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

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.

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.

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%.

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.