New Way to Shock Heart Back to Normal Effective in Animals

A new kind of electric shock has proved effective in restoring a normal heartbeat in animals, and, if successful in humans, it could represent a gentler alternative to traditional defibrillation.

It's a familiar scene on TV or in the movies – a person's heart is beating rapidly, out of control. It's a potentially deadly arrhythmia. The doctor applies paddles to the patient's chest, applies a jolt of electricity and the patient's normal heartbeat is restored.

Cardiac defibrillation was first demonstrated more than a century ago, and the underlying technology hasn't changed in decades. Now, researchers at Johns Hopkins University in Baltimore think they're on the track of a better way to shock the heart back to a normal rhythm.

Defibrillators work by applying a very brief jolt of high-voltage electricity – direct current – to the heart. The shock lasts only about one-tenth of a second, but Harikrishna Tandri, MD, says that's usually enough to get the heart beating correctly again. "But there have been more and more studies stating that, for one, that high voltage, that brief high-voltage, can cause damage to the heart-muscle cells itself."

And in the case of implantable defibrillators, that brief jolt can be very painful.

As an alternative to a direct current defibrillator, Tandri and his colleagues are developing one that uses alternating current. That's the same kind of electricity most people use at home, that powers lights and appliances. In fact, it's the kind that can actually trigger arrhythmia at the frequencies usually found at home.

"As you get to the frequency of 50 to 60 Hertz, you're more likely to put it into fibrillation," he explains. "But when you go up on the frequency to about 200 Hertz to 500 Hertz, that's when you see this phenomenon that the heart is excited but then doesn't relax."

In effect, that means that heart muscles, which are randomly contracting and relaxing, are frozen in place by the high-frequency alternating current. In tests on laboratory rabbits, the researchers applied the current for about one-third of a second to stabilize the animals' heartbeats.

"So as long as you hold the current, you are trapping the heart cell in whatever position it was in. And when you let go of it, it relaxes back to baseline."

So now, the muscle cells are in the same relaxed condition, and as the heart starts beating again, all the cells are in sync, the way they're supposed to be to effectively pump blood through the body.

Tandri says the next step will be tests on larger animals, probably pigs, which are often used by researchers as stand-ins for humans.

If all goes well, he says the new approach to defibrillation is likely to be used alongside existing direct-current devices. In fact, both direct- and alternating current defibrillators could be be designed into one device – whether it be the full-size units used in hospitals and ambulances, or the miniaturized ones implanted in heart patients.

Harikrishna Tandri's paper on a new way of shocking the heart back to a normal rhythm is published in the journal, Science Translational Medicine.