By Michael H. Crawford, MD
Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco
Dr. Crawford reports no financial relationships relevant to this field of study.
SYNOPSIS: Coronary calcium scan on standard CT scans performed for other indications is of equivalent prognostic value to that seen on ECG-gated coronary studies and should be included in radiology test reports.
SOURCES: Hughes-Austin JM, Dominguez A 3rd, Allison MA, et al. Relationship of coronary calcium on standard chest CT scans with mortality. JACC Cardiovasc Imaging 2016;9:152-159.
Hecht HS. “See No Evil.” JACC Cardiovasc Imaging 2016;9:160-162.
Coronary artery calcium (CAC) scores performed on ECG-gated, 3 mm sliced CT scans are strong predictors of coronary artery disease (CAD), cardiac events, and mortality. Physicians perform standard 6 mm sliced chest CT scans much more often for a variety of reasons. A study by Hughes-Austin et al is a case-controlled analysis of patients who underwent both scan types between 2000 and 2003 and were followed for eight years to assess whether CAC observed on a standard CT scan was as useful as that on a coronary-specific CT scan. Among 4,544 community living subjects who underwent whole body CT scans, which included both types of chest CT imaging, 157 subjects who died were matched with 494 controls by sex and age. Subjects with known CAD were excluded. Researchers calculated a CAC score on all CT scans using the Agatston method. They read the 3 mm gated scans at the time of acquisition. Readers blinded to the 3 mm results later studied the 6 mm scans. The group collected clinical data as well, and the primary endpoint was all-cause mortality. The mean age of the 651 subjects was 68 years, and 63% were men. The mortality cases had higher median CAC scores on both scan types. The correlation between the two was excellent (r = 0.93), but the median Agatston score on the 6 mm scans was 22 vs. 104 on the gated 3 mm scans. CAC scores adjusted for traditional CAD risk factors showed identical risk ratios (RR) for mortality on the two scan types (RR, 1.5). The authors concluded standard chest CT scans performed for other reasons can provide useful information on CAD risk.
It seems like a no brainer that radiologists reading standard chest CT scans should report on coronary calcium the way they do lung nodules and other incidentalomas. This knowledge would help clinicians with primary prevention decisions without having to order other tests, some of which would add radiation exposure. However, scant available data suggest that clinicians report less than half of observed CAC and infrequently conduct formal scoring. Dr. Hecht plays the devil’s advocate in an accompanying editorial, noting there is no evidence that reporting CAC on a standard CT scan results in better outcomes. Also, it takes time, especially if a physician performs a formal CAC score, adding more time to an already-crowded schedule. Additionally, there are downstream effects of reporting. The ordering physician, who may have little understanding of the issues involved, has to deal with information that no one requested. This could start a test cascade that could lead to cardiac catheterization and an unnecessary percutaneous intervention. To prevent this, physicians may need education. As Dr. Hecht notes, this occurs in the radiology report for nodules, etc. and could be templated in the electronic medical record for coronary calcium.
Standard CT scans are performed eight times more frequently than coronary CT scans, and this is rising with the 2014 lung cancer screening guidelines. A semi-quantitative (mild, moderate, severe) coronary calcium reporting dictum would make a lot of sense and not cause excessive extra work.