DENVER — Programming implantable defibrillators using specific shock-reduction strategies safely reduced shock rates by 17%–28% in an observational study of nearly 89,000 cardiac device recipients at more than 2,500 U.S. centers.
This study of unprecedented size, featuring 221,000 patient-years of comprehensive follow-up, clearly demonstrates that implanting cardiac resynchronization therapy defibrillators (CRT-Ds) or implantable cardioverter defibrillators (ICDs) using preprogrammed, default-mode settings needlessly exposes device recipients to the morbidity of extra shocks, Dr. Bruce L. Wilkoff said in presenting the study findings at the meeting”
“This is important data because it allows physicians to reconsider the choices that they're making,” added Dr. Wilkoff, professor of medicine and director of cardiac pacing and tachyarrhythmia devices at the Cleveland Clinic Foundation.
He reported on 88,804 patients who received a dual-chamber ICD or CRT-D and were followed for an average of 2.5 years through Medtronic's CareLink database, which provides complete data on all device interrogations.
During follow-up, 64% of patients had no shocks or episodes of antitachycardia pacing (ATP), 14% had ATP only, and 22% experienced a collective 72,239 shock episodes.
A multivariate analysis identified the key shock-reduction device programming strategies. Switching on the supraventricular tachycardia discriminator was independently associated with a 22% decrease in the rate of shock episodes per 100 patient-years. Switching on ATP for fast ventricular tachyarrhythmias reduced the shock rate by 28%. Lengthening the number of intervals required to detect ventricular tachychardia/ventricular fibrillation (VT/VF) to 24/32 or 30/40, thereby allowing some episodes to terminate spontaneously, decreased the shock rate by 17%.
“The clinical implications are that physicians should choose strategic programming, including increasing VT/VF detection rates and duration thresholds, and turning on SVT discriminators and ATP for fast VTs,” he stressed.
The analysis also highlighted those device programming settings resulting in increased shock rates. For example, 37% of devices were set to detect VT/VF after 12/16 intervals, and patients with those devices had a 55% increase in their shock rate. Devices programmed for a slower VT/VF detection threshold had a shock rate up to 148% greater than with longer detection durations.
Importantly, patients with atrial fibrillation with a rapid ventricular response of 180 bpm or more had a shock rate 244% greater than patients without atrial fibrillation, and 149% greater than patients with atrial fibrillation and a controlled ventricular response, Dr. Wilkoff said.
Disclosures: The registry study was supported by Medtronic. Dr. Wilkoff is a consultant to Medtronic and the other major device companies.
My Take
Program Devices to Minimize Shocks
This huge registry study convincingly corroborates what has been seen in earlier, far smaller studies.
Shocks are not benign. Whether appropriate or inappropriate, they are associated with increased mortality. People are still teasing out whether the shocks themselves are dangerous or just markers, but clearly we know that the more shocks patients have, the worse their outcome and their quality of life.
The registry shows that more than 40% of patients have devices programmed with traditional default-setting rate cutoffs and detection intervals. Clearly, there is a great opportunity to reduce shocks further with better adoption of these evidence-based programming strategies. The lesson that the registry tells us is we have a long way to go to do what we've proven should be done.
MICHAEL R. GOLD, M.D., is professor of medicine, chief of cardiology, and medical director of the Heart and Vascular Center at the Medical University of South Carolina, Charleston. He made his remarks as the designated discussant of the paper. Dr. Gold disclosed that he is a consultant for Medtronic and several other major device companies.
