RELATION BETWEEN MYOCARDIAL FRACTIONAL FLOW RESERVE CALCULATED FROM CORONARY PRESSURE MEASUREMENTS AND EXERCISE-INDUCED MYOCARDIAL-ISCHEMIA

Background Myocardial fractional flow reserve (FFR(myo)) is a function al index of stenosis severity that can be derived from intracoronary p ressure measurements performed during maximal vasodilatation. It is de fined as the maximal myocardial perfusion during hyperemia in the pres ence of a stenosis in the epicardial artery expressed as a fraction of its normal maximal expected value. To determine threshold values of F FR(myo), of hyperemic translesional pressure gradient (Delta P-max), a nd of resting translesional pressure gradient (Delta P-rest) that are uniformly associated with exercise-induced ischemia, we studied the re lation between these pressure-derived indexes and the results of exerc ise ECG. Methods and Results We studied 60 patients with an isolated l esion 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 cath eterization. Intracoronary pressure measurements were taken at rest an d during hyperemia with a pressure monitoring guide wire. ST-segment d epressions at peak exercise (considered abnormal when greater than or equal to 0.1 mV) were compared with FFR(myo), Delta P-max and Delta P- rest. Thirty-seven patients had an abnormal and 23 patients a normal e xercise EGG. A significant linear correlation was found be-tween the m agnitude of ST-segment depressions and both FFR(myo) and Delta P-max ( r=-.75, SEE=0.53; r=.71, SEE=0.56). A weaker correlation was noted bet ween ST-segment depressions and Delta P-rest (r=.53, SEE=0.67). Sensit ivity and specificity curves were constructed for the prediction of an abnormal exercise ECG for the three pressure-derived indexes. The val ues that most accurately predicted an abnormal exercise ECG were 66% f or FFR(myo), 31 mm Hg for Delta P-max, and 12 mm Hg for Delta P-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 Delta P-max than of Delta P-rest f or predicting the results of the exercise ECG. Conclusions In the pres ent study, cut off values of FFR(myo) and translesional pressure gradi ents are established from the relation between intracoronary pressure- derived indexes and ECG signs of myocardial ischemia during maximal ex ercise. These values can be helpful for clinical decision making in ca ses with dubious angiographic results. Furthermore, our data support t he concept that stenosis physiology is better reflected by hyperemic t han by basal measurements.