HRS: Strategize! It reduces shocks with ICDs, CRT-D
DENVER—Strategic programming of implantable cardioverter-defibrillators (ICDs) and cardiac resynchronization therapy-defibrillators (CRT-D) reduces shocks, based on the results of a late-breaking clinical trial presented today at the Heart Rhythm Society’s 31st annual scientific sessions.

Lead author Bruce L. Wilkoff, MD, HRS program chair and director of cardiac pacing and tachyarrhythmia devices at the Cleveland Clinic, explained that previous clinical trials found that programming can reduce shocks; however, this trial is the largest of its kind to analyze the impact of programming strategies on patients.

“Implantable cardiac devices are unique because they are malleable and under the control of the physician and the programming choices that he or she makes,” Wilkoff said. While acknowledging the limitations of registry data, he added that “it is very important to understand how devices are being used in real-world clinical practice. Even Medicare is interested in finding out if the same results are obtained in real-world practice as are obtained in clinical trials.”

This shock reduction trial is an observational study based on “every interrogation” from a large cohort of 88,804 patients from more than 2,500 institutions with an average follow-up of more than two years. Researchers obtained the data from Medtronic’s CareLink Network. They included all patients if they had a CRT-D or dual-chamber ICD.

The researchers reviewed four shock reduction strategies, as well as clinical characteristics: slowest ventricular tachycardia/ventricular fibrillation (VT/VF) detection threshold; VF number of intervals to detect; supraventricular tachycardia discriminators On; anti-tachycardia pacing On for Fast VTs; and atrial fibrillation (AF) with Rapid Ventricular Response. Overall, the study sought to determine the number of spontaneous all-cause shocked episodes per 100 patient years.

Wilkoff reported that results showed strategic programming of faster VT/VF detection thresholds, longer detection durations, supraventricular tachycardia discriminators, and anti-tachycardia pacing for Fast VT reduced shocks. They found that strategic programming resulted in significant reductions in shock, including:
  • 28 percent shock reduction with anti-tachycardia pacing activated for Fast VT episodes;
  • 22 percent shock reduction with supraventricular tachycardia discriminators activated;
  • 17-55 percent shock reduction depending on the duration of VT for detection; and
  • 21-148 percent shock reduction depending on the rate of VT detection limit.
In addition, Wilkoff and his colleagues found that AF has a dramatic impact on the incidence of shocks and is dependent on the rapid ventricular rate observed during the atrial fibrillation; and AF with rapid ventricular rate increases shock risk by 244 percent compared to patients without AF.

Strategic programming results in overall shock reduction between 17 and 28 percent depending on the programming of specific variables, according to Wilkoff.

However, with remote interrogation alerts, it is possible to identify patients at risk for future shocks since there often is a delay between the onset of the AF with Rapid Ventricular Response and the shock, he said.

In his response to the trial, Michael R. Gold, MD, PhD, from Medical University of South Carolina in Charleston, said, "This trial corroborates what we already know, but it is very important data, as appropriate or inappropriate shocks are not benign, and can be associated with increased mortality.”

“Our study is not only unique in methodology and size, but demonstrates that the choices clinicians make at the time of programming can make a difference in patient outcomes and potentially overall survival,” said Wilkoff. “Reducing the total number of shock episodes that patients experience results in more effective care and improves the quality of life for patients.”

Based on the findings of this trial, the researchers determined that clinical actions to reduce morbidity from shocks should include ensuring adequate rate control for patients with AF as well as programming to increase the VT/VF detection rate and duration threshold.

“Programming of devices is an extremely important component of trying to reduce shocks, which will at minimum improve quality of life for patients,” Gold said. “This registry has taught us that despite recent study results, we still have greater than 40 percent of patients whose devices are programed with traditional rate cutoffs at detection intervals.

“From the perspective of quality, there is a great opportunity to reduce shocks further with better adoption of these evidence-based programming strategies, and this registry shows us we have a long way to go to adhere to the suggestions of the literature,” Gold concluded.