Adding coronary artery calcium (CAC) score testing with CT in patients with a normal SPECT scan could help identify those at high long-term risk for cardiac events, in whom an earlier focus on aggressive risk factor modification and other medical therapies may be beneficial, according to new findings published in the Nov. 10 issue of the Journal of the American College of Cardiology.
By relying solely on a patient's clinical risk profile or the results of one imaging test when assessing patients with chest pain, physicians may be missing important, early signs of atherosclerotic disease and opportunities to intervene, the authors cautioned.
"Typically, when a patient presents with chest pain and the [SPECT] test result is normal, we tell them everything looks fine, but this may not be the case," said the study’s principal investigator John J. Mahmarian, MD, a cardiologist at the Methodist DeBakey Heart and Vascular Center in Houston. "If a large extent of calcium is present in the coronary arteries, which can't be measured by functional SPECT imaging, he or she is at high long-term risk for a cardiac event. Based on our findings, using both tests to define risk is better than either test alone."
Investigators followed 1,126 asymptomatic patients without a previous history of coronary artery disease who had a CAC score test and stress SPECT scan performed within a close period of time (median of 56 days). The study period was from December 1995 to May 2006.
The study found that approximately half of all patients with a normal SPECT result had a CAC score of at least moderate severity, signaling cardiac risk that would not otherwise have been predicted. Increasing CAC score severity is associated with a greater likelihood of cardiac events and deaths, the authors wrote.
According to the researchers, the risk of death or a heart attack over time increased by 3.55-fold when the calcium score was severe (more than 400) in patients with a normal SPECT. The CAC score also was found to be a stronger predictor of cardiac events than diabetes, which is considered synonymous with having coronary artery disease.
For this reason, the authors urged a CAC test be performed in patients with a normal SPECT who have an intermediate or high clinical risk factor profile for coronary artery disease (e.g., smoking, high cholesterol, high blood pressure, diabetes, family history). If the CAC score is high, patients should be treated aggressively to prevent the progression of disease, added Mahmarian.
"Although a normal SPECT result predicts excellent short-term event-free survival, it doesn't tell us anything about long-term risk, and long-term outcome is significantly worse if the CAC score is severe," said Mahmarian. "By integrating these two tests, we can identify patients at high long-term risk for heart problems and may, thereby, have a better shot at preventing further development of obstructive disease and improving outcomes."
The authors found that separation of the survival curves occurred at three years after initial testing for all cardiac events and at five years for death or myocardial infarction (MI).
"Our results reinforce the need to press forward and look at how an integrated approach to imaging can be cost-effective in preventing downstream events and improving outcomes," said Mahmarian.
The authors said that the next step is to conduct prospective trials to evaluate how adding a CAC score to functional SPECT scans can guide the intensity of therapy targeted to individual patients and whether such an approach can improve outcome in a cost-effective manner.