VENTRICULAR ARRHYTHMIAS DETECTED AFTER TRANSVENOUS DEFIBRILLATOR IMPLANTATION IN PATIENTS WITH A CLINICAL HISTORY OF ONLY VENTRICULAR-FIBRILLATION - IMPLICATIONS FOR USE OF IMPLANTABLE DEFIBRILLATOR

Background Patients with a history of ventricular fibrillation (VF) ha ve been shown to have a clinical profile, response to electrophysiolog ical testing (EPS), and response to antiarrhythmic therapy that distin guishes them from patients with a history of sustained monomorphic ven tricular tachycardia (MVT). Despite these differences, it is not clear whether VF in these patients is triggered by MVT or occurs de novo. T he incidence of MVT and VF in such patients after their index VF event has important implications for therapeutic decisions regarding implan table defibrillator selection and programming. Methods and Results The records of 111 consecutive patients who had undergone transvenous car dioverter/defibrillator (ICD) implantation for malignant ventricular a rrhythmias were reviewed retrospectively. For each patient, all device tachyarrhythmia detections were examined and classified as VF, MVT, r apid polymorphic VT, or other. The number of events, time to first arr hythmia detection, and cycle length of MVTs were recorded. There were 55 patients with a history of only VF and 56 with a history that inclu ded an episode of MVT. Over 14 months of follow-up, with all patients initially off of antiarrhythmic medications, MVT was detected by only 18% of patients with a history of only VF compared with 54% of those w ith a history that included MVT (P=.002). Among patients who did detec t MVT, those with a history of only VF had fewer episodes (7+/-7 versu s 20+/-31, P=.001) and a shorter mean MVT cycle length (279 versus 314 ms, P=.03) than those with a clinical history of MVT. Abrupt onset of VF not preceded by MVT was detected in 11% of patients with VF only. In addition to a history of MVT, male sex, age <60 years, and MVT indu cible on EPS were all significantly associated with an increased likel ihood of MVT detection. On multivariate analysis, the inducibility of MVT was the primary independent predictor of MVT detection but was of minimal incremental predictive value in the subgroup of patients with a history of only VF. When EPS results were not considered, arrhythmia history was the primary independent predictor of MVT detection. Concl usions Patients with a history of only VF infrequently have MVT detect ed by their defibrillators. When these patients do detect MVT, it is f aster than that detected in patients with a clinical history of MVT be fore ICD surgery. A significant percentage of VF survivors detected th e abrupt onset of VF not preceded by MVT, suggesting that the deterior ation of rapid MVT to VF is not the only clinically important mechanis m of VF induction. These findings may have important implications for the understanding of the mechanism of VF induction and for use of an i mplantable defibrillator.