People, who exercise vigorously and have long QT syndrome (LQTS), an inherited disorder of the heart’s electrical system that leads to chaotic heartbeats, do not have a higher risk of adverse cardiac events compared to those who exercise moderately or not at all, a National Institutes of Health (NIH)-supported study has found.

The study, published in Circulation, helps answer a longstanding question about whether vigorous exercise increases the risk for life-threatening abnormal heartbeats, called ventricular arrhythmias, in individuals being treated for LQTS.

The new data also help fill an evidence gap that often has led to recommended restrictions from exercise for those with the inherited disease.

The observational study, funded by NIH’s National Heart, Lung, and Blood Institute (NHLBI), enrolled 1,413 individuals with LQTS at 37 medical sites in five countries from May 2015 to February 2019.

The study participants were aged 8-60 and either carried the gene that causes LQTS or were diagnosed based on an abnormal EKG reading.

Importantly, at the time of the study, all participants were being treated for their condition with medication or surgically fixed devices such as an implantable cardioverter-defibrillator (ICD), which can detect arrhythmias.

Fifty-two percent of the study participants were already vigorous exercisers, such as runners, while the other 48% either participated in moderate exercise, such as walking or yard work, or did not exercise.

The researchers then followed the groups for three years and looked at the occurrence of four main cardiovascular events during that period: sudden deaths, resuscitated sudden cardiac arrests, arrythmias that were treated by an ICD, and the most dangerous type of fainting caused by arrythmias, known as arrhythmic syncope.

Based on a unique study design called non-inferiority, which asks if one treatment is equal to another – in this case is vigorous exercise equal to moderate exercise – the results were not statistically significant.

The researchers found that in individuals with LQTS who exercised vigorously, the overall rate of adverse cardiac events was low, with 2.6% experiencing a likely LQTS-triggered cardiac event during the three-year follow up period. Notably, the outcome was similar for those exercising moderately or not at all, with 2.7% having a cardiac event.