Objective: Coronary calcification detected by CT is a marker for atherosclerotic disease with prognostic significance. However, potentially unstable plaque is characterized by a high lipid content rather than calcification, which may make detection using the calcium score difficult. To assess the prevalence and severity of atherosclerotic disease in patients without coronary calcification, we evaluated findings in patients with a normal calcium score undergoing coronary CT angiography (CTA).
Materials and methods: Data from 794 consecutive coronary CTA examinations performed between February 2005 and May 2007 were reviewed. The calcium scores were determined as part of coronary CTA examinations, and calcium was quantified according to the Agatston method. Patients underwent coronary CTA because of high risk for coronary artery disease (53%) or atypical symptoms or abnormal stress test results (47%). On coronary CTA, plaque was characterized as mild disease without hemodynamically significant stenosis, moderate disease without hemodynamically significant stenosis, moderate stenosis (50-70% luminal narrowing), or severe stenosis (> 70% luminal narrowing).
Results: Of the 729 patients included in the study, 325 (45%) had a normal calcium score. Of these, 167 (51%) had noncalcified plaque on coronary CTA. Twelve (3.7%) of those with a normal calcium score had at least moderate stenosis, five (1.5%) of whom had severe stenosis. Eight of the 12 patients with significant stenosis underwent invasive angiography and coronary stenting.
Conclusion: A considerable atheroma burden including significant stenoses may be present in patients with no coronary calcification. Although the calcium score does add prognostic value to standard risk factors and serum markers, imaging the vessel wall directly may be helpful to identify noncalcified plaque and guide therapy.