Amongst the advanced cardiac imaging modalities, multislice computed tomography (MSCT) coronary angiography is emerging as a reliable non-invasive method for the assessment of coronary artery disease (CAD), coronary anatomy and cardiac function [1–17]. Improvements in computed tomography technology hold the promise of replacing the standard invasive procedure of conventional coronary angiography in selected patient groups. Multiple studies involving over several thousands of patients have established that MSCT angiography is highly accurate for delineation of the presence and severity of coronary atherosclerosis [18–23]. The technique provides independent prognostic information over baseline clinical risk factors in patients with known and suspected CAD [24]. MSCT may also reveal the total plaque burden, i.e., both calcified and non-calcified components, for individual patients with coronary atherosclerosis [25–32]. This holds in particular for detecting patients with left main disease as this disease is associated with a poor prognosis. Timely detection of atherosclerosis of the left main stem is crucial as it may determine future interventional therapy. The standard of care for left main coronary artery disease is coronary artery bypass surgery (CABG), but technical advances in percutaneous coronary intervention (PCI) and stenting technology have emboldened the interventional cardiology community to test the feasibility of and document the procedural results for stenting the left main coronary artery [33–36]. MSCT may therefore play an important role for guiding interventional therapy by early detection and establishing the severity and extent of coronary atherosclerosis of the left main coronary artery.

Rodriquez-Granillo et al. [34] explored the differences in plaque burden at different segments of the left main bifurcation and its relationship with the bifurcation angle using high-resolution MSCT. A total of 50 patients were evaluated using a 40-row MSCT scanner. The localization, severity and distribution of plaques within the left main bifurcation were determined. Seventeen (34%) patients presented wall irregularities in the left main stem and in the ostial left circumflex coronary artery, whereas the ostial left descending coronary artery was affected in 32 (64%) patients. More than 90% of plaques were located opposite to the flow divider. Of the 18 patients with a normal ostial left anterior descending coronary artery, 13 (72%) had a bifurcation angle <88.5°, whereas the 63% of the patients with any disease of left anterior descending coronary artery had an angle ≥88.5°(P = 0.018). At the left main bifurcation, atherosclerotic plaques were commonly eccentric and located opposite to the flow divider. A relationship was therefore clearly present between the angle of the left main bifurcation and the presence of plaques within the bifurcation.

Multislice computed tomography has also been shown to provide a noninvasive alternative to conventional coronary angiography in the follow-up of left main coronary stenting. Gilard et al. [35] investigated the ability of 16-slice MSCT to discriminate any restenosis after left main coronary artery stenting in 29 consecutive patients. MSCT was able to detect all stents and to analyze the lumen in 27 of 29 patients. Van Mieghem et al. [36] showed that current MSCT technology, in combination with optimal heart rate control, allowed reliable noninvasive evaluation of selected patients after LMCA stenting. MSCT was safe to exclude left main in-stent restenosis and may therefore be an acceptable first-line alternative to coronary angiography.

In the present issue of the International Journal of Cardiovascular Imaging Gemici et al. [37] evaluated the prevalence of left main disease in 1,000 patients referred to MSCT (64-slice) coronary angiography. Left main coronary artery was classified into three groups: (1) normal left main coronary artery, (2) non-significant left main disease with coronary plaques resulting in <50% luminal stenosis, and (3) significant left main disease corresponding to >50% luminal stenosis. Significant left main disease was found in 24 (2.4%) of the 1,000 patients. Predominantly non-calcified plaques were found in patients with non-significant left main disease, and mixed plaques in patients with significant left main CAD. Left main disease was associated with age, male gender, diabetes, hypertension, hyperlipidemia, typical symptoms, history of previous myocardial infarction and previous PCI. Only age and male gender were found as independent predictors for left main disease. Follow-up angiography confirmed the presence of significant left main disease in all 24 patients. Although artifacts due to severe coronary calcification are commonly the main cause of false-positive results in MSCT, calcifications are not a major problem in patients with significant left main CAD because of more accurate visualization of proximal coronary artery lesions by MSCT.

Interestingly, the prevalence of non-significant left main disease was much higher than usually found with conventional coronary angiography (20 vs. 3.3%, respectively). This might be related to the superior sensitivity of MSCT for non-significant plaque imaging. The clinical implication of these findings is of major importance because non-significant plaques in the left main stem revealed by MSCT have already been associated with an adverse outcome [24]. In that particular study, Pundziute et al. [24] showed an 8% one-year event rate for patients with nonobstructive CAD versus 0% for patients without any signs of CAD. The study by Gemici et al. [37] adds therefore important information to the capability of MSCT in assessing local plaque burden in patients with left main disease, in particular in those patients with non-significant left main disease. Timely detection of atherosclerosis of the left main coronary artery will therefore become a major challenge.