A first of its kind randomized trial has found that defibrillator testing (DT) at the time of implantable cardioverter defibrillator (ICD) implantation is safe, but does not improve clinical shock efficacy or prevent death. The findings are part of the Shockless Implant Evaluation (SIMPLE) trial, which was designed to answer whether or not routine DT at time of implant actually improves patient outcomes. The results were released in a Late Breaking session at Heart Rhythm 2014, the Heart Rhythm Society's 35th Annual Scientific Sessions.

DT is conducted to evaluate the ability of the ICD to detect and terminate ventricular fibrillation (VF). Although DT has traditionally been a part of the ICD implant procedure and considered necessary to ensure ICD efficacy, its usefulness and safety has recently been debated. Cohort studies have previously documented rare but serious complications due to DT, and secondary analyses from randomized trials suggest possible harm from ICD shocks.

In this trial, patients undergoing their initial ICD implant were randomly assigned to have DT done at the time of implant or not. The protocol required at least one successful termination of VF at 17J or two successes at 21J, with system revision if the criteria were not met. Both groups were evaluated to test whether ICD implantation without DT was non-inferior to implantation with DT, using a primary outcome of failed appropriate ICD shock or arrhythmic death. The primary safety outcome was assessed 30 days following ICD implantation using a composite that included death, myocardial infarction and stroke.

In 18 countries, there were 2,500 patients randomized to two treatment approaches and followed for an average of 3.1 years. The main result of the study was that for the primary outcome, ICD implantation without DT was clearly non-inferior to implantation with DT, with a non-inferiority p-value of less than 0.001. The 30-day safety outcome and total mortality also occurred at similar rates in both patients groups.

"This is the first time the relationship between defibrillator testing and patient outcome has been studied independently in a randomized setting and with these results, we can confidently say that defibrillator testing, although safe, is not necessary at the time of ICD implantation," said lead author Jeff Healey, M.D., FHRS, Directory of Arrhythmia Services at Hamilton Health Sciences and Associate Professor at Population Health Research Institute at McMaster University in Hamilton, Ontario. "These results should change physician practice and could help reduce costs without compromising patient outcomes."