Left Ventricular Outflow Tract Obstruction Provoked by Catecholamine in Acute Myocardial Infarction: Mechanistic Insights From An Animal Experiment

Background. Basal posterior left ventricle (LV) hyperkinesis following catecholamine infusion in anteroseptal acute myocardial infarction (AMI) can potentially reduce mitral annular size, leading to excessive leaflets beyond coaptation and left ventricular outflow tract (LVOT) obstruction.Methods. Dobutamine was infused (40μg/kg/min) in 24 anesthetized open-chest dogs with anteroseptal AMI by the direct ligation of the proximal left anterior descending artery. Systolic thickening of the basal posterior wall, antero-posterior mitral annular dimension, and LVOT pressure gradient were measured by Doppler and 2-dimensional echocardiography.Results. 1) LVOT obstruction [pressure gradient (PG)30 mmHg] was produced in 13 of 24 dogs. 2) LVOT PG was significantly correlated with increased posterior wall thickening (r2 = 0.45, p<0.05) and decreased annular dimension (r2 = 0.75, p<0.001).Conclusion. LVOT obstruction following catecholamine infusion in anteroseptal AMI is related to basal posterior LV hyperkinesis, leading to reduced mitral annular dimension with potential excessive leaflets beyond coaptation.