Improving heart defibrillation

Researchers in the US have modelled a system where an implantable heart defibrillator focuses in on rogue electrical waves created during heart arrhythmia and dissipates it, preventing cardiac arrest.

When it comes to affairs of the heart, love taps are preferred over love jolts.

That is the result of a team of heart researchers including Igor Efimov, Ph.D., associate professor of biomedical engineering at Washington University in St. Louis, trying to effect a better implantable heart defibrillator. Efimov and his colleagues have modelled a system where an implantable heart defibrillator focuses in on rogue electrical waves created during heart arrhythmia and dissipates it, preventing cardiac arrest.

The jolt is much milder than that produced by presently used implantable devices, in theory sparing the heart any damage from the trauma, lessening the shock to the patient and reducing the amount of energy required for the device to do its life-saving work.

The smaller energy requirement, five to ten times less than what is needed today, opens up the possibility of manufacturing even smaller devices that would last longer and be more comfortable to wear. This would spare cardiac patients the discomfort and danger of having to have a device replaced frequently.

The largest killer of Americans is heart disease, claiming one million Americans annually. About 300,000 of these deaths are attributed to arrhythmia. The first line of defence against arrhythmia is defibrillation, which requires that the victim be near a trained physician and a defibrillator, unless the victim is one of 175,000 patients worldwide who wears an implantable defibrillator.

“Improvements in heart defibrillation devices can save hundreds of thousands of lives,” Efimov said. “Consider that 300,000 Americans die from arrhythmia yearly. Of all stricken, only two to three percent of them survive. Under optimal conditions, the survival rate can be brought up to 50 to 60 percent.”

Eighty percent of the US population wearing defibrillators have had a previous infarction, which plays a role in how Efimov’s model works. An implantable defibrillator functions like a computer, comprised mainly of a battery and large capacitor, and senses electrical activity in the heart. An electrode extends through a vein inside of the heart and continuously records an ECG. If the computer reads an abnormal ECG, it will deliver a strong electrical shot to the whole heart.

When arrhythmia starts, it generates electrical wave vortices that stop the heart pumping. Efimov and his collaborators knew that these little vortices are naturally attracted to scarred heart muscle. Current implantable defibrillators target the entire heart with an electric current of between 3 and 10 joules of energy to disrupt these vortices and shock the heart back to producing normal electrical activity.

“We thought: Why don’t we just affect the important part of the heart that sustains arrhythmia?’ Efimov said. “Instead of shocking the whole heart, let’s shock just the vortices activity around the scar. It’s much gentler and requires less use of energy.”

Efimov and his collaborators calculate the energy output from their mild shock would be half a joule. The shock dislodges and eliminates the electrical vortices, displacing it from the scarred tissue and flinging it toward healthy muscle where it disappears or is eliminated by mild antitachycardia pacing, a therapy that uses small bursts of low-power electrical pacing pulses to return a racing heart to its normal rhythm.

Next for Efimov and Washington University colleagues Vladimir Nikolski, Ph.D., assistant professor of biomedical computing, and graduate student Crystal Ripplinger, are in vitro studies of rabbit heart undergoing arrhythmia where the phenomenon will be photographed with imaging techniques to see how the waves propagate.

If the in vitro studies prove successful, clinical trials in humans will be next.