Myocardial flow reserve quantified using rubidium-82 (82Rb) PET predicts hard cardiac events and major adverse cardiac events independent of the summed stress score and other parameters, according to research published Aug. 9 in the Journal of the American College of Cardiology. Therefore, the researchers recommended that routine assessment of 82Rb PET-quantified myocardial flow reserve could improve risk stratification for patients being investigated for ischemia.
The clinical value of myocardial flow reserve quantification using 82Rb PET beyond relative myocardial perfusion imaging (MPI) “remains uncertain,” the authors wrote. “Among available validated PET tracers for flow quantification, 82Rb has the most potential for broad clinical application.” It is more widely available in North America than other cyclotron-based PET tracers. Still, no large studies have evaluated the prognostic value of flow quantification using 82Rb PET.
Maria C. Ziadi, MD, of the National Cardiac PET Centre in the division of cardiology at the University of Ottawa Heart Institute in Ottawa, prospectively enrolled 704 consecutive patients; 96 percent completed follow-up (median 387 days).
Patients were divided into four groups:
- I: Normal summed stress score ( <4) and normal myocardial flow reserve ( >2);
- II: Normal summed stress score and myocardial flow reserve <2;
- III: Summed stress score >4 and myocardial flow reserve >2; and
- IV: Summed stress score >4 and myocardial flow reserve <2.
For patients with a normal summed stress score and those with an abnormal summed stress score, there were significant differences in outcomes for hard events (cardiac death and MI) between patients with myocardial flow reserve >2 and those with myocardial flow reserve <2 (I: 1.3 percent vs. II: 2 percent; III: 1.1 percent vs. IV: 11.4 percent) and for major adverse cardiac events, according to the researchers.
In the adjusted Cox model, Ziadi et al reported myocardial flow reserve was an independent predictor of hard events (hazard ratio: 3.3) and major adverse cardiac events (hazard ratio: 2.4). The incremental prognostic value of the myocardial flow reserve over the summed stress score was demonstrated by comparing the adjusted summed stress score model with and without the myocardial flow reserve for hard events and major adverse cardiac events.
Routine integration of 82Rb myocardial flow reserve with relative MPI could represent “a valuable tool” for the clinician to better stratify a patient's risk of adverse cardiac events, the researchers concluded. “Abnormal 82Rb myocardial flow reserve means worse outcomes in any category of relative MPI, and this could affect management decisions for these patients,” Ziadi and colleagues noted. “Even in those with mildly abnormal relative MPI who may be considered for medical therapy, impaired 82Rb myocardial flow reserve had worse outcomes.”
Clinical integration of myocardial flow reserve with relative PET MPI will enhance risk stratification in this patient population, they concluded.