But in the study published in the Journal of the American Heart Association they say it is safe to walk straight through.

The implanted devices are designed to tell when the heart has stopped and issue a shock to restart it.

But there were fears that prolonged exposure to the electronic beam in security gates could fool the defibrillators into delivering an unwanted electric shock to the patient.

Dr Douglas Zipes said: "There is absolutely no danger from a slow stroll through the gates, even if it takes 10 or 15 seconds.

"One should not lean on or linger in theft detection devices because adverse effects can happen, no question."

An estimated 400,000 people worldwide have the defibrillators implanted, and there have been three reports of the security gates causing them to fire unnecessarily.

The effect is described as a "giant mule kick" in the chest.

But in each case the patient had lingered in the machine, and in one had leant on the gate.

In tests on 169 patients, the researchers, from Indianopolis Medical School found no problems.

However, when the patients received "extreme" exposure to the beam, 19 had evidence of interference with defibrillators - in seven the incidents were described as "significant".

Patients are told to warn people scanning them with hand held detectors in airports to warn security personnel that they have the devices implanted.