Life-saving films for the heart
Most cases of sudden heart failure are preceded by a burst of rapid and seemingly chaotic heart activity known as tachycardia (heart racing) or fibrillation (fibrillation). Despite the fact that it is the leading cause of death in the industrialized world, heart failure is still not well understood. New methods of visualizing ventricular fibrillation could lead to the development of more reliable electrical tools and medicines, thereby saving the lives of tens of thousands every year. Two reports in the March 5, 1998 issue of Nature provide a detailed description of the electrical activity underlying cardiac fibrillation. Both research groups used dyes that change their properties depending on the electrical activity. Using video images, they recorded fibrillation activity in sheep, rabbit and dog hearts. They discovered that despite the occurrence of erratic, chaotic activity, there is an unexpectedly strong spatial and temporal order-including rotating waves of electrical activity.
Richard Gray of the State University of New York He alth Science Center and his colleagues found a way to describe the activity mathematically, so that with just a few measurements they can now present a detailed picture of arrhythmic activity. Their calculations can reveal the "sources" of the rotating waves. They indicate that up to 15 rotational patterns are formed in the human heart during fibrillation.
Francis X. Witkowski of the University of Alberta, Canada, and his colleagues were able to distinguish two distinct stages of ventricular fibrillation: In the early phase, helical waves emanate from sources known as "rotors". With prolonged episodes of fibrillation, rotor activity ceased and more three-dimensional activity came to the fore.
Treatment of fibrillation in humans is currently an imprecise science. According to Witkowski, it consists in the fibrillating heart "suffering a major shock, recovering from it, and returning to its normal rhythm. This is the only known therapy for ventricular fibrillation."
"Patients suffering from recurrent ventricular fibrillation are often treated by implantation of an automated defibrillation system," he continues. But "explanations of how the shocks terminate ventricular fibrillation are purely speculative."
The new results pave the way for a more detailed analysis of what happens in heart failure. Eventually, with the recently developed techniques for controlling chaotic systems, a gentler therapy than the usual electroshock treatment could be developed.
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