The integration of angio-IMR, QFR and FFR for the detection of ischemia

Abstract

Abstract Background Fractional flow reserve (FFR) and quantitative flow ratio (QFR) are important tools to assess coronary-specific ischemia, but ischemia may be obscured in the presence of coronary microvascular dysfunction (CMD). Wire free angiography based index of microcirculatory resistance (angio-IMR) might aid in identifying ischemic territories with normal FFR or QFR. Purpose First we sought to validate angio-IMR against invasive resistance indices and [15O]H2O positron emission tomography (PET) derived resistance. Secondly, we investigated whether angio-IMR can help identifying ischemic vessels with normal FFR/QFR. Methods In this PACIFIC 1 and 2 sub study symptomatic patients underwent [15O]H2O PET and invasive coronary angiography with routine three vessel FFR. Invasive hyperemic microvascular resistance (HMR) and IMR were measured in a sub set of patients. A FFR/QFR ≤0.80 and hyperemic myocardial blood flow (hMBF) ≤2.3 ml/min/g were considered ischemic. Microvascular resistance on PET was defined as the ratio of mean distal coronary pressure to MBF. Angio-IMR, QFR and PET analyses were performed by core labs blinded to invasive angiography results. Results Among 259 patients (mean age 61 ± 9 years, 188 (73%) male) 494 vessels were included. Invasive IMR and or HMR were measured in 95 vessels. Angio-IMR did not correlate with invasive HMR/IMR for the right coronary artery (RCA) but correlated weakly with invasive HMR (r=0.39, p=0.03) and moderately (r=0.48, p<0.01) with invasive IMR for the left coronary artery (LCA). The RCA was excluded for further analysis. A very weak correlation between angio-IMR and PET resistance was observed (r=0.17, p<0.01). Territories with ischemia and a normal FFR showed a higher angio-IMR than ischemic territories with reduced FFR (31.3 ± 13.8 vs 22.2 ± 10.3, p<0.01). The same was observed after stratification by QFR/PET results (34.3 ± 15.5 vs 23.9 ± 9.9, p<0.01). Results remained consistent after stratification for diameter stenosis percentage. Conclusions A weak to moderate correlation was found between angio-IMR and invasive resistance indices for the LCA. In territories with an ischemic perfusion angio-IMR was higher in those with a normal FFR/QFR compared to patients with a reduced FFR/QFR. Integration of FFR/QFR and angio-IMR might lead to superior vessel-specific ischemia detection.