Survival climbs, risk of unnecessary shocks plummets
A new study at the University of Rochester Medical Center Rochester, NY, shows that defibrillators, which are designed to detect and correct dangerous heart rhythms, can be programmed to help users live longer, better lives, than they currently do.
Researchers found that a small, simple change in the way physicians set or programmed the device led to a dramatic 80 to 90 percent reduction in inappropriate therapies— painful shocks delivered for rhythms that weren’t dangerous or life threatening. And, they found that the new programming significantly increased survival rates, lowering the risk of death by 55 percent compared to patients whose devices used traditional programming— above and beyond the usual decrease in mortality associated with defibrillator therapy, leading to an overall 70 percent reduction in death. The researchers, led by Professor Arthur J. Moss, MD, a world-renowned expert in the treatment and prevention of cardiac arrhythmias and sudden cardiac death, and longtime professor of Cardiology at the University of Rochester Medical Center, found that by simply raising the heart rate at which the device was set to deliver therapy made all the difference.
Implantable cardioverter defibrillators or ICDs constantly monitor the rate and rhythm of the heart and are supposed to deliver electrical shocks in response to very fast and potentially fatal heart rhythms. In 2002, Moss and research group showed that ICDs are extremely effective in preventing death in patients at risk of irregular heart rhythms and sudden cardiac death, including individuals who’ve suffered a heart attack. The work changed medical guidelines nationwide, making thousands of heart attack survivors eligible for ICD therapy. Currently, around 200,000 ICDs are implanted in the US every year.
But, according to a 2008 study in the Journal of the American College of Cardiology, approximately 20 to 25 percent of defibrillator therapy is inappropriate, delivering shocks to less dangerous rhythms not likely to pose any immediate danger to patients. These shocks are painful as well as stressful.
Moss’ team conducted the trial, sponsored by Boston Scientific, to determine if different ways of setting the device— performed by a heart rhythm specialist prior to device implantation in a patient’s chest—could reduce the occurrence of inappropriate therapy. From September 2009 through October 2011 the team enrolled 1,500 patients in 98 hospital centers in the US, Canada, Europe, Israel, and Japan. All patients had heart disease and received a Boston Scientific ICD or CRT-D.
Most defibrillators are set to initiate therapy when the heart rate exceeds around 170 beats per minute, but rates of 180 or 190 are not always dangerous, are usually short-lived, and could be related to increased activity or exercise. Setting the device to fire at a higher rate of 200 beats per minute reduced the risk of experiencing a first inappropriate therapy by 79 percent compared to standard programming. Fewer shocks also corresponded with less energy delivered to the heart, which study authors believe contributed to the reduced risk of death.
To view a video about this study, visit http://www.techbriefs.com/tv/defibrillators.