DIURNAL CHANGE IN QT INTERVALS IN DILATED CARDIOMYOPATHY AND HYPERTROPHIC CARDIOMYOPATHY

In patients with cardiomyopathy, cardiovascular responses to catecholamines and related substances are known to differ from those in normal subjects. 1-4 In the case of hypertrophic cardiomyopathy (HC), the presence of hyperreactivity of the adrenergic system is suggested by several clinical features.5 The increase in left ventricular contractility induced by isoproterenol or epinephrine is greater in patients with HC than in normal subjects.1,2 In dilated cardiomyopathy (DC) or failing hearts, systemic levels of norepinephrine are often elevated markedly, indicating generalized sympathetic activation to compensate for congestive heart failure.6 The positive inotropic effect of β-adrenergic receptor agonists is, however, known to be attenuated in patients with DC.3,4 In the present study, we determined cardiac responses to change in autonomic nervous tone in patients with HC and in those with DC by using 2 indirect measures of autonomic nervous function: diurnal change in QT intervals7,8 and variation in RR intervals.9,10. © 1991.