A temperature-sensitive mutant protein could cause sudden cardiac death for some people with heart arrhythmia who become overheated.

Heart arrhythmia — a fast, slow or irregular heartbeat — has several causes, including inheritable mutations in our DNA. These mutations can affect the structure and function of proteins in heart cells. These proteins send electrical signals to the heart to, ideally, keep it functioning properly.

One particular mutant protein is especially temperature-sensitive, according to findings by Peter Ruben, a professor in Simon Fraser University’s department of biomedical physiology and kinesiology.

“We hear of soccer and basketball players who sometimes drop dead in the middle of a game,” Ruben said. “In the sub-population of people who have this particular genetic mutation, temperature can be a trigger for one of these events.”

When muscle cells in our hearts contract rhythmically and in a well-coordinated way, the heart efficiently pumps blood throughout our bodies. When the rhythmic pumping action is disrupted by an arrhythmia, our hearts can no longer distribute blood.

There are different kinds of arrhythmia, including bradycardia (slow heartbeat) and tachycardia (fast), each with their own variations, depending on whether the heart’s atria or ventricles. One estimate suggests two to three per cent of the population in North America and Europe experience atrial fibrillation, a form of tachycardia.

The DNA mutation that creates more temperature-sensitive proteins is rare, but it can produce deadly results when combined with another arrhythmia trigger, such as changes in the acid content of our blood that occur normally as a by-product of exercise and sleep, particularly sleep apnea.

“Generally speaking, if you have this mutation, you will have arrhythmia,” Ruben said. “Now, whether that arrhythmia becomes catastrophic or not depends on the circumstances. Lots of people go through life with mutations and they never know about it.”

Ruben and study co-authors Mena Abdelsayed and Colin Peters think that athletes may be particularly vulnerable.

In extreme conditions, athletes are operating at high body temperatures, and at a low blood PH (high acidity).

Arrhythmias can be detected early through electrocardiogram screening, and also by looking at one’s family history, Ruben says.

“If one has a history of sudden cardiac deaths in the family, or if an individual has a history of fainting, then those are early indicators that there may be problems,” he said.

“Then you can go a little bit deeper and do some genetic screening, and look at the actual genetic code for the proteins that are most suspect. If you find one of these mutations, then it’s possible to take steps to try to prevent these arrhythmias from becoming catastrophic.”