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Understanding the risks for sudden cardiac arrest among athletes — but not overstating them

Toronto, July 15, 2019

By Jennifer Stranges

Dr. Paul Dorian
Dr. Paul Dorian

A runner is in the final stretch of the marathon they’ve trained months for. In the distance awaits their family, friends and some well-earned rest. Suddenly, without warning, they drop to the ground. Medical staff rush to the athlete’s side. “Are you OK?” they ask. “Are you alright?”

These medical emergencies often make the news, especially when they end in death, but a review published in CMAJ by St. Michael’s Hospital cardiologist Dr. Paul Dorian states they’re rare.

The article, which provides a snapshot of the current landscape for screening athletes for potential cardiac issues, emphasizes there is a need to better understand the risks for athletes and whether cardiac events could be better predicted and prevented.

The rate of sudden cardiac arrest during exercise is about 0.75 per cent per 100,000 athletes per year, and researchers are working to understand how to lower that already low rate.

“This area of research aims to understand if sudden cardiac arrests and deaths can be predicted,” said Dr. Dorian. “And if they can be predicted, can they be prevented? But the current research shows that prediction is unfortunately extremely difficult. Even if we can predict that an athlete is potentially destined to suffer from sudden cardiac arrest, the methods of prevention are not yet well enough understood.”

In pre-participation screening with athletes who are at high risk of sudden cardiac death, a physician can identify any history of dizziness, episodes of fainting, and family experience with severe cardiac disease. A physical examination is also conducted to listen to the heart’s rhythm through a stethoscope and measure blood pressure.

It’s the next step in the pre-participation screening process that Dr. Dorian says is not so reliable in predicting cardiac issues.

“Electrocardiograms, or ECGs, provide information, and that information is partially accurate. The information offers value, but there is debate about how much value it offers,” said Dr. Dorian.

“Many athletes who have a cardiac issue are not detected by the ECG. The ECG is not very sensitive – in fact, 90 per cent of the results are false-positives. And when it does detect an abnormality, you need additional testing.”

Dr. Dorian’s review highlights that for every 100,000 athletes screened, about 300 will be identified as possibly at risk. Fewer than one athlete will die suddenly. With those odds, it’s easy to understand why athletes might continue with their sport despite an identified risk. And Dr. Dorian adds there’s also little evidence to suggest that athletes at risk of cardiac issues who discontinue their sport have a reduced risk of death.

“The belief that recommending an athlete restrict or withdraw from their competitive sport to substantially reduce their risk of sudden cardiac death is based on incomplete science,” said Dr. Dorian.

Until research shows a clearer value of ECGs or a stronger connection between pre-screening and reduced cardiac death, Dr. Dorian believes shared decision making is the best path forward for athletes who have cardiac issues.

“What I would say to a patient is this: ‘Based on our best understanding, here is your risk of dying suddenly. If you continue sport, here is your risk. If you stop sport, here is your risk.’ I’m going to give them all the information, discuss how important sport is in their life, and let’s come to a decision together. Let’s talk about how meaningful sport is to you.”

Though prediction and prevention require further exploration, an effective treatment is already available. Dr. Dorian notes that in Japan, where medical personnel patrolled a marathon route on bicycles with AEDs strapped to their backs, there was a 100 per cent survival rate among 28 athletes with witnessed sudden cardiac arrest after prompt resuscitation. His final message is clear: “These events are absolutely treatable.”


This paper is an example of how St. Michael's Hospital is making Ontario Healthier, Wealthier, Smarter.

About St. Michael's Hospital

St. Michael’s Hospital provides compassionate care to all who enter its doors. The hospital also provides outstanding medical education to future health care professionals in more than 27 academic disciplines. Critical care and trauma, heart disease, neurosurgery, diabetes, cancer care, care of the homeless and global health are among the Hospital’s recognized areas of expertise. Through the Keenan Research Centre and the Li Ka Shing International Healthcare Education Centre, which make up the Li Ka Shing Knowledge Institute, research and education at St. Michael’s Hospital are recognized and make an impact around the world. Founded in 1892, the hospital is fully affiliated with the University of Toronto.

About Unity Health Toronto

Unity Health Toronto, comprised of Providence Healthcare, St. Joseph’s Health Centre and St. Michael’s Hospital, works to advance the health of everyone in our urban communities and beyond. Our health network serves patients, residents and clients across the full spectrum of care, spanning primary care, secondary community care, tertiary and quaternary care services to post-acute through rehabilitation, palliative care and long-term care, while investing in world-class research and education. For more information, visit www.unityhealth.to.


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