Image: Mark L. Riccio/Cornell University µCT Facility for Imaging and Preclinical Research and Flavio H. Fenton/Cornell University
13 July 2011—Watch any TV medical drama and you’ll see a defibrillator in action. During tense moments, defibrillators bring patients back from the brink of death with a dramatic shock. But what you don’t see on TV is the cell membrane, muscle, and skin damage that a defibrillator’s shock can cause. Even implanted defibrillators are painful to patients and damaging to tissue. But gentler devices may be on the way. A research team led by Stefan Luther of the Max Planck Institute and Flavio Fenton of Cornell University has found a new approach that greatly reduces the intensity of defibrillating shocks.
A defibrillator delivers a dose of electrical energy to the heart to fix rapid, irregular, and uncoordinated contractions, which are potentially fatal. This dose resets the difference in voltage between the interior and exterior of the cells in the muscle—a process known as depolarization. A standard defibrillation device uses a single high-energy shock to accomplish this feat, which stops any arrhythmia and reestablishes normal rhythm. "No one knows exactly why, but it requires a voltage gradient of about 5 volts per centimeter to terminate electrical turbulence in the heart, which can require up to 350 joules if delivered as one shock," says Fenton.
Instead of using one big shock, Luther and Fenton’s team delivered a series of five electric-field pulses of less than a joule each to fibrillating dog hearts. The result, described this week in Nature, was an 84 percent reduction in the average amount of energy versus standard defibrillation.
Robert Gilmour Jr., one of the physiologists on the research team and associate dean for research and graduate education at Cornell, says it has been known since the 1970s that placing an electrode directly on an area of heart tissue can stop fibrillation in that region, but that doesn’t do much good for fibrillation in the rest of the heart. Installing electrodes all over the heart might bring the entire muscle back to a normal rhythm, but "such an approach would not be feasible clinically; you can’t make a pincushion out of the heart," he says.