Production of systolic anterior motion of the mitral valve in dogs.

Production of an experimental preparation of systolic anterior motion (SAM) of the mitral valve was attempted for the purpose of clarifying its causal factors. Fourteen thoracotomized dogs under pentobarbital anesthesia were administered dobutamine, and the echocardiogram, left ventricular pressure, and aortic pressure of each were simultaneously recorded. In two of the dogs in which SAM was produced, two-dimensional echocardiograms were also obtained. Although SAM was absent in all 14 dogs before the administration of dobutamine, it appeared in nine of them after the drug was given. In seven of these dogs, the magnitude of SAM and outflow pressure gradient varied in a dose-dependent manner. No signs of asymmetric septal hypertrophy were observed in any of these dogs. SAM tended to occur even when there was no reduction in preejection period when narrowing of the left ventricular outflow tract was observed. On the two-dimensional echocardiograms, the position of coaptation of the mitral valve was shifted closer to the base of the anterior leaflet in the presence of dobutamine-induced SAM than before the drug was administered. Although the left ventricular cavity became narrow, it was not completely obliterated. This study demonstrates that experimental preparations of SAM can be produced by the administration of dobutamine with a relatively high success rate in normal dogs, and that experimental SAM is accompanied by an outflow tract pressure gradient.