Risky Test Not Necessary for Subcutaneous ICD Implants

People getting a subcutaneous implantable cardioverter-defibrillator (S-ICD) did fine skipping the defibrillation test after all, according to the PRAETORIAN-DFT randomized trial.

In people randomized to de novo S-ICD placement, a failed first shock for spontaneous ventricular arrhythmias (a proxy for ineffective defibrillation) was rarer in those without defibrillation testing guided by the PRAETORIAN score — a predictor of defibrillation outcomes based on chest x-rays — versus those with defibrillation testing (1.7% vs 2.3%, P<0.001).

The PRAETORIAN-guided patients also showed no uptick in all-cause mortality (HR 0.9, 95% CI 0.6-1.4) or arrhythmic death (HR 0.4, 95% CI 0.04-3.4) over follow-up of more than 3 years, reported Reinoud Knops, MD, PhD, of Amsterdam University Medical Centre, and colleagues.

The trial was presented at the Heart Rhythm Society annual meeting held in Chicago. A full manuscript was published in Circulation.

“PRAETORIAN score-guided omission of DF [defibrillation] testing after S-ICD implantation did not increase the risk of failed first shocks for spontaneous ventricular arrhythmias and reduced procedural risk without increasing S-ICD revisions,” study authors reported.

“This is the first randomized comparative trial to demonstrate that S-ICD implantation without defibrillation testing, guided by the PRAETORIAN score, does not compromise long-term S-ICD efficacy, and is non-inferior to implantation with defibrillation testing,” Knops and colleagues concluded.

The PRAETORIAN score is a noninvasive test that gives a score from 30 to 900, which can be interpreted as low risk (<90 points), intermediate risk (90-149 points), and high risk (150 points or higher). This score has been validated for a score <90 as a predictor of defibrillation testing success.

The score was developed as an alternative to defibrillation testing to gauge if the ICD positioning is optimal for effective shock therapy.

Defibrillation testing has already fallen out of favor for transvenous (TV) ICD implantation given the extra procedural burden, need for anesthesia, and evident risk of serious complications.

Yet current guidelines still recommend defibrillation testing for S-ICD implants. “Since the S-ICD is entirely subcutaneous and effective defibrillation by the S-ICD is dependent on specific criteria for implant positioning, findings on DF testing for TV-ICDs cannot be extrapolated to DF testing for S-ICDs,” Knops and colleagues explained.

It was therefore reassuring that omission of defibrillation testing did not increase the risk of unrecognized ineffective ICD therapy in PRAETORIAN-DFT.

What’s more, 30-day complications were significantly down in the no-testing group compared with the defibrillation-testing group (1.7 % vs 4.8%, HR 0.34, 95% CI 0.15-0.77), driven by differences in refractory ventricular fibrillation, unplanned intensive care unit stay, and cardiac decompensation, according to the investigators.

They nevertheless cautioned that an individualized approach remains warranted, particularly in patients with PRAETORIAN scores ≥90 who were a small minority in the study.

The PRAETORIAN-DFT trial was conducted at 37 international centers from 2018 to 2023.

Participants were 965 patients getting S-ICDs to terminate spontaneous ventricular arrhythmias and prevent sudden cardiac death. The cohort had a mean age of 54 years and was 24% women. Average left ventricular ejection fraction was 40%. The S-ICD was implanted for secondary prevention in 34% of cases.

The cohort was randomized 1:1 to defibrillation testing or no defibrillation testing. Follow-up lasted a median 41 months.

In the defibrillation-testing group, an initial successful result was achieved for 97.4% of the group. Of 12 failed patients, five underwent repositioning of the lead or generator in the same procedure and one patient underwent lead repositioning the following day.

In the no-defibrillation-testing group, 96.8% turned out to have a low PRAETORIAN score. Fourteen individuals had an intermediate score and one a high score.

Postoperative S-ICD revisions due to inadequate positioning occurred in two cases in each group.

The primary endpoint counted failed first shocks as a measure of defibrillation success. This was estimated based on the lack of termination of ventricular tachycardia or ventricular fibrillation within 5 seconds of shock delivery. Investigators allowed for testing for non-inferiority with a 3% absolute risk margin.

As for shocks for spontaneous ventricular arrhythmias, these occurred in 13.8% of the no-defibrillation-testing group and 15.0% of the defibrillation-testing group.

Across PRAETORIAN score categories, 57 patients in the low-risk category experienced shocks for ventricular arrhythmia, three patients did in the intermediate/high-risk category, and one patient for whom the score could not be calculated.

Potential testing-related complications occurred in 1.7% in the defibrillation-testing group. These included six patients with refractory ventricular fibrillation (defined as requiring more than one external rescue shock), one patient with respiratory arrest, and one patient whose ventricular fibrillation was converted to atrial fibrillation, resulting in an inappropriate shock.

Among the trial’s limitations, the relatively young age and lower comorbidity burden of the study population may limit the generalizability of the study findings, Knops and colleagues cautioned.