What are the chances of your heart suddenly stopping? Scientists think they can tell

A world-first online database will help people calculate their risk of sudden cardiac arrest in a milestone for the use of genetic sequencing to diagnose and treat potentially deadly conditions before symptoms appear.

Long QT syndrome, a heart rhythm disorder causing fast, chaotic heartbeats, is one of the most common inherited heart diseases in Australia, but often people find they have it only when they collapse and go into sudden cardiac arrest. For about 10 to 15 people every year, this is fatal.

Jess Berenyi credits her then-infant son Hamish for saving her life after his screams helped pull her back to consciousness. Credit: Justin McManus

“It has the potential to be lethal, and it is something for which there is a potential treatment,” said Professor Jamie Vandenberg, whose team at Sydney’s Victor Chang Cardiac Research Institute tested hundreds of specific gene mutations associated with the condition to predict which were most likely to lead to sudden cardiac arrest.

The discovery means anyone who has had a genetic test, such as pre-pregnancy screening for hereditary conditions, will be able to crosscheck their genetic results with a public database to see whether they are at risk of sudden cardiac arrest and, if so, the likelihood of that risk eventuating.

Jess Berenyi had her first blackout episode aged 14, but it took doctors 20 years to discover the cause – after she collapsed while breastfeeding her then three-month-old, Hamish.

“His screaming pulled me out of the episode,” Berenyi said. “I believe that Hamish saved my life.”

She was taken to hospital, where a specialist noticed her QT interval – the line on an electrocardiogram showing the time it takes for the heart’s ventricles to contract and recover – was longer than it should be. She was diagnosed with long QT syndrome, and eventually had a defibrillator implanted to detect abnormal heart rhythms and deliver a shock if needed.

Although Berenyi fortunately did not pass the condition onto her son, genetic testing revealed her mother, grandmother, and several aunties and cousins all carried the gene.

Hundreds of gene mutations are associated with long QT syndrome, but the research, published in the journal, Circulation, on Tuesday, is the first time scientists have been able to predict the severity of each individual change.

Vandenberg’s team investigated more than 500 gene mutations and variants affecting the function of the hERG potassium gene channel – the “gatekeeper” regulating the flow of electrical signals across the cell.

By running electrical tests through these channels and matching the results with the patient’s real clinical records, they discovered some mutations reduced the function of proteins by up to 90 per cent, resulting in a 13-fold increase in the risk of arrhythmia or sudden death.

Berenyi said knowing the individual risk associated with her gene when she had been younger could have helped her avoid more episodes.

A diagnosis has not stopped Berenyi’s episodes – her most recent coming on a long-haul flight from Canada – but it has helped her avoid certain medications and types of exercise that elevate her risk.

“The reality that I could die, I have to face that every day,” she said. “To have a better understanding of how at risk you might be, it just helps you to make those decisions … to try and keep yourself safe.”

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