Abstract 14710: Myocardial Bridging: Novel Insights from Exercise Echocardiographic Correlations with Hemodynamic Measurements - The Venturi Effect
BACKGROUND - A non-invasive method for detection of myocardial bridges (MB) is not routinely used in clinical practice today. Though patients with MB and no significant coronary artery disease may suffer from chest pain, the mechanism by which this anatomic variant causes ischemia is poorly understood. This study reports a novel exercise echo finding for myocardial bridging and seeks to explain this finding with hemodynamic measurements made in the catheterization lab.
METHODS and RESULTS - 18 patients with typical and/or variant angina and focal end-systolic to early-diastolic buckling in their antero-septal wall on exercise echo were prospectively enrolled for invasive studies with contrast coronary arteriogram and LAD intravascular ultrasound (IVUS). If the presence of an MB could be characterized by IVUS, pressure and Doppler flow velocity recordings were then obtained proximal, within, and distal to the bridge both at rest and with dobutamine stress. Aortic pressure was also measured throughout. Diastolic fractional flow reserve (dFFR) was measured at all positions at baseline and at peak stress. In our cohort, no patient had significant coronary artery disease. Only 5 patients showed visible compression of the LAD on resting coronary angiogram; however, all 18 patients harbored an LAD MB on IVUS. Mean arterial compression on IVUS was 23.1 ± 2.32 % with mean MB length of 24.8 ± 2.7 mm. For 14 patients in whom we could make hemodynamic measurements during dobutamine stress, 13 had an abnormal dFFR (≤ 0.75) within the MB, and 1 had an abnormal dFFR only distal to the bridge. A total of 4 patients had an abnormal distal dFFR. All patients showed a characteristic intra-bridge increase in Doppler flow velocity with concomitant decrease in diastolic pressure upon pharmacologic stress. In ten patients with non-significant distal dFFR, there was partial pressure recovery with decrease in Doppler flow velocity distal to the bridge
CONCLUSIONS - Our findings suggest that the symptoms and novel exercise echo findings of our patient sample are due to myocardial ischemia from an LAD MB. In particular, for the majority of patients with only an abnormal dFFR inside the bridge, we posit that the ischemia is local to the tunneled segment of the coronary vessel due to a Venturi effect.
- © 2012 by American Heart Association, Inc.