Defibrillation threshold (DFT) testing to confirm an implantable cardioverter-defibrillator (ICD) could effectively terminate ventricular fibrillation is widely accepted as part of routine practice without much evidence of efficacy. However, advances in ICD technology and evidence of initial shock efficacy have called into question the importance of DFT testing. While testing rarely results in immediate complications, ICD shocks can have adverse long-term consequences and DFT requires sedation that adds costs and complexity to the procedure. Healey and colleagues explored the efficacy and safety of ICD implantation with and without DFT testing in the single blind, multicenter, randomized non-inferiority Shockless IMPLant Evaluation (SIMPLE) trial. ICD candidates (including secondary prevention and cardiac resynchronization recipients) were randomized to each arm (1247 without DFT and 1253 receiving standard therapy). After a mean of 3.1 years of follow-up, there were no differences between groups in the primary combined outcome of failed appropriate shock or arrhythmic death (90 [7% per year] in the no-testing group and 104 [8% per year] in the standard group; HR 0.86, 95% CI 0.65–1.14; pnon-inferiority <0.0001) with consistent results for each respective individual endpoint as well as total mortality and time to first appropriate shock. Researchers also examined two 30-day composites of safety outcomes, which also failed to show differences between treatment arms.

Conclusion

While routine DFT testing following ICD implantation appears safe, this strategy did not result in improved patient outcomes when compared to device implantation without testing. SIMPLE provides evidence that DFT testing should be reconsidered as a routine aspect of clinical practice in ICD implantation.

Summarized by Jehu S. Mathew and Steven M. Bradley

• Healey JS, Hohnloser SH, Glikson M, et al. Cardioverter defibrillator implantation without induction of ventricular fibrillation: A single-blind, non-inferiority, randomised controlled trial (simple). Lancet. 2015;385:785–91.