AUTONOMIC FUNCTION IN HYPERTROPHIC CARDIOMYOPATHY

Background-Autonomic dysfunction has been found to be a powerful predi ctor of arrhythmic events and sudden death after myocardial infarction . Hypertrophic cardiomyopathy carries a risk of sudden death and this risk is increased by the occurrence of syncope. Objectives-To determin e if autonomic dysfunction occurs in patients with hypertrophic cardio myopathy and if it is associated with the occurrence of syncope.Patien ts and methods-Autonomic function was measured in 30 patients with hyp ertrophic cardiomyopathy, 15 with and 15 without a history of syncope, and in 28 healthy volunteers. Results-Tests of parasympathetic activi ty showed that the mean (SD) variation in heart rate during deep breat hing was reduced in patients compared with controls, 17 (9) v 22 (9) b eats/min, p = 0.03, the Valsalva ratio was also reduced in patients, 1 .52 (0.33) v 1.70 (0.36), p = 0.05 but the immediate heart rate respon se to standing, the 30:15 ratio, was similar in both groups. Tests of sympathetic activity-namely the diastolic blood pressure response to s ustained handgrip and the change in systolic blood pressure on standin g-did not differ between patients and controls. There was no significa nt difference in autonomic function between patients with and without a history of syncope. A secondary predetermined analysis showed that t he degree of impairment in variation of heart rate with breathing was correlated with the severity of left ventricular hypertrophy, r = 0.39 , p = 0.03. Conclusions-Patients with hypertrophic cardiomyopathy have a selective impairment of variability of heart rate with deep breathi ng and the Valsalva manoeuvre indicating decreased cardiac parasympath etic activity. The data suggest that the afferent limb of these reflex es is impaired and that the severity of impairment is related to the d egree of left ventricular hypertrophy.