Background: Invasive, selective coronary angiography remains the "gold standard" of direct visualization of epicardial coronary arteries. Technical advances in recent years and improvements in image quality in both electron beam computed tomography (EBT) and multislice spiral/helical computed tomography (MSCT) brought along an increasing interest in the potential clinical role of noninvasive computed tomographic coronary angiography (CTCA).
Potential and limitations: Measurement of coronary calcification permits quantitative estimation of overall coronary plaque burden and thereby allows assessment of cardiovascular risk and likelihood of the presence of a significant stenosis. However, the precise site and degree of stenoses cannot be measured. Contrast-enhanced CTCA lumenography permits visualization of epicardial coronary artery stenoses with a sensitivity and specificity of about 90%. Noncalcified plaques may also be detected in individual cases, but very few data are available on this aspect of CTCA. Image artifacts due to rapid motion, especially in the distal segments of the right and circumflex coronary arteries, may preclude reliable assessment of 20-30% of these segments. Also, in-stent restenoses and distal bypass anastomoses will, in the foreseeable future, remain difficult to confidently diagnose by CTCA. Combined assessment of calcified plaque burden and CTCA may enhance diagnostic accuracy especially in patients with low or moderate calcium scores. In the presence of heavy calcifications, stenoses may be masked.
Indications: Noninvasive CT-based evaluation of coronary arteries seems useful in patients with a low to intermediate pretest likelihood for significant coronary artery disease (CAD). This holds for several ACC/AHA class II indications described for invasive, selective coronary angiography and for few class I indications. Further prospective studies are required to establish the clinical value of combined assessment of coronary calcium quantification and CTCA.