Standard Chest CT: A Missed Opportunity for CAD Detection Warranting New Guidelines and Attitudes

Routine chest X-rays are ordered for a variety of clinical situations, but a study suggests that there may be a new use for them in the arena of preventive cardiology—measurement of coronary artery calcium (CAC). 

Take Home: Standard Chest CT: A Missed Opportunity for CAD Detection Warranting New Guidelines and Attitudes

In a study published online in JACC: Cardiovascular Imaging, Joachim H. Ix, MD, of University of California San Diego, and colleagues looked at 4,544 asymptomatic people (mean age 68 years; 63% men) who were referred for both a standard chest CT and an ECG-gated CT (specifically for CAC measurement) between 2000 and 2003. Morality was assessed through 2009. A nested case-control design yielded 651 participants—157 deaths matched to 494 controls.

When CAC was measured, there was a strong correlation between scores on the ECG-gated CT and the chest CT (Spearman correlation r = 0.93; P < .001), although calcium scores were lower, on average, with chest CT (22 vs 104 Agatston units, respectively; P < .001).

Additionally, CAC scores measured by both types of CT showed correlation with all-cause mortality.

Mortality Hazard Associated With Calcium Scores

Avoiding Risks and Expense

“Most insurance providers do not routinely cover the expense of 3 mm ECG-gated scans for CAC scoring, and conversely approximately 7 million chest CT scans are done annually in the US for other clinical indications,” Ix and colleagues write. “Persons who have chest CTs for other clinical indications may benefit from systematic reading of CAC to garner additional information on CVD risk without the added expense and radiation exposure required for dedicated 3mm ECG-gated scans.”

The researchers add that the frequency with which chest X-rays are done suggests that many people already have scans that can be used to measure their CAC score. “Thus, if our results are confirmed, healthcare providers may consider utilizing previously obtained CT scans to assess CAC while avoiding the potential risks and expense of repeat CT scans designed specifically for CAC measurement.”

However, Ix and colleagues caution that the study population consisted of mostly older non-Hispanic white adults, many of whom had no particular reason to have whole-body CT scans other than for preventive care. Additionally, they say, the differences seen in CAC scores between the chest CT and ECG-gated scan require further study, with the suggestion being that specific CAC values should be interpreted in the context of the scan type.

Thorny Issues

In an editorial, Harvey S. Hecht, MD, of Mount Sinai St. Luke’s Medical Center (New York, NY), says the study is the first to show comparable mortality prediction ability for CAC scores derived from gated vs non-gated CT. But it also raises a number of “thorny issues,” he notes, including whether there is a responsibility on the part of physicians reading chest X-rays to report all information in the field of view even when RCT evidence for implementation of that information is lacking.

The US Preventive Services Task Force considers CAC a non-traditional risk factor for CAD and does not currently recommend CAC screening. But the 2014 endorsement by the task force of low-dose lung CT scanning for cancer detection, as well as the Centers for Medicare & Medicaid Services decision to cover lung scans makes the issue of what to do with CAD information found on chest scans of timely relevance, Hecht adds.

Despite the barriers, he says, radiologists cannot in good conscience fail to report CAC findings. Therefore, Hecht suggests that:

  • The American College of Radiology and/or the Society of Thoracic Radiology issue new guidelines requiring reporting of CAC on all non-contrast, non-gated CT  
  • Efforts be made to conduct intensive education of radiologists and primary care physicians and to support a pathway toward reimbursement, given the incremental work required to measure CAC 
  • Cardiologists and all referring physicians reach out to their radiology colleagues to encourage reading for CAC, particularly in the subset of smokers who will be undergoing lung cancer screening 
  • Depending on extent of CAC, simple recommendations should be included in CT reports similar to the standard inclusion of recommendations regarding pulmonary nodules Expertise in incorporation of CAC into risk assessment and treatment plans will be required of those ordering physicians who will directly implement the information or towhom patients will be referred 
  • Lung cancer screening should be viewed by all as an opportunity to detect the early stages of CAD 

 


Sources: 
1. Hughes-Austin JM, Dominguez A, Allison MA, et al. Relationship of coronary artery calcium on standard chest computed tomography scans with mortality. J Am Coll Cardiol Img. 2016;Epub ahead of print.
2. Hecht HS. See no evil [editorial]. J Am Coll Cardiol Img. 2016;Epub ahead of print. 

Disclosures:

  • Ix reports no relevant conflicts of interest. 
  • Hecht reports serving as a consultant for Philips Medical Systems.

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