Studies on Heart Cell Cultures Could Improve ICDs

Originally Published MDDI January 2005

R&D DIGEST

Maria Fontanazza

Research conducted at The Johns Hopkins University (Baltimore) suggests that reprogramming implanted cardioverter-defibrillators (ICDs) may help prevent a rare episode in patients suffering from ventricular tachycardia, or abnormally rapid heartbeat.

The device usually jolts the heart back to a normal rhythm. However, in rare instances, the pulse has an adverse effect and sets off a faster, more hazardous rhythm. The rapid pumping of the heart can become indistinguishable from ventricular fibrillation, a condition that can cause death in minutes if medical attention isn't provided. When this happens, the ICD delivers a painful shock in an attempt to reestablish a normal heartbeat.

Biomedical engineers at Johns Hopkins performed a study on heart cell cultures and found that the cause of these dangerous arrhythmias may be a result of multiarm spirals. The spirals are waves of electrical activity that form when the pulse from an ICD is applied. Upon electrical stimulation, the single wave, or arm, can multiply.

"Multiarm spirals could be a mechanism by which ICDs sometimes accelerate the ventricular tachycardia, making it more dangerous and more likely to turn into fibrillation, rather than stopping it," says Nenad Bursac, assistant professor in the biomedical engineering department at Duke University (Durham, NC). Bursac performed the research and data analysis at Johns Hopkins.

Bursac explains that the regular jolt of an ICD can cause harm by trying to alleviate all the spirals at once. "ICDs could be programmed to try to first annihilate one of the spiral arms and slow down the tachycardia, making it safer, before attempting to finally terminate it," he says.

Based on the experiments, it may be possible to program a pacing rate slower than that of accelerated tachycardia in ICDs. "Current devices always use a faster rate than the tachycardia rate in order to terminate it, which sometimes can worsen the situation," says Bursac.

The optimal antitachycardia algorithm has yet to be determined. "Eventually, it is possible that these studies can improve understanding on how tachycardias get accelerated into fibrillation by rapid pacing, and yield ways to prevent it," says Bursac.

The research was funded by the Mid-Atlantic Affiliate of the American Heart Association (Baltimore) and the National Institutes of Health.

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