SIMPLE: Routine ICD Defibrillation Threshold Testing? Just Say No

May 09, 2014

SAN FRANCISCO, CA — Overwhelmingly, most patients receiving an implantable cardioverter defibrillator (ICD) do not benefit from perioperative defibrillation threshold (DFT) testing, which may well be safe but does not improve the efficacy of delivered shocks or prolong survival, concluded researchers here, on the basis of the randomized, 2500-patient Shockless Implant Evaluation (SIMPLE) trial. DFT testing may well have been useful in an earlier era when ICDs were less reliable, they said, but with contemporary devices such testing is worthwhile probably only in occasional special cases[1].

In SIMPLE, designed as a noninferiority trial, the primary end point of failed appropriate shocks or arrhythmic death edged lower for patients randomized not to undergo DFT testing, compared with those who were tested. It did not show superiority for the group, but "it met noninferiority by a wide margin," according to the trial's principal investigator Dr Jeffrey S Healey (Population Health Research Institute, Hamilton, ON), who presented the trial here at the Heart Rhythm Society (HRS) 2014 Scientific Sessions .

Dr Jeffrey S Healey

To heartwire , Healey said he was not surprised by the outcome but was surprised by "how robust the results were. It was like kicking the ball 10 yards over the goalpost, it was that clear-cut that it was noninferior."

The safety of DFT testing was evaluated with two composite end points, one of which marginally suggested harm from testing over the following month. But perioperative complications were few in absolute terms, Healey said.

"We think that implanting an ICD without routine testing should be the preferred approach now," he said. In Canada, DFT testing is avoided in 80% of ICD implantations. "In other countries like the United States, most defibrillators still go in with the testing procedure. But whether it's done where there's a lot of testing or not a lot of testing, we think [SIMPLE] has the potential to change the way tens of thousands of people are managed every year."

Dr Stuart Connolly

Speaking with heartwire , SIMPLE trialist Dr Stuart Connolly (Population Health Research Institute) said, "I think the guidelines should say you don't need to test, that it should not be done. This is pretty definitive." In fact, he said, there was that signal of harm from DFT testing (p=0.047), for a secondary end point including events with a high likelihood of being testing-related (such as need for resuscitation, unplanned intubation, stroke, death, or heart failure). "Occasionally patients get into trouble [at DFT testing]. It's uncommon, but it happens," Connolly said. "So I think there's actually a reason not to do it."

In SIMPLE, conducted in 18 countries, patients receiving their first transvenous ICD for primary or secondary prevention (no pulse-generator change-outs, no planned right-sided implantations) were randomized to undergo perioperative DFT testing (n=1253) or not (n=1247). The testing protocol, Healey said, required at least one successful termination of ventricular fibrillation with a shock of 17 J or two successful terminations at 21 J; the first shock energy was programmed to 31 J in both treatment arms. Events were centrally adjudicated, and follow-up averaged 3.1 years; only 1.7% of patients had been lost to follow-up, Healey said.

The annual rate of the primary end point, failed appropriate shock or arrhythmic death, was 7.2% in the no-testing group and 8.3% in the testing group, for a hazard ratio (HR) of 0.86 (95% CI 0.65–1.14; p<0.001 for noninferiority, p=0.30 for superiority).

There was no significant difference in all-cause mortality for the two groups (HR 1.04, 95% CI 0.86-1.26; p=0.65).

DFT testing wasn't associated with excess events for the primary composite safety end point, which included "any complication that could conceivably be related to DFT testing," according to Healey. There was a signal of harm from DFT testing for the secondary safety end point.

Rates (%) of Safety End Points at 30 Days in SIMPLE, No DFT Testing vs DFT Testing

End points No DFT testing, n=1237 DFT testing, n=1242 p
Primary safetya 5.4 6.5 0.25
Secondary safetyb 3.0 4.5 0.047
DFT=defibrillation threshold
a. Death, MI, stroke, anoxic brain injury, systemic or pulmonary embolism, heart failure, need for chest compressions or aortic balloon pump, need for intraoperative vasoconstrictors, nonelective intubation, pneumothorax, cardiac perforation, ICD infection, arterial-line complication, aspiration pneumonia, or unplanned ICU stay
b. Death, MI, stroke, anoxic brain injury, systemic or pulmonary embolism, heart failure, need for chest compressions or aortic balloon pump, need for intraoperative vasoconstrictors, nonelective intubation, cardiac perforation, arterial-line complication, aspiration pneumonia

Dr Paul A Friedman

"I think the impact [of SIMPLE] will be significant," Dr Paul A Friedman (Mayo Clinical, Rochester, MN), who was not involved in the trial, commented to heartwire . "The question today is not whether defibrillation testing should be done, but what is the subpopulation—I think there probably won't be a lot of disagreement that there will remain subpopulations where testing is important." They might include patients with advisory leads, he said, or those getting pulse-generator change-outs. But "the number of tests done routinely will significantly diminish."

Connolly further proposed that patients with planned right-sided device positioning or those with abandoned leads from a prior device might well benefit from DFT testing. "So, rare situations."

As for subgroups in the trial, none of those evaluated derived any special benefit from testing, according to Healey. "In patients with very low LVEF, those with biventricular pacemakers, advanced heart failure, or atrial fibrillation—in all the prespecified subgroups, we did not see any deviation of the effect; it was the same regardless of the group."

Finally, after Healey's formal presentation of the trial, it received a stamp of approval from one of the ICD field's pioneers. Dr Roger A Winkle (Sequoia Hospital, Redwood City, CA) stood up during the question-and-answer period and observed that DFT testing came about because "in the beginning, these devices didn't work very frequently." He said DFT testing "has been antiquated for a long time," that SIMPLE represents "the state of the art, and you're right on with your conclusions and your findings."

Healey disclosed receiving consulting fees or honoraria Boehringer Ingelheim, St Jude Medical, and Bayer Health and research grants from Bristol-Myers Squibb, Boston Scientific, St Jude Medical, Boehringer Ingelheim, Medtronic, Bristol-Myers Squibb, and Pfizer.

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