Positron emission tomography (PET) myocardial flow reserve (MFR) is an established marker of cardiovascular risk, but the prognostic significance of subendocardial flow reserve remains less well defined. A multicenter PET registry analysis published in Circulation evaluated whether subendocardial myocardial flow reserve (MFRSE) provided incremental prognostic information beyond transmural myocardial flow reserve (MFRTM).
The study included patients with normal perfusion on stress/rest Rb-82 PET imaging and excluded those with prior coronary artery bypass graft surgery, heart transplantation, or left ventricular ejection fraction below 40%. Patients were stratified into concordant-normal, discordant low-MFRSE with preserved MFRTM, and abnormal MFRTM groups. Major adverse cardiovascular events (MACE) included death, myocardial infarction, revascularization, or heart failure hospitalization.
Findings
- Among 6,603 patients, 885 had discordant low MFRSE despite preserved MFRTM, while 4,103 had normal values for both measures and 1,615 had abnormal MFRTM.
- During a median follow-up of 4.9 years, 1,661 MACEs occurred.
- Patients with discordant low MFRSE had a higher risk of MACE than the concordant-normal patients (HR, 1.41; 95% CI, 1.22–1.64).
- Discordant low MFRSE was also associated with higher all-cause mortality risk (HR 1.36; 95% CI 1.14–1.61).
- Adjusted annualized MACE rates were 5.79% in the discordant group, compared with 3.99% in the concordant-normal group and 8.35% in the abnormal MFRTM group (P<0.001).
The findings suggest that reduced subendocardial myocardial flow reserve identifies clinically significant risk heterogeneity among patients with preserved transmural flow reserve and normal perfusion imaging.
