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Heart-Felt Chaos

In almost every episode of the TV hospital drama ER, doctors rush to a gurney, yell "Vfib!" and slap electric paddles onto a patient's chest. It's a drama that occurs far too often in real life as well: A patient's heart, damaged by a blocked artery, stops its regular beating and begins fibrillating--convulsing without pumping blood. But a study in the current issue of the Journal of Clinical Investigation suggests that this kind of heart attack, called ventricular fibrillation, could be foreseen and perhaps even averted. The key: monitoring the electrical activity of the heart for signs of the mathematical patterns known as chaos.

The regular beat of a normal heart results from waves of electrical activity that tell muscle cells to contract. Usually, the wave starts at the bottom of the heart and ceases at the top. But in a damaged heart, the wave sometimes spirals back into the muscle, where it breaks down into many smaller waves that convulse the heart. "It writhes like the surface of boiling water," says Alan Garfinkel, a cardiologist at the University of California, Los Angeles, "and then you're in trouble."

These convulsions seem so disorderly that cardiologists have traditionally dismissed them as random. But in the early 1980s, researchers began to find hints of chaotic behavior in isolated heart cells. Now Garfinkel and his team have seen chaos wracking the whole heart. The reseachers implanted electrodes into a dog heart and into diseased human hearts that had been removed from heart-transplant recipients. To get a clearer signal, they slid electrode-bearing catheters into the hearts of five patients suffering from a less life-threatening arrhythmia called atrial fibrillation. "It's like recording the orchestra from inside the pit, rather than having your ear pressed to the wall of the building," says Garfinkel.

What he and his colleagues recorded was a signature of chaos: a behavior that is essentially unpredictable but, unlike simple randomness, can be described by simple equations. "There's order within the mess," says Garfinkel. Richard Verrier, a cardiac physiologist at Harvard Medical School, agrees, calling the work "the strongest case yet" that chaos plays a role in sudden heart attacks.

What's more, just before dissolving into chaos, the electrical signals in the heart go through a recognizable "prechaotic stage" lasting up to a few minutes in which the voltage spikes on the electrogram begin to deviate from their normal periodicity. "That's the amazing thing; it really knocked us over," says Garfinkel. These patterns, he says, could eventually provide a warning signal for the onset of ventricular fibrillation. They might also hasten the development of smarter pacemakers, which could recognize that fibrillation is likely and nudge the heart back into line.