Correlation of Fractional Flow Reserve With Ischemic Burden Measured by Cardiovascular Magnetic Resonance Perfusion Imaging.

Cardiovascular magnetic resonance (CMR) perfusion imaging and fractional flow reserve (FFR) assess myocardial ischemia. FFR measures the pressure loss across a stenosis determining hemodynamic significance but does not assess the area subtended by the stenotic vessel. CMR perfusion imaging measures the extent of myocardial blood flow reduction (=ischemic burden). Both techniques allow for continuous rather than categorical evaluation, but their relationship is poorly understood. This study investigates the relationship between the FFR value and the extent of myocardial ischemia. Forty-nine patients with angina underwent CMR perfusion imaging. FFR was measured in vessels with a visual diameter stenosis >40%. The extent of ischemia for each coronary artery was measured by delineating the perfusion defect on the CMR images and expressing as a percentage of the left ventricular myocardium. The correlation between the extent of ischemia measured by CMR and FFR was good (r = -0.85, p < 0.0005). The mean FFR value was 0.67 ± 0.17, and the mean perfusion defect was 8.9 ± 9.3%. An FFR value of ≥0.75 was not associated with ischemia on CMR. The maximum amount of ischemia (23.0 ± 1.5%) was found at FFR values 0.4 to 0.5. In patients with 1 vessel disease (49%), the mean ischemic burden was 15.3 ± 8.3%. In patients with 2 vessel diseases (18%), the mean ischemic burden was 26.0 ± 12%. Reproducibility for the measurement of ischemic burden was very good with a Kappa coefficient (k = 0.826, p = 0.048). In conclusion, there is good correlation between the FFR value and the amount of myocardial ischemia in the subtended myocardium.