RR Variability and Baroreflex Sensitivity in Patients with Ventricular Tachycardia Associated with Normal Heart and Patients with Ischemic Heart Disease

Recent studies have suggested that disordered autonomic function, particularly the loss of protective vagal reflexes are associated with an increased incidence of arrhythmic deaths following myocardial infarction (MI). Heart rate variability (HRV) and baroreflex sensitivity (BRS) are measures of myocardial autonomic function and predict arrhythmic deaths post-Mi. Patients with ventricular tachycardia associated with a “normal heart” frequently have exercise-induced arrhythmia suggesting that the autonomic nervous system is important in the genesis of this form of ventricular tachycardia (VT). This study examines HRV and BRS in patients with VT associated with a “normal heart” and compares these values to patients post-Mi with and without evidence of arrhythmia. Twenty patients with VT associated with a “normal heart,” 16 patients with MI but without arrhythmia on follow-up, and 11 patients with MI and VT on follow-up were studied. HRV was measured from 24-hour Holter recordings and BRS was measured from plots of change in systolic blood pressure versus change in heart rate following an intravenous injection of 0.4–0.6 mg phenylephrine. HRV was significantly higher in the patients with VT associated with a normal heart (34.2 ± 10.8 msec) compared to the patients post-Mi, without (23.7 ± 6.7 msec) and with (14.8 ± 3.8 msec) arrhythmia (F = 9.2, P < 0.001) and these differences were unaffected by adjustment for age. Baroreflex sensitivity was also higher in patients with VT associated with a “normal heart” (10.1 ± 6.8 msec/mmHg) compared to patients post-Mi, without (6.1 ± 3.2 msec/mmHg) and with 3.2 ± 3.1 msec/mmHg) arrhythmia, (F = 7.2, P < 0.02), though statistical significance was lost after adjustment for age (F = 1.2, P = 0.3). We conclude that patients with VT associated with “normal hearts” have HRV and BRS that is higher than in patients post-MI. Alterations of autonomic tone are, therefore, unlikely to be important in VT associated with a “normal heart,” whereas these appear to be important in patients with arrhythmic events post-MI.