Fact check: Is a coronary calcium score the best indicator of heart attack risk?

Published at May 10, 2018

The claim

The death of former Australian Ironman Dean Mercer at age 47 shocked the sporting world. How could a seemingly fit and healthy man die of cardiac arrest at such a young age?

Interviewed about Mercer’s death on ABC Radio, Sydney cardiologist Dr Ross Walker said that common health checks for blood pressure and cholesterol were not the best predictors of heart attacks.

Dr Walker instead suggested people worried about their heart health should be undergoing a scan for coronary calcium.

Also known as coronary artery calcium (CAC) scoring, the test is one that Dr Walker pioneered in Australia in the late 1990s in conjunction with the Sydney Adventist Hospital.

“I think all males at 50 and all females at 60 should have a coronary calcium score,” Dr Walker told The World Today.

“It’s the best predictive test for heart disease risk.”

He continued: “Your cholesterol is not the best predictive test; your blood pressure is not the best predictive test — this coronary calcium score is.

“It’s the best way to see if you’re going to drop dead of a heart attack.”

Is this coronary calcium score really the best indicator of heart disease, and is it a necessary test for older all Australians?

RMIT ABC Fact Check investigates.

The verdict

There is more to the story than Dr Walker’s claim suggests.

Studies conducted primarily in the US have shown that coronary calcium scans are able to identify heart disease in patients, with the resulting calcium “scores” having been found to correlate with future cardiovascular events.

The Cardiac Society of Australia and New Zealand describes the test as a “robust” way to estimate future risk of cardiac events.

By contrast, the sub-committee of the Australian Health Ministers’ Advisory Council responsible for new and emerging technologies cautions that calcium scoring for predicting heart disease “is of unproven clinical benefit or utility”.

The sub-committee raised concerns about the radiation dose involved (the equivalent of 50 chest x-rays per scan) as well as the impact on downstream tests and treatments.

Cardiologists contacted by Fact Check agreed the test was better at predicting heart attacks than traditional blood pressure or cholesterol checks, but were hesitant to back the test as strongly as Dr Walker.

When it comes to mandating the test for men over 50 and women over 60, cardiologists pointed to guidelines published by the Cardiac Society of Australia and New Zealand suggesting that only people of a certain age and at intermediate risk of heart disease, or with a strong family history of heart disease, undergo a calcium scan.

Coronary heart disease and calcium scoring

According to the Heart Foundation, coronary heart disease is Australia’s single biggest killer, accounting for 12 per cent of deaths.

The Foundation defines coronary heart disease as the narrowing of the arteries leading to the heart due to a build up of plaque, fatty material that clings to the artery walls.

This, in turn, can reduce blood flow to the heart, and is the leading underlying cause of cardiac arrest.

Professor Gemma Figtree, of the University of Sydney, told Fact Check that the process of plaque developing in the arteries leading to the heart, known as atherosclerosis, “most often begins years before a heart attack”.

She said that the process is accelerated by risk factors such as “high cholesterol, smoking, high blood pressure and diabetes”.

Professor Figtree, a cardiologist who sits on the Heart Foundation’s Clinical Issues Committee, explained that a coronary calcium score is obtained by taking a computed tomography (CT) scan of the heart.

The scan measures the amount of calcium in the arteries to the heart, which accumulates with the plaque over time and is a pointer to the presence of heart disease.

The resultant CAC score is used both to categorize patients into groups based on their risk of a heart attack in the subsequent 10 years, and for evaluating treatment options for each patient.

The Cardiac Society of Australia and New Zealand publishes the following treatment guidelines for doctors when considering a patient’s calcium score:

CAC Score10-year mortality riskGuidance
0Very Low (<1%)ReassureMaintenance of healthy diet and lifestyle.
101 – 400Moderate (10-20%)Aspirin recommendedStatins considered reasonable
101–400 & >75th percentileModerately High (15–20%)Reclassify as high riskAspirin recommendedStatins considered reasonable
>400High (>20%)Aspirin recommendedStatin recommended, to achieve target LDL <2.0 mmol/LConsider functional assessment.

* Suggested management based on CAC results for asymptomatic patients

SOURCE: 2017 CSANZ Calcium Scoring Position Statement

Traditional risk factors

Dr Walker claimed that blood pressure and cholesterol were not the best predictors of risk of heart disease.

A 2014 study in the peer-reviewed journal of the American Heart Association, Circulation: Cardiovascular Imaging, states: “Although risk factors have proven to be useful therapeutic targets, they are poor predictors of risk.”

The study explains that, traditionally, doctors have used a test called the Framingham Risk Score to categorise patients according to their risk of heart disease.

In Australia, doctors use a tool developed by the National Vascular Disease Prevention Alliance called the Australian absolute cardiovascular disease risk calculator, based on the Framingham Risk Score, to assess a patient’s risk of heart disease.

While there are slight differences between the outcomes of the two, both measures take into account the same factors.

The Framingham Risk Score takes into account age and sex, as well as risk factors such as smoking, blood pressure, cholesterol and diabetes, to produce a 10-year cardiovascular risk prediction for each patient.

However, the Framingham Risk Score often fails to predict cardiovascular events: the Circulation study found 75 per cent of young people suffering from a particular type of coronary heart disease were deemed to be at low risk (under this system) the day before their cardiovascular event.

The research suggests that, while traditional risk scores can be used as a starting point for categorising patients’ risk of heart disease, they are not definitive in identifying heart disease.

Dr John Younger, a consultant cardiologist with the Queensland Cardiovascular Group and director of cardiac CT services at St Andrew’s War Memorial Hospital, elaborated on the limitations of traditional risk factors as predictors of coronary heart disease.

“The standard risk assessment would just consider your current values, and might say you are at low risk, but it is naive to think that the past 20 years might not have had some impact on your risk of [a cardiovascular] event,” Dr Younger told Fact Check.

The best predictor of risk

Dr Christian Hamilton-Craig, who chairs the Cardiac Society of Australia and New Zealand Working Group on CAC Scoring, and lead author of the society’s position statement on calcium scoring, told Fact Check: “The truth behind Dr Walker’s statements is valid.”

He said the calcium score was “the best predictive test”, adding that it was much better at identifying the narrowing of arteries than other heart checks offered to patients.

Dr Younger also said that CAC scores were the best predictor of coronary heart disease.

“Calcium scoring can be combined with standard risk factors, such as age, gender, blood pressure, smoking, diabetes and cholesterol levels, to provide a very accurate risk prediction of subsequent events,” Dr Younger said.

He said that coronary calcium scores provided “a summary of how your life and lifestyle to date have affected your coronary arteries” and “seem to be a very accurate predictor of risk”.

The University of Sydney’s Dr Figtree said the score was a helpful and evidence-based test that could improve patient management in a way that lowered the rate of cardiovascular events.

“[The test] is very helpful in stratifying risk, and helping physicians target therapy particularly in patients with intermediate risk, such as those with moderately high cholesterol and a family history of coronary heart disease,” Dr Figtree said.

However, Professor Stephen Nicholls, of the University of Adelaide and the South Australian Health & Medical Research Institute, who is an investigator in a clinical trial of CAC scoring, told Fact Check that Dr Walker had oversimplified the usefulness of calcium scores.

“Predicting the risk of heart attacks is not easy,” Dr Nicholls said.

“There are likely to be other causes of heart disease that we know less about and that tests are not available for. In other words, no test is perfect.”

While agreeing that calcium scoring had been shown in some people to improve risk prediction, Dr Nicholls urged caution in promoting its widespread use.

“There is also no data at all that shows that having a calcium score leads to a change in treatment and change in outcome. That’s why we need more clinical trials in the space.”

Much of the evidence regarding the usefulness of coronary calcium testing is drawn from the Multi-Ethnic Study of Atherosclerosis — a large-scale, long-term study of the characteristics of heart disease — and ancillary studies.

One such study, published in the American Heart Journal, found that coronary calcium scores were a good predictor of heart disease and cardiovascular events.

The study, which focused on people with no symptoms of heart disease, found that those with a coronary calcium score of one to 10 were three times more likely to have a cardiovascular event than those with a score of zero.

Further to this, the 2014 American Heart Association study published in Circulation concluded that coronary calcium scoring was “at the present time, superior to any combination of risk factors” in terms of being an accurate risk prediction tool.

Dr Younger told Fact Check that some older studies had found only one-third of heart attack patients would have been found to be “high risk” by traditional calculators such as the Framingham Risk Score, whereas 95 per cent of heart attack patients will have evidence of coronary calcium, as identified by a CAC score.

The Cardiac Society of Australia and New Zealand’s 2017 position statement on calcium scoring says there have been “a number of large scale prospective studies published in the literature that have proven the prognostic value of CAC in asymptomatic patients, especially in the sub-group at intermediate cardiovascular risk profile”.

The statement concludes: “Coronary Artery Calcium scoring is a robust and reproducible way of detecting coronary atherosclerosis and to estimate future risk of cardiac events. It has incremental benefit beyond traditional risk prediction tools and biomarkers.”

Embed: CSANZ’s 2017 position statement on CAC scoring.

A lack of official backing

A search of the Heart Foundation website finds no references to coronary calcium scoring.

In a statement, the Heart Foundation told Fact Check that “it is not possible for the foundation to cover every issue on its website”.

“Calcium scores are not always definitive, and the interpretation of the scores by a healthcare professional often varies,” the statement said.

The foundation said it believed doctors should determine the need for CAC testing on an individual basis and reiterated its recommendation that everyone over the age of 45 (or 35 for Aboriginal and Torres Strait Islanders) ask their GP for regular heart health checks.

Governments have also been wary of endorsing the calcium scan.

The Health Policy Advisory Committee on Technology (HealthPACT), a sub-committee of the Australian Health Ministers’ Advisory Council, assessed the use of coronary calcium scoring in 2015.

Embed: HealthPACT’s 2015 report.

The committee failed to recommend the routine use of CAC scoring, citing concerns about the radiation dose involved (the equivalent of 50 chest x-rays per scan) as well as the impact on downstream tests and treatments.

Its advice to the ministers was that the test “is of unproven clinical benefit or utility” and “therefore, HealthPACT does not support the use of CT calcium scoring in clinical practice at this time for screening asymptomatic patients”.

However, its report said there was evidence that CT calcium scoring could accurately predict cardiovascular events in individuals not showing symptoms of heart disease and the scanning “has been shown to perform better than traditional risk factor assessment, although the magnitude of that difference in clinical terms is not clear”.

“It should be noted that the use of CT calcium scoring for predicting Coronary Artery Disease risk is a widely debated area in which a plethora of opinion is available, some of which is based on evidence and some which is not,” the committee said.

The test is also not covered by Medicare, so the cost of a coronary calcium score comes as an out-of-pocket expense to the patient.

In a statement, a spokeswoman for the Federal Department of Health told Fact Check that the test was not currently listed on the Medical Benefits Scheme, and that Medicare benefits were claimable only for “relevant clinical services”.

“A clinically relevant service is one which is generally accepted by the relevant profession as necessary for the appropriate treatment of the patient,” the department told Fact Check.

Applications for public funding for new medical services are made to the Medical Services Advisory Committee.

Dr Hamilton-Craig told Fact Check that for an application to be made to the committee, it needed to come from a peak body, such as the Cardiac Society.

“At this point in time, there has not been sufficient economic data to support an application for reimbursement in Australia,” Dr Hamilton-Craig said.

The National Health and Medical Research Foundation has allocated $2.6 million to a randomised clinical trial of coronary calcium for risk evaluation and prevention in people with a strong family history of coronary artery disease.

summary of the trial, running for five years from 2015, describes calcium scoring as “a promising marker of subclinical risk” which “has been shown in observational studies to provide prognostic information that is incremental to the clinical assessment of [heart disease] risk”.

Its aims include assessing the cost-effectiveness of preventive strategy based on calcium scoring.

Who should be getting a coronary calcium score?

While Dr Walker recommends coronary calcium scoring for all men and women of a certain age, other cardiologists only recommend it for a specific group of people at intermediate risk of heart disease.

Professor Nicholls said that the scan should not be used for patients diagnosed with heart disease as they should already be being “treated aggressively”.

People at low risk do not need the score either.

The Cardiac Society of Australia and New Zealand’s 2017 position statement on calcium scoring sets out parameters for the use of the test.

Flowchart shows recommended conditions for coronary calcium score test

A flowchart showing the recommended conditions for undertaking a coronary calcium score test. Sources: CSANZ’s 2017 position statement; Dr Christian Hamilton-Craig.

(RMIT ABC Fact Check)

The society recommends the test for people at intermediate risk of heart disease, for those at low risk but with a family history, and those at high risk but who are reluctant to accept treatment.

Dr Hamilton-Craig told Fact Check that calcium scoring was not a screening test for all people of a certain age, but for the recommended group the test could lead to better treatment.

“Coronary calcium scoring leads to an appropriate increase in prescriptions for cholesterol medications and aspirin, and leads to greater patient adherence to medications,” he said.

View original article – Credit: ABC.net.au


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