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Primary prevention implantable cardioverter-defibrillators (ICDs) equipped for antitachycardia pacing (ATP) offered fewer first device shocks but perhaps at a cost, the APPRAISE ATP randomized trial showed.

ICDs with this programming significantly reduced first all-cause ICD shock compared with shock-only devices over the average follow-up of 38 months (HR 0.72, 95% CI 0.57-0.92, P=0.005 for superiority), with 14.6% versus 19.4% estimated to have a shock by 60 months in the Kaplan-Meier analysis, according to researchers led by Claudio Schuger, MD, of the University of Rochester Medical Center in New York.

This applied across subgroups, including by ischemic and nonischemic etiologies, history of atrial fibrillation, age, and sex.

"With a 1% absolute reduction in all-cause shock due to ATP, the results of this trial should be considered during shared decision-making in the selection of ICD hardware in primary prevention cohorts," Schuger and colleagues wrote in .

However, ATP didn't lead to a statistically significant reduction in total shock burden (12.3 vs 14.9 per 100 patient-years, P=0.70) and was associated with a numerical increase in all-cause mortality (HR 1.15, 95% CI 0.94-1.41) and significant excess in ventricular tachycardia/ventricular fibrillation (VT/VF) storm burden (HR 2.26, 95% CI 1.18-4.30).

"These data solidify ATP before shock as standard of care and suggest strong consideration for an ATP-first ICD programming strategy," according to an by Paul Varosy, MD, of VA Eastern Colorado Health Care System in Aurora, and colleagues.

However, the data also point to a cost, they noted.

ATP can disrupt a VT circuit painlessly from a remote site, but carries risk of accelerating what might otherwise be fairly benign VTs into more rapid and unstable rhythms like VF.

The lower risk of a first shock stemmed from ATP terminating some monomorphic VTs and preventing some inappropriate shocks triggered by supraventricular tachycardias or atrial fibrillation. Notably, the termination rate for the first VT was just 54.0%, fairly low for ATP success. ATP plus shock was no better than shock-only programming for rhythms classified as polymorphic VT or VF in zone 2.

"Although ATP was once considered relatively benign, APPRAISE ATP raises the notion that perhaps the decision to use ATP first is not nearly as simple or benign as many in the field of electrophysiology previously believed," Varosy and colleagues concluded.

"Perhaps the trial's most salient contribution is demonstrating that ATP, an elegant method to painlessly address malignant ventricular arrhythmias, may come at a price," the group added. "Trial design may account for these findings ... because patients in the shock only group were censored after their first event while those in the ATP plus shock group were followed up until future arrhythmic events occurred."

Moreover, the APPRAISE ATP trialists acknowledged that nearly a quarter of people had been lost to follow-up, and 22% withdrew before reaching the primary endpoint.

APPRAISE ATP was an international, double-blind trial conducted from 2016 to 2021. Investigators randomly assigned people to modern ICD programming with or without ATP. Participants were 2,595 primary prevention ICD recipients with a reduced left ventricular ejection fraction who had gotten single- or dual-chamber devices. Key exclusion criteria included history of spontaneous sustained ventricular arrhythmias and cardiac resynchronization therapy indications.

The enrolled cohort had a mean age of 63.9 years, with 22.4% women. Patients were roughly split between single- and dual-chamber ICDs.

Times to both first appropriate shock (delivered for VT or VF; HR 0.73, 95% CI 0.56-0.95) and first inappropriate shock (for any other rhythm; HR 0.65, 95% CI 0.44-0.97) were reduced comparing the ATP group to the shock-only group.

Varosy and colleagues urged future research on effective communication of ATP's nuances to patients "in an era of rapidly evolving technology."

While ATP-first programming is already common in clinical practice for ICDs, the editorialists noted implications for device selection in primary prevention: "ATP requires a lead that is either endocardial or close enough to the heart in the extravascular space that it can readily electrically capture, or pace, myocardial tissue at a low enough energy that renders it painless. Therefore, among newer ICD therapies for surveillance and treatment of ventricular arrhythmias, ATP is not possible with the subcutaneous ICD, but because its lead is in the space between the sternum and pericardium, the extravascular ICD can deliver ATP."

Researchers, however, have been working on pairing subcutaneous ICDs with a leadless pacemaker to enable ATP.

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