Relation Between Myocardial Fractional Flow Reserve Calculated From Coronary Pressure Measurements and Exercise-Induced Myocardial Ischemia

Abstract

Background Myocardial fractional flow reserve (FFR_myo) is a functional index of stenosis severity that can be derived from intracoronary pressure measurements performed during maximal vasodilatation. It is defined as the maximal myocardial perfusion during hyperemia in the presence of a stenosis in the epicardial artery expressed as a fraction of its normal maximal expected value. To determine threshold values of FFR_myo, of hyperemic translesional pressure gradient (ΔP_max), and of resting translesional pressure gradient (ΔP_rest) that are uniformly associated with exercise-induced ischemia, we studied the relation between these pressure-derived indexes and the results of exercise ECG. Methods and Results We studied 60 patients with an isolated lesion in one major epicardial coronary artery, normal left ventricular function, and no left ventricular hypertrophy. Maximal exercise ECG (off anti-ischemic medication) was performed within 6 hours before catheterization. Intracoronary pressure measurements were taken at rest and during hyperemia with a pressure monitoring guide wire. ST-segment depressions at peak exercise (considered abnormal when ≥0.1 mV) were compared with FFR_myo, ΔP_max, and ΔP_rest. Thirty-seven patients had an abnormal and 23 patients a normal exercise ECG. A significant linear correlation was found between the magnitude of ST-segment depressions and both FFR_myo and ΔP_max (r=−.75, SEE=0.53; r=.71, SEE=0.56). A weaker correlation was noted between ST-segment depressions and ΔP_rest (r=.53, SEE=0.67). Sensitivity and specificity curves were constructed for the prediction of an abnormal exercise ECG for the three pressure-derived indexes. The values that most accurately predicted an abnormal exercise ECG were 66% for FFR_myo, 31 mm Hg for ΔP_max, and 12 mm Hg for ΔP_rest. No patient with a FFR_myo value >72% showed an abnormal exercise ECG. In addition, receiver operating characteristic curves demonstrated a greater accuracy of FFR_myo and of ΔP_max than of ΔP_rest for predicting the results of the exercise ECG. Conclusions In the present study, cutoff values of FFR_myo and translesional pressure gradients are established from the relation between intracoronary pressure–derived indexes and ECG signs of myocardial ischemia during maximal exercise. These values can be helpful for clinical decision making in cases with dubious angiographic results. Furthermore, our data support the concept that stenosis physiology is better reflected by hyperemic than by basal measurements.