After two years, fewer than 7 percent of patients who were implanted with a subcutaneous implantable cardioverter-defibrillator (S-ICD) had spontaneous ventricular tachyarrhythmia or ventricular fibrillation events, according to a pooled analysis of two trials. More than 90 percent of the events were terminated with one shock.
Lead researcher Martin C. Burke, DO, of the Heart Rhythm Center at the University of Chicago, and colleagues presented their results online in the Journal of the American College of Cardiology on April 20. The S-ICDs are an alternative to transvenous implantable cardioverter-defibrillators and are used to prevent sudden cardiac death.
The analysis included 882 patients who underwent an implantation procedure: 568 were from the EFFORTLESS (Boston Scientific Post Market S-ICD Registry) trial, 301 were from the IDE (S-ICD System IDE Clinical Investigation) study and 13 were from both studies. The mean age was approximately 50, and 72.5 percent of the patients were men.
Researchers defined spontaneous ventricular tachyarrhythmia or ventricular fibrillation events as those that triggered the device to charge and store an electrogram and broke them into two categories: discrete episodes or episodes that included three or more treated episodes within 24 hours in the same patient.
Of the 111 events, spontaneous ventricular tachyarrhythmia or ventricular fibrillation events found in 59 patients, more than 98 percent were terminated within five available shocks. Researchers said the three-year inappropriate shock rate was 13.1 percent, while the estimated three-year, all-cause mortality rate was 4.7 percent.
After three years, 11.1 percent of patients experienced device-related complications, and none had electrode failures or S-ICD-related endocarditis or bacteremia.
Combining information from two databases that included prospectively enrolled patients introduced a risk of bias, according to the researchers. However, they said the patient populations were similar because the studies had common inclusion and exclusion criteria and both enrolled patients starting in 2009.