Simultaneous assessment of fractional and coronary flow reserves in cardiac transplant recipients - Physiologic investigation for transplant arteriopathy (PITA study)

Background - The utility of measuring fractional flow reserve (FFR) to assess cardiac transplant arteriopathy has not been evaluated. Measuring coronary flow reserve (CFR) as well as FFR could add information about the microcirculation, but until recently, this has required two coronary wires. We evaluated a new method for simultaneously measuring FFR and CFR with a single wire to investigate transplant arteriopathy. Methods and Results - In 53 cases of asymptomatic cardiac transplant recipients without angiographically significant coronary disease, FFR and thermodilution-derived CFR (CFRthermo) were measured simultaneously with the same coronary pressure wire in the left anterior descending artery and compared with volumetric intravascular ultrasound (IVUS) imaging. The average FFR was 0.88 +/- 0.07; in 75% of cases, the FFR was less than the normal threshold of 0.94; and in 15% of cases, the FFR was less than or equal to 0.80, the upper boundary of the gray zone of the ischemic threshold. There was a significant inverse correlation between FFR and IVUS-derived measures of plaque burden, including percent plaque volume (r = 0.55, P < 0.0001). The average CFRthermo was 2.5 +/- 1.2; in 47% of cases, CFRthermo was ≤2.0. In 14%, the FFR was normal ( ≥ 0.94) and the CFR was abnormal ( < 2.0), suggesting predominant microcirculatory dysfunction. Conclusions - FFR correlates with IVUS findings and is abnormal in a significant proportion of asymptomatic cardiac transplant patients with normal angiograms. Simultaneous measurement of CFR with the same pressure wire, with the use of a novel coronary thermodilution technique, is feasible and adds information to the physiological evaluation of these patients.