Abstract 15187: Comparison of Resting and Hyperemic Coronary Physiological Indices to Evaluate Myocardial Bridging in Patients With Angina and No Obstructive Coronary Arteries

Abstract

Introduction: A hemodynamically significant myocardial bridge (MB) is an important diagnosis in patients with angina and no obstructive coronary arteries (ANOCA). The most appropriate intracoronary functional assessment to distinguish an incidental vs. hemodynamically significant MB remains unclear. We compared the ability of several resting and hyperemic physiological indices to identify a hemodynamically significant MB. Methods: We prospectively studied 11 patients with ANOCA and an MB confirmed by intravascular ultrasound (IVUS). All patients had intracoronary functional testing at rest, including instantaneous wave-free ratio (iFR), resting full-cycle ratio (RFR), and the ratio of distal coronary pressure (Pd)/aortic pressure (Pa). These measurements were repeated at hyperemia, including adenosine fractional flow reserve (FFR), dobutamine diastolic FFR (dFFR), iFR, and RFR. Resting iFR and RFR ≤ 0.89; resting Pd/Pa ≤ 0.91; hyperemic FFR, iFR, and RFR ≤ 0.8; and dFFR ≤ 0.76 were considered indicative of hemodynamic significance of an MB. Dobutamine dFFR was considered as reference standard. Results: At rest, iFR and RFR were significant in 6 and 7 patients respectively, while Pd/Pa was significant in 6. Adenosine FFR was significant in only 4 patients. With dobutamine, iFR and RFR were significant in 8 and 9 patients, respectively, and dFFR was significant in 9. Resting Pd/Pa and hyperemic iFR had a strong positive Spearman's rank correlation coefficient with dFFR (Figure). By kappa statistics, dobutamine iFR and RFR had almost perfect agreement with dobutamine dFFR. Conclusion: In patients with ANOCA who have an MB by IVUS, intracoronary physiology assessment is necessary to determine if the MB is hemodynamic significant. While adenosine FFR is an insufficient measure, diastolic indices such as dobutamine dFFR, iFR, or RFR may identify hemodynamic significance, although whether one diastolic index outperforms another requires further evaluation.