"Rather than fight the chaotic pattern, we want to have the chaos do most of the work for us." -- Dr. William L. Ditto
A TEAM OF RESEARCHERS from the Georgia Institute of Technology and Emory University has begun limited human testing 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 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.
"We will be trying to actively put signals into the human atrium to see if we can achieve partial control of a heart undergoing atrial fibrillation," explains Dr. William L. Ditto, a physicist in Georgia Tech's Applied Chaos Laboratory. "If the technique is successful, we would try the engineering challenge of miniaturizing the equipment to make it implantable."
Existing defibrillators use large electrical shocks to overwhelm harmful cardiac rhythms and return the heart to a normal pattern. The technique being developed by Ditto, Emory University cardiologist Dr. Jonathan J. Langberg, and Dr. Mark L. Spano from the Naval Surface Warfare Center will apply small electrical signals to 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," Ditto explains. "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."
Starting this spring, Ditto, Langberg and Spano will study and attempt to treat atrial fibrillation in 10 to 20 patients by administering control signals through an electrode threaded into their hearts. If successful, they may be able to apply the technique to ventricular fibrillation.
"Atrial fibrillation is the most common arrhythmia requiring treatment intervention, affecting 5 percent of all individuals over 60 years of age," says Langberg, professor of medicine (cardiology) and director of electrophysiology at Emory University School of Medicine.
"The rhythm disorder may cause palpitation, shortness of breath and weakness, and may predispose those affected to blood clots and stroke," Langberg adds. "Medications are incompletely effective and associated with frequent and sometimes dangerous side effects. A chaos control pacemaker would be a very useful option for treatment of patients with episodic atrial fibrillation."
At the same time the study of atrial fibrillation is beginning, Ditto and Spano are collaborating with University of Alberta cardiologist Dr. Frank Witkowski to study chaos control of ventricular fibrillation in animal hearts. Plans also call for a study of ventricular fibrillation in diseased human hearts removed from transplant patients.
In August, Ditto was part of a team reporting early success at altering chaotic patterns of brain activity similar to those associated with certain types of epileptic seizures. That work could one day provide a new option for severe cases of epilepsy that now can only be treated with brain surgery.
That research team, which included Spano and Dr. Steven J. Schiff from the Children's National Medical Center, studied three separate techniques for altering chaotic patterns observed in slices of tissue from the hippocampal section of the rat brain. Published August 25 in the journal Nature, the report also described the application of "anticontrol" techniques for maintaining chaotic patterns that appear to be helpful in normal brain activity.
"In typical control, we try to take a chaotic system that is highly irregular and make it regular," Ditto explains. "In the brain, we tried to take a system that is pathologically regular and kick it back into a more healthy chaotic state. The idea is that a small amount of chaos may be good for you while a large amount may be very bad."
Anticontrol may also be applied to the heart, where researchers speculate that some irregularity between beats is necessary to maintain healthy rhythms.
As in other work, the chaos researchers tested "anticontrol" in mechanical systems before attempting to apply it to biological systems. While there are many obvious differences, the similarities have contributed to rapid advances in both physics and biology. "The interplay between physics and biology has been very fruitful for us," Ditto adds. "You really can reverse engineer techniques from biology and apply them to engineering."
One of the primary missions of Ditto's Applied Chaos Lab is to facilitate the crossover of important technologies between medicine, biology and physics. One such example is an ongoing effort to use chaos control to encode information into brain tissue and electronic neural networks in an attempt to both better understand the working of the human brain and to make electronics as flexible as biological systems.
In mechanical systems, new research shows that chaos can be maintained by irregularly applying stimuli on the average of once every thousand seconds. The key is knowing exactly when to apply the stimulus, and chaos researchers have established analytical techniques for determining that.
The chaos research has been sponsored by the U.S. Office of Naval Research, by the pacemaker company Medtronics, Inc., and by the Georgia Institute of Technology. Patented techniques for cardiac control have been licensed to Medtronics and a company called Control Dynamics, Inc., that has been formed by Ditto and others to apply and commercialize chaos control and antichaos control techniques in biology, medicine, electronics and engineering.
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