Listening in on the whispering heart

A new implantable device that could send an early-warning signal to your doctor before heart rhythm problems arise, may now be possible thanks to research described in the latest issue of the Institute of Physics journal, Physiological Measurement.

More than five million people worldwide have been diagnosed with the heart disorder atrial fibrillation (AF). In AF, the upper chambers of the heart, the atria, quiver and beat rapidly: a condition that can often lead to heart failure and stroke, making AF a major cause of hospital admission. Similarly, another disorder of the heart’s rhythm, ventricular fibrillation (VF) can be just as bad for your health. Biomedical engineer Kityee Au-Yeung of Duke University, in North Carolina, says there is an urgent need to find a safe and effective treatment for AF.

Au-Yeung and her colleagues Chad Johnson and Patrick Wolf, have now developed an implantable electronic device that could help doctors listen in to the whispering heart, and prevent serious attacks of AF before it happens.

AF can often be stopped by a short, sharp electrical shock to the heart, a method known as electrical cardioversion, or defibrillation, a method familiar to anyone who watches TV hospital dramas. The method is designed to resynchronize the heart beat and restore its normal rhythm. Cardioversion is very successful in stopping an AF or VF episode and there are calls for the installation of defibrillators in many public places. But, the electrical shocks delivered to the patient can be very painful.

“AF is not an immediately life-threatening condition, and does not require immediate attention like VF does,” explains Au-Yeung, “Defibrillating an AF episode, if not done properly, could itself lead to a fatal ventricular arrhythmia.”

Au-Yeung and her colleagues are investigating a new version of electrical defibrillation that uses lower energy shocks, which they say would be far less painful for the patient as well as carrying less risk of complications. “We want to determine if AF can be terminated by using a series of lower energy electrical shocks, instead of a single high energy one,” explain Au-Yeung, who is a graduate researcher in Wolf’s laboratory at Duke.

To test the concept the team has designed and built a device that can be implanted under the skin close to the heart, like a pacemaker. Sensors on the implantable cardiac telemetry system pick up the heart’s electrical pattern and send out a continuous radio signal, which is picked up by a notebook computer fitted with a receiver. With this set up, the researchers could record an electrocardiogram directly on to the computer without the need for external sensors and wiring.

This is not a one-way system though. The computer can send a signal back to the device telling it to deliver a short burst of electrical pulses directly to the heart. The sensors measure the effect on the heartbeat and send the information straight back to the computer. “We hope that with this novel system, we can learn more about AF and subsequently, find a more effective way to treat it,” Au-Yeung says.

“A version of this device would most likely be targeted at patients who have already been implanted with a pacemaker or an ICD (implantable cardioverter defibrillator),” adds Au-Yeung, “For example, the remote monitoring and low energy pacing techniques could be incorporated into a pacemaker design.” Remote monitoring from a patient’s home could alert their doctor to an AF episode and the doctor could then administer appropriate pacing therapy and monitor its effects.