Physicists and other researchers are developing ways to describe human heartbeats mathematically, with the ultimate goal of intelligently altering heart rhythms electrically to treat cardiac disorders. A research team from the Georgia Institute of Technology and Emory University will begin human testing this spring on an experimental technique that may help control irregular cardiac rhythms by altering chaotic patterns in the electrical signals controlling the heart.

If successful, the technique could lead to the development of a new type of implantable device that would be smaller and apply less electrical energy than the defibrillators now used to correct the erratic heartbeat of atrial fibrillation. Atrial fibrillation is the most common arrhythmia requiring treatment intervention, affecting five percent of all individuals over 60 years of age, according to Jonathan J. Langenberg, an Emory cardiologist.

Existing defibrillators use large electrical shocks to overwhelm harmful cardiac rhythms and return the heart to a normal pattern. The new technique will apply small electrical signals through an electrode threaded into the heart at carefully chosen points in the heartbeat cycle. The researchers believe the small signals will encourage the heart itself to correct the irregularities.

"The analogy would be judo," said William L. Ditto, a physicist in the Applied Chaos Laboratory at Georgia Institute of Technology who described the research during a Wednesday morning session. "If a very large person attacks you, you could try to overpower him if you had enough energy--which is typical of the way we now do defibrillation--or you could try to make their violence work in your favor. We are hoping this technique will use the energy of the harmful behavior to move the heart back into good behavior. Rather than fight the chaotic pattern, we want to have the chaos do most of the work for us."

Chaos theory techniques are also being explored in the treatment of chaotic patterns of brain activity, such as certain types of epileptic seizures. Because brain activity, like the heart, is naturally chaotic, the objective again is to take a system that is pathologically regular and kick it back into a more healthy chaotic state, rather than trying to regularize an irregular chaotic system. "The idea is that a certain amount of chaos may be good for you, while a large amount may be very bad," said Ditto.

His team first demonstrated the possibility of applying their chaos-control techniques to physiological and biological systems in a series of experiments with rabbit heart tissue two years ago. While unpredictable in the long-term, chaotic systems are predictable in the short-term, and it is this feature that Ditto hopes to exploit to eventually enable medical personnel to intervene more quickly and effectively during cardiac arrests.

In addition, scientists at McGill University in Montreal are working with cardiologists to better understand the chaotic rhythms of the heart in order to improve diagnoses of disease. According to physicist Leon Glass, one third of Americans die from sudden cardiac attacks, some prematurely due to inadequate medical treatment.

Chaos has been a popular field of study among physicists and mathematicians for more than two decades, but the rapid advances in computer speed and data storage are enabling researchers like Ditto to study heart rhythms in real time, and to react to irregularities as they occur. "Computers made possible the study at a fundamental level of things that had been analytically impossible," said David Campbell (University of Illinois, Urbana-Champaign), editor of the journal CHAOS.

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