Multislice computed tomography coronary angiography: A study in search of a clinical niche

Cardiology Review

The study presented in this issue of by Schuijf and colleagues investigated various aspects of what is rapidly becoming an accepted imaging modality for the assessment of coronary artery disease. The authors evaluated 100 subjects who underwent multislice computed tomography (MSCT) to assess coronary artery disease.¹ The entire sample had a mean follow-up period of 16 months, with clinical endpoints consisting of cardiac death, nonfatal myocardial infarction (MI), unstable angina requiring hospitalization, and the need for coronary artery revascularization. The subject population consisted of 73 men and 27 women with an average age of 59 years who were evaluated in an outpatient clinic setting. Contrast MSCT angiography was performed in standard fashion. Exclusion criteria included previous coronary artery bypass graft surgery, contraindications to iodinated contrast agents, and atrial fibrillation. Thus, the study population was truly reflective of patients undergoing initial evaluation for coronary disease.

Scans were acquired, analyzed, and categorized with regard to the following characteristics. Normal scans versus abnormal scans were noted. Abnormal scans were further classified as having obstructive coronary artery disease (having at least 1 lesion exceeding 50% luminal narrowing), nonobstructive coronary artery disease (less than 50% luminal narrowing), significant coronary artery disease in the left main or left anterior descending artery, or the presence of "mixed" plaque type. The mixed plaque type consisted of both calcified and noncalcified plaques

as

determined by this imaging modality.

Twenty subjects had normal scans. Obstructive coronary disease was noted in 32 subjects, with involvement of the left main or left anterior descending artery in 23 patients. The remaining subjects had nonobstructive coronary disease. Plaque type (with regards to calcified, noncalcified, or "mixed") was noted for all patients with abnormal studies.

At the 1-year follow-up, there were zero events in the subjects with normal MSCT. Five percent of subjects with abnormal coronary arteries on MSCT experienced a "hard" cardiac event, meaning an acute MI or unstable angina.

When expanding the clinical endpoints to include both acute and elective coronary revascularization, the event rate was 30% in the subjects with abnormal MSCT during the follow-up period. Multivariant analysis showed that the presence of any coronary artery disease on MSCT, obstructive coronary artery disease, obstructive coronary artery disease in the left main or left anterior descending artery, age of the subject, and the number of segments with calcified and "mixed" plaques were independent predictors of cardiac events. Other traditional coronary artery disease risk factors were not significant in this analysis.

The clinical take-home points from this study can be summarized as follows. Multislice computed tomography has an excellent negative predictive value, with a 100% event-free first-year survival rate. Thus, the value of an entirely normal study has been established. For patients with abnormal studies, characteristics such as location and type of atherosclerotic plaques can provide valuable prognostic information for follow-up clinical management. Of note, traditional coronary angiography lacks the ability to characterize plaques with regard to being calcified versus mixed. Further evaluation with imaging modalities such as intravascular ultrasound (IVU) can accomplish this. However, these diagnostic modalities are invasive and, in the case of IVU, border on interventional. One must be aware that there are standard risks inherent in these procedures. Multislice computed tomography does involve the use of contrast and a one-time radiation exposure risk. However, it is still a noninvasive imaging modality.

The clinical niche that MSCT will occupy is still unclear. The present study suggests that as an initial screening modality, MSCT shows promise with regard to stratifying and categorizing patients. Furthermore, based on initial MSCT, patients may be selected for further invasive diagnostic and interventional procedures. The use of MSCT as a follow-up diagnostic modality is uncertain. One must balance the radiation and contrast exposure against the benefit of the expected diagnostic information. Perhaps further studies in larger and different patient cohorts may address these questions.