Originally Published MDDI October 2004

R&D DIGEST

Heather Thompson

Internal cardioverter-defibrillators (ICDs) have become rather mainstream in the medical device world. But these lifesaving devices are constantly being upgraded and perfected by engineers to make them easier for surgeons to implant and easier for patients to live with.

A defibrillator acts as a miniature computer that employs application-specific integrated circuits to monitor, regulate, and control the delivery of electrical impulses to the heart. When it detects a potentially life-threatening cardiac fibrillation, an ICD applies a high-voltage pulse between two electrodes connected to the heart. The pulse can be as high as 800 V, with the resulting current (during a few milliseconds) reaching several tens of amperes. By administering an electric pulse, the defibrillator coordinates the individual muscle twitches to form a regular heartbeat.

A group of scientists from Institut Non Lineaire de Nice (Valbonne, France) and the biomedical engineering department of Case Western Reserve University (Cleveland) may have found a way to stimulate the heart without needing high levels of voltage. Such a device could potentially reduce the size of the defibrillator and alleviate a patient's anxiety and pain that comes from such a high-voltage shock.

To design the device, researchers took into account the tendency for electricity to get trapped around objects that are different from surrounding tissue. Scar tissue, an inevitable by-product of heart attacks, often serves as a vortex for such electric waves in cardiovascular cells, much like eddies in a pool of water. Dispersing these eddies allows the normal voltage to activate cells. A small volt can be used to dispel the so-called pinned waves, but, until now, the electrode had to be near the dead zone.

By analyzing electric field position with computer models, the researchers found that they could deliver an electric pulse to the core of a pinned wave. They were able to do so even if the wave's exact position was unknown and direct access was impossible.

By manipulating the rotating electrical waves created from scar tissue, the scientists believe that they can use a lower-than-normal amount of energy—approximately half a joule—to counteract fibrillation. Delivering a small electric pulse into the core of a wave unpins and removes the electricity surrounding scar tissue, thereby reducing the need for further energy to resynchronize heart cells.

According to a review by psychologists at Tel Aviv University, (Tel Aviv, Israel) a common fear for patients coping with an ICD is triggering a shock and feeling a sensation during it. However, most patients say they adjust and grow accustomed to the device. The researchers are currently collaborating with Medtronic Inc. (Minneapolis) and hope to have a viable defibrillator developed within three to five years.

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