Can CT coronary angiography effectively rule out coronary disease in a patient admitted with chest pain?

A large randomized controlled trial, Coronary Computed Tomo­graphy for Systematic Triage of Acute Chest Pain Patients to Treatment (CT-STAT), is planned to definitively study the use of coronary CT angiography in low-risk patients with chest pain. The large-scale study will involve 750 patients in 15 U.S. hospitals.

CT angiography remains limited despite many recent advances. A stable rhythm is a prerequisite, precluding use in patients with atrial fibrillation or frequent extra-systoles. Also, the required dose of 80 cc to 100 cc of iodinated contrast puts patients at risk for contrast-induced nephropathy, especially those with renal insufficiency.

Finally, radiation exposure is higher than that required for cardiac catheterization.13 Coronary calcification interferes with the images obtained by CT. Therefore, patients with heavy coronary calcium burden (CAC more than 400) may have reduced specificity and negative predictive value. Because this calcification increases with age, the diagnostic accuracy of CT angiography may decrease with age.

Morbidly obese patients may also have decreased image quality. Raff. et al., found significant stenosis in patients with normal body-mass index (BMI) (less than 25 kg/m2). Sensitivity, specificity, and positive and negative predictive values were all 100% and remained accurate in overweight patients. When BMI was more than 30, sensitivity and specificity were reduced to 90% and 86%, respectively.

Visualization of the coronary artery within a stent may be less accurate with CT angiography due to beam artifact, but evaluation of native coronary arteries and bypass grafts maintain similar sensitivity and specificity in these patients.14 A final concern is that CT angiography is only diagnostic. Although only 25% to 30% of diagnostic cardiac catheterizations reveal disease that meets criteria for stent placement, the study is redundant in these high-risk patients, who likely will be referred for traditional coronary angiography with stenting.

Back to the Case

The patient underwent nuclear stress testing the morning following admission. He had minimal attenuation in the infero-lateral distribution. A 64-slice CT angiogram was obtained, and images of the coronary anatomy demonstrated no plaque. The patient was reassured, and no further cardiac imaging was pursued. TH

Dr. Jenkins is an associate clinical professor and associate chief of hospital medicine in the Department of Family Medicine and Community Health at the University of Massachusetts medical school, Worcester.

References

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