TUESDAY, May 14 (HealthDay News) -- Patients prone to dangerously fast heart rhythms may get just as much help and have fewer complications with less-expensive implanted defibrillators that run one wire to the heart instead of two, a new study shows.

Implantable cardioverter defibrillators, or ICDs, are like having an emergency "crash cart" in the chest. The devices can sense runaway heart rhythms and deliver powerful shocks to jolt the heart back to a normal, steady pace.

Studies have shown that the devices cut deaths in patients at risk for sudden cardiac arrest because their heart muscles are too weak to effectively pump blood throughout the body, a condition called cardiomyopathy.

But little evidence exists to help doctors decide when it's better to choose a single-chambered ICD for patients or the more complex dual-chambered model.

The study, published in the May 15 issue of the Journal of the American Medical Association, compared the fates of more than 32,000 Medicare patients who received ICDs, from 2006 through 2009. None of the patients also needed a pacemaker, a device that speeds up a slow heartbeat.

"There is evidence for greater risk of complications. Not clear evidence of benefit. That risk-benefit ratio really doesn't support the routine use of dual-chamber devices for primary prevention," said study co-author Dr. Pamela Peterson, an associate professor of medicine at the University of Colorado at Denver.

About one-third of patients received a single-chamber ICD, in which an electrical lead is attached to the heart's lower right pumping chamber. The other two-thirds got dual-chamber devices, in which wires are attached to the upper and lower chambers of the heart's right side.

After a year, patients who got single-chamber ICDs were no more likely to die or be hospitalized than patients who got the more expensive dual-chamber models. They were, however, slightly less likely to face serious complications, including fluid build-up around the heart or lungs and mechanical problems with the device that required a second surgery to fix.

That was true even after researchers adjusted their results to control for any differences between patients who got single- and dual-chamber devices.

Overall, close to 4 percent of patients with single-chamber ICDs had complications with their devices compared to about 5 percent of patients with dual-chamber models, the investigators found.

The study was observational, which means researchers couldn't prove that the type of ICD was the only reason patients fared the way they did. Though they tried to carefully control their data for important differences between the two groups, other factors they couldn't measure, such as medications people were taking, may have influenced the results.

The study was funded by a grant from the U.S. Agency for Healthcare Research and Quality.

An expert who was not involved in the research praised the study, but said its findings come with an important caveat. The study wasn't able to measure so-called "inappropriate" shocks, instances when the devices misfire after sensing an irregular, but harmless, heartbeat.

Patients describe the powerful jolt as feeling like they're being kicked or hit with a baseball bat. Inappropriate shocks can be a major quality-of-life issue for patients who get them frequently.

Dr. Gregg Fonarow, director of the Cardiomyopathy Center at the University of California, Los Angeles, said the dual-chamber defibrillator may have an advantage in that regard.

"A dual-chamber ICD device, along with its extra atrial lead, is frequently chosen in the belief that it will better discriminate fast heart rates originating in the upper versus lower chambers of the heart and thereby reduce the risk of inappropriate shocks from the device," said Fonarow.

Peterson agreed that not being able to study inappropriate shocks to patients was a limitation of the study. However, she said, "data that has looked at that doesn't demonstrate that there's a benefit of dual-chamber devices in decreasing inappropriate shocks."

Another question they weren't able to address in the study was cost. Single-chamber devices are initially less expensive than dual-chamber models.

A study published in September 2005 in the Journal of the American College of Cardiology said it costs roughly $34,000 for a single-chamber device and about $38,000 for a dual-chamber model.

But that study also found that the cost savings of single-chamber devices can be wiped out if patients need to upgrade to the dual-chamber model because their condition gets worse, a situation that occurs in about 5 to 6 percent of patients in clinical trials.

More information

For more on implantable cardioverter defibrillators, head to the U.S. National Heart, Lung, and Blood Institute.