While implantable heart defibrillators reduce the risk of death from sudden cardiac arrest in patients with mild to moderate heart failure, patients who receive defibrillator shocks for rhythm disturbances have a higher future risk of death, primarily from heart failure, a new study has found. The study, conducted at the University of Washington, Duke University Medical Center and the Seattle Institute for Cardiac Research, will appear in the Sept. 4 issue of the New England Journal of Medicine.
This new finding stems from the largest and most comprehensive study of ICD use to prevent sudden death in patients with mild to moderate heart failure —Sudden Cardiac Death in Heart Failure Trial, SCD-HeFT— the results of which were published in the New England Journal of Medicine in 2005. Implantable heart defibrillators or implantable cardioverter-defibrillators (ICDs), as they are known, are small battery-powered generators that are implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation.
That study demonstrated a clear survival advantage for patients treated with an ICD and medications for heart failure therapy compared to patients treated only with medications for heart failure.
In the new study, Dr. Jeanne E. Poole and colleagues prospectively studied 811 patients enrolled from 1997 to 2001 in SCD-HeFT who received an ICD, representing one-third of the randomized patients. The remaining patients received either the anti-arrhythmia drug amiodarone or a placebo.
“In our analysis, we aimed to compare outcomes in patients who developed heart rhythm disturbances with those patients who did not,” said Dr. Jeanne E. Poole, a cardiologist at the University of Washington and lead author of the study. “The results of our study show that these patients who are saved from an otherwise life-threatening heart rhythm are now identified as a high-risk group that has a higher chance of future death from heart failure.”
Researchers in this study examined the heart rhythms that triggered ICD therapy over the course of this six-year trial. Data retrieved from the patients’ ICDs during clinic visits were examined by a panel of experts. These investigators then looked at whether patients were more likely to subsequently die if they were in the group who had received an ICD shock.
Poole said the study findings provide important information for physicians. “Doctors should be vigilant in monitoring heart failure patients to ensure patients are on appropriate and available therapies,” she said. “Providers should also make sure that a new disorder or progression in the patients’ disease is not responsible for any increased risk.”
Researchers from the University of Washington who contributed to the study include Dr. Daniel Fishbein, professor of medicine, and Dr. Gust Bardy, professor of medicine. Poole also collaborated on this study with researchers Anne Helkamp, Daniel Mark and Kerry Lee from the Duke Clinical Research Institute, and George Johnson and Jill Anderson from the Seattle Institute for Cardiac Research. Other co-authors included physician experts in heart rhythm disorders from universities across North America who helped review and interpret the rhythms treated by the ICD. SCD HeFT and the research cited above by Poole et al. was funded by the National Heart, Lung, and Blood Institute at the National Institutes of Health.