Assessment of intermediate severity left main coronary artery (LMCA) lesions is often performed in the cardiac catheterization laboratory because obstructive disease in this location is associated with a worse long–term prognosis.1–3 Some studies also suggest that the passage and delivery of interventional equipment through a diseased LMCA accelerates disease progression in this segment.4,5 Although traditionally considered a surgical disease, an increasing body of evidence supports percutaneous revascularization with drug-eluting stents, particularly in isolated LMCA disease.6 As a result, it is likely that more and more patients with intermediate severity LMCA disease will be evaluated to determine its hemodynamic significance.
Although coronary angiography is commonly used to diagnose LMCA disease, due to the difficulty in imaging lesions located in the ostium and bifurcation and the inability to accurately capture the extent of plaque deposition in diffusely diseased left main arteries, alternative imaging techniques are also used in these challenging circumstances. These include either intravascular ultrasound (IVUS) or fractional flow reserve measurements (FFR) to enhance the diagnostic capacity of angiography. Of these, IVUS is more commonly used because it provides both accurate and detailed tomographic information of the vessel wall and atherosclerotic plaque, including plaque size and composition. Several studies have reported minimum luminal area (MLA) measurements with IVUS that correlate with worse long-term outcomes.7,8 Fassa et al reported that patients with MLA measurements 0.8 for volume measurements within plaques. However, the ICC was between 0.5–0.8 when measuring small diameters and for area calculations. Obvious limitations of this analysis include its small sample size (n = 65), IVUS analysis by only a single observer (hence lacking inter-observer variability) and the exclusion of patients with severe LMCA stenosis or subtotal stenosis. In addition, the average MLD in this patient population was 3.6–3.7 mm, whereas the average MLA was 13.5–14.6 mm2, which would suggest mild-to-moderate LMCA disease. The authors also observed a stronger correlation for lesion-specific measurements such as fibrous volume, fibrolipidic volume and larger-sized vessels, whereas only a moderate degree of correlation was observed for the measures of hemodynamic severity of the lesion such as MLA and MLD and in smaller vessels. Since the hemodynamic severity assessment of intermediate lesions is particularly important in the LMCA with diffuse disease, the less-than-ideal correlation in smaller LMCA is a cause for concern. Although the authors argue that this might be expected due to the contour detection errors and inability to differentiate lumen from tissue, one wonders whether this difference is related to the particular IVUS technology used in this study or to the methodology in general.
Nonetheless, for the average interventionalist, the choice of measuring LMCA stenosis with IVUS via the LAD or the LCx should be based on some simple rules of thumb. When imaging through either the LAD or the LCx provides additional information to help guide the interventional technique, the LMCA should be imaged through that particular branch. One example of this would be the need to determine whether the left main disease extends into the ostium of either the LAD or the LCx, or both. In all other cases, the artery that provides the best and most distortion-free image (which in most cases is the LAD) should be chosen. This should obviate any measurement bias in the LMCA when the tomographic images are obtained from an oblique angle as opposed to being coaxial within the lumen. Under these circumstances, the results of this article from Suter et al should serve to reassure the operator that when it comes to measuring the severity of lesions in the LMCA, pullback from either the LAD or the LCX provides equivalent information, particularly in the presence of mild-to-moderate LMCA disease.
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From the Montefiore Medical Center, New York, New York.
The authors report no conflicts of interest regarding the content herein.
Address for correspondence: V.S. Srinivas, MBBS, FACC, 1825 Eastchester Road, Suite W1-120, Bronx, NY 10461. E-mail: vsriniva@montefiore.org
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