Hypertrophic cardiomyopathy: a 1987 viewpoint.

HYPERTROPHIC CARDIOMYOPATHY (HCM) is characterized by symmetric or asymmetric hyper-trophy of the left and/or right ventricle (table 1). * It is a primary disorder of heart muscle in which the site and extent of the hypertrophic process are important in determining the disease manifestations.' Ventricular (asymmetric) septal hypertrophy is the commonest form of HCM (table 1) and is characterized by abnormalities of systolic and diastolic function as well as rhythm disturbances. Systole is characterized by the presence or absence of an intraventricular pressure gradient, which when present may be persistent (gradient at rest), labile (spontaneously variable), or latent (provocable).", 2 Diastole is characterized by abnormalities of ventricular relaxation3 and passive chamber stiffness.4 Patients with extensive hyper-trophy are more likely to manifest the abnormalities of systolic and diastolic function, as well as being more prone to atrial and ventricular arrhythmias and sudden death.' During the almost three decades that HCM has been recognized as a clinical entity with regard to the significant morbidity and mortality, our knowledge and understanding of the diastolic and rhythm abnormalities have advanced in a fairly orderly, if perhaps modest, fashion. Such is not the case, however, with interpretation of the significance of the systolic intra-ventricular pressure differences. Most investigators accept that the characteristic pressure gradient, caused by prolonged mitral leaflet-septal contact, represents obstruction to left ventricular outflow and offer these patients surgical relief of the obstruction if they are unresponsive to medical therapy."'`5,6 However, *In an attempt to limit the number of references, the author has referred to a recent review article (ref. 1) for much of the work coming from the Toronto General Hospital, and to a lesser extent in summarizing the literature. there is a small cadre of investigators7-9 who believe there is no hemodynamic evidence of obstruction to outflow and suggest that the intraventricular pressure differences are the result of excessively rapid early systolic ejection with resultant cavity obliteration7 or elimination.8 It is the purpose of this commentary to discuss two aspects of HCM: (1) to review the evidence for and against obstruction to left ventricular outflow in obstructive HCM and (2) to emphasize and contrast the important differences between ventricular relaxation and passive chamber stiffness in regulating ventricular diastolic filling. Systole Evidence for obstruction to left ventricular outflow (the obstructive viewpoint) Types of intraventricular pressure differences in HCM. Before considering the significance of intraventricular pressure differences in HCM, it is necessary to …