When it comes to affairs of the heart, love taps are preferred over love jolts.
That’s the result of a team of heart researchers including Igor R. Efimov, Ph.D., associate professor of biomedical engineering, trying to devise a better implantable heart defibrillator. Efimov and his colleagues have modeled a system where an implantable heart defibrillator focuses in on rogue electrical waves created during heart arrhythmia and busts up the disturbance, dissipating it and 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, 5-10 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 free cardiac patients from the discomfort and danger of having to have a device replaced frequently.
The largest killer of Americans is heart disease, claiming 1 million annually. About 300,000 of these deaths are attributed to arrhythmia.
The first line of defense against arrhythmia is defibrillation, which requires that the patient be near a trained physician and a defibrillator, unless the person is one of 175,000 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 2 percent to 3 percent of them survive.
“Under optimal conditions, the survival rate can be brought up to 50 percent to 60 percent.”
Efimov and his colleagues Valentin Krinsky, Ph.D., and Alain Pumir, Ph.D., of the Nonlinear Institute of Nice, France, published their results in a recent issue of Physical Review Letters.
Eighty percent of the 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, comprising mainly a battery and large capacitor, and senses electrical activity in the heart. An electrode extends through a vein inside of the heart and records an electrocardiogram (ECG) at all times.
If the computer reads an abnormal ECG, it will deliver a strong electrical shock to the whole heart.
When arrhythmia starts, it generates electrical wave vortices — think of little tornadoes dithering about the heart muscle. These are what stop the heart’s pumping.
Efimov and his collaborators knew that these little tornadoes are naturally attracted to scarred heart muscle. State-of-the-art implantable defibrillators target the entire heart with an electric current of 3-10 joules of energy to disrupt these tornadoes and shock the heart back to producing normal electrical activity.
A joule is a standard energy unit equal to one watt of power generated or dissipated for one second.
“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 tornado 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 a half-joule. The shock dislodges and eliminates the electrical tornado, displacing it from the scarred tissue and flinging it toward healthy muscle.
There 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 WUSTL colleagues Vladimir P. Nikolski, Ph.D., assistant professor of biomedical computing, and graduate student Crystal Ripplinger are in vitro studies of rabbit hearts undergoing arrhythmia, where the phenomenon will be photographed with sophisticated imaging techniques to see how the waves propagate.
If the in vitro studies prove successful, clinical trials in humans will be next.