Patients with single-chamber (VVI) implantable cardioverter-defibrillators (ICDs) programmed with longer intervals for detecting arrhythmias experienced significant reductions in appropriate therapies, shocks and all-cause mortality when compared to patients with standardly programmed ICDs, according to a study published online Nov. 20 in JACC: Clinical Electrophysiology.

A total of 267 patients were included in the long detection group (30 of 40 intervals) and 278 in the control group (18 of 24 intervals). Eighty-five percent of the study population was male.

Over one year of follow-up, 112 therapies—including both shocks and antitachycardia pacing (ATP)—occurred in the long detection arm versus 257 in the control arm. Intervention reduced all-cause and cardiovascular hospitalizations by nearly one-third and was associated with a 59 percent reduction in mortality. Three percent of the patients in the long detection arm died during follow-up versus 7.2 percent of subjects in the control arm.

“The programming strategy tested in VVI ICDs was strongly and consistently effective across a range of tested metrics,” wrote lead author Maurizio Gasparini, MD, and colleagues. “Consensus exists that unnecessary ICD therapies (appropriate or inappropriate) should be avoided, as evidence mounts for their adverse effects, including impaired quality of life, increased health care utilization, and an association with increased mortality. Shocks (appropriate or inappropriate) may cause cell injury, negative inotropy, and hemodynamic compromise, and they may be proarrhythmic.”

Gasparini et al. noted prolonged detection intervals had previously shown promise in studies of dual-chamber (DDD) ICDs, but the effect of this programming adjustment was unknown in VVI ICDs.

In addition, they pointed out previous studies—including their own research of three types of ICDs—have shown a reduction in overall appropriate therapies and ATP, but not appropriate shocks when considered individually. However, patients with VVI ICDs in this trial experienced both fewer appropriate shocks and fewer appropriate ATP therapies.

“Here, during follow-up, 30 of 258 patients (11.6 percent) programmed to standard settings received appropriate shocks compared to 15 of 251 (5.9 percent) in the long detection group,” they wrote. “This finding suggests that the population of patients receiving a VVI ICD in this trial represents patients with a specific arrhythmic profile characterized by the frequent occurrence of short ventricular arrhythmias lasting less than 18 beats but prone to self-termination within 29 beats, and that therapy for these events is unnecessary.”

Inappropriate therapies were low across the entire study group, but the shorter detection arm experienced double the amount—78 therapies in 17 patients versus 39 therapies in 14 patients of the longer detection arm. Due to the small numbers, that difference didn’t reach statistical significance.

The study analyzed a subset of patients from the ADVANCE III trial, which tested the effect of long detection intervals in VVI, DDD and cardiac resynchronization therapy ICDs. Gasparini and colleagues pointed out the VVI group had a higher incidence of coronary artery disease, shorter QRS durations and fewer patients with left bundle branch block compared to the overall study cohort. Therefore, they said it is possible this sicker group of patients could benefit more from the longer detection strategy.

Also, the researchers only tested devices from Medtronic, which supported the trial and participated in its design and execution. Their findings may not apply to ICDs from other manufacturers, they wrote.