Midventricular Obstruction

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Abstract
Clinical echocardiographic, hemodynamic and angiographic features of 7 patients aged 12-51 yr with midventricular obstruction, are described. All had cardiac catheterization and left ventricular cineangiography with catheter entrapment avoided. Biventricular cineangiography was performed in 2 subjects and autopsy in another. Carotid upstroke was rapid in all but 1. Echocardiogram, in 6 patients, showed septal thickness in all, but systolic anterior motion of the mitral valve was absent in 5 individuals. A resting gradient of 58-185 mmHg (mean 117 mmHg) was detected across the midventricular narrowing in 6 patients. In 1 patient with no resting gradient, 40 mmHg pressure difference was provoked between the apex and inflow tract following i.v. administration of isoproterenol. Midventricular obstruction, distinctly different from subaortic narrowing in hypertrophic obstructive cardiomyopathy (HOCM) was present in cineangiogram. Ventricular septal bulging was present in 2 patients with biventricular cineangiogram and another at autopsy. Disappearance of gradient following i.v. administration of propranolol and its return after sublingual administration of nitroglycerin suggest a dynamic nature of the obstruction. Midventricular obstruction must be distinguished from HOCM by its characteristic hemodynamic and angiographic features for proper surgical approach, consisting of midventricular myectomy with or without papillary muscle resection and mitral valve replacement.

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