A new study based on a large cohort of patients proves strategic programming of implantable cardiac defibrillators (ICDs) and cardiac resynchronization therapy devices (CRT-D) reduces shocks. The results are part of a shock reduction late-breaking clinical trial presented today at Heart Rhythm 2010, the Heart Rhythm Society's 31st Annual Scientific Sessions. According to the trial, strategic programming results in overall shock reduction between 17 and 28 percent depending on the programming of specific variables.

This shock reduction trial is an observational study based on a large cohort of 88,804 patients from over 2,500 institutions with an average follow-up of over two years. Patients were included in the study if they had a CRT-D or dual chamber ICD. Four shock reduction strategies as well as clinical characteristics were reviewed in the study: slowest ventricular tachycardia/ventricular fibrillation (VT/VF) detection threshold, VF number of intervals to detect (NID), supraventricular tachycardia (SVT) discriminators On, antitachycardia pacing (ATP) On for Fast VTs (FVT) and atrial fibrillation (AF) with Rapid Ventricular Response (RVR). Overall, the study sought to determine the number of spontaneous all-cause shocked episodes per 100 patient years.

Results showed strategic programming of faster VT/VF detection thresholds, longer detection durations, SVT discriminators, and ATP for FVT reduced shocks. Strategic programming resulted in significant reductions in shock, including:

• 28 percent shock reduction with ATP activated for fast VT episodes
• 22 percent shock reduction with SVT discriminators activated
• 17 - 55 percent shock reduction depending on the duration of VT for detection
• 21 - 148 percent shock reduction depending on the rate of VT detection limit
  In addition, atrial fibrillation (AF) has a dramatic impact on the incidence of shocks and is dependent on the rapid ventricular rate (RVR) observed during the atrial fibrillation.
• AF with RVR increases shock risk by 244 percent compared to patients without AF

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 RVR and the shock.

"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 lead author Bruce L. Wilkoff, M.D., FHRS, Heart Rhythm Society Scientific Sessions Program Chair and Director of Cardiac Pacing and Tachyarrhythmia Devices at the Cleveland Clinic in Cleveland, Ohio. "Reducing the total number of shock episodes that patients experience results in more effective care and improves quality of life for patients.
Previous, controlled clinical trials found that programming can reduce shocks;

owever, this trial is the largest of its kind to analyze the impact of programming strategies on patients. Based on the findings of this trial, 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.