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Subcutaneous implantable cardioverter defibrillators (S-ICDs) performed on par with conventional transvenous ICDs (TV-ICDs) in the first head-to-head randomized trial.

The overall primary composite endpoint of inappropriate shocks and complications came out nearly identical (HR 0.99, 95% CI 0.71-1.39, P=0.01 for noninferiority) over a median 4 years in the PRAETORIAN trial, which was presented at the virtual Heart Rhythm Society annual conference.

S-ICDs had numerically fewer device-related complications (5.9% vs 9.8%, HR 0.69, P=0.14) but numerically more inappropriate shocks (9.7% vs 7.3%, HR 1.43, P=0.14).

"The S-ICD should be considered in all patients with a need for ICD who don't have a pacing indication," said study lead author Reinoud Knops, MD, PhD, of Academisch Medisch Centrum in Amsterdam, at an HRS press briefing.

While the first S-ICD was approved by the FDA in 2012, it "has mainly been used as a niche device for younger patients and those with congenital cardiomyopathies or genetic arrhythmia syndromes, a very niche population," Knops said.

A sub-analysis found a "big difference" in lead-related complications. These occurred in 1.4% of the S-ICD group compared with 6.6% of the TV-ICD patients (HR 0.24, 95% CI 0.10-0.54).

The study findings will help physicians and patients make decisions about the best ICD strategy, Knops said. TV-ICD may be appropriate "if you weigh the inappropriate shock as being as important as the ," he said. "I have my opinion: Surgical complications where you need repeated surgery weigh heavier. But obviously, I'm not the patient receiving the inappropriate shock."

Wilber Su, MD, director of cardiac electrophysiology at Banner-University Medicine Heart Institute in Phoenix, said that about 10% of his facility's patients who receive defibrillators for primary or secondary prevention get S-ICDs.

"We do expect some growth in this segment," he said. "Patient access needs, such as hemodialysis, central-line placements, and risk for infection with minimizing hardware are all possible advantages of S-ICD over TV-ICD. However, one also needs to be considerate of possible high defibrillation thresholds and the need for pacing/resynchronized pacing later in life."

Peter Zimetbaum, MD, of Harvard Medical School and Beth Israel Deaconess Medical Center in Boston, said the study "adds to the evidence that this [the S-ICD] is a very reasonable alternative to the standard device." However, he said, "a major limitation remains the size of the device. If the patient is small in stature, the device is still quite large."

In the international, multicenter PRAETORIAN trial, patients with a class I or IIa indication for ICD therapy who didn't need pacing were randomized to one of two groups: 426 were assigned to get an S-ICD, and 423 were assigned to get a TV-ICD. Overall, 20% of participants were women, and the median age was 63.

The two groups had similar mortality rates over a median of 4 years, both overall (16.4% vs 13.1%, P=0.20) and from cardiac causes.

Further follow-up will provide more insight into the pros and cons of S-ICDs, Su said. "It may reveal how frequently the S-ICD population will need the addition of a pacemaker or Bi-V [biventricular] pacemaker, which may defeat some of the purposes of avoiding transvenous hardware. However, leadless pacing technologies are coming in the future to work with the S-ICD."

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