The case for scanning the missing middle in heart disease

If you have lost a family member early to heart disease, you will want to know your own risk. A new Australian study that tracked patients for three years shows what you can do if you are in the ‘intermediate’ zone.

Risk of cardiovascular disease is usually calculated for populations, not individuals. Illustration: iStock

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About 1.3 million adult Australians live with heart, stroke or vascular disease, a major cause of death and disability, according to the 2022 National Health Survey.

Following years of falling cardiovascular disease death rates, these have increased since 2020. It’s not a good picture for a disease that has become largely preventable.

How could we do better? Perhaps the first thing to consideris whether mostpeople know enough about their risks, or whether our systems are sufficient to solve this problem.

The Baker Institute’s recent community-based recruitment for a cardiovascular risk reduction trial in Melbourne’s west identified that half of the eligible, middle-aged patients had never had a cholesterol test or risk evaluation. Improving the availability of the Heart Health Check may increase access, and other steps could include broadening the healthcare providers able to assess and manage risk, including pharmacists and nurses.

About 1.3 million adult Australians live with heart, stroke or vascular disease. Picture: Getty Images

But there is perhaps an even bigger concern, that the risk calculators we use are not up to the task of predicting risk in individuals. The initial cardiovascular risk calculator was derived from epidemiologic work after World War IIin Framingham, Massachusetts. Subsequently, many others have been developed, but the commonality is that they apply risks defined in populations, to individuals. That works quite well in people at high risk (who need preventive treatment) or low risk (who do not), but it leaves a large group (up to 40 per cent of the population) at “intermediate risk” (say, 1 to 2 per cent risk per year of a major event), where the value of treatment is undefined.

Indeed, the notion of being able to attribute risk on the basis of risk factors is flawed on an individual level. We all know people who live apparently risk-free lives who succumb to a heart attack, and others who smoke and don’t take an interest in their health, but remain untroubled by illness into their ninth and 10th decades. Clearly, some processes of vascular injury (or protection mechanisms against injury) are not measured by the tools we currently use.

The interesting, and perhaps provocative fact is that we no longer need to rely exclusively on guessing risk. We can actually measure the presence and extent of calcium (a marker of plaque, with coronary artery calcium scoring) – or indeed plaque itself – using a CT scan of the coronary arteries. The people who should have such a test are those who have the greatest problem with coronary disease – those in rural and remote Australia, our lowest socio-economic areas and First Nations people. Another group at increased risk are patients with a family history of disease. In some senses, this vulnerable group is subject to the greatest stress – if you’ve lost a family member prematurely to heart disease, understanding your risk of suffering the same fate is critical.

A recent Australian randomised controlled trial of the use of CACS in decision-making, led by the Baker Heart and Diabetes Institute, may point the way forward. The CAUGHT-CAD trial, which involved seven hospitals in Tasmania, Victoria, Queensland and South Australia, screened nearly 1100 people at “intermediate risk” aged 40 to 70. Their inclusion was based on having a first-degree relative (such as a mother, father, sister or brother) who developed coronary artery disease before 60 years, or a second-degree relative (such as an uncle or aunt) with onset before 50 years. Of these participants, 450 with CAC were randomly allocated to either usual care or a combination of practitioner-led, CAC-informed education and lifestyle intervention, including moderate-intensity statin therapy. More than 360 patients returned after three years to check their response to treatment.

The study found that having aCAC score was valuable. First, it provided extra information about risk – for half of these people at intermediate risk, with a family member with the disease, the CAC score was zero. As events are very uncommon with a CAC score of zero, this was a very reassuring finding for these participants.

Professor Tom Marwick is a foremost researcher in coronary calcium scoring.

Second, in those people with a non-zero CAC score, using the CT image as part of their education produces a shift in their mindset. Instead of possibly being at risk, they know they have heart disease. In standard practice, adherence to “primary prevention” statin therapy at one year is about 50 per cent. In contrast, greater than 90per cent adherence to statins after CACS-guided education and management in this trial was associated with a reduction in dangerous lipids like low-density lipoprotein cholesterol and a slower build-up of plaque, compared with usual care. The resulting control of plaque progression with statin therapy would be expected to save heart attacks and death over subsequent decades.

Classifying risk on the basis of standard criteria works well in half of the population. In the other half, the reclassification of risk with a simple heart scan can reassure some and focus others on what needs to be done to prevent cardiovascular disease. The current Medical Benefits Scheme settings mean that individuals have to pay for these non-rebated tests. Perversely, the people who are at most risk are least able to pay for the test. We can and should do better to reduce the burden of cardiovascular disease.

Professor Tom Marwick is head of imaging research at the Baker Heart and Diabetes Institute and professorial research fellow at Menzies Institute for Medical Research. The research paper, Effects of Combining Coronary Calcium Score with Treatment on Plaque Progression in Familial Coronary Artery Disease is published in the Journal of the American Medical Association (JAMA).