CT-based calcium score may provide long-term outlook on CAD risk

Researchers evaluating the relative value of long-term forecasts for risk among low-risk patients without coronary artery disease (CAD) found that coronary artery calcium scores (CACS) derived from CT scans may hold the biggest prediction bang.

The research team from Houston Methodist DeBakey Heart and Vascular Center, led by Su Min Chang, MD, examined calculated risk against the outcomes for a cohort of 946 patients, derived from an earlier study, across a 10-year span. Other modalities used included exercise treadmill testing and stress myocardial perfusion SPECT. They also assessed patients for the appropriateness or inappropriateness of functional testing according to current guidelines.

The overall rate of cardiac events was low, about 1.6 percent per year among low-risk patients. However, they found that when comparing risk predictors, some patterns stood out. When CACS was evaluated independently, values of 10 or less had cardiac event rates of 0.6 percent per year, while a cardiac event rate of 3.7 percent was seen for CACS values of over 400.

Area under the curve improved most when CACS was added to Framingham risk scores as opposed to exercise treadmill testing or SPECT. CACS also significantly adjusted absolute and relative integrated discrimination (3.5 percent, 285 percent) and net reclassification (30.2 percent) improvement methods for assessing Framingham calculated risk. Adding CACS to functional exercise treadmill testing or SPECT shifted 50.7 percent of patients on level of risk as calculated through a Framingham model.

Chang et al noted that the results demonstrated an incremental long-term prognostic value with CACS that went beyond Framingham risk and other categories generally associated with defining risk.

“Our results reaffirm that functional testing is inappropriate in clinically low-risk patients but also demonstrate that CACS enhances risk prediction in those in whom functional testing is currently considered an appropriate initial strategy,” they wrote. Over the long term, they noted exercise treadmill testing and SPECT had little prognostic effect, and suggested that a determination of low risk by these methods had short “warranty periods,” particularly compared to CACS.

They suggested that based on the data, using CACS to identify atherosclerosis early could allow physicians to treat aggressively in a three- to four-year window before cardiac event risk increases.

Leslee J. Shaw, PhD, from Emory University in Atlanta, wrote in an attached editorial that these findings are needed in light of the shift towards more personalized, long-term healthcare. “On the basis of the findings from Chang et al., one may envision the development of a management strategy whereby the burden of CAC may crudely reflect anatomic burden and, coupled with exercise test findings, preliminary ischemia-guided management strategies may be devised,” Shaw wrote.

“It is time for research to progress beyond the usual risk-prediction models and to move toward the development of diagnostic management strategies on the basis of index test markers, with the aim of long-term risk reduction.”

The study was published in the February issue of the Journal of the American College of Cardiology: Cardiovascular Imaging.