ICD Implantation Without Defibrillation Testing | Journal Scan

Study Questions:

Does defibrillation testing performed during placement of an implantable cardioverter-defibrillator (ICD) affect hard outcomes?


SIMPLE (Shockless IMPLant Evaluation) was a single-blind, randomized, multicenter, intention-to-treat, noninferiority trial carried out in 18 countries at 85 hospitals. Primary efficacy was a composite outcome of arrhythmic death or failed appropriate shock. The noninferiority margin was a hazard ratio (HR) of 1.5 calculated from a proportional hazards model with no-testing versus testing as the only covariate. The primary safety composite included death, myocardial infarction, stroke, embolism, heart failure requiring intravenous diuretics or inotropes, the need for chest compressions or an aortic balloon pump during the implantation procedure, use of intraoperative vasoconstrictors for more than 15 minutes, nonelective intubation, arterial-line complications, an unplanned stay in the intensive care unit (ICU), other anoxic brain injury, pneumothorax, cardiac perforation, ICD infection, or aspiration pneumonia. A second safety composite excluded pneumothorax, tamponade including cardiac perforation, ICD infection, and an unplanned ICU stay.


A total of 1,253 patients were randomly assigned to defibrillation testing and 1,247 to no-testing. The follow-up was 3.1 years (standard deviation 1.0). The primary outcome of arrhythmic death or failed appropriate shock occurred in fewer patients in the no-testing group (90 [7% per year]), than patients who did receive it (104 [8% per year]; HR, 0.86, 95% confidence interval [CI], 0.65-1.14; p for noninferiority < 0.0001). The first safety composite outcome occurred in 69 (5.6%) of 1,236 patients with no-testing and in 81 (6.5%) of 1,242 patients with defibrillation testing, p = 0.33. The second safety composite outcome, which included only events most likely to be directly caused by testing, occurred in 3.2% of patients with no-testing and in 4.5% with defibrillation testing, p = 0.08. Heart failure needing intravenous treatment with inotropes or diuretics was equally prevalent in both groups.


The authors concluded that while routine defibrillation testing at the time of ICD implantation is generally well tolerated, it does not improve shock efficacy or reduce arrhythmic death.


Despite the fact that defibrillation testing has never been shown to independently improve patient outcomes, it was an integral part of the ICD implantation procedure for decades. The purpose was twofold: to assure that there is appropriate sensing of the fine ventricular fibrillation (VF) waveform, and that there is enough ‘energy’ for successful defibrillation. The original ICDs used epicardial patches and monophasic shock waveforms, and accurate sensing and termination of VF could not be taken for granted. However, with the introduction of transvenous systems, biphasic waveforms, and active cans, the failure to sense and treat VF became much less common. The current study is the largest and most robust trial to date suggesting that routine defibrillation testing is probably not needed in most patients.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Defibrillators, Implantable, Arrhythmias, Cardiac, Ventricular Fibrillation, Electric Countershock, Stroke, Embolism, Heart Failure, Intubation, Myocardial Infarction, Vasoconstrictor Agents, Intensive Care Units, Primary Prevention, Single-Blind Method, Proportional Hazards Models

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