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

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. 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.