New type of electrotherapy makes implantable defibrillators less shocking
By Ben Coxworth
November 21, 2012
While regular pacemakers attempt to rectify arrhythmias (irregular heart beat rhythms) using constantly-delivered electric pulses, implantable cardioverter defibrillators do something a bit different. As long as everything stays normal, they don’t do any shocking – when they detect a dangerously fast heart beat, however, they respond by delivering a massive jolt of electricity to the heart. While this may save the patient’s life, it’s also very traumatic and painful. Now, a team of scientists from Washington University in St. Louis may have come up with a solution to that problem.
Ordinarily, implantable cardioverter defibrillators (ICDs) deliver shocks measuring between 600 and 900 volts. Not only is that highly unpleasant for the patient, but it’s enough to damage the heart muscle and may even ultimately be linked to increased mortality. Some patients reportedly go so far as to request that the device be removed, even though they realize that it has previously saved their life.
ICDs work by monitoring the heart beat, specifically looking for a potentially lethal type of arrhythmia known as ventricular tachycardia, in which the heart beats too quickly. When this occurs, they attempt to “reset” the heart by applying a carefully-timed electric shock, with the idea that the heart’s natural built-in pacemaker node will then have a chance to get it beating again at the proper rate.
What the St. Louis scientists discovered was that a series of closely-timed low-voltage shocks actually worked better. Not only did the shocks’ initial application not depend so much on exact timing, but the peak shock voltage could be reduced to just 20 volts. Even when the total energy of all the shocks was added together, the sum was still a fraction of the 600 or more volts that would be delivered by a conventional ICD.
Additionally, it was found that the peak shock voltage could be reduced by a further 50 percent if the ICD’s current was applied in a different location than is currently standard. Presently, the electricity must travel through the chest wall muscles and associated sensory nerves. By placing the ICD’s electrodes on the right ventricle and a nearby blood vessel known as the coronary sinus, however, the current could get straight to the heart. Not only does this require less voltage, but it should also reduce patient discomfort. In fact, the researchers hope that the technology may eventually reach the point that the shocks are small enough to fall below patients’ threshold of pain.
The team, led by Drs. Ajit H. Janardhan and Igor Efimov, have recently received a National Institutes of Health grant to develop a prototype for use in humans. They hope to begin clinical trials soon.