15 Clinical value of fully quantitative stress perfusion CMR in the non-invasive assessment of cardiac allograft vasculopathy

<h3>Introduction</h3> Stress CMR has class I indication in patients with known or suspected coronary artery disease. Cardiac allograft vasculopathy (CAV) is a dreaded complication long-term after heart transplantation. We aimed to assess the diagnostic and prognostic yield, as well as the clinical utility in gatekeeping to angiography, for fully quantitative stress perfusion cardiovascular magnetic resonance (QP-CMR) compared with visual assessment of inducible ischemia in an outpatient population of heart transplant recipients. <h3>Materials and Methods</h3> Orthotopic heart transplant recipients undergoing clinically indicated stress CMR for CAV assessment were included and followed up to a median(IQR) of 1.8(0.9,2.7) years. We calculated sensitivity, specificity, positive (PPV), and negative (NPV) predictive values, as well as the area under the curve (AUC) for diagnostic accuracy of qualitative and fully quantitative stress CMR parameters against a reference of invasive or CT coronary angiography. Receiver operating characteristics curves were compared using the bootstrap method. Unadjusted hazard ratios for major adverse cardiovascular events (MACE, composite of unplanned cardiac hospitalization or death) were obtained to assess for prognostic significance. Clinical utility was assessed with decision curve analysis and measured as the net benefit purported by undergoing stress CMR as gatekeeper to angiography at a prespecified threshold range (10–40%). <h3>Results</h3> Of 60 outpatients identified, 18(30%) had significant CAV on angiography, and 11(18.3%) incurred MACE. The myocardial perfusion reserve (MPR) index had a sensitivity of 85.7%, specificity of 70.3%, PPV of 52.2%, and NPV of 92.9% at a Youden threshold of 2.1, and was significantly more accurate than visual assessment (p &lt; 0.001). Presence of inducible ischemia was not a significant predictor of MACE at follow-up (HR 2.23[0.57,8.66], p=0.2), while the MPR index was (HR 0.26 [0.07,0.93], p=0.015). At the assessment of decision curves, the MPR index conferred incremental benefit over the visual assessment of inducible ischemia, with a net reduction in unnecessary angiographies. <h3>Conclusion</h3> In patients with previous heart transplantation, fully quantitative stress CMR with MPR index was incrementally accurate and prognostic over visual assessment. A strategy of QP-CMR was effective and would lead to a significant reduction in referrals to computed tomography or invasive coronary angiography. These findings warrant prospective validation.