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iFR (instantaneous wave-free ratio) is a new vasodilator-independent index correlated to FFR (fractional flow reserve). Recent studies proved non-inferiority of iFR- as compared to FFR-guided revascularization. However, the use of iFR is restricted to a single device with software using a fully automated algorithm acting over the wave-free period of a minimum of five heartbeats. We hypothesized that a diastolic pressure ratio (dPR) calculated using different software might have similar diagnostic accurary as compared to FFR and resting Pd/Pa.
This is an observational, prospective, single-center cohort study including 100 consecutive patients undergoing pressure wire (PW) or microcatheter-based FFR measurements. Dedicated software (Rubo DICOM, Rubo Medical Imaging BV) was used to calculate the dPR from DICOM pressure curves used to calculate Pd/Pa and hyperemic indices. By indicating the “flat” period of the Dp/Dt signal (the “wavefree” period) in 5 consecutive heartbeats, the Rubomed viewer collected the Pa and Pd values of the indicated region. Measurements were performed by 3 independent operators to assess inter-observer variability.
One hundred patients who underwent FFR by using either the microcatheter system (n=50) or a PW system (n=50) were assessed. Mean age was 66±11 years and 80 (80%) were males. No significant differences were found in baseline characteristics between Navvus vs. PW system. Mean FFR, resting Pd/Pa and dPR calculated by the novel algorithm was 0.85±0.09; 0.94±0.05; and 0.93±0.07, respectively. There was a significant linear correlation between dPR and FFR and between dPR and resting Pd/Pa (R2=0.78, p<0.001 and R2=0.95, p<0.001, respectively). The correlation coefficient in the Navvus cohort was higher compared with the PW-system cohort (R2=0.81, p<0.001, and R2=0.76, p<0.001, respectively). Pd/Pa and dPR had good accuracy in the identification of patients with significant FFR values defined as FFR1≤0.80 (AUC of 0.86 (95% CI: 0.79-0.94) and 0.84 (95% CI: 0.75 to 0.92) respectively).
Resting, adenosine-independent diastolic pressure ratio dPR, calculated by a novel algorithm, had a linear correlation with the hyperemic index FFR and resting Pd/Pa and it had a high inter-observer reliability.