Features January 2013 Issue

Small ICD Programming Change May Extend Lives, Reduce Needless Shocks

New study shows that setting the devices to respond at higher heart rates may improve a patient’s quality of life and cut down the amount of energy delivered to the heart.

When you experience a dangerous heart rhythm, an implantable cardioverter defibrillator (ICD) can help get your heart working correctly again by delivering a little shock. But a new groundbreaking study found that some minor adjustments to an ICD may eliminate most needless shocks and help add years to the lives of patients with heart disease.

Images: ICD: NIH / EKG: Wikicommons

An ICD is programmed to send a shock to the heart when the device detects a rapid heart rate that may be dangerous.

The MADIT-RIT (Multicenter Automatic Defibrillator Implantation Trial-Reduce Inappropriate Therapy) trial found that by setting ICDs to fire at a higher heart rate than they are normally programmed for, you can reduce the risk of experiencing unnecessary therapy by 79 percent. And surprisingly, the adjustment also lowered the risk of death in ICD patients by more than half. The findings, published in the Nov. 6, 2012 issue of the New England Journal of Medicine and presented at the American Heart Association’s Scientific Sessions, are particularly encouraging, as the number of people with ICDs is climbing every year. More than 1 million Americans currently have the implanted devices and about 200,000 patients a year receive ICDs.

“These results are very big because this is a 55-percent reduction in death and 79-percent reduction in therapies including shocks from the ICD,” says Bruce Wilkoff, MD, Director of Cardiac Pacing and Tachyarrhythmia Devices at Cleveland Clinic. “If this was a new therapy then it would be the biggest new therapy of the year, but these results are on top of the already impressive value of ICDs. These results say that we had undervalued the impact on preventing deaths and overestimated the negative affects of ICDs. However, it requires that the ICDs are correctly programmed. These results should be seen not only with the Boston Scientific ICDs (subjects of the trial), but also with Medtronic, St. Jude Medical or any other manufacturer, if these principles are followed.”

ICDs at Work
ICDs are small devices implanted in the chest (though sometimes they are located in the abdomen) and are attached with thin, flexible electronic wires to the heart’s ventricles. The device is programmed by a physician to send low-energy pulses to the heart when it detects that the heart is out of its normal rhythm. That change in rhythm can be a heart rate that is too fast, too slow or erratic. The pulses are meant to bring the heart back into a healthy rhythm, though sometimes a high-energy pulse is needed if the initial low-energy pulses don’t work.

Most ICDs are set to initiate therapy, or send a pulse, when the heart rate exceeds 170 beats per minute (bpm). And while ICDs have been proven to be life-saving devices, there has been concern for some time in the medical community that they could be used even more effectively.

In the MADIT-RIT study, devices were set to fire at a rate of 200 bpm. Researchers noted that a heart rate of 180 or even 190 bpm is still safe for many people, provided the arrhythmia (abnormal heart rhythm) doesn’t last too long and subsides on its own. By cutting down on the number of shocks an ICD delivers, a patient enjoys fewer unpleasant and uncomfortable episodes and the heart receives less outside energy.

Researchers suggested that less energy being delivered to the heart may have accounted for the lower mortality rate.

Rate and Rhythm
Dr. Wilkoff explains that MADIT-RIT used two techniques to make certain of the need to treat the patient. The first was to make sure that the rhythm didn’t stop on its own and the second was to make sure that the rhythm was fast enough to be treated. Many people experience arrhythmias that are short-lived and infrequent, so the feeling was that these ICD patients won’t need as aggressive a treatment as a patient who has more sustained and more severe episodes. And by setting 200 bpm as a threshold, researchers believed that life-saving therapy would still be delivered effectively.

“It isn’t just the heart rate but the heart rhythm that can be troublesome,” Dr. Wilkoff says. “During exercise, it is appropriate to elevate your heart rate significantly. However, even a lower heart rate can cause a patient to feel lightheaded, cause them to faint or even die if the rhythm is abnormal. This rhythm, called ventricular tachycardia, is responsible for more deaths in the USA than any other disease. The key is to make sure that we treat only abnormal heart rhythms that are fast enough and sustained enough to threaten life.”