Background Implantable cardioverter defibrillators (ICDs) reduce mortality in high-risk individuals by preventing sudden cardiac death owing to ventricular tachyarrhythmias. Programmed electrical stimulation (PES) is useful for risk-stratifying patients for sudden cardiac death (SCD). However, the prognostic value of induced fast ventricular tachycardia (FVT) (cycle length ≤ 230 msec) is uncertain. The purpose of this study is to compare the risk of appropriate shock for ventricular tachycardia (VT) or ventricular fibrillation (VF) in ICD recipients induced into FVT, monomorphic VT (MVT) (cycle length > 230 msec), polymorphic VT (PVT)/VF, and no ventricular tachyarrhythmias at the time of PES.
Methods A single-center retrospective review was performed on patients who underwent PES, ICD implantation, and follow-up between 1992 and 2003. The primary end point was time to first appropriate ICD shock. Baseline variables were compared using appropriate tests of significance. Time-to-appropriate shock was compared for each type of induced rhythm using survival analysis. Cox regression was used to assess the impact of baseline variables on the primary end point.
Results A cohort of 289 patients with a mean age of 64 ± 14 years, ejection fraction (EF) 33 ± 15%, 65% with ischemic cardiomyopathy, and 50% with secondary prophylaxis indications was studied. Inducible FVT was present in 18%, MVT in 40%, and PVT/VF in 21%, and 20% were noninducible. The mean cycle length was 212 ± 15 msec for FVT and 286 ± 59 msec for MVT (p < .001). Compared with patients inducible into FVT, MVT patients had a lower EF (31% vs 36%; p = .013) but otherwise had no significant differences in other baseline variables. Patients were followed for 2.2 ± 2.3 years, during which time 26% received appropriate ICD therapy for VT/VF, with 16% of the FVT patients, 39% of MVT patients, 11% of PVT/VF patients, and 21% of noninducible patients receiving appropriate therapy. Patients induced into MVT had a significantly increased risk of appropriate ICD therapy (hazard ratio 2.6; 95% CI 1.2-5.5; log rank p < .001), whereas patients induced into FVT had a similar risk of shocks as PVT/VF patients and noninducible patients (p > .05 for all comparisons). After adjusting for baseline differences, only MVT and EF remained as significant predictors of appropriate ICD therapy (adjusted hazard ratio 2.2 for MVT; 95% CI 1.01-4.84; p = .048 and adjusted hazard ratio 0.98 for each 1% increase in EF; 95% CI 0.96-0.99; p = .008).
Conclusion FVT induced on PES is a nonspecific finding with a similar long-term risk of spontaneous VT/VF as induction into PVT/VF or a lack of induction of ventricular tachyarrhythmia at the time of PES. However, noninducible patients and those inducible into FVT and PVT/VF still had a risk of appropriate ICD therapy for spontaneous ventricular tachyarrhythmias of 5%/year, suggesting that the induction of MVT as the sole predictor of future arrhythmic events may be inadequate.