July 15, 2011
For decades, a powerful electric shock has been a standard way to treat someone whose heart has stopped.
But a new study suggests normal heart rhythm can also be restored through a rapid series of safer smaller shocks.
You've probably seen it on TV or in a movie: the patient goes into arrhythmia or her heart stops. The doctor or technician wheels out the defibrillator, applies the paddles, and a powerful electric shock jolts the heart back to a normal rhythm.
Physicist Flavio Fenton of Cornell University says that big shock has a big downside, too.
"If it's external shock like in the movies, you need 280-360 Joules," he says. "That's 1,000 volts, 30-40 amps, for about 12 milliseconds. So that's a really large shock. It is very, very strong. It can damage tissue. And it's extremely painful."
Fenton and his colleagues studied the electrical activity of the heart in a state of atrial fibrillation. That's when the heart is beating very fast and at an unsteady pace, so it can't effectively push blood through the body.
Co-lead author Stefan Luther says they theorized that, instead of one big shock, they could restore normal heart rhythm through a rapid series of smaller shocks.
"So pulse-by-pulse you transform the disordered, asynchronously-beating heart into something that's very synchronously beating, and then normal rhythm can take over," Luther says.
After testing the theory on computer models, they demonstrated that it worked on laboratory animals.
Luther says that what they call "low-energy antifibrillation pacing," or LEAP, should be effective against various causes of fibrillation and in different devices, including implantable defibrillators and in automatic defibrillators designed to be used by lay people.
Devices that use the new LEAP method may not be available for years, until after the system is proved in human clinical trials. Current defibrillators may be adapted to deliver a series of smaller shocks.
Fenton and Luther describe their low-energy approach to cardiac defibrillation in the journal Nature.