Dan Arking | A New Genetic Risk Factor for Sudden Cardiac Death
In the Genes: Sudden Cardiac Death From Extreme Exercise
In people with this arrhythmia gene, extreme exercise can cause irregular heartbeat, heart failure, and even sudden cardiac death.
By Jennifer J. Brown, PhD
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Endurance exercise and frequent exercise are dangerous for people with an inherited heart rhythm condition known as ARVD/C, found a study published in the Journal of the American College of Cardiology. When people with this type of arrhythmia compete in sports, they have a five-fold increased risk of sudden death, according to researcher Cynthia A. James, PhD, from the Johns Hopkins ARVD Program in Baltimore.
The gene mutation that causes the ARVD/C heart arrhythmia is related to the connections between heart cells, which have to beat together synchronously for a normal heartbeat. For people with the mutation, a defect in cell-to-cell connections within the heart alters the heartbeat during exercise. This change can cause a life-threatening disruption of the heart’s normal rhythm.
How much is too much, when it comes to exercise? Dr. James said it is hard to know for the general population, but people with arrhythmias face known risks. “We looked at competitive team sports — vigorous aerobic exercise — and risks were considerably higher for arrhythmia and for heart failure. We saw that the amount of risk spiked at higher levels of exercise," she said. For those people at highest risk, exercise of more than 150 hours each year was riskier, according to James.
Rising Heart Risks of Vigorous Exercise
To make sense of the risks people with the inherited genetic condition and their families may face during exercise, James and other investigators at Johns Hopkins interviewed 87 members of an ARVD/C disease registry about their exercise patterns throughout their lives.
What they found was surprising: Not only people with the mutation, but also family members who were carriers of the gene, experienced dire heart health risks associated with exercise.
These results point to the importance of restricting exercise for people with the arrhythmia condition, and for ARVD/C gene carriers in the family as well.
“Certainly in the clinic, we strongly recommend that healthy carriers restrict vigorous exercise and competitive exercise,” said investigator James. This includes long and middle-distance running, competitive swimming, basketball, soccer and distance cycling, among other popular aerobic sports.
Did the first person to run a marathon in Greece — who died when he finished — have an arrhythmia? “We may never know for sure,” said study investigator Dr. James, but for competitive athletes today, “Pre-sports screening can tell us who is most at risk.”
Because a large number of young people in competitive sports have died from sudden cardiac death in Italy’s Veneto region, pre-sports cardiac screening is now vigorous there — and as a result, the death rate has gone down, James noted.
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Arrythmia Gene Screening in Our Future
In the United States, we are years away from routine genetic testing for the arrhythmia gene ARVD, which affects about one in 5,000 people. Many more people are carriers of the mutation and simply don’t realize it. They too are at risk for heart health problems when participating in vigorous exercise.
Experts say it is too early in their understanding of the risk to implement screening across the board, but a genetic screen for the issue may be in our future.
According to cardiologist Paul D. Thompson, MD, Chief of Cardiology at Hartford Hospital in Hartford. Conn., screening for the arrhythmia gene mutation in clinical practice is not usually done. “I don’t think anyone gets the screening routinely,” Dr. Thompson said. “If a person had a lot of arrhythmias and we had a suspicion, we might screen, but screening is not that common.”
“The problem with genetic screening is you often find variants of uncertain significance, and you don’t know what those things mean," Thompson added.
As James explained, “The genetics is still being uncovered. Genetic testing for this condition is new.” Right now, James added, the Heart Rhythm Society (HRS) recommends genetic testing for members of a family when one person in the family is diagnosed with arrhythmia caused by the ARVD mutation.
The first genetic screen to identify the condition in a family is expensive, costing approximately ,000, according to James. Once a family is known to carry a mutation, the subsequent screen for each family member costs between 0 and 0, she said.
Extreme Exercise: Too Much of a Good Thing
James noted that the new study was small and further work is needed before generalizing the arrhythmia-exercise risk findings to a broader population.
How much exercise is too much for those in the general population or for athletes who don't have documented arrhythmia risks is something that “we don’t know the answer to,” said Thompson.
“There have been reports of increased atrial fibrillation in athletes,” he added. Not everyone who trains for endurance sports develops heart arrhythmia. “Atrial fibrillation varies with inheritance, how much exercise they are doing, and how many years they have been doing it," he said, adding that, “In endurance sports and in older athletes, the risk of atrial fibrillation increases.”
One example is a June 2013 study of cross country skiers participating in a 90-kilometer race, published in the European Heart Journal. Skiers who had faster finishing times and a higher number of completed races also had higher risks of heart arrhythmia, wrote Kasper Anderson of Uppsala University in Uppsala Sweden, the author of the study.
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