Up or down? The experts behind the new heart disease guidelines explain the added extras that change the final risk score.
The new Heart Foundation cardiovascular disease risk calculator has some risk factors as optional extras rather than part of the main risk calculator.
Risk factors such as coronary calcium score and family history are included in the new Australian CVD risk calculator as “reclassification factors” to be considered after entering data on age, sex, smoking status, systolic blood pressure, cholesterol, medication, atrial fibrillation history and post code.
Authors of the new guidelines were questioned at the Cardiac Society of Australia and New Zealand annual scientific meeting this month about why coronary calcium score was included as a “reclassification factor” rather than a first step of the risk calculator.
Cardiologist Professor Clara Chow said the five “reclassification factors” had been added to help improve risk estimates when a patient’s final risk score was close to another risk threshold.
“These new Australian guidelines incorporate the concept of reclassification factors, and these are applied after the risk is calculated by the equation and might increase or decrease your assessment of these patients overall,” said Professor Chow, the clinical lead of community based cardiac services at Westmead Hospital.
The Heart Foundation’s chief medical advisor and interim CEO, Professor Garry Jennings, said the committee was often asked “why isn’t my favourite risk factor in there?”, particularly referring to CT coronary calcium.
“We’re getting a lot of that,” he said.
But Professor Chow said the routine use of coronary CTCA across the population was clearly not indicated for risk prediction.
“Risk versus benefit, there’s no clear benefit of doing that. The risks outweigh the benefits,” she said.
Professor Jennings said inclusion was based on current evidence.
“We’ve got things that are related to risk, but they don’t contribute anything above what’s already in the equation. And that’s why people are surprised that BMI isn’t in there,” he said.
“BMI is very important in that it’s associated with risk, no question. It’s just that once you’ve got blood pressure and diabetes and all these other things in there, it doesn’t add a lot more.
“We don’t want GPs putting in things they don’t need to put in.”
Other risk factors were not included because they were out of scope, or the evidence was conflicting or not relevant to an Australian population, he said. On the other hand, other variables were now included in the risk calculator in keeping with the latest evidence.
For the first time the risk calculator accounted for social disadvantage and was more accurate for diabetes by accounting for variables within the disease, Professor Jennings said.
It also included kidney-specific risk factors “which are increasingly important in various sections of the community in Australia”, he said.
“It’s got more variables, but we recognise that no equation will ever have enough variables to account for what is called the art of medicine: the ability to have a look at what comes out of an equation and say, ‘but I know more about this patient, I know things about this or something doesn’t quite gel, I need to up the risk or down the risk’, and we’re calling those reclassification factors,” he said.
Professor Chow said for coronary artery calcium score, the risk prediction advises reclassifying up a category if a patient’s score is greater than 99 units, or more than or equal to the 75th percentile for age and sex.
A calcium score of zero should reclassify a patient down, while a calcium score of 99 or above or greater than the 75th percentile for age and sex should reclassify them up.
“Coronary calcium score is not recommended for everybody,” Professor Chow told the conference.
“Do not consider a coronary artery calcium score if the patient is already quite clearly at high risk. That is, they’ve got a history of myocardial infarction, or revascularisation, or the patient is already known to be at high CVD risk.”
When assessing cardiovascular disease risk, reclassifying risk level due to calcium score could be considered when treatment decisions were uncertain, when risk of cardiovascular disease was assessed as low or intermediate using the calculator and other risk concerns were present that were not accountable by the calculator, and when further information was required to inform discussions between the practitioner and the person with respect to therapy, Professor Chow said.
Family history of premature cardiovascular disease, chronic kidney disease and severe mental illness would up-classify risk, while ethnicity and coronary artery calcium score would either up-classify or down-classify risk, she said.
“A lot of these reclassifications become most relevant when people are at the borderline of the risk classification, either between low and intermediate or between intermediate and high, so for example 4%,” she said.
Professor Chow suggested clinicians consider reclassifying estimated risk to a higher category in First Nations people and people with Maori, Pacific Islander and South Asian ethnicities whose risk was close to the threshold.
For people of East Asian ethnicity, consider reclassifying their risk to a lower category if their risk was close to the low-risk threshold, she said.
As for family history, it could be difficult to define, Professor Chow said. According to the new guidelines, family history may be poorly recalled by individuals and may also be poorly documented in primary care records.
“If you’re not confident about whether that person does or doesn’t have a family history of coronary heart disease, maybe you shouldn’t be plugging into that calculator,” Professor Chow said.
“If you’re very clearly confident that a person has a family history of premature current disease, maybe that is very clear, it’s reasonable to reclassify that person because of that.”
For men under 55 and women under 65 with a family history of premature cardiovascular disease, the guidelines suggest reclassifying their risk to a higher risk category, “particularly if calculated risk is close to a higher risk threshold”, Professor Chow said.
People with moderate-to-severe chronic kidney disease were at clinically determined high risk and the risk calculator should not be used, she said.
The guidelines define severe mental illness as “a current or recent mental health condition requiring specialist treatment, whether received or not, in the five years prior to the CVD risk assessment”.
“For people living with severe mental illness consider reclassifying estimated cardiovascular risk to a higher category particularly if calculated risk is close to a higher risk threshold,” Professor Chow said.
“It’s noted in the guidelines that treatment with second generation antipsychotic agents is one of those treatments that may be associated with a higher risk.”
Ankle-brachial index, high-sensitivity C-reactive protein and chronic inflammatory conditions such as rheumatoid arthritis are associated with cardiovascular risk but were not included in the risk calculator, she said.
“It was recommended that they add little to cardiovascular risk estimation above what is already in the calculator and therefore should not be routinely measured, though again, a consideration,” she said.
Professor Chow said pregnancy complications such as preeclampsia, gestational diabetes and premature early menopause elevated a patient’s cardiovascular risk, and that should encourage monitoring of blood pressure and diabetes.
Professor Mark Nelson, chair of the discipline of general practice and senior member of the Menzies Research Institute and University of Tasmania, said he was hopeful that the guidelines would be integrated into clinical software in the next 12 to 18 months.
“Absolute risk approach doesn’t take away decision making from the doctor and their patient, that just gives them evidence-informed decision making,” he said.