Seeking clues to sudden death
DOES ELECTRICAL INSTABILITY HOLD THE KEY?

Dr.Vijay Chauhan and his team are looking for abnormalities in the heart’s electrical system in arrhythmia patients who die suddenly.

Researchers have long struggled to understand why and how cardiac arrhythmias can cause sudden death in some patients with heart disease, while not seriously affecting others. It’s a question that Dr. Vijay Chauhan and a team at the Peter Munk Cardiac Centre may be getting closer to answering.

Cardiac arrhythmia essentially refers to abnormal electrical activity in the heart. The heart may beat too slowly or too fast, or it may be irregular, or even seem to skip beats. It is the complex nature of arrhythmias that some may seem merely annoying to the person (such as the feeling that their heart sometimes skips a beat) while others have no symptoms at all. However, the sobering fact is that some arrhythmias can unexpectedly lead to sudden death, even in heart patients who seem apparently stable.

“Sudden death from lethal arrhythmia is a major worldwide problem,” states Dr. Chauhan, Director of Electrophysiology Training at the Centre. “In North America alone it is linked to approximately 400,000 deaths a year. This is significantly more than many other better known conditions, such as stroke, lung cancer and breast cancer combined.”

Dr. Chauhan is a clinician-scientist who has been with University Health Network for seven years. After receiving his medical degree from the University of Ottawa, he received specialty training in electrophysiology in London, Ontario and at Duke University in North Carolina.

This training combined with his extensive clinical experience is proving invaluable in his quest to unlock the mysteries of arrhythmia and sudden death.

“What is abnormal about the electrical system in heart patients with arrhythmias who suffer sudden death?” Dr. Chauhan asks. “That is the first question that needs to be answered. We feel that these people have some degree of electrical instability from their heart disease that becomes more pronounced during physical activity or sleep. If that is the case, then we have to find some way to measure this electrical instability during activities of daily living, rather than at one point in time.”

“Once we have identified an index of electrical instability, the challenge then becomes how well and how accurately we can identify patients at the highest risk and, therefore, those who need and will get the most benefits from treatment, such as use of a defibrillator [a device that applies a therapeutic dose of electrical energy to the heart to treat a cardiac arrest].”

“Because resources are not unlimited, the treatment dilemma is to not provide defibrillators to patients who don’t need them, but to ensure we don’t miss those who really do,” Dr. Chauhan adds.

Guiding treatment decisions
The overall objective of the research at the Centre is to develop efficient risk stratification algorithms – a kind of model of the decision pathway that would guide clinicians to the appropriate and timely treatment.

“The team here includes myself, post doctorate fellows and engineers,” says Dr. Chauhan. “We are working with special ECG equipment – a specially designed 120 electrode vest – to provide sophisticated measurement of the heart’s electrical function. Naturally, you can’t measure those signals in the heart itself, but you can through the skin. This is a process called Body Surface Mapping (BSM).”

“To be precise, we are measuring something called T-wave alternans,” he continues. “These are periodic beat-to-beat variations in the oscillations of the electrical signature of the heart. Compare this to a suspension bridge swinging to-and-fro. If the amplitude of those swings continues to increase, the bridge will suffer structural damage and eventually collapse, no matter how strong it is.”

Sudden death from cardiac arrhythmia is a major problem in North America and around the world.

Combining techniques
However, the research at the Centre is taking this a step further by adding MRI images of the heart – specifically scar tissue in the heart, which may indicate where the abnormal electrical activity is arising. “These two techniques already exist, but we are the first centre to combine the two in an attempt to understand arrhythmia and sudden death,” notes Dr. Chauhan.

The team will look specifically at the distribution of the scar tissue – its location and structure (e.g., is it solid or patchy?). “Our work will look at if and how the abnormal electrical function and distribution of the scar tissue are linked,” Dr. Chauhan says. “Any risk stratification algorithm is naturally going to be more accurate and useful with multiple parameters, in this case electrical activity and scar distribution.”

At present, the research, which is being funded by the Heart and Stroke Foundation of Canada and the Canadian Foundation for Innovation, is focusing on perfecting the most accurate way of measuring electrical and scar properties of the heart, and there is still a lot of work to do.

“Once we are satisfied with the accuracy of our measures of arrhythmia risk, we need to test it in a large patient group before it moves to final development and clinical use,” explains Dr. Chauhan. “But we feel this work is exciting and has great potential to help clinicians everywhere to better meet the challenges of arrhythmia and sudden death management.”

A Body Surface Mapping image of the chest (front and back). All images show some degree of abnormal electrical activity in the form of large amplitude oscillations of T-wave alternans (in normal activity the image would be completely blue). Image D illustrates excessive oscillations indicating a high risk of sudden death.

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