Doctors using a subcutaneous implantable cardioverter-defibrillator (S-ICD) may now skip routine defibrillation testing. A scoring system can confirm a good device position. That is the PRAETORIAN-DFT result.

The PRAETORIAN-DFT trial findings were presented at Heart Rhythm Society (HRS) 2026 in Chicago. They also appear in Circulation. The data suggest a long-standing safety check may no longer be needed.

What the PRAETORIAN-DFT trial measured

The trial enrolled 973 adults. They came from 37 centres across Europe, Israel, and the United States. The modified intent-to-treat group held 965 patients. All had guideline-concordant S-ICD indications. Median follow-up ran 41 months.

One arm had routine defibrillation testing. The other had testing only when the PRAETORIAN score flagged a problem.

The PRAETORIAN-DFT trial findings show no extra risk from skipping. Patients who skipped routine testing were no more likely to fail the first shock for spontaneous ventricular arrhythmia. Rates were 1.7% versus 2.3% (P < .001 for noninferiority). A failed first shock stands in for ineffective ICD therapy.

The primary endpoint was failure to end ventricular tachycardia or fibrillation within five seconds of a shock.

Mortality and S-ICD revisions matched in both arms. Routine testing alone caused complications in 1.7% of patients.

The findings push S-ICDs to follow transvenous ICDs. Those devices dropped routine testing years ago. The procedure carries costs, anaesthesia, and risks of stroke, prolonged resuscitation, and death.

"Avoiding defibrillation testing may improve procedural safety and simplify S-ICD implantation," said lead investigator Reinoud E. Knops (Amsterdam University Medical Centre, Netherlands).

Why impedance alone is not enough

Defibrillation testing is recommended in consensus documents. The PRAETORIAN-DFT trial findings should "absolutely" prompt updated guidelines, said discussant Andrea M. Russo (Cooper Medical School of Rowan University, Camden, New Jersey).

Russo added that many operators already skip the test, guiding implantation with fluoroscopy or impedance — a practice with medical and legal exposure.

The implanting physician calculates the PRAETORIAN score before discharge. It rates S-ICD position on chest x-rays. Inputs are sub-coil fat, sub-generator fat, generator position to the mid-axillary line, and BMI.

Low-voltage impedance can help when paired with the score, but should not stand alone, Knops said. Anterior placement near the lead can give low impedance even when the shock misses the heart. He added: "Step two in the PRAETORIAN score is really important to correct for that. So, only the impedance will never be enough."

Higher complication rate with routine testing

In the routine arm, a failed test triggered device or lead repositioning. The no-routine arm tested only when the PRAETORIAN score crossed the 90-point threshold (the scale runs 30 to 900).

Safety did not differ in all-cause mortality (HR, 0.9; 95% CI, 0.6–1.4). Arrhythmic death also matched (HR, 0.4; 95% CI, 0.04–3.4). No patient died from S-ICD failure or testing.

Complications within 24 hours of testing occurred only in the routine arm (1.7%). Six cases were refractory ventricular fibrillation. One needed cardiopulmonary resuscitation. Another patient had respiratory arrest. That patient needed mask ventilation. One ventricular fibrillation case became atrial fibrillation. The result was an inappropriate shock.

The researchers reported a significantly higher 30-day complication rate in the testing group: 4.8% versus 1.7%. Drivers included refractory ventricular fibrillation, unplanned ICU stay, and cardiac decompensation.

Limitations

Defibrillation testing use was not blinded. Operators in the no-routine arm adjusted the device or lead under fluoroscopy more often. They also checked impedance more often. The authors said this likely reflected extra attention to implant position.

The implanters were highly experienced. Knops said the PRAETORIAN-DFT trial findings matter more for newer operators. The score shortens their learning curve.

The trial population skewed young. Mean age was 54. Women made up 24%. The mean left ventricular ejection fraction was 40%.

Where scores hit 90 or higher, the authors urged testing or repositioning, weighing re-op risk against it.

The investigator-initiated trial was funded by Boston Scientific.

The PRAETORIAN-DFT trial findings could reshape S-ICD care. Coverage on Medigear.uk shows why hospital teams must follow how these PRAETORIAN-DFT trial findings shape device-implant practice.

Source: Originating coverage based on the PRAETORIAN-DFT randomized trial reported at the Heart Rhythm Society (HRS) 2026 meeting in Chicago and published in Circulation — Knops et al., Amsterdam University Medical Center, with discussion by Andrea M. Russo, MD (Cooper Medical School of Rowan University). Funded by Boston Scientific.