In vitro test-retest repeatability of invasive physiological indices to assess coronary flow

Aims: Several invasive techniques are available in clinical practice to assess coronary flow. Nevertheless, the test–retest repeatability of these techniques in a controlled setting has not been reported. Therefore, we sought to evaluate fractional flow reserve (FFR), coronary flow reserve (CFR), index of microvascular resistance (IMR), and absolute coronary blood flow (ABF) with absolute microvascular resistance (AMR) test–retest repeatability using a coronary flow simulator. Methods and Results: Using a coronary flow simulator (FFR WetLab version 2.0; Abbott Vascular, Santa Clara, CA), we created stenoses ranging from 0% to 70%, with 10% increments. Three different flows were established with their hyperemic phases, and two consecutive measurements were obtained, evaluating the following indices: FFR, CFR, IMR, ABF, and AMR, using a pressure/temperature wire and an infusion catheter. One hundred and thirty-eight pairs of measurements were performed. Test–retest reliability was compared in 48 FFR, 18 CFR, 24 IMR, 24 ABF, and 24 AMR. Test–retest repeatability showed excellent reproducibility for FFR, ABF, and AMR; respectively 0.98 (0.97–0.99), 0.92 (0.81–0.97) and 0.91 (0.79–0.96) (P < 0.0001 for all). However, test–retest repeatability was weaker for IMR and poor for CFR; respectively 0.53 (0.16–0.77) (P = 0.006) and 0.27 (−0.26–0.67) (P = 0.30). Conclusions: Using a coronary flow simulator, FFR and ABF with AMR had excellent test–retest reliability. IMR and CFR demonstrated weaker test–retest reliability.