Effect of changes in the definition of ventricular tachycardia on the prevalence of complex ventricular ectopy.

The presence of ventricular tachycardia (VT) is commonly considered to represent a risk factor for sudden cardiac death as well as an indication for antiarrhythmic drug therapy. Although spontaneous VT is generally diagnosed by the presence of three or more consecutive ectopic beats, proposed criteria for induced VT require six or more complexes at rates exceeding 90 or 100 beats/min. To determine the clinical implications of a similar change in the diagnostic criteria for spontaneous VT, the authors examined 324 consecutive 24-hour ambulatory electrocardiograms. Of these, 111 (34.3%) had episodes of three or more ventricular premature beats. If six or more beats were required, only 34 (30.6%) would have been diagnosed as having VT. Requiring a minimum rate of 90 or 100 beats/min had less consequence, eliminating only 10 (9.0%) and 12 (10.8%) patients, respectively. Patients with only three to five beat runs had significantly fewer isolated premature beats (4,462.8 +/- 588.4 vs 7,158.1 +/- 1,688.1) and ventricular couplets (186.2 +/- 39.2 vs 294.3 +/- 74.4) per day, and slower average rates (142.1 +/- 4.6 vs 171.8 +/- 6.7 beats/min) during ventricular tachycardia than did those with runs of six or more beats. Thus, altering the definition of spontaneous VT has marked effects on the prevalence of this arrhythmia. Those patients excluded did, however, have a lower prevalence of associated electrocardiographic risk factors.