- Nongated chest CT scans are usually performed for reasons other than to assess cardiovascular risk.
- Incidental coronary artery calcium (CAC) scores extracted from nongated chest CT scans accurately predicted cardiovascular risks in a community-based cohort.
- Patients with moderate or severe nongated CAC had significantly higher risks of cardiovascular disease and coronary heart disease versus those with zero CAC.
Incidental coronary artery calcium (CAC) scores extracted from nongated chest CT scans accurately predicted cardiovascular risks, a cohort study showed.
Patients with moderate nongated CAC had significantly higher risks of cardiovascular disease (CVD; HR 2.31, 95% CI 1.32-4.04) and coronary heart disease (CHD; HR 2.67, 95% CI 1.14-6.27) versus those with zero CAC, and the same was true for those with severe nongated CAC (CVD: HR 2.89, 95% CI 1.68-4.96; CHD: HR 5.22, 95% CI 2.37-11.5).
Additionally, with participants having undergone gated and nongated chest CT scans on the same day, log-standardized CAC results between the two modes were highly correlated (r=0.961, P<0.001). The area under the receiver operating characteristic curves, C-statistic, and Brier scores were also statistically similar for gated and nongated CAC, reported Dhiran Verghese, MD, of Massachusetts General Hospital and Harvard Medical School in Boston, and colleagues.
“In assessing the predictive value of nongated CAC, we observed a stepwise increase in events across CAC tiers,” they wrote in Circulation. “A nongated CAC score of 0 was associated with low event rates during follow-up, reinforcing the ‘power of zero’ even when CAC is assessed on nongated scans.”
Nongated CT is usually performed for reasons other than to assess cardiovascular risk; these scans lack the ECG functionality to capture images between heartbeats, as there is less need to reduce motion artifacts when scanning outside the heart.
“Our findings provide validation for the use of nongated CAC while in addition highlighting the importance of incorporating quantitative nongated CAC, as it offers greater accessibility while maintaining predictive accuracy comparable with the less commonly available gated CAC scans,” Verghese and team noted. “This could eliminate the need for repeat ECG-gated CAC scanning, thereby reducing both radiation exposure and healthcare costs.”
CAC that is identified opportunistically on these simpler, widespread scans has already been shown to predict future cardiovascular events. Prior work has also found that notifying patients and clinicians of incidental CAC can boost prescription of and adherence to lipid-lowering therapy.
Thus, U.S. guidelines now strongly endorse the use of incidental CAC scoring from nongated CT scans for atherosclerotic cardiovascular disease risk stratification and to guide lipid-lowering therapy.
In an accompanying editorial, Fatima Rodriguez, MD, MPH, and Curtis Langlotz, MD, PhD, both of Stanford University in California, noted that “the time for clinical implementation is now.”
“Systematically identifying CAC in millions of chest CTs performed each year for noncardiac purposes should be prioritized because of its potential for public health impact,” they wrote. “This new method of CAC detection represents the promise of precision prevention at scale — leveraging existing data to identify high-risk individuals and offering tailored interventions to motivate sustained change.”
“Nevertheless, clinicians should exercise caution when interpreting a CAC score of 0 derived from incidental, nongated imaging, particularly in high-risk individuals,” they cautioned. “Due to the inherent technical limitations and higher rate of false negatives associated with incidental scans, a 0 score should not be used to falsely reassure patients or de-escalate necessary preventive therapies.”
Even so, the degree of misclassification observed by Verghese and colleagues was largely limited to people in the zero or mild CAC categories. A nongated CAC score of 0 but detectable CAC on gated imaging had a low median calcium score of 5.6, suggesting that most misclassification reflects minimal disease unlikely to substantially change risk stratification, the study authors argued.
Verghese and team relied on a cohort from MESA (Multi-Ethnic Study of Atherosclerosis) to analyze the predictive value of CAC from same-day gated and nongated chest CT scans. This community-dwelling cohort has been prospectively followed since the year 2000.
They included 2,472 patients with noncontrast CT scans from April 2010 to December 2011 who had no previous CVD or CHD. Median age was 68, and 53% were women.
Nongated CAC scores were categorized as zero (n=783), mild (1-99 Agatston units; n=806), moderate (100-299 Agatston units; n=364), or severe (300+ Agatston units; n=519).
CVD events were defined as a composite of fatal or nonfatal myocardial infarction, stroke or stroke death, resuscitated cardiac arrest, and CHD death. CHD events were defined as a composite of fatal or nonfatal myocardial infarction, resuscitated cardiac arrest, and CHD death.
The results were consistent in sensitivity analyses excluding participants who were receiving statin therapy at baseline.
Nonetheless, residual confounding remains a possibility, and survival bias might have influenced the findings by excluding patients who’d had events predating these CT scans or a higher baseline risk, Verghese and colleagues acknowledged.
