Has 'obstruction' hindered our understanding of hypertrophic cardiomyopathy?

HCM is a disorder associated with significant morbidity and mortality and a propensity to cause sudden, often unexpected death. The similarity to the symptom complex of aortic stenosis and the presence of a pressure gradient justified the initial assumption that obstruction was of prime importance in HCM and that relief of obstruction was the focal point of rational therapy. However, it is our belief that the dogma of obstruction has impeded progress in and obscured the understanding of HCM and interpretation of its manifestations. The purpose of this article is to call attention to significant discrepancies in the obstructive concept that have been reinforced as new techniques emerged that have allowed further study of the disease. Since neither the presence of a gradient nor SAM can be justifiably equated with the presence of an obstruction, it is proposed that the appellation "obstruction" be reserved for those cases in which the rate of outflow or the rate or degree of ventricular emptying are demonstrably impeded, as in aortic stenosis. Therapy with beta-adrenergic-receptor and calcium channel-blocking agents have shown promise for alleviating symptoms and possibly prolonging life without systematically or predictably affecting the pressure gradient, probably because of their beneficial effects on ventricular relaxation and diastolic filling. Antiarrhythmic therapy has been effective in reducing mortality. Ideally, prevention or regression of the pathologic hypertrophy should be the major focus of future therapeutic interventions in hypertrophic cardiomyopathy.