TOPLINE:
Among recipients of subcutaneous implantable cardioverter defibrillators, the omission of defibrillation testing (DT) was not associated with significant differences in mortality, or in the rates of appropriate and inappropriate shocks. Obesity and high shock impedance, however, predicted testing failure.
METHODOLOGY:
- Current guidelines recommend DT during the implantation of a subcutaneous implantable cardioverter-defibrillator (S-ICD); omissions of DT has yielded conflicting results regarding mortality and shock efficacy.
- Researchers analyzed data from an ongoing observational study, including 4924 patients who were implanted with S-ICD systems in France between October 2012 and December 2019.
- The analysis compared outcomes in patients who underwent DT (n = 4066; mean age, 49.6 years; 23.6% women) and those who did not (n=858; mean age, 51.2 years; 22.1% women) over a mean follow-up of 4.2 years.
- The outcomes included overall mortality, cardiovascular mortality, sudden cardiac death, a composite of sudden cardiac death or death of unknown origin, and appropriate and inappropriate shocks.
TAKEAWAY:
- The omission of DT was not associated with an increased risk for any of the outcomes, including all death-related endpoints, or inappropriate and appropriate shocks.
- DT was successful in 99% of patients; independent predictors of test failure were obesity (adjusted odds ratio [aOR], 2.17; P = .042) and shock impedance ≥ 89 Ω (aOR, 4.60; P < .001).
- Ineffective appropriate shocks occurred only in patients who underwent testing.
- Serious complications related to testing occurred in 0.07% of patients, and two related deaths were reported.
IN PRACTICE:
“These findings suggest that omitting DT [defibrillator testing] may be safe for most S-ICD recipients, challenging the necessity of routine testing in all cases,” the researchers reported.
“Fourth, to our knowledge, this is the first study to report the incidence of complications directly associated with S-ICD testing, estimated at < 1 per 1000, including a 1 per 2000 risk” for death related to testing, they wrote. “However, the occurrence of DT-related deaths in patients with severely impaired LVEF [left ventricular ejection fraction] highlights the importance of a careful risk-benefit assessment in this vulnerable subgroup,” they added. In these cases, the risks associated with testing “may outweigh its potential benefits, warranting individualized clinical decision-making.”
“The risk-benefit ratio of routinely performing DT seems to favor not doing routine testing,” Raul Weiss, MD, and Jose Sleiman Morales, MD, wrote in an editorial accompanying the journal article.
“A commonsense approach, therefore, would be to perform a low-risk 10-J synchronized shock in sinus rhythm to evaluate the system HV [high-voltage] impedance. If the impedance is elevated, (z > 90 U), then the system implantation features should be reevaluated with attention to posterior and preferably intermuscular implantation of the generator and minimal distance between the shocking coil and the sternum. These measures are likely to reduce the HV impedance. If the value remains elevated, then perhaps, in this scenario, DT offers clinical value,” they added.
SOURCE:
This study was led by Fawzi Kerkouri, MD, MPH, of European Georges Pompidou Hospital in Paris, France. It was published online on June 30, 2025, in the Journal of the American College of Cardiology.
LIMITATIONS:
Clinicians may have omitted DT in patients with low risk or those with favorable procedural characteristics, introducing selection bias. Residual confounding may have persisted despite adjustments. Some cases of sudden cardiac death may have been misclassified as deaths of unknown origin.
DISCLOSURES:
This study was funded by the French Federation of Cardiology and the French Society of Cardiology. The studied device was manufactured by Boston Scientific, which supported the annual meeting of the study investigators. Several authors reported serving as consultants and/or receiving fees from Boston Scientific.
This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.