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CAC analysis on standard chest CT accurately predicts mortality risk
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Coronary artery calcium scores are almost the same on standard 6 mm chest CT as they are on 3 mm ECG-gated CTs, and similarly predict mortality risk, according to recent study findings.
According to the study background, the current practice is to use 3 mm ECG-gated CT for measuring coronary artery calcium (CAC), but that technology is not commonly used otherwise, while standard 6 mm chest CTs are used often for many clinical indications, although they have not generally been used to quantify CAC.
Researchers conducted a case-control study of individuals who had 3 mm ECG-gated CT and standard 6 mm chest CT between 2000 and 2003, and who were followed for mortality until the end of 2009. From the pool of 4,544 individuals, researchers matched, based on age and sex, 157 people who died during follow-up with 494 controls (mean age, 68 years; 63% men).
They quantified CAC on both scan types based on the Agatston method and analyzed the association between CAC score and mortality for both scan types.
Mortality risk similar by scan type
Jan M. Hughes-Austin, PT, MPT, PhD, and colleagues found that the Spearman correlation of CAC scores between the different types of scans was 0.93 (P < .001), and that median CAC scores were 22 Agatston units on 6 mm CT vs. 104 Agatston units on 3 mm ECG-gated CT (P < .001).
After adjustment for traditional risk factors, they found that each standard deviation higher CAC score on 6 mm CT conferred a 50% higher odds of death (OR = 1.5; 95% CI, 1.2-1.9), and the same was true for 3 mm ECG-gated CT (OR = 1.5; 95% CI, 1.1-1.9).
“Chest CTs performed for other clinical indications may provide an untapped resource to garner CVD risk information without additional radiation exposure or expense,” Hughes-Austin, from the department of family and preventive medicine at University of California, San Diego, and colleagues wrote.
Opportunity to save lives
In a related editorial, Harvey S. Hecht, MD, from Icahn School of Medicine at Mount Sinai, wrote that “this paper is one of an increasing number that correlate nongated and gated CAC scores but, most importantly, is the first to demonstrate comparable mortalities. Thus, with minimal effort and no extra radiation, critical prognostic data for the greatest killer in the United States, and increasingly throughout the world, can be extracted from the approximately 7.1 million annual routine, noncontrast CT scans.”
He concluded that, although there are many logistical barriers to performing CAC analysis and reporting the results after routine CT scans for other indications, it is “an unparalleled opportunity to save lives. As a responsible medical community, we cannot ‘see no evil’ (ignore the CAC), ‘speak no evil’ (not report the results) and ‘hear no evil’ (not listen to and act on the results).” – by Erik Swain
Disclosure: The researchers report no relevant financial disclosures. Hecht reports consulting for Philips Medical Systems.
Perspective
Back to TopMushabbar Syed, MD, FACC
Previous studies have shown agreement between dedicated calcium scoring scan (3 mm, ECG-gated) and standard chest CT scan (6 mm, non-gated). This study confirms previous results, but, more importantly, is the first study to compare both scan techniques using mortality as endpoint. Results show that both techniques have similar predictive value for all-cause mortality.
I believe that radiologists reading chest CT scans should at least report on the presence or absence of CAC on every scan. This will have important implications for early detection of CAD, as CAC is a marker of coronary plaque.
The bigger question is whether calcium scores should be measured on all chest CT scans. I think this needs further evaluation. Current guidelines don't recommend routine CAC scoring, primarily due to lack of data on CAC score measurement affecting change in clinical outcomes. The same guideline recommendation also holds true for CAC scoring by chest CT. More outcome studies are needed to address this limitation.
Additionally, CAC scores by chest CT are underestimated as compared to 3 mm ECG-gated scans due to decreased sensitivity in detecting small plaques. Therefore, a zero score by chest CT scan may not be accurate and needs further study. The current study found a zero score in 34% of participants by chest CT and in 24% by ECG-gated CT, highlighting this limitation of chest CT.
The benefit of measuring CAC on a standard CT chest scan is early detection of CAD, which may help in changing medical management in some patients. Reporting presence or absence of CAC on chest CT is relatively easy. However, scoring will require more post-processing time and use of dedicated software, which may not be available in every practice. Due to underestimation of CAC score by chest CT, new cutoff values will need to be developed.
This study used a specific population, which was primarily older white adults. More studies are needed in other age and racial groups to confirm these findings.
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