Coronary artery calcification (CAC) scores can accurately predict 15 year all-cause mortality in asymptomatic patients, according to findings from a long term observational study published online July 8, 2015 in the Journal of the American College of Cardiology Cardiovascular Imaging and in the July 7, 2015 issue of Annals of Internal Medicine. The higher the score is, the greater the risk is of an individual dying.
The study has major implications with respect to identifying risk in asymptomatic patients, both with respect to guideline-directed treatment and to motivate patients to make lifestyle-modification behavioral changes to improve their health. Additionally, principal investigator Leslee J. Shaw, Ph.D., professor of medicine in the department of cardiology at Emory School of Medicine in Atlanta, and co-investigators suggest that an understanding of the relevance of low- to high-risk CAC scores may be useful in defining the effect of cardiovascular screening on life expectancy estimates among patients.
Atherosclerosis, the process of progressive thickening and hardening of the walls of medium-sized and large arteries as a result of fat deposits on their inner lining, is the leading cause of morbidity and mortality in Western countries. It is a disease that infiltrates the arterial wall well in advance of causing obstruction of blood flow and symptoms. More than half of all first coronary heart disease events are sudden cardiac deaths or acute myocardial infarctions in previously asymptomatic individuals. For this reason, much emphasis has been placed on identifying high-risk individuals. CAC indicates an individual’s predisposition to develop thromboembolic and ischemic events.
The 9,715 consecutive patient of asymptomatic individuals with no known coronary artery disease(CAD) had undergone a coronary calcium CT scan at a single outpatient clinic in Nashville, TN from 1996 to 1999. They had been referred by their primary physicians as part of a cardiology outreach screening program. None of the patients had symptoms of coronary artery disease. The patients varied widely in age, from 30 to 85 years, although the majority were between 40 and 59 years of age. Approximately 40% were current smokers. Almost 70% had a family history of premature CAD, 63% had dyslipidemia, 43% had hypertension, and 8% percent had diabetes mellitus. Almost three-quarters of the original group had two or more cardiac risk factors.
The patient cohort was stratified by age, Framingham risk score (FRS), and National Cholesterol Education Program Adult Treatment Panel III (NECP ATP III) categories. CAC scores were categorized into six groups: no evidence of CAC, and five additional groups (1-10, 11-99, 100-399, 400-999, and 1000+). The multicenter research team developed models that included the CAC score and cardiac risk factor variables. Patients with higher-risk CAC scores tended to be older, were more likely to be male, and had a greater prevalence and extent of cardiac risk factors.
The primary endpoint of the analysis was time to all-cause mortality, which expanded the evidence base beyond traditional cardiovascular disease outcomes. The authors pointed out that risk estimations projecting through approximately 15 years more closely approach the concept of lifetime risk projections than shorter-duration studies.
A total of 936 individuals died during the mean 14.6 year follow-up period. Of these, 3% had no CAC. For the remainder, an increasing percentage of each CAC score category died. Nearly half (49%) of the patients who died had scores CAC scores of 400-999 (21%) or 1000+ (28%), whereas the percentage diminished with each lower category (101-399 – 14%, 11-100 – 9%, and 1-10 – 6%.
The fact that patients with CAC scores of 400 or greater had a 15-year all-cause mortality rate that exceeded 20% confirms the importance of length of follow-up in defining substantive high risk status, the authors stated. They said, “For asymptomatic patients, long-term mortality estimates allow for calculation of projected premature mortality, and provide insight into the societal benefit of CAC scanning. This benefit may offset the minimal projected risk for cancer after exposure to ionizing radiation from CAC scanning.”
They noted that the study findings may prompt additional research to develop therapeutic strategies aimed at improving outcomes particularly for patients with high-risk CAC scans.
Coronary artery calcification (CAC) scores predict mortality risk of asymptomatic patients. Appl Radiol.
Cynthia E. Keen is a New York City area-based medical writer specializing in clinical subjects and healthcare technology. She writes feature articles for Applied Radiology and the contents of the Applied Radiology newsletter.