Physiologic Evaluation of Myocardial Bridging: A New Analysis for an Old Disease

Background: Myocardial bridging (MB) is the most common congenital coronary anomaly. However, the functional relevance of MB is not well understood. Methods: Eighteen patients with lone MB were consecutively enrolled. Fractional flow reserve (FFR) was measured before and after dobutamine infusion. Diastolic FFR was calculated by offline analysis. Cutoff values for functional significance of FFR and diastolic FFR were 0.75 and 0.76, respectively. Results: Baseline systolic percent diameter stenosis and lesion length of MB were 70 +/- 16% and 24 +/- 7 mm. FFR and diastolic FFR were 0.92 +/- 0.05 and 0.89 +/- 0.07 at maximal hyperemia induced by adenosine, respectively (P = 0.006). Despite the angiographic stenosis, only 1 lesion was functionally significant. After dobutamine infusion, percent diameter stenosis (84 +/- 11%, P = 0.002) and lesion length (26 +/- 6 mm, P = 0.019) were aggravated and diastolic FFR was lowered (0.84 +/- 0.10, P = 0.006). Two additional lesions became functionally significant after dobutamine infusion. Angiographic percent diameter stenosis at diastole was correlated with dobutamine diastolic FFR (R = -0.58, P = 0.04), but stenosis at systole was not. During median follow-up of 54 months, 2 patients underwent target-lesion revascularization. Conclusions: Dobutamine increased the morphologic and functional severity of MB. Dobutamine-FFR seems to be helpful in the functional assessment of MB.