| Abstract: | Background: Spontaneous variability of ventricular arrhythmia has been described in patients with chronic stable ventricular arrhythmias and in patients with chronic heart failure. However, no data are available on spontaneous variability in patients with sustained ventricular tachyarrhythmias. Thus, the present study was designed to prospectively determine the extent of spontaneous variability of ventricular arrhythmia in patients with sustained ventricular tachyarrhythmias and in survivors of cardiac arrest. Methods: Ventricular arrhythmia variability was determined in 470 patients (413 men, 57 women), age (mean ± SD) 64.6 ± 9.5 years with documented ventricular tachycardia (VT), cardiac arrest, or syncope who were prospectively enrolled in a randomized trial of the comparison of electrophysiological testing with Holter monitoring to predict antiarrhythmic drug efficacy. Coronary artery disease was present in 398 (85%) patients, and the mean left ventricular ejection fraction was 0.32 ± 0.13. They underwent two 24-hour ambulatory recordings separated by 1 day. Spontaneous variability was determined for total premature ventricular complexes (PVCs), pairs, and VT events. Results: Arithmetic mean of hourly total PVCs on day 1 was 315 ± 425. The 95% confidence limit of spontaneous reduction in total PVC count was 71%. Corresponding values for pairs, VT events of 3–15 beats, < 15 beats, or < 15 seconds were 72%, 80%, 94%, and 95%, respectively. The percentage increases in total PVCs, pairs, and VT events 3–15 beats, < 15 beats, and < 15 seconds were 243%, 259%, 397%, 1553%, and 1756%, respectively. The percentage reduction required to show a true drug effect was 63% for patients with an ejection fraction > 0.32 and 76% for those with an ejection fraction ltm 0.32 (P = 0.024). Patients who presented with unmonitored syncope showed less spontaneous variability than either patients with documented, sustained VT or cardiac arrest. Conclusions: Marked spontaneous variability of ventricular arrhythmias is observed in patients with sustained ventricular tachyarrhythmias. Variability is affected by the degree of left ventricular dysfunction. The lowest variability was observed in patients presenting with unmonitored syncope. Thus, large changes in arrhythmia frequency must be observed in this population, as in others, to be ascribed to drug effect. |
