MONDAY, Nov. 26 (HealthDay News) -- The defibrillators that are implanted in people for instant correction of abnormal heartbeats pose no special risks for heart patients who drive, researchers report.

"What this confirms is what we already thought, that overall there is not a huge risk in this population," said study lead author Dr. Christine M. Albert, director for the Center for Arrhythmia Prevention at Brigham and Women's Hospital in Boston.

About 50,000 defibrillators are implanted annually in the United States. Among the famous recipients is Vice President Dick Cheney, who experienced an irregular heartbeat Monday and was being examined by his doctors.

There have been worries that the shock delivered by the device to correct an abnormal heartbeat might be dangerous for drivers, Albert said.

The study included 1,188 people with such a device, whose formal name is implantable cardioverter-defibrillator (ICD). The patients were followed for an average of 562 days, during which time the devices delivered a total of 193 shocks within one hour of driving -- a rate of one shock for every 25,116 person-hours driving. None of the shocks resulted in an accident.

Overall, the study found that the incidence of having an ICD shock was not higher while a participant was driving. One oddity in the findings was that an ICD shock was twice as likely to be delivered during the 30 minutes after someone drove a car, Albert said, an indication of possible strains caused by driving.

"These data provide reassurance that driving by ICD patients should not translate into an important rate of personal or public injury," the researchers wrote.

The findings are published in the Dec. 4 issue of the Journal of the American College of Cardiology.

"This is very strong evidence that our worries were not based on fact but were theoretical," said Dr. Bruce Wilkoff, director of cardiac and tachyarrhythmia devices at the Cleveland Clinic.

But common sense factors into the safety issue of ICDs and drivers, Wilkoff added. "People who have frequent shocks tend not to drive in the first place," he said. Twenty percent of the ICD recipients in the study did not drive at all, Wilkoff noted.

Current guidelines say that someone who is given an ICD after experiencing a major arrhythmia -- an irregular heartbeat -- should not drive for at least one week after the implant. The one-week restriction also applies for patients who have not experienced an arrhythmia to allow for recovery from the surgery. Driving restrictions then should be decided during consultation with a physician, Albert said.

In practice, that works out to "don't drive when you're not feeling well," Wilkoff said.

More information

Learn more about ICDs from the American Heart Association.