Determinants of the response of left ventricular ejection fraction to vasodilator stress in electrocardiographically gated ⁸²rubidium myocardial perfusion PET

Purpose: Myocardial perfusion imaging with ⁸²Rb PET allows for ECG-gated studies to be obtained early after radiotracer injection, capturing ventricular function close to peak pharmacologic action of dipyridamole. This is different from gated SPECT and may potentially provide additional diagnostic information. We sought to identify potential correlates of the PET-derived ejection fraction response to vasodilator stress. Methods: One hundred ten consecutive patients undergoing ⁸²Rb PET myocardial perfusion imaging during evaluation for coronary artery disease were included. Using a GE Discovery STRx PET-CT scanner, ECG-gated images (eight bins) were obtained at rest and 4 min after dipyridamole infusion, 90 s after infusion of 1,480-2,220 MBq of ⁸²Rb. Summed rest, stress, and difference scores (SRS, SSS, and SDS) were determined using a five-point scoring system and 20-segment model. Ejection fraction was calculated using automated QGS software. Results: Significant reversibility (SDS≥4) was found in 23 patients (21%). Mean LVEF in all patients was 47±13% at rest and 53±13% during dipyridamole. LVEF increased in 89 patients, and decreased in 17 patients during vasodilation. The change in LVEF was inversely correlated with SDS (r=-0.26; p=0.007). Additionally, it was inversely correlated with resting LVEF (r=-0.20; p=0.03) and SSS (r=-0.25; p=0.009). No significant correlations were observed with SRS, heart rate, blood pressure, age, hypertension, hypercholesterolemia, or pretest likelihood of disease. At multivariate regression analysis, SDS was an independent predictor of the change in LVEF. Conclusions: Gated ⁸²Rb PET during pharmacologic stress allows for assessment of the functional response to vasodilation. The magnitude of LVEF increase is determined by stress perfusion/reversible perfusion defects. Functional response to hyperemia may thus be incorporated in future evaluations of diagnostic and prognostic algorithms based on ⁸²Rb PET.