. No differences in blood flow normalized to the rate pressure product were observed between the two groups. Blood flow response to cold: Myocardial blood flow did not increase in patients (0.85 6 0.17 vs 0.87 6 0.31 ml/g/min; p 5 NS) and was unrelated to the rate pressure product during cold pressor testing (r 5 0.28; p 5 NS). In contrast, it increased in the control group from 0.64 6 0.13 to 0.79 6 0.18 ml/min/g (p , 0.005) and remained significantly correlated to the rate-pressure product (r 5 0.59; p , 0.05). Accordingly, blood flow normalized to the rate-pressure product declined in patients (0.83 6 0.15 vs 0.65 6 0.21 ml/min/g; p , 0.001), but not in controls (0.90 6 0.13 vs 0.85 6 0.19; p 5 NS). Hyperemic blood flow and flow reserve: Dipyridamole induced hyperemic blood flow (1.45 6 0.65 vs 2.30 6 0.32 ml/min/g; p , 0.001) and normalized flow reserve (1.78 6 0.61 vs 2.54 6 0.79; p , 0.01) were lower in patients than in controls. Minimal coronary vascular resistance during dipyridamole (mean arterial blood pressure/myocardial blood flow)19 was higher in patients than in controls (70 6 20 vs 40 6 9 mmHg/ml/min/g; p , 0.0001). Relationship between myocardial blood flow, flow

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reserve and changes in coronary morphology by IVUS: Neither blood flow at rest, during cold pressor testing or dipyridamole was correlated with changes in coronary morphology. However, significant correlations were observed between normalized myocardial flow reserve and changes in total vessel area (r 5 0.55; p 5 0.02) and lumen diameter (r 5 0.52; p 5 0.034). Specifically, the normalized myocardial flow reserve of the LAD territory tended to be correlated with changes in lumen area (r 5 0.47; p 5 0.08) and was significantly correlated with changes in total vessel area (r 5 0.52; p , 0.05).

DISCUSSION Cardiac transplant recipients exhibit abnormalities in coronary vasomotion and vasodilatory capacity suggesting abnormalities in endothelial dependent and independent coronary vasomotion. The degree of abnormalities in endothelial independent coronary function as detected by PET one to two years after transplantation is associated with subsequent changes in coronary morphology by IVUS.

Changes in coronary morphology by IVUS Consistent with previous reports of a time-dependent progression of transplant vasculopathy the current study demonstrated a decrease in total vessel area and lumen diameter during the observation period. Interestingly, this decrease was not accounted for by increases in maximal intimal thickness or intimal index, that, in fact decreased from the baseline to the follow-up IVUS study. This contradicts several studies which indicated progressive coronary intimal thickening in transplant recipients.20 It should be noted, however, that all of the current study patients underwent an IVUS study early, 7 6 2 weeks after transplantation. Therefore, we were able to analyze the true natural course of the disease by IVUS. The intimal index and intimal thickness increased significantly between the measurement at 7 6 2 weeks after transplantation and the second IVUS measurement which was performed at the time of PET (16 6 6 months after cardiac transplantation). Consequently lumen diameter decreased during this time. In contrast, the total vessel area did not change during this period. The significant decrease in total vessel area and lumen diameter occurred between the time of the second IVUS study (16 6 6 months after transplantation) and the final IVUS (31 6 6 months after transplantation). It might therefore be speculated that after an initial increase in intimal thickness the subsequent disease

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process might be attributed to vascular remodeling or “vessel shrinkage” as proposed by Gibbons and Lim.21,22 In support of this theory, Pethig et al. demonstrated that not only intimal hyperplasia but pattern and degree of vascular remodeling are of considerable importance for the vasculopathic process.23 In fact, negative vascular remodeling (or relative vasoconstriction) appeared to be the major predictor of the severity of vasculopathy in this study. Further, it might also be speculated that the treatment of all but two of the current study participants with HMG-CoA reductase inhibitors may have halted or even reversed the progression of intimal proliferation.24

Relationship between endothelial dependent coronary function and morphology While the pathophysiological mechanisms underlying the disease process are still not completely understood, an immune-mediated damage to the coronary endothelium24 –26 that results in endothelial dysfunction appears to play an important role in the development of transplant vasculopathy. Consistent with this notion are several studies that demonstrated a paradoxical coronary vasoconstriction in response to intracoronary acetylcholine in transplant recipients. Fish et al. observed a reduction in coronary artery lumen in response to acetylcholine in transplant recipients by 26 6 10% (p , 0.05) that was ascribed to coronary endothelial dysfunction.27 More recent studies have confirmed this notion and revealed an abnormal endothelial dependent myocardial blood flow response to cold pressor testing.5,28 Thus, the presence of endothelial dysfunction in heart transplant recipients has been established. However, it is unknown whether its degree allows us to predict the course of the disease. Davis et al, using intracoronary acetylcholine, assessed endothelial-dependent vasomotion 16 6 1 days after cardiac transplantation and observed a significant correlation between the degree of acetylcholine induced vasoconstriction and the development of allograft vasculopathy as determined by IVUS during the first year after transplantation.7 In contrast, Aptecar et al and Burns et al failed to observe a significant relationship between the coronary response to acetylcholine early after transplantation and the subsequent progression of disease as determined by coronary angiography and IVUS.8,29 The current study sought to evaluate a possible correlation between the degree of abnormalities in

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endothelial dependent myocardial blood flow 1–2 years after cardiac transplantation and the subsequent progression of disease. Because the coronary blood flow response to acetylcholine is correlated with cold, cold pressor testing was used to probe endothelial dependent coronary vasomotion. Cold evokes a mixed nervous response by inducing the release of catecholamines from the adrenal medulla and from terminal nerve endings which in turn activate coronary a1, a2 and b2 receptors, myocardial b1 receptors and coronary endothelial a2 receptors. As a net effect, coronary blood flow increases in response to cold in healthy individuals.30 Consistent with the notion that transplant recipients exhibit coronary endothelial dysfunction, the overall blood flow response to cold was markedly abnormal in the current patient population. However, the degree of abnormality was not associated with the course of transplant vasculopathy by IVUS. Several factors might account for this finding. First, early after cardiac transplantation the allograft is essentially dennervated. However, coronary reinnervation occurs to various degrees during the first 2 years after transplantation. Depending on the degree of reinnervation the coronary response to catecholamines might vary considerably between transplant recipients. Furthermore the amount of catecholamines released from terminal nerve endings is likely to vary.31 Second, alterations in the sensitivity of coronary a-adrenoreceptors to circulating catecholamines in the partially dennervated heart could be responsible for the abnormal vasomotor response observed during CPT.32 Moreover, the density of coronary a1, a2 and b2 receptors might have varied between patients depending on the degree of coronary reinnervation. Thus, the individual blood flow response to cold pressor testing is determined not only by the degree of endothelial dysfunction but also by the autonomic nervous supply of the coronary arteries. Third, cyclosporine, administered to all current study patients, results in relative reductions in coronary flow in response to acetylcholine in animal experimental studies. Other immunosupressive drugs might have also affected endothelial function to various degrees in the transplant recipients.33 Other pathological alterations such as glucose intolerance, hyperinsulinemia and dyslipidemia observed frequently in patients treated with corticosteroids might have also altered endothelial function.34 – 41 ACE-inhibitors, administered to three patients in the current study, and HMG-CoA reductase inhibitors given to all but two study patients, improve

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endothelial function in patients with coronary artery disease, and might have further contributed to the variability in the myocardial blood flow response to cold.21,42 Because of the complex interplay between coronary innervation, receptor density and receptor sensitivity, and varying medical treatment regimens, an intervention such as cold pressor testing might be less than ideal to probe endothelial dependent coronary function in transplant recipients.

Relationship between endothelial independent coronary function and morphology The current study demonstrates that the normalized myocardial flow reserve is markedly attenuated in the transplant patients and that the degree of its attenuation is significantly correlated with subsequent changes in coronary morphology (ie, changes in total vessel area and lumen diameter). This observation is in contradiction to previous studies that reported a normal hyperemic flow response and flow reserve in rejection-free cardiac allograft recipients using IVUS, intracoronary Doppler flow velocity measurements43 or PET.44 – 46 Several recent reports have disputed these findings. Kofoed et al studying transplant patients with PET during dipyridamole-induced hyperemia reported a significant decrease of the myocardial flow reserve 1 to 2 years after cardiac transplantation.5 Consistently, Chou et al. demonstrated a decreased flow reserve in transplant recipients.47 Further support of this theory was provided by Wolpers et al, who reported a homogeneously-reduced coronary flow reserve throughout the myocardium without a clear relationship to angiographic stenoses in transplant recipients with angiographic evidence of vasculopathy.48 Similarly, Mullins et al described an impairment of coronary flow reserve in transplant recipients with only mild occlusive disease of the large coronary arteries.49 Only three of the current study participants had angiographic evidence of mildly obstructive, epicardial coronary artery disease. Thus, a diffuse obstructive, angiopathic process of the microvascular bed, diagnostically inaccessible to IVUS and quantitative coronary angiography, is likely to account for the reduction in hyperemic blood flow and flow reserve. Further, the correlation between impairment of flow reserve and morphological changes of the coronary arteries suggests that the microvasculopathic process progresses linearly with time, eventually resulting in a loss of the normal endothelial inde-

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pendent dilatory capacity of the small resistance vessels.50

STUDY LIMITATIONS The current study has several limitations. First, only an IVUS but no PET study was performed early after cardiac transplantation. Thus, the degree of transplant vasculopathy could not be related to coronary function early after transplantation. The second IVUS study, performed at the time of PET, was termed the baseline study. The current findings of reductions in intimal index and maximal thickness between the current baseline and follow-up IVUS study do not therefore imply an overall regression of the disease. In fact, disease progression was evident by a) a “shrinkage” of the left anterior descending coronary artery, ie, reductions in total vessel area and lumen diameter; and b) progression of intimal thickening between immediate post-transplant IVUS and the “baseline”-IVUS. However, intimal proliferation did not progress during the observation period of this study, which might be ascribed to treatment of all but two study participants with HMG-CoA reductase inhibitors. Second, transplant recipients represent a heterogeneous study population regarding numbers of episodes of rejection, medication, age of donor heart, CMV status and many more. Due to the small size of the study group it was impossible to determine whether any of these parameters exerted an independent influence on the progression of the disease. However, the significant correlation between indices of endothelial independent myocardial blood flow and morphological parameters of disease progression argues against such independent influence. Lipid lowering drugs such as HMG-CoA reductase inhibitors might affect endothelial dependent and independent myocardial blood flow.21 However, 17 of the 19 study patients were treated with HMGCoA reductase inhibitors. Thus, because of the lack of a sizable control group of transplant recipients without lipid lowering therapy, a specific effect of these drugs could not be determined in the current study.

CLINICAL IMPLICATIONS Quantitative PET might provide a novel non-invasive approach to predict the course of transplant vasculopathy. Quantitative imaging of myocardial blood flow might allow monitoring the effects of acute or chronic pharmacological interventions on endothelial dependent and independent myocardial

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blood flow in cardiac transplant recipients. Whether measurements of myocardial blood flow early after cardiac transplantation yield a more accurate prediction of the progression of transplant vasculopathy needs to be established in future studies. We want to thank Ron Sumida, Larry Pang, Francine Aguilar, Der-Jenn Liu, Priscilla Contreras, and Sumon Wongpiya for their excellent technical assistance in performing the PET studies; Diane Martin and David Twomey for preparing the artwork.

REFERENCES 1. Miller LW, Schlant RC, Kobashigawa J, Kubo S, Renlund DG. Twenty-fourth Bethesda conference: cardiac transplantation. Task Force 5: complications. J Am Coll Cardiol 1993;22:41–54. 2. Johnson DE, Gao SZ, Schroeder JS, DeCampli WM, Billingham ME. The spectrum of coronary artery pathologic findings in human cardiac allografts. J Heart Transplant 1989;8:349 –59. 3. Johnson DE, Alderman EL, Schroeder JS, et al. Transplant coronary artery disease: histopathologic correlations with angiographic morphology. J Am Coll Cardiol 1991;17:449 – 57. 4. Mugge A, Heublein B, Kuhn M, et al. Impaired coronary dilator responses to substance P and impaired flow-dependent dilator responses in heart transplant patients with graft vasculopathy. J Am Coll Cardiol 1993;21:163–70. 5. Kofoed K, Czernin J, Johnson J, et al. Effects of cardiac allograft vasculopathy on myocardial blood flow, vasodilatory capacity and coronary vasomotion. Circulation 1997; 95:600 – 6. 6. Clausell N, Butany J, Molossi S, et al. Abnormalities in intramyocardial arteries detected in cardiac transplant biopsy specimens and lack of correlation with abnormal intracoronary ultrasound or endothelial dysfunction in large epicardial coronary arteries. J Am Coll Cardiol 1995;26:110 –9. 7. Davis SF, Yeung AC, Meredith IT, et al. Early endothelial dysfunction predicts the development of transplant coronary artery disease at 1 year post-transplant. Circulation 1996;93: 457– 62. 8. Aptecar E, Benvenuti C, Loisance D, Cachera JP, Nitenberg A. Early impairement of acetylcholine-induced endotheliumdependent coronary vasodilation is not predictive of secondary graft atherosclerosis. Chest 1995;107:1266 –74. 9. Billingham ME, Cary NR, Hammond ME, et al. A working formulation for the standardization of nomenclature in the diagnosis of heart and lung rejection: Heart Rejection Study Group. The International Society for Heart Transplantation. J Heart Transplant 1990;9:587–93. 10. Pucci AM, Forbes RDC, Billingham ME. Pathologic features in long-term cardiac allografts. J Heart Transplant 1990;9: 339 – 45. 11. Hausmann D, Lundkvist A, Friedrich G, Mullen W, Fitzgerald P, Yock P. Intracoronary ultrasound imaging: intraobserver and interobserver variability of morphometric measurements. Am Heart J 1994;128:674 – 80. 12. Potkin B, Bartorelli A, Gessert J, et al. Coronary artery imaging with intravascular high-frequency ultrasound. Circulation 1990;81:1575– 85.

The Journal of Heart and Lung Transplantation March 1999 13. Czernin J, Mu ¨ller P, Chan S, et al. Influence of age and hemodynamics on myocardial blood flow and flow reserve. Circulation 1993;88:62–9. 14. Spinks TJ, Jones T, Gilardi MC, Heather JD. Physical performance of the latest generation of commercial positron scanner. Trans Nucl Sci 1988;35:721–5. 15. Smits P, Lenders JW, Thien T. Caffeine and theophylline attenuate adenosine induced vasodilation in humans. Clin Pharmacol Ther 1990;48:410 – 8. 16. Weinberg IN, Huang SC, Hoffman EJ, et al. Validation of PET-acquired functions for cardiac studies. J Nucl Med 1988;29:241–7. 17. Gambhir SS, Schwaiger M, Huang SC, et al. Simple noninvasive quantification method for measuring myocardial glucose utilization in humans employing positron emission tomography and Fluorine-18 deoxyglucose. J Nucl Med 1989; 30:359 – 66. 18. Kuhle W, Porenta G, Huang S-C, et al. Quantification of regional myocardial blood flow using 13N-ammonia and reoriented dynamic positron emission tomographic imaging. Circulation 1992;86:1004 –17. 19. Marcus ML, Wilson RF, White CW. Methods of measurements of myocardial blood flow in patients: a critical review. Circulation 1987;76:873– 85. 20. Rickenbacher PR, Pinto FJ, Chenzbraun A, et al. Incidence and severity of transplant coronary artery disease early and up to 15 years after transplantation as detected by intravascular ultrasound. J Am Coll Cardiol 1995;25:171–7. 21. Gibbons GH. The pathogenesis of graft vascular disease: implications of vascular remodeling. J Heart Lung Transplant 1995;14:S149 –58. 22. Lim TT, Liang DH, Botas J, Schroeder JS, Oesterle SN, Yeung AC. Role of compensatory enlargement and shrinkage in transplant coronary artery disease. Circulation 1997; 95:855–9. 23. Pethig K, Heublein B, Wahlers T, Haverich A. Mechanism of luminal narrowing in cardiac allograft vasculopathy: inadequate vascular remodeling rather than intimal hyperplasia is the major predictor of coronary artery stenosis. Am Heart J 1998;135:628 –33. 24. Kobashigawa JA, Katznelson S, Laks H, et al. Effect of pravastatin on outcomes after cardiac transplantation. N Engl J Med 1995;333:621–7. 25. Salomon R, Hughes C, Schoen F, Payne D, Pober J, Libby P. Human coronary transplantation-associated arteriosclerosis: evidence for a chronic immune reaction to activated graft endothelial cells. Am J Pathol 1991;138:791– 8. 26. Yeung AC, Anderson T, Meredith I, et al. Endothelial dysfunction in the development and detection of transplant coronary artery disease. J Heart Lung Transplant 1992;11: S69 –73. 27. Duquesnoy RJ, Demetris AJ. Immunopathology of cardiac transplant recipients. Curr Opin Cardiol 1995;10:193–206. 28. Fish R, Nabel E, Selwyn A. Responses of coronary arteries of transplant recipients to acetylcholine. J Clin Invest 1988;81: 21–31. 29. Benvenutti C, Aptecar E, Mazzucotelli J, Jouannot P, Loisance D, Nitneberg A. Coronary artery response to cold pressor test is impaired early after operation in transplant recipients. J Am Coll Cardiol 1995;26:446 –51. 30. Burns D, Hollenberg SM, Tamburro P, et al. Progressive microvascular endothelial dysfunction after heart transplantation. J Heart Lung Transplant 1997;16:48.

The Journal of Heart and Lung Transplantation Volume 18, Number 3 31. Zeiher AM, Drexler H, Wollschlaeger H, Saurbier B, Just H. Coronary vasomotion in response to sympathetic stimulation in humans: importance of the functional integrity of the endothelium. J Am Coll Cardiol 1989;1181–90. 32. Schwaiger M, Hutchins GD, Kalff V, et al. Evidence for regional catecholamine uptake and storage sites in the transplanted human heart by Positron Emission Tomography. J Clin Invest 1991;87:1681–90. 33. Aptecar E, Dupouy P, Benvenuti C, et al. Sympathetic stimulation overrides flow-mediated endothelium-dependent epicardial coronary vasodilation in transplant patients. Circulation 1996;94:2542–50. 34. Sudhir K, MacGregor JS, DeMarco T, et al. Cyclosporine impairs release of endothelium-derived relaxing factors in epicardial and resistance coronary arteries. Circulation 1994; 90:3018 –23. 35. Tesfamariam B. Free radicals in diabetic endothelial cell dysfunction. Free Radic Biol Med 1994;16:383–91. 36. Cohen RA. Dysfunction of vascular endothelium in diabetes mellitus. Circulation 1993;87:V67–76. 37. Stern MP, Kolterman OB, Fries JF, McDevitt HO, Reaven GM. Adrenocortical steroid treatment of rheumatic diseases: effects on lipid metabolism. Arch Int Med 1973;132: 97–101. 38. Becker DM, Chamberlain B, Swank R, et al. Relationship between corticosteroid exposure and plasma lipid levels in heart transplant recipients. Am J Med 1988;85:632–7. 39. Harris KPG, Russel GI, Parvin SD, Veitch PS, Walls J. Alterations in lipid and carbohydrate metabolism attributable to cyclosporine A in renal transplant recipients. Br Med J 1986;292:16. 40. Roth D, Milgrom M, Esquenazi V, Fuller L, Burke G, Miller J. Post-transplant hyperglycemia: increased incidence in cyclosporine-treated renal allograft recipients. Transplantation 1989;47:278 – 81. 41. Kobashigawa JA, Kasiske BL. Hyperlipidemia in solid organ transplantation. Transplantation 1997;63:331– 8.

Allen-Auerbach et al.

219

42. Noll G, Lu ¨scher TF. Influence of lipoproteins on endothelial function. Thromb Res 1994;74(Suppl)1:S45–54. 43. Mancini GB, Henry GC, Macaya C, et al. Angiotensinconverting enzyme inhibition with quinapril improves endothelial vasomotor dysfunction in patients with coronary artery disease. Circulation 1996;94:258 – 65. 44. McGinn AL, Wilson RF, Olivari MT, Homans DC, White CW. Coronary vasodilator reserve after human orthotopic cardiac transplantation. Circulation 1988;78:1200 –9. 45. Rechavia E, Araujo LI, De-Silva R, et al. Dipyridamole vasodilator response after human orthotopic heart transplantation: quantification by oxygen-15-labeled water and positron emission tomography [see comments]. J Am Coll Cardiol 1992;19:100 – 6. 46. Senneff MJ, Hartman J, Sobel BE, Geltman EM, Bergmann SR. Persistence of coronary vasodilator responsivity after cardiac transplantation. Am J Cardiol 1993;71:333– 8. 47. Chan SY, Kobashigawa J, Stevenson LW, Brownfield E, Brunken RC, Schelbert HR. Myocardial blood flow at rest and during pharmacological vasodilation in cardiac transplants during and after successful treatment of rejection. Circulation 1994;90:204 –12. 48. Chou TM, Sudhir K, Amidon TM, et al. Comparison of adenosine to dipyridamole in degree of coronary hyperemic response in heart transplant recipients. Am J Cardiol 1996; 78:908 –13. 49. Wolpers HG, Koster C, Burchert W, et al. Coronary reserve after orthotopic heart transplantation: a quantification with N-13 ammonia and positron emission tomography. Z Kardiol 1995;84:112–20. 50. Mullins PA, Chauhan A, Sharples L, et al. Impairement of coronary flow reserve in orthotopic cardiac transplant recipients with minor coronary occlusive disease. Br Heart J 1992;68:266 –71. 51. Treasure CB, Vita JA, Ganz P, et al. Loss of the coronary microvascular response to acetylcholine in cardiac transplant patients. Circulation 1992;86:1156 – 64.