Cardiac computed tomography has revolutionized cardiac imaging in recent years by providing exquisitely detailed cardiac anatomy, including, but not limited to, coronary anatomy.
Non-invasive coronary angiography by computed tomography (CTA) is performed in ever increasing numbers, over 150,000 per year in the United States. However, the specific role of CTA in the diagnostic pathways of cardiology remains to be defined, and practice patterns of the technique often neglect established insights into coronary artery disease. The following characteristics of CTA need to be understood:
- CTA is very good and reliable at excluding coronary artery disease (CAD), with negative predictive values approaching 100%. It is far less good at assessing the hemodynamic relevance of overt disease. Head to head comparisons with nuclear perfusion data show that about half of coronary lesions graded as > 50% diameter stenosis by CTA do not induce ischemia under stress.
- CTA entails substantial radiation (varying widely between 6 and 11 mSv in a recent report) and contrast media exposure (60-80 ml), both with attending risks of malignancy and renal damage, respectively.
- Current accuracy and radiation exposure data from CTA come from highly specialized, experienced centres. It is very unlikely that this quality is maintained when the technique is applied by less experienced operators.
Next, some fundamental insights into CAD should be remembered: