Absence of Coronary Artery Calcium on CT Scoring Confers a 15-Year “Warranty”

Absence of Coronary Artery Calcium on CT Scoring Confers a 15-Year “Warranty” Against Incident Mortality for Asymptomatic Individuals
Dr Yu-Ming Tang, South Coast Radiology

CT Coronary Calcium Scoring (CTCS) is a low dose, non-contrast CT scan that measures coronary artery calcium (CAC) and has been proven to be a very useful tool for predicting cardiac events in asymptomatic individuals. It is best used in patients with intermediate risk according to charts, such as the Australian absolute cardiovascular risk calculator (www.cvdcheck.org.au) or NICE guidelines (www.nice.org.uk).

Previously the Multi--Ethnic Study of Atherosclerosis (MESA) trial demonstrated that CTCS was the most accurate tool for predicting long-term cardiac events, over-and-above traditional risk factors. The MESA study was designed to investigate the prevalence and progression of subclinical atherosclerosis, in asymptomatic, primary prevention population. The study concluded that CTCS will reclassify 23% of intermediate patients into the high risk category, and an additional 13% reclassified to the low risk category. Along with several other large prospective studies, MESA established CAC as a strong prognosticator of cardiac events, significantly superior and additive to all risk-factor–based assessments, which can enable changes to patient therapy and medication regime.

CT calcium scoring has been criticised in the past for lack of long term data and interpretation guidelines. In 2015, an important paper was published in the Journal of American College of Cardiology which documented the long term prognosis associated with a zero calcium score. Research by Valentina Valenti et al. at Weill Cornell Medical College, New York, assessed the long-term prognosis in asymptomatic individuals with a coronary artery calcium (CAC) score of 0 and its associated warranty period. A total of 9,715 individuals undergoing CTCS were stratified by age, Framingham risk score (FRS), and National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) categories and followed for a mean of 14.6 years.  A warranty period was pre-defined as <1% annual mortality rate.  The study concluded that:
• A CAC score of 0 confers a 15year warranty period against mortality in individuals at low to intermediate risk that is unaffected by age or sex.
• In individuals considered at high risk by clinical risk scores, a CAC score of 0 confers better survival than in individuals at low to intermediate risk but with any CAC score.
• The CAC score was the strongest predictor of death that enabled discrimination and consistent reclassification beyond the FRS and NCEP ATP III.

In line with the American College of Cardiology’s position statement, South Coast Radiology recommends consideration of CTCS to determine future risk of cardiovascular disease among asymptomatic individuals 40-70 years of age (if the results of the test could influence treatment decisions). CTCS is not recommended for high-risk individuals - known CAD, previous MI, CABG, stents or evaluation of CAD symptoms.

An additional benefit is that CTCS has the potential to improve therapy adherence in patients with a score >0. The Eisner trial demonstrated that patients with positive scans were more adherent to statin therapy, had greater reduction in their Framingham risk score, and their systolic blood pressure, as well as, a trend towards a greater reduction in waste circumference compared to those who did not undergo CTCS.

CT Calcium scoring provides an indivualised risk for CAD with a positive CAC score confirming the presence of CAD, and rising scores are directly proportional to increased CHD risk. The need for further testing (for example, stress test, CTCA or cardiac catheterisation) should be directed by the CAC score, clinical history and other conventional clinical criteria.

References
Valenti, V., et al. (2015). A 15-year warranty period for asymptomatic individuals without coronary artery calcium: a prospective follow-up of 9,715 individuals. JACC: Cardiovascular Imaging, 8(8), 900-909.

Rozanski, A., et al. (2011). Impact of coronary artery calcium scanning on coronary risk factors and downstream testing: the EISNER (Early Identification of Subclinical Atherosclerosis by Noninvasive Imaging Research) prospective randomized trial. Journal of the American College of Cardiology, 57(15), 1622-1632.