Quantitative CZT SPECT Myocardial Blood Flow for Physiological Assessment and Risk Stratification of Cardiac Allograft Vasculopathy

BACKGROUND: Cardiac allograft vasculopathy (CAV) remains a major cause of morbidity and mortality after orthotopic heart transplantation. Although positron emission tomography myocardial perfusion imaging with quantitative myocardial blood flow (MBF) effectively detects CAV, access remains limited. Cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) enables quantitative MBF assessment and may provide a more accessible alternative. However, the diagnostic and prognostic value of quantitative CZT SPECT-derived MBF for CAV is unknown. METHODS: We retrospectively studied 110 consecutive orthotopic heart transplantation recipients who underwent coronary angiography and CZT SPECT quantitative MBF imaging within 12 months. Stress MBF, rest MBF, MBF reserve, coronary flow capacity, and total perfusion deficit were compared across International Society for Heart and Lung Transplantation CAV categories. The diagnostic performance of the established (Bravo) and modified (Hart) flow-based algorithms was evaluated by receiver operating characteristic analysis. Associations with CAV-related events were assessed. RESULTS: Over 2.3±1.0 years, stress MBF declined progressively with increasing CAV severity ( P =0.007) and was lower in patients with CAV 2 to 3 than in those with CAV 0 to 1 (1.25±0.52 versus 2.03±0.81 mL/min per g; P =0.003). The Bravo and Hart algorithms showed similar discrimination of advanced CAV by paired DeLong comparison (area under the curve, 0.773 versus 0.717; Δ area under the curve, 0.056; P =0.606). Severely reduced coronary flow capacity was associated with higher event rates (28.6% versus 5.2%; P =0.015). The Hart framework demonstrated exploratory prognostic separation (35.3% versus 3.2%; P =0.001). CONCLUSIONS: Quantitative CZT SPECT-derived MBF and coronary flow capacity provide physiological assessment and risk stratification of CAV, with preliminary associations with CAV-related events. These findings support the prospective multicenter evaluation of CZT SPECT MBF as a widely available, noninvasive orthotopic heart transplantation surveillance strategy.