Coronary artery stenosis assessed by CT angiography is a more reliable predictor of major short-term cardiac events—including intervention, heart attacks, and death—than is coronary calcium scoring, according to a study by researchers at a hospital in Michigan.
"Don't hang your hat on the calcium score," said principal investigator Dr. Kavitha Chinnaiyan, director of cardiovascular imaging education at the Williams Beaumont Hospital in Royal Oak.
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The prognostic utility of coronary artery calcium scoring in asymptomatic patients is well established, but CTA's incremental value has been unclear. Chinnaiyan and colleagues sought to identify which of the two was the best predictive test for short-term outcomes in symptomatic patients. V Short-term outcomes ranged from emergency room visits, stress tests, catheter coronary angiography, surgical intervention, and revascularization to major adverse cardiac events such as acute coronary syndrome or death. The investigators retrospectively analyzed data from a cohort of 1568 patients who had undergone both calcium scoring and CT angiography exams.
Patients were split into four groups:
- patients who had a calcium score of ≤400 Agatston units plus CTA-determined stenosis of <50%
- patients with a calcium score of ≤400 AU plus stenosis >50%
- patients with a calcium score >400 AU and stenosis <50%
- patients with a calcium score >400 AU and stenosis >50%
Despite having fewer risks factors, patients in the second group (calcium score ≤400, stenosis >50%) had the highest rate of hospitalization, coronary interventions, and combined major cardiac events. The difference was statistically significant (p <0.0001). A multivariable risk factor analysis showed that stenosis severity as assessed by CTA was the strongest independent predictor of cardiac events. Chinnaiyan released findings at the 2009 Society of Cardiovascular Computed Tomography meeting in Orlando, FL.
Physicians know that in asymptomatic patients, calcium scoring is very good at stratifying risk and predicting intermediate and long-term outcomes. When it comes to symptomatic patients, however, it's a totally different ballgame, Chinnaiyan said. "Calcium score is probably not enough," she told Diagnostic Imaging.
Several studies have shown that younger patients tend to have low or zero calcium scores but can still have an acute coronary syndrome. In that case, the angiogram provides a better risk stratification and prognostic tool, Chinnaiyan said.
Coronary calcium scoring has traditionally been advocated in asymptomatic patients who might otherwise be at risk for coronary artery disease. But recent clinical literature points to the growing popularity of coronary CTA as a first-line exam. The issue remains controversial. Though regarded as highly accurate, radiation exposure from CTA has implications for young patients and women. Calcium scoring, on the other hand, cannot detect noncalcified plaque, a potentially more serious risk for acute coronary syndrome.
A limitation of the study is that it includes short-term patient data from only a single institution. It also based risk factors, such as hypertension, on patient reports instead of clinical records. Larger studies that include intermediate and long-term data are needed. In the meantime, CTA and calcium scoring should be considered complementary tests, Chinnaiyan said.
"Calcium scoring costs a fraction of what an angiogram costs, and we need to know when to apply which test," Chinnaiyan said. "This is one step in that direction."
