Comparison of Coronary Physiological Indices in Identifying Functionally Significant Myocardial Bridges in ANOCA.

Abstract

Background: A functionally significant myocardial bridge (MB) is an important cause of angina with nonobstructive coronary arteries. However, distinguishing a functionally significant versus incidental MB remains challenging. Resting and hyperemic intracoronary functional indices are available, but no studies have compared their diagnostic performance in MBs.

Methods: We prospectively studied 64 patients with angina and nonobstructive coronary arteries, all of whom had an MB confirmed by intravascular ultrasound. We evaluated the diagnostic performance of instantaneous wave-free ratio (iFR) and resting full-cycle ratio (RFR) under Dobutamine stress, with Dobutamine diastolic fractional flow reserve (dFFR) as a reference standard. Dobutamine iFR and Dobutamine RFR were assessed in the first 18 patients, while only Dobutamine RFR was assessed in the remaining 46. Dobutamine dFFR ≤0.76 was considered indicative of a functionally significant MB.

Results: There was a strong correlation between Dobutamine iFR (R²=0.67, P<0.001) and Dobutamine RFR (R²=0.80, P<0.001) with Dobutamine dFFR. Receiver operating characteristics curve analysis to identify the cutoff for Dobutamine dFFR ≤0.76 was 0.81 for Dobutamine iFR (area under the curve 0.961) and 0.76 for Dobutamine RFR (area under the curve 0.996). The diagnostic accuracy of Dobutamine iFR was 94.4%, with a sensitivity of 100% and specificity of 85.7%. For Dobutamine RFR, the diagnostic accuracy was 96.9%, with a sensitivity of 95.8% and specificity of 100%.

Conclusions: In patients with angina and nonobstructive coronary arteries and an MB confirmed by intravascular ultrasound, Dobutamine iFR and Dobutamine RFR may serve as alternatives to Dobutamine dFFR in identifying a functionally significant MB, with Dobutamine RFR having superior diagnostic accuracy.