Jewish World Review Jan. 31, 2003 / 28 Shevat, 5763


Defibrillator result without the harm

By Charles Choi

http://www.NewsAndOpinion.com | (UPI) Instead of powerful electric jolts from defibrillator paddles to restore a normal heartbeat, a more gentle rhythmic stimulation might accomplish the same thing without causing unnecessary harm to the patient, new research released Thursday suggests.

Using complex mathematical models, a team of European scientists determined that a heart beating irregularly -- or stopped in a potentially fatal condition called cardiac arrest -- could be restored to normal function through precise electrical stimulation. This stimulation could be much less powerful than the jolts of up to 300 volts now delivered to patients with stopped hearts.

"I can imagine there might be certain (more precise) ways to control the properties of cardiac tissue," researcher Alexander Mikhailov, an applied mathematician and theoretical physicist at the Fritz Haber Institute in Berlin, told United Press International.

Healthy hearts beat at a steady pace because electrical pulses generated inside the heart spread in waves through cardiac muscle. However, this regularity can be replaced by erratic electric excitation patterns that can lead to fibrillation -- a rapid, uncoordinated twitching of the heart.

Mikhailov and colleagues theorized that three-dimensional excitation patterns called "scroll waves" played a crucial role in such heart problems.

"If you stack spirals, they take on the form of a scroll. Imagine a piece of paper that you roll up (at an angle), for instance," explained physical chemist Ken Showalter of West Virginia University in Morgantown.

A scroll wave radiates outward from a central line. "If (it) became unstable, you could imagine it snaking about, twisting around and coming back on itself and fragmenting, closing into rings," Showalter said. This same type of chaos -- in the form of turbulence in the heart's excitation patterns -- leads to fibrillation.

In findings appearing Jan. 31 in the journal Science, Mikhailov and colleagues at the University of Barcelona in Spain found that in computer models they could, selectively, suppress or increase heart turbulence by causing weak rhythmic perturbations at certain frequencies.

Specifically, at a frequency slightly less than the rate at which the spiral wave normally turns, the chaos is quieted, making the scrolls shrink and disappear. A greater-than-normal frequency makes stable scrolls expand and become turbulent.

"This is a very nice and important piece of work. Anytime you talk about a three-dimensional medium, the computations become much more demanding," Showalter said. "It's a very nice proof of principle that you can control this type of turbulence with periodic perturbation. I think it's really cool."

Mikhailov cautioned that researchers still need to develop strategies for how to perturb real heart tissue in this way. "Similar investigations should further be undertaken for realistic models of the cardiac tissue and, eventually, experiments should be performed," he said.

One concern is how to perturb the heart in a completely uniform manner.

"Who knows? Maybe there could be a pacemaker-type device," Showalter said. "Instead of the using these paddles to defibrillate with a massive shock, maybe there could be a nice alternative to that. But that's a long way away. This is just a proof of principle. First they'll want to look at more realistic models of the heart."

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