Exploring Inner Space:

Dr. John Sapp tests heart-mapping technology for finding and fixing arrhythmias

As a cardiac electrophysiologist, Dr. John Sapp’s job is to find and fix electrical short circuits in the heart. These short circuits – caused by aging, heart-attack scarring or structural problems – disrupt electrical activity in the heart. This leads to irregular heartbeats, or arrhythmias, which can be deadly.

Fixing such short circuits requires a procedure known as catheter ablation. “This involves inserting a long wire called a catheter into the heart through a blood vessel, and delivering a surge of electricity through the wire to cauterize the short circuit,” explains Dr. Sapp, associate professor in Dalhousie Medical School’s Division of Cardiology and a member of the new Cardiovascular Research Group. “The challenge is to pinpoint the precise location of the short circuit and deliver the right amount of energy. Too little won’t fix the problem; too much can damage the surrounding tissues.”

Dr. Sapp is testing new equipment that locates short circuits by using a catheter to probe deep within the heart muscle to record its electrical activity. He and his colleagues are also pioneering a non-invasive technique called body surface mapping. “By placing about 120 electrodes on the patient’s upper body, we can create a map of the heart’s electrical activity,” he says. “These maps reveal information about short circuits as well as the overall electrical and mechanical function of the heart. We’re learning that a weak electrical system is linked to inefficient pumping.”

Body surface mapping may also improve cardiologists’ ability to precisely position and program a new kind of defibrillator designed to re-synchronize the pumping action of the heart. Dr. Sapp and colleague Dr. Ratika Parkash are co-heading part of a major national study of re-synchronization defibrillators. “We’re very keen to see if this device will reduce arrhythmias; at the same time we’ll be exploring how arrhythmias may lead to heart failure – and vice versa.”

In addition to his many laboratory and clinical studies, Dr. Sapp is working with Dr. Stacy O’Blenes and others to assess how well skeletal muscle cells repair heart attack damage – and function as heart cells – when transplanted into injured hearts.