Noninvasive PET quantitative myocardial blood flow with regadenoson for assessing cardiac allograft vasculopathy in orthotopic heart transplantation patients

BackgroundRisk stratification and early detectionof cardiac allograft vasculopathy (CAV) is essential in orthotopic heart transplantation (OHT) patients. This study assesses the changes in myocardial blood flow (MBF) noninvasively in OHT patients using quantitative cardiac PET with regadenoson.MethodsTwelve patients (Group 1) (8 males, 4 females, mean age 55±7 years) with no history of post OHT myocardial ischemia were enrolled 5.4±2.0 years after OHT. Fifteen patients (Group 2) (9 males, 6 females, mean age 71±9 years) with intermediate pretest probability but not documented evidence for coronary artery disease (CAD) were also included to serve as control. Global and regional MBFs were assessed using dynamic 13N-NH3 PET at rest and during regadenoson-induced hyperemia. The coronary flow reserve (CFR) was also calculated as the ratio of hyperemic to resting MBF.ResultsMean regadenoson-induced rate-pressure products were similar in both groups, while there was an increase in resting rate-pressure product in Group 1 patients. Both mean and median values of resting MBF were higher in Group 1 than Group 2 patients (1.33±0.31 and 1.01±0.21mL/min/g for Groups 1 and 2, respectively, P<.001), while mean hyperemic MBF values were similar in both Groups (2.68±0.84 and 2.64±0.94mL/min/g, P=NS) but median hyperemic MBF values were lower in Group 1 than Group 2 patients (2.0 vs. 2.60mL/min/g, P=.018). Both mean and median CFR values demonstrated a significant reduction for Group 1 compared to Group 2 patients (2.07±0.74 vs 2.63±0.48, P=.025).ConclusionsThis study suggests that the MBF in OHT patients may be abnormal at resting state with diminished CFR. This hints that the epicardial and microvascular coronary subsystem may be exacerbated after OHT leading to the gradual progression of CAV.