Dynamic obstruction to left ventricular outflow: the case for its existence in hypertrophic cardiomyopathy.

The debate and controversy over the hemodynamics of obstruction and left ventricular ejection in HCM is an interesting and complex one in which periodic disagreement has appeared during the last 20 years. We believe that the available data unequivocally support the concept that in those patients with HCM who have left ventricular outflow gradients measured at catheterization (and who have associated marked SAM) a mechanical impediment to forward flow, and thus true obstruction to left ventricular outflow, does exist. Most importantly, the gradient has critical clinical implications by virtue of the markedly elevated intraventricular systolic pressures associated with it. These chronically elevated pressures are potentially detrimental to the left ventricle (a view held even by investigators opposed to the term "obstruction"), by virtue of increasing systolic myocardial wall stress and myocardial oxygen demand. Therefore, surgical abolition of the obstruction and normalization of these pressures remains an important and rational therapeutic objective in those severely symptomatic patients who have obstruction to left ventricular outflow and who have failed to benefit from drug therapy.