Malignant premature ventricular beats in ambulatory patients.

The characteristics of premature ventricular beats predisposing to ventricular tachycardia or fibrillation were assessed by 24-h ambulatory monitoring and maximal treadmill exercise testing in 339 cardiac patients with premature ventricular beats. Premature ventricular beats were divided into early (Q-premature ventricular beat less than QT), late (within the last 20% of the cardiac cycle), and midcycle. Ventricular tachycardia was recorded in 45 patients and ventricular fibrillation, in three. The frequency of ventricular tachycardia or fibrillation was 32% in patients with late, 16% in patients with early, and 7% in patients with midcycle premature ventricular beats (P less than 0.05). Patients with frequent (less than 10/min) multiformed premature ventricular beats had a frequency of ventricular tachycardia or fibrillation of 44%, while only 13% of patients with frequent uniformed premature ventricular beats had ventricular tachycardia (P less than 0.05). Ambulatory patients with ventricular tachycardia or fibrillation have frequent multiformed premature ventricular beats, and the ventricular tachycardia or fibrillation is usually triggered by late premature ventricular beats.