Sometimes, the heart just stops for no perceivable reason. Sudden cardiac arrest (SCA) is a prevalent hidden killer, even for younger people: 40% of those who die from SCA are under 50 years old.
“SCA is not as rare as we would like it to be,” says cardiologist Elizabeth Paratz, who’s undertaking her PhD at the Baker Heart and Diabetes Institute, Melbourne. “In the last year in Victoria, 750 young people under 50 have suffered an SCA. This is almost exactly five times the road toll over the same time in this age group, yet we hear a lot more publicity about road fatalities in young people.”
Paratz is researching the prevalence and causes of SCA, as well as looking at ways to diagnose it better. There are multiple causes of SCA, and they’re hard to pinpoint in young people.
“The heart may stop due to a whole range of causes – such as the heart pump failing [heart failure, cardiomyopathy], electrical problems [arrhythmia], genetic problems, or a blockage in the coronary arteries stopping oxygen delivery [heart attack],” says Paratz.
One way to keep a closer watch is through the unexplained cardiac death registry. This records all SCA cases as they come, instead of just survivors in hospitals, giving a better image of the scope and number of people who suffer an SCA. The registry has three aims: to identify cases of SCA to help look for patterns; to provide a central resource for affected families to help with screening and psychological support; and to build a biobank of genetic samples.
In its first year, the registry helped identify 750 cardiac arrests, from which there was only a 10% survival rate. This was a vastly higher number than expected, because previous data had relied on information of survivors in hospital, which was only a small component of the cases. Hopefully, the registry will highlight trends that could help identify common causes of SCA.
The difficulty of diagnosis
The causes of cardiac arrest in those under 50 are difficult to identify because of how few people survive and because there may be myriad causes. In people over 50, the most common cause of SCA is due to coronary artery blockages, but this doesn’t seem to be so prevalent in the younger cohort.
“In young people, SCA is more likely to be due to other causes such as genetics and we are still very much in the discovery phase of identifying who is at risk and how we can prevent SCA,” says Paratz. “This is why research in this area is so vital.”
The difficulty is that few people survive an SCA and the normal diagnostic practises can’t be used post-mortem.
“Many of our tests in living people rely on assessing the heart’s function – for example, looking at how vigorously it contracts or how widely valves open,” says Paratz. “Obviously, none of these things can be determined easily after death, and we really can only examine structure rather than function.”
Just as importantly, the sheer number of cases of SCA is a recent discovery; previously, the problem seemed a lot smaller than it actually is.
“The main reason we think this has gone so undetected is that this is the first time all the cases have been systematically identified to get the overall numbers,” says Paratz. “The other main reason is that tragically 90% of people do not even survive to hospital, and so even hospital doctors are unaware of the scale of the problem, as they only see 10% of the patients.”
This might be due to lack of cross-talk between practitioners and scientists, so the data collected from both could be lost or missed. As both a clinician and a researcher, Paratz has a unique perspective that will hopefully bring this information together.
Technologies of the future
The way forward is to improve diagnostic technologies, and to use multiple diagnostics to properly assess the causes of SCA.
“In cardiology, we are really fortunate to be at the cutting edge of medical technologies in many ways,” says Paratz. “We have tests that look inside tiny arteries [coronary angiograms], high-level imaging tests [ultrasound, MRI] and emerging genetic tests. There is also increasing interest in performing tests while someone is exercising to assess the impact of the heart increasing its workload on its efficiency.”
Recently, a paper published in the journal Forensic Science, Medicine and Pathology showed how calcium scoring in the coronary artery might be a useful tool in diagnosing SCA.
This method uses CT scans to measure how much plaque builds up in the arteries. Calcium is a component of the plaque, so it can be used to measure the abundance of plaque that may lead to an SCA. It’s a great tool but it isn’t perfect, because there’s not always time for plaque to build up in young people, even if they have heart disease. Regardless, this method could be used in conjunction with other diagnostics and is extra useful because it can be used post-mortem.
“In our study – using data from 100 Victorian victims of sudden cardiac arrest aged 18 to 50 – we proved this is also a non-invasive technique that can help identify heart disease retrospectively in those who have died,” says Paratz.
Post-mortem diagnostics are useful because of the low survival rate of people suffering from SCA, so there’s an abundance of data to collect. However, diagnostic technologies are only now starting to focus more on post-mortem data, because of how few cases were known before the registry.
“One novel technique we want to investigate next is examining data from pacemakers after death, to see if that can provide helpful insights,” says Paratz. “As part of our registry project, we are also screening family members and collecting genetic samples so they can learn from the clues these samples provide.”
Improved diagnostic tests greatly benefit the biological knowledge needed to improve treatments, which in turn should promote an SCA death-toll decrease in the future.
“Our research is intended to advance the diagnosis of SCA, which still remains a highly fatal and mysterious condition for too many families,” says Paratz. “Advancing diagnosis and improving treatments will help prevent future cases.
“We hope tools like these can help provide the missing pieces of the puzzle when it comes to unexplained cardiac death.”