Scientists solving the big mysteries of the heart

Sydney’s City2Surf running event is usually a happy occasion, enjoyed by 80,000 runners who jog 14km from the CBD to Bondi Beach. But in 2014, it was marred by tragedy when a fit and healthy 27-year-old man, Chris Head, went into cardiac arrest metres from the finish line, collapsed and died.

The tragic case is a classic example “of how a genetic heart disease can lead to sudden death with no prior warning,” says Professor Chris Semsarian, Director of the Genetic Heart Disease and Hypertrophic Cardiomyopathy Clinic at Royal Prince Alfred Hospital in Sydney.

About 160 Australians under 35 die from sudden cardiac arrest every year. For roughly half of these “the first presentation of their disease is death,” explains the cardiologist, who has been working for several decades to understand why these deaths occur and what can be done to prevent them.

Life-saving, personalised medical treatments

Professor Semsarian, also head of Molecular Cardiology at the Centenary Institute, is among a cluster of NSW researchers now unravelling the mysteries of the heart and using the knowledge gleaned to develop life-saving, personalised treatments. Other colleagues are studying congenital heart problems in babies or the later impacts on adults that survive childhood heart surgery.

Professor Semsarian says he first became interested in understanding sudden cardiac death while he was a trainee in the 1990s. “I sat down with a mum and dad who had just lost their 21-year-old son. He’d been running along a beach, previously healthy, never had a symptom in his life,” he says. “When they asked me why their son had died suddenly, I didn’t know the answer.”

The budding cardiologist soon realised there was very little knowledge on the topic. “I had no answers and the world had no answers. I thought I should devote my life to finding some,” he says.

Work by Professor Semsarian and others in the intervening decades has shown that sudden cardiac deaths in young people are often due to genetic or inherited defects. “Today we know about hundreds of genes involved in heart problems that can lead to sudden death,” he says.

Screening for genes behind faulty hearts

The faulty hearts fall into three main types: ‘cardiomyopathies’, where the heart muscle is too thick or thin, or doesn’t pump properly; ‘rhythm disorders’, where the heart’s electrical system is faulty; and congenital heart diseases, where the hearts of babies don’t develop properly during pregnancy.

When a patient dies of sudden cardiac arrest, or is diagnosed as at risk, they and their family members can be screened for these genes and may then be put on treatments or a preventative program. This might include taking beta blockers, avoiding strenuous sports, or having a small ‘implantable cardioverter-defibrillator’, or ICD, implanted in their chest.

“This protects the heart and delivers a shock if it detects a cardiac arrest,” says Professor Semsarian. “In genetic heart diseases, it’s the only intervention that actually stops young people dying.”

The ultimate goal would be high-tech genome-editing techniques that could correct the faults in peoples’ DNA. Applying these technologies in humans is still years away, however, he says. “We haven’t done it in humans yet, but we can certainty do it in cell models and animal models.”

Perfectly fitting heart tubes

Other experts are developing precision medicine for different kinds of heart abnormalities.

Professor David Winlaw is a researcher at the University of Sydney and also Head of Paediatric Cardiothoracic Surgery in the Sydney Children’s Hospitals Network. He is developing ways to improve the lives of children born with congenital heart diseases.

Many babies he operates on have only one artery or outflow from their hearts instead of two, which is corrected using human donor or animal tissue. Unfortunately, these donor tissues don’t grow with the child, and must be replaced many times over during a patient’s childhood and adolescence.

Professor Winlaw’s team is developing a tube made of a novel biomaterial to “perfectly match the anatomy of the individual patient” and encourage growth of the body’s own tissues. This material would eventually dissolve away, leaving a tube of living tissue that would grow with the child.

“It’s an important step towards making something…that can take them into the future,” he says. “If we can save two open heart operations in childhood, that’s a significant improvement to that child and family’s life.”

He’s also screening the genomes of children with congenital heart diseases to find statistical patterns in their DNA that might indicate they’re likely to suffer complications following heart surgeries – a problem that currently affects one in five patients for some kinds of operation.

“If we can understand – ideally, even before the baby is born – that they will be susceptible…we can manage them differently and put in place things to improve their growth and development,” says Professor Winlaw. “I think we could halve the incidence of these complications.”

Uncharted territory for survivors

One in every 110 babies is born with abnormalities such as malformed chambers and holes in the heart, in addition to the problems with the arteries. About 90% of these kids with congenital heart diseases now make it to adulthood, but the surgeries that allowed this only began routinely in the 1960s.

David Celermajer is the Scandrett Professor of Cardiology at the University of Sydney and the Director of Adult Congenital Heart Services at Royal Prince Alfred Hospital. He heads up the team that looks after about 5000 adult survivors, some of whom are now over 50 years old.

“By the 1980s, the first few young adults with repaired heart disease came onto the scene. Prior to that, unfortunately, most passed away. So, this is an entirely new population and it is growing rapidly,” he says

Professor Celermajer is studying them to understand problems that might inform surgeries being performed on children today. “We are feeding back to the heart specialists ways of treating the children that will lessen their complications on the basis of what we see in young adult life,” he says.

Overall, the highly targeted therapies under development by researchers in NSW are creating a very much brighter future for children and young adults who were born with defects in their hearts.

By John Pickrell