Angiographic assessment of coronary lesions with intermediate severity (ie, luminal narrowing with a diameter stenosis >40% but <70%) continues to be a challenge. Magdy Rashwan, MD, University of Alexandria, Alexandria, Egypt, discussed some of the techniques that can be used to assess these lesions and how their composition affects prognosis.

Fractional flow reserve (FFR) is a useful technique for measuring the functional severity of narrowing in the coronary arteries, as it can measure the pressure gradient and flow across different regions. FFR is the standard in many catheterization labs; however, it is an invasive technique. Several studies have assessed the correlation between noninvasive approaches and FFR results to determine the quality of the correlation.

Lockie and colleagues recently reported that high-resolution 3.0 T cardiac magnetic resonance (CMR) perfusion can detect hemodynamically significant coronary stenosis, as determined by FFR [J Am Coll Cardiol 2011]. In contrast, a poor correlation between stenosis severity, as determined by computed tomography coronary angiography (CTA) or conventional coronary angiography, and ischemia that is measured by FFR was previously shown [Meijboom WB et al. J Am Coll Cardiol 2008]. These results were recently confirmed by Voros and colleagues, who showed better functional correlation with intravascular ultrasound (IVUS) than with CTA [J Am Coll Cardiol Intv 2011]. Prof. Rashwan said that in the catheterization lab, the ideal assessment for intermediate lesions is by FFR or IVUS; however, for a noninvasive approach, myocardial perfusion by MRI is the most promising technique.

The PROSPECT trial was a large, prospective, natural history study in 700 patients with acute coronary syndromes (ACS). Subjects were enrolled after undergoing successful and uncomplicated percutaneous coronary intervention for the treatment of all coronary lesions that were believed to be responsible for the index event and after the completion of any other planned interventions. The primary purpose of the study was to confirm the hypothesis that ACS arises from atheromas with certain histopathological characteristics and that these characteristics are not necessarily dependent on the degree of angiographic stenosis at the site. Grayscale and radiofrequency intravascular ultrasonographic imaging was used prospectively to characterize coronary atherosclerosis before longitudinal follow-up. Although the major adverse coronary events (MACE) that occurred during the 3 years of follow-up were equally attributable to recurrence at the site of culprit lesions and to nonculprit lesions, the nonculprit lesions were frequently angiographically mild, and most were thin-cap fibroatheromas or were characterized by a large plaque burden, a small luminal area, or some combination of these characteristics [Stone GW et al. New Engl J Med 2011]. Prof. Rashwan also presented data from a very recent (unpublished) study from Vazquez and colleagues, showing the correlation between plaque composition of intermediate lesions and the incidence of MACE. In that study, higher calcium density corresponded with fewer MACE, while a larger plaque burden, fibrofatty area, and fibrofatty percent corresponded with higher rates of MACE.

Plaque stability deserves an important consideration and is related to its histological composition. In a recent study, Kubo and colleagues [Kubo T et al. J Am Col Cardiol 2010] used virtual histology (VH) IVUS to investigate the natural history of coronary artery lesion morphology. Lesions were classified into pathological intimal thickening (PIT), 6 thin-capped fibroatheroma (TCFA), thick-capped fibroatheroma (ThCFA), fibrotic plaque, and fibrocalcific plaque. Over the 12 months of follow-up, most VH-TCFAs healed; however, new VH-TCFAs also developed. PITs, VH-TCFAs, and ThCFAs showed significant plaque progression compared with fibrous and fibrocalcific plaque, indicating that this is a dynamic disease.