Unlocking the mystery of systolic anterior motion: the key is timing.

Though a generation has elapsed since the recognition of hypertrophic cardiomyopathy, controversy continues to rage regarding its pathophysiology. Central to the controversy is the mechanism and significance of the pressure gradient. Systolic anterior motion (SAM) of the mitral valve, as demonstrated by angiography and echocardiography, is accepted as the cause of the pressure gradient by some groups but not others. The latter authors suggest that: SAM is an incidental effect of vigorous contraction which is itself the cause of the pressure gradient and that the pressure gradient does not represent left ventricular outflow obstruction. These views are examined in light of recent studies that have assessed the temporal and quantitative relationship between SAM and the pressure gradient. It is concluded that SAM with early mitral septal contact is the cause of the pressure gradient, and represents true left ventricular outflow obstruction.