Normal values for ¹³N-ammonia PET-derived metrics in heart transplant patients

Cardiac PET is an established tool for detecting cardiac allograft vasculopathy (CAV), however, transplant-patient-specific normal values for myocardial blood flow (MBF), myocardial blood flow reserve (MBFR), and left ventricular parameters are limited. We aimed to define normal ranges in heart transplant (HT) recipients using two software programs and to assess agreement between software-derived metrics.

We retrospectively evaluated 266 HT recipients undergoing ¹³N-ammonia PET between 2021-2023. Studies without ischemia or scar were included and compared with invasive coronary angiography and intravascular ultrasound. Normal values for MBF, MBFR, left ventricular volumes, and left ventricular ejection fraction were derived in patients without angiographic CAV and in a subset without micro-intimal disease, using two different software programs, Corridor4DM and Cedars-Sinai. Agreement between software-derived metrics was assessed using correlation and Bland-Altman analyses.

Ninety-three patients without angiographic CAV (56 without micro-intimal disease) met criteria for normal reference value derivation. Rate-pressure-product-correction had a significant influence on the MBFR, with lower limits of normal for uncorrected MBFR and rate-pressure-product-corrected-MBFR ranging between 1.80-2.04 and 2.10-2.37, respectively, depending on the software program and use of residual subtraction. Values of software-derived metrics demonstrated strong monotonic relationship and moderate-to-good absolute agreement but the intraclass correlation coefficient was <0.90 for most metrics and there were wide limits of agreement for MBF metrics.

This study establishes software-specific normal reference values for ¹³N-ammonia PET metrics in HT recipients without CAV. These findings support the use of software-specific thresholds and consistent post-processing for longitudinal assessment in transplant populations.