Prognostic Value of Rubidium-82 Positron Emission Tomography in Patients After Heart Transplant

Abstract

CAV results in diffuse concentric intimal thickening of the epicardial vessels affecting both the proximal and distal vessels as well as the microcirculation.3 This progressive luminal narrowing and loss of vasodilatory capacity culminates in myocardial ischemia and contractile dysfunction. Immunemediated injury plays a significant role in the development of epicardial vessel stenosis in addition to traditional risk factors. 4 Clinical symptoms such as angina are typically absent in cases of CAV because of allograft denervation, and therefore annual screening is used in most centers.Recent guidelines recommend periodic invasive coronary angiography for at least the first 3 to 5 years after transplantation. 5 However, this is inconvenient and adds risk. Hence, many centers have elected to monitor patients with noninvasive testing, but this strategy may be suboptimal because of the lower sensitivity for the detection of early CAV. 6,7 Rubidium-82 (Rb-82) positron emission tomography (PET) myocardial perfusion imaging is a noninvasive imaging modality that has the ability to quantify myocardial blood flow (MBF) 8 and has been shown to have prognostic value in patients being assessed for ischemia.9-11 This technique may facilitate earlier detection of CAV and thus may have prognostic value in HT patients. The objective of this study was to evaluate the prognostic value of Rb-82 PET in patients with a history of HT.Background-Cardiac allograft vasculopathy is a key prognostic determinant after heart transplant. Detection and risk stratification of patients with cardiac allograft vasculopathy are problematic. Positron emission tomography using rubidium-82 allows quantification of absolute myocardial blood flow and may have utility for risk stratification in this population. Methods and Results-Patients with a history of heart transplant undergoing dipyridamole rubidium-82 positron emission tomography were prospectively enrolled. Myocardial perfusion and left ventricular ejection fraction were recorded. Absolute flow quantification at rest and after dipyridamole stress as well as the ratio of mean global flow at stress and at rest, termed myocardial flow reserve, were calculated. Patients were followed for all-cause death, acute coronary syndrome, and heart failure hospitalization. A total of 140 patients (81% men; median age, 62 years; median follow-up, 18.2 months) were included. There were 14 events during follow-up (9 deaths, 1 acute coronary syndrome, and 4 heart failure admissions). In addition to baseline clinical variables (estimated glomerular filtration rate, previously documented cardiac allograft vasculopathy), relative perfusion defects, mean myocardial flow reserve, and mean stress myocardial blood flow were significant predictors of adverse outcome. Conclusions-Abnormalities on rubidium-82 positron emission tomography were predictors of adverse events in heart transplant patients. Larger prospective studies are required to confirm these findings. (Circ Cardiovasc Imaging. 2014;7:930-937.)

Reduced Myocardial Flow in Heart Failure Patients With Preserved Ejection Fraction

“…14,15 In short, patients were positioned in a Discovery 690 or RX PET-CT system (GE Healthcare, Waukesha, WI). After a low-dose computed tomography scan acquired for attenuation correction, 14,15 10 MBq/kg of Rb-82 was administered intravenously as a 30-second square-wave using a feedback-controlled elution system (Jubilant DraxImage, Montreal, QC). Dynamic Rb-82 PET images were acquired during 10 minutes using a list-mode acquisition.…”

Predicting Outcomes in Heart Transplantation

“…11 Wu et al 12 studied 27 patients an average of 2.5 years out from transplant with normal coronary angiograms, normal left ventricular function, and no rejection and found an inverse correlation between MFR and plaque volume as assessed by IVUS. The study by Mc Ardle et al 8 extends these mechanistic findings by suggesting that MFR is an important surrogate of the pathobiology of CAV.…”

“…In this issue of Circulation: Cardiovascular Imaging, Mc Ardle et al 8 sought to determine the prognostic value of Rubidium-82 positron emission tomography (PET) in heart transplant patients. Between 2009 and 2013, 140 patients greater than 1 year post-transplant were enrolled in a prospective PET registry.…”

“…When performed with dipyridamole stress, PET imaging integrates global and regional vasodilatory capacity, as well as endothelium-dependent vasomotor and epicardial conduit vessel function. 13 The data by Mc Ardle et al 8 suggest that PET imaging may provide a more reliable tool for detecting early CAV and targeting high-risk patients, while avoiding unnecessary coronary angiography and IVUS in those at low risk of future events. However, several unique features of the transplanted heart may alter the response to dipyridamole stress.…”

“…While waiting for larger multicenter data sets with more events (only 6% of the patients in the study by Mc Ardle et al 8 had documented CAV, with only 4 cardiac deaths in followup), PET imaging has other potential clinical and research uses in heart transplantation ( Table 3). [15][16][17][18][19][20] Although specificity is limited, Chan et al 15 showed an improvement in MFR after treatment of acute cellular rejection.…”