Medical guidelines say that people with implantable cardioverter defibrillators (ICDs) — colloquially referred to as "heart-zappers" — installed in their chests should avoid intense sports like basketball and soccer, and stick to milder sports like golf and bowling.

However, a new study published Monday in the journal Circulation casts doubt on these guidelines.

"We probably don't need the blanket restrictions in place," said Dr. Rachel Lampert, lead author and cardiologist of Yale University.

Many people receive recommendations to avoid high-intensity sports after getting a defibrillator, but go ahead and play their favorite intense sports anyway.

Defibrillators work by detecting abnormal heartbeats and automatically shocking the heart into maintaining a regular heartbeat. More than 100,000 Americans receive defibrillator implantations each year. Most of those implantations are for older people who don't play high-intensity sports.

Increasingly, however, teenagers and young adults deemed susceptible to arrhythmias are receiving the implants, the Associated Press reports.

The study, which was paid for by three defibrillator manufacturers, found that the health risks of high-intensity sports may not be as bad for people with implanted defibrillators as thought.

The study followed 372 people who continued to play competitive sports after receiving an implant, and found that the devices worked when needed.

"This is good guidance for many of the sports," said Dr. Gordon Tomaselli, former president of the American Heart Association who wasn't involved with the new study. "It should be reassuring that in fact many people can participate."

Tomaselli also cautioned that questions remain, including whether the devices are strained by competitive sports, whether they deliver painful shocks more frequently, and whether they might break following a hit to the chest in a high-impact sport.

Lampert's study explored these questions by tracking athletes with implanted defibrillators for 2 ½ years. Patients included high-school and college athletes, runners, skiers, rock climbers, and people who casually played basketball, soccer, or tennis.

During physical activity, the devices had to fire more often than normal. Seventy-seven people, or 21 percent, received shocks during the study. Of these, 10 percent required defibrillation during sports, 8 percent during other physical activities, and 6 percent while resting. Two-thirds of those who received shocks decided to continue playing their sport rather than quit.

No one died, had to be resuscitated, or suffered shock-related injury.

"Despite the fact that people got shocked, they didn't have anything dangerous happen to them: The device worked," Lampert said.

Tomaselli cautioned that the study failed to address the top concern-whether impacts during contact sports like football and hockey might loosen the implant. Too few of those patients enrolled in the registry to produce meaningful results.

Tomaselli recommended that when patients with defibrillators decide to play intense sports anyway, they should prepare for the extra risk by keeping an external defibrillator close at hand, in case the implanted device fails.

"One of the reasons for having a defibrillator is to restore as much of a normal life as you possibly can," Tomaselli said. For many people, "taking away competitive athletics is taking away a part of them."

If you are wondering how an implantable cardioverter defibrillator will affect your lifestyle, a few points are worth considering, according to the National Heart, Lung, and Blood Institute.

The low-energy electrical impulses emitted by the device are not painful, but may be noticeable as a flutter. However, high-energy impulses may be painful, depending on their strength. They may feel like a thumping or a painful kick in the chest.

Your doctor may want to see you after you receive a strong shock from your device. If you receive multiple strong shocks in a short period of time, visit your doctor or the emergency room immediately.

Once your device is installed, it is best to avoid close or prolonged contact with electrical devices with strong magnetic fields, such as cell phones and MP3 players, certain appliances like microwaves, high-tension wires, metal detectors, industrial welders, and electrical generators.

For more information on living with an ICD, visit the National Heart, Lung, and Blood Institute website.