Increase in heart rate precedes episodes of ventricular tachycardia and ventricular fibrillation in patients with implantable cardioverter defibrillators: Analysis of spontaneous ventricular tachycardia database

Patients with heart disease and decreased heart rate variability (HRV)have an increased risk of all-cause mortality as well as arrhythmic death. The q uestion of acute changes in HRV immediately preceding arrhythmic events rem ains unanswered. We analyzed data from patients with implantable cardiovert er defibrillators who had ventricular tachycardia (VT) or ventricular fibri llation (VF) detected by the device. The device stores 1,000 consecutive RR intervals preceding the arrhythmic event detection and before device inter rogation. Compared to this control segment, the mean heart rate (HR)increas ed prior to the arrhythmic event for both VT (88.5 vs 72.7 beats/min, P < 0 .0005) and VF (85.4 vs 73.3 beats/min, P < 0.05) patients. No difference in HRV (as analyzed by a time-domain, frequency-domain [fast Fourier transfor m], and a nonlinear technique) has been detected. We estimated the amount o f ectopic beats from the number of RR intervals that differed from the prec eding RR interval by > 10%. The frequency of such beats was significantly h igher in the prearrhythmic data segments than in the control segments for V T (10.7 vs 6.6/50 beats, P < 0.05) although not for VF (9.8 vs 6.1/50 beats , NS). We conclude that the HR and frequency of ectopic beats are higher pr ior to onset of the arrhythmic events, although HRV does not change markedl y. These results are consistent with sympathetic activation being the predo minant autonomic change prior to VT/VF onset in this patient population.