[Is reduced left ventricular volume related to mechanisms of dynamic mid-ventricular obstruction provoked by...

Forty-seven patients with unexplained chest pain and normal resting echocardiograms were examined to see whether dynamic mid-ventricular obstruction (MVO) is induced by dobutamine infusion. Dynamic MVO was provoked in 17 patients (MVO group), but not in the other 30 patients (Non-MVO group). Before dobutamine infusion, the blood pressure in the MVO group was higher than that in the Non-MVO group (p < 0.05), but end-diastolic volume index (p < 0.001), end-systolic volume index (p < 0.01), stroke volume index (p < 0.001), cardiac index (p < 0.001), end-diastolic volume (p < 0.01) and end-systolic volume (p < 0.05) of the apical territory of the left ventricle in the MVO group were significantly less than those in the Non-MVO group. The left atrial function, left ventricular ejection fraction and ejection fraction of the apical territory of the left ventricle did not differ between the groups. Seven patients in the MVO group were re-examined by dobutamine stress echocardiography after beta-blocker administration, showing that the dynamic MVO was completely suppressed. The end-diastolic volume tended to increase after beta-blocker administration, but no significant difference was found in any other variables except heart rate. The results suggest that a smaller left ventricle and higher blood pressure are important characteristics in patients with dobutamine-induced dynamic MVO, and additionally, the difference in local myocardial contractility may be an important cause of the induction of dynamic MVO.