Alteration of Left Ventricular Function with Dobutamine Challenge in Patients with Myocardial Bridge

Background/Aims: The aim of this study was to identify changes in left ventricular (LV) performance in patients with a myocardial bridge (MB) in the left anterior descending coronary artery during resting and in an inotropic state. Methods: Myocardial strain measurement by speckle-tracking echocardiography and conventional LV wall-motion scoring was performed in 18 patients with MB (mean age, 48.1 ${\pm}$ 1.7 years, eight female) during resting and intravenous dobutamine challenge (10 and 20 ${\mu}$g/kg/min). Results: Conventional LV wall-motion scoring was normal in all patients during resting and in an inotropic state. Peak regional circumferential strain increased dose dependently upon dobutamine challenge. Longitudinal strains of the anterior and anteroseptal segments were, however, reduced at 20 ${\mu}$g/kg/min and showed a dyssynchronous pattern at 20 ${\mu}$g/kg/min. Although there were no significant differences in radial strain and displacement of all segments at rest compared with under 10 ${\mu}$g/kg/min challenge, radial strain and displacement of anterior segments at 20 ${\mu}$g/kg/min were significantly reduced compared with posterior segments at the papillary muscle level (44.8 ${\pm}$ 14.9% vs. 78.4 ${\pm}$ 20.1% and 5.3 ${\pm}$ 2.3 mm vs. 8.5 ${\pm}$ 1.8 mm, respectively; all p < 0.001), and showed plateau (40%) or biphasic (62%) patterns. Conclusions: Reduced LV strain of patients with MB after inotropic stimulation was identified. Speckle-tracking strain echocardiography identified a LV myocardial dyssynchrony that was not demonstrated by conventional echocardiography in patients with MB.