Abstract 18232: The Magnitude of Hyperemic Microvascular Resistance Determines the Functional Consequences of Fractional Flow Reserve-Positive Coronary Stenoses, as Well as the Optimal Fractional Flow Reserve Cut-Off Value for Stenosis-Specific Inducible Myocardial Ischemia

Abstract

Background: Although myocardial ischemia is a consequence of both epicardial and microvascular abnormalities, clinical decision-making by fractional flow reserve (FFR) is purportedly based on the extent of epicardial disease only. Nonetheless, FFR is recognized to be sensitive to the magnitude of hyperemic microvascular resistance (HMR), which is not accounted for in FFR-guided diagnostic strategies. We aimed to determine pertinence of hyperemic microvascular resistance for the occurrence of inducible myocardial ischemia in FFR-positive (FFR≤0.80) and FFR-negative (FFR>0.80) lesions, as well as for the optimal FFR cut-off value to identify stenosis-specific inducible myocardial ischemia. Methods: We evaluated 299 coronary lesions by intracoronary pressure and flow velocity measurements to determine FFR and HMR. Myocardial perfusion scintigraphy (MPS) was performed to identify inducible myocardial ischemia. High HMR was defined as HMR>1.9 mmHg/cm/s. The association between FFR and inducible ischemia was evaluated according to the presence of a high or low HMR using logistic regression analysis. Receiver-operating characteristics curve analysis was performed to determine the optimal FFR cut-off value for inducible myocardial ischemia. Results: Overall, the odds ratio of positive versus negative FFR for inducible myocardial ischemia on MPS was 4.6 (95% confidence interval (CI): 2.6-8.0; p<0.001). The odds ratio of positive versus negative FFR for myocardial ischemia amounted to 2.1 (95% CI: 0.5-3.6; p=0.14) when HMR was low, and to 8.1 (95% CI: 4.0-16.5; p<0.001) when HMR was high. The optimal FFR cut-off value for inducible myocardial ischemia was 0.65 when HMR was low, compared with 0.76 when HMR was high. Conclusion: The 0.80 cut-off value provides limited discriminative value, since the odds for myocardial ischemia originating from FFR-positive lesions are to a large extent determined by the magnitude of distal microvascular resistance. The optimal FFR cut-off value to identify stenosis-related inducible myocardial ischemia depends on the magnitude of HMR, and is substantially lower when HMR is low, compared with when HMR is high.