Defibrillation testing: Safe but not necessary

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Despite the fact that defibrillation threshold testing at the time of device implantation is generally safe, it does not improve implantable cardioverter defibrillator (ICD) shock efficacy or reduce mortality compared to a no-testing strategy, according to results from the SIMPLE (Shockless implant evaluation) study, which is the largest randomised clinical trial of ICD recipients to date.

Primary data were presented at a Late-breaking trial session at the 35th Heart Rhythm Society (HRS) Annual Scientific Sessions (7–10 May, San Francisco, USA) by Jeffrey S Healey (Population Heath Research Institute, McMaster University, Hamilton, Canada).

Healey told delegates: “Traditionally ICDs have been implanted with the conduct of defibrillation threshold testing, and this procedure has been part of all major randomised ICD clinical trials; however, over the last 10–20 years potentially serious complications with defibrillation testing have been observed.” He also said that there have been significant improvements in ICD efficacy over the last 10 years and as a result “many clinicians have begun to question the need for routine defibrillation testing at the time of ICD insertion.” Therefore, he noted, the SIMPLE trial was designed to answer the question of whether routine defibrillation testing is safe and whether it is required.

“Our findings from the SIMPLE study demonstrate that those patients who received ICDs without defibrillation testing did as well as those who underwent the standard defibrillation testing at the time of implant,” Healey said. “Defibrillation testing is generally low risk, but complications can occur.” He told Cardiac Rhythm News: “In our study, we occasionally did see serious complications which were likely due to the testing; however, the rate was uncommon enough that our safety composites were not significantly different between arms.”

Specifically, he said, the trial showed non-inferiority for the primary endpoint of ineffective clinical shock or arrhythmic death (7.2% in the no-defibrillation testing group vs. 8.3% in the routine defibrillation testing group; hazard ratio 0.86; 95% confidence interval 0.65-1.14; non-inferiority p<0.0001). The rate of survival from arrhythmic death was 94.8% in the no-defibrillation group vs. 94.4% in the routine defibrillation testing group (p=0.50). The primary safety endpoint, comprised of complications within 30 days of the implant, was also similar between the two patient groups (5.4% in the no-defibrillation group vs. 6.5% in the routine defibrillation testing group, p=0.25).

Between January 2009 to April 2011, the SIMPLE trial randomised 2,500 patients in 18 countries at 85 centres to two groups receiving (n=1,253) or not receiving (n=1,247) defibrillation testing. Patients undergoing their initial ICD implant for standard primary or secondary prevention were included. ICDs and some other ICDs with cardiac resynchronisation therapy (CRT-D) from Boston Scientific were studied. Average follow-up was over 3.1 years and was completed in February 2014. Only 1.4% of patients in the no-defibrillation arm and 2.1% in the defibrillation arm were lost to follow up.

The testing protocol, Healey said, required at least one successful termination of ventricular fibrillation at 17J or two successful terminations at 21J; the first shock energy in all zones was programmed to 31J in both treatment arms. Baseline characteristics of patients were balanced, he noted, mean age for the defibrillation testing arm was 63 and for the no-defibrillation arm was 62.6. Most of the patients were males (no-defibrillation testing arm: 81.4%, defibrillation testing arm: 80.5%).

“This is the first time the relationship between defibrillation testing and patient outcome has been studied independently in a randomised setting and with these results, we can confidently say that defibrillator testing, although generally safe, is not necessary at the time of ICD implantation,” Healey concluded.

Healey told Cardiac Rhythm News that according to the results of SIMPLE, which show that routine defibrillation testing “is not helpful”, current guidelines should be changed suggesting that “the no testing approach to routine ICD implantation should be preferred.”

Physicians’ reaction

Nick Linker (James Cook University Hospital, Middlesbrough, UK) told Cardiac Rhythm News that the results of the SIMPLE trial do not address the opposite question of which patients should have defibrillation tests. “This is an important area that will need to be evaluated,” he said. “This is a difficult group to tease out and there will clearly be individual clinical decisions to be made. However, I would think that patients having a right-sided ICD implant and those with abandoned leads should be tested. Patients with advisory leads may also require defibrillation threshold testing.”


John D Day (Intermountain Heart Rhythm Specialists, Murray, USA) president-elect, Heart Rhythm Society told Cardiac Rhythm News: “Defibrillation testing at the time of ICD implantation is something that we have been doing, at least in this country [USA], since the first ICD was approved in 1985. The SIMPLE trial results are important in that they challenge this practice.”

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