Objectives. We aimed to assess the differences in the adaptive response of patients with hypertrophic cardiomyopathy (HCM) compared with normal subjects, as well as any association with increased susceptibility to the test. Background. Diastolic function contributes importantly in the adaptation of the normal heart to head-up tilting. This mechanism may be disturbed by an impaired relaxation in HCM. Methods. Twenty-one male patients with HCM (46 ± 6 years old) and 22 healthy men (44 ± 8 years) were studied using Doppler echocardiography after 1 and 10 min of head-up tilting at 20°, 40°and 60°. Results. In control subjects, tilting was associated with 1) a predominance of diastolic pulmonary venous flow and early left ventricular (LV) filling (atrium functioning as an open conduit); 2) right ventricular (RV) shrinkage; and 3) no LV dimensional variations. In patients with HCM, tilting was associated with 1) a prevalence of systolic pulmonary venous flow (atrium functioning as a reservoir in which filling depends on atrial relaxation and compliance) and late diastolic transmitral flow (atrium working as a booster pump); 2) LV shrinkage; and 3) no RV dimension variations. These mechanisms did not prevent stroke volume (SV) from decreasing at 40°and 60°in both groups. Because of a lower increase in heart rate (HR), a reduction in cardiac output (CO) was greater in patients with HCM. The responses were similar after 1 and 10 min of tilting in control subjects, whereas in patients, blood pressure (BP), SV and LV dimension fell more after 10 min. Conclusions. Adaptation of the normal heart to tilting is based on a ventricular interaction and LV diastolic properties; HCM relies on left atrial diastolic and systolic functions. An inadequate HR reaction to a fall in BP and SV in HCM (depressed reflexogenic activity) contributes to making CO more vulnerable by greater and more prolonged displacements. (C) 2000 by the American College of Cardiology.
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