Left ventricular outflow obstruction induced by tamponade in hypertrophic cardiomyopathy.

Echocardiographic abnormalities of valvular movement described in patients with pericardial effusions have included systolic anterior motion (SAM) of the mitral valve. Published illustrations have shown, however, "pseudo-SAM" rather than true SAM. We report a patient with asymmetric septal hypertrophy whose echocardiogram during tamponade showed true SAM, which was no longer apparent and could not be provoked following resolution of tamponade. Two prior cardiac catheterizations revealed no intraventricular pressure gradients in either normal or postextrasystolic beats. Tamponade was the only stimulus that provoked signs of obstruction in this patient with asymmetric septal hypertrophy.