Abstract Body (Do not enter title and authors here): Background:
Cardiac allograft vasculopathy (CAV) is a major cause of morbidity and mortality following heart transplantation (OHT). Noninvasive methods to detect CAV and risk stratify OHT patients are needed. The value of fully quantitative stress cardiac magnetic resonance imaging has been recently validated and may be a promising technique for OHT surveillance. We aimed to evaluate the feasibility of quantitative stress CMR after OHT.

Methods:
We enrolled asymptomatic OHT recipients without coronary artery disease to undergo regadenoson stress CMR (1.5T GE HealthCare) with cine imaging, tissue mapping, and late gadolinium enhancement (LGE) imaging for routine CAV surveillance. Using the dual sequence technique, quantitative perfusion values were determined using Fermi deconvolution. Myocardial perfusion reserve (MPR) was calculated as the ratio of stress to rest myocardial blood flow (MBF).

Results:
Fifty-three subjects (mean age 47.06 ± 17.14 years) were included. OHT recipients (n=11, mean 6.77 ± 4.34 years post-transplant) were compared with healthy controls (n=43). No life-threatening adverse events, brief or prolonged atrioventricular block or other arrhythmias occurred with regadenoson. Coronary angiography was performed in 9 OHT patients before CMR, with an average of 1.99 ± 2.05 years between studies. No visual inducible ischemia was reported. Post OHT, rest MBF was significantly higher (1.69 ± 0.52 mL/g/min vs 1.01 ± 0.24 mL/g/min, p=0.004) and stress MBF was lower (2.33 ± 0.69 mL/g/min vs 2.95 ± 0.88 mL/g/min, p=0.02) compared to controls. MPR was significantly lower in OHT recipients compared to controls (1.46 ± 0.51 vs 3.11 ± 1.12, p<0.001), and remained lower when corrected for rate pressure product (1.23± 0.32 vs 3.94 ± 1.5, p<0.001) (Figure 1).

Conclusions:
Regadenoson stress perfusion CMR is safe and feasible in OHT recipients. We observed reduced coronary microvascular function (higher resting MBF, lower MPR) post OHT, despite normal perfusion on visual inspection. In addition to cardiac structure, function, and myocardial tissue characterization, quantitative assessment of MPR by CMR may have incremental value over qualitative assessment of ischemia and should be evaluated in future studies.