Shockless IMPLant Evaluation | Clinical Trial - SIMPLE


The goal of the trial was to assess the safety and efficacy of no defibrillation threshold (DFT) testing in patients receiving an implantable cardioverter-defibrillator (ICD) implantation.

Contribution to the Literature: The SIMPLE trial suggests that routine DFT testing may no longer be necessary at the time of implantation for contemporary ICD devices.

Study Design

Patients were randomized in a 1:1 fashion to either routine DFT testing (n = 1,253) or no testing (n = 1,247).

Patient Population:

  • Total number of enrollees: 2,500
  • Duration of follow-up: 3.1 years
  • Mean patient age: 63 years
  • Percentage female: 19%
  • Primary prevention ICD: 73%
  • New York Heart Association class III: 30%
  • Left ventricular ejection fraction: 32%
  • History of atrial fibrillation (AF): 24%; permanent/persistent AF: 11%
  • Single-chamber ICD: 45%; dual-chamber: 25%; CRT-D: 28%

Inclusion criteria:

  • Age >18 years
  • Boston Scientific transvenous ICD for standard indications

Exclusion criteria:

  • Pregnant
  • On the active transplantation list
  • Participating in another randomized trial
  • ICD implant on the right-hand side of the chest

Principal Findings:

The primary outcome, composite of failed appropriate shock or arrhythmic death, was similar between the no DFT testing and DFT testing groups (7.2% vs. 8.3%; hazard ratio, 0.86; 95% confidence interval, 0.65-1.14; p for noninferiority < 0.0001; p for superiority = 0.30).

Secondary outcomes (no DFT testing vs. DFT testing groups):

  • Arrhythmic death: 5.2% vs. 5.8% (p = 0.5)
  • Failed appropriate shock 2.2% vs. 3.0% (p = 0.17)
  • Congestive heart failure admission: 11.2% vs. 10.7% (p = 0.72)
  • Post-procedurally, need for chest compressions: 0% vs. 0.4% (p = 0.06)
  • Post-procedurally, nonelective intubation: 0.1% vs. 0.6% (p = 0.03)


The results of this single-blinded trial indicate that no DFT testing is noninferior to routine DFT testing at the time of ICD implantation for subsequent failed appropriate shocks/arrhythmic death. Some periprocedural adverse outcomes such as need for chest compressions and intubations were reduced in the no testing group. This is an important question, and has the potential to simplify ICD implantation and lower costs (due to need for anesthesia with DFT testing).

In the initial years, DFT testing was considered mandatory to document adequate capture at the time of ICD implantation. More recently, the devices have undergone several refinements and are much more reliable. Many centers have already moved away from routine DFT testing; this trial provides evidence to support this practice.


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;Feb 22:[Epub ahead of print].

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

Keywords: Defibrillators, Implantable, Electric Countershock, Arrhythmias, Cardiac, Atrial Fibrillation, Ventricular Fibrillation, Intubation, Shock, Primary Prevention, Single-Blind Method, Anesthesia

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