Abstract
Hypertrophic cardiomyopathy (HCM) is known to cause diastolic dysfunction. However, little studies have evaluated alterations in global and regional diastolic function during exercise in this disease. We studied 9 patients with HCM with asymmetric septal hypertrophy and normal systolic function with simultaneous recordings of micromanometer left ventricular (LV) pressure and M-mode echocardiogram. All patients had normal epicardial coronary arteries. The modulus of chamber stiffness was obtained by curve-fitting the diastolic pressure-volume (Teichholtz) data in exponential form. The modulus of regional myocardial stiffness was obtained by curve-fitting the relation between the mean wall stress and the natural logarithm of reciprocal of wall thickness of interventricular septum and the posterior wall in diastole in exponential form. Data were obtained at rest and during supine bicycle exercise (25 watts). LV end-diastolic pressure increased from 19 ± 6 to 33 ± 6 mmHg (p < 0.01), but LV end-diastolic dimension was unchanged. LV minimum pressure increased from 10 ± 3 to 18 ± 6 mmHg (p < 0.05), and the time constant of isovolumic relaxation (Raff and Glantz) increased from 72 ± 14 to 82 ± 7 msec (p < 0.05). The left ventricular diastolic pressure-dimension (volume) relation shifted upward in all patients. The modulus of chamber stiffness increased from 0.7 ± 0.4 to 1.9 ± 1.3 (p < 0.05). The modulus of regional myocardial stiffness at rest was greater in interventricular septum than that of the posterior wall (7.7 ± 4.2 vs. 5.2 ± 1.9, P < 0.05). The regional myocardial stiffness constant increased significantly during exercise in interventricular septum (p < 0.05), whereas it was not significantly changed in the posterior wall. In conclusion, both impaired relaxation and increased chamber stiffness are responsible for exercise-induced diastolic dysfunction in HCM, suggesting that exercise-induced ischemia of the hypertrophied myocardium may playa role.
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