The assessment of intermediate coronary lesions using intracoronary imaging

Abstract

Intermediate coronary artery stenosis, defined as visual angiographic stenosis severity of between 30-70%, is present in up to one quarter of patients undergoing coronary angiography. Patients with this particular lesion subset represent a distinct clinical challenge, with operators often uncertain on the need for revascularization. Although international guidelines appropriately recommend physiological pressure-based assessment of these lesions utilizing either fractional flow reserve (FFR) or quantitative flow ratio (QFR), there are specific clinical scenarios and lesion subsets where the use of such indices may not be reliable. Intravascular imaging, mainly utilizing intravascular ultrasound (IVUS) and optical coherence tomography (OCT) represents an alternate and at times complementary diagnostic modality for the evaluation of intermediate coronary stenoses. Studies have attempted to validate these specific imaging measures with physiological markers of lesion-specific ischaemia with varied results. Intravascular imaging however also provides additional benefits that include portrayal of plaque morphology, guidance on stent implantation and sizing and may portend improved clinical outcomes. Looking forward, research in computational fluid dynamics now seeks to integrate both lesion-based physiology and anatomical assessment using intravascular imaging. This review will discuss the rationale and indications for the use of intravascular imaging assessment of intermediate lesions, while highlighting the current limitations and benefits to this approach.

Keywords: Optical coherence tomography (OCT); coronary artery disease (CAD); intravascular ultrasound (IVUS).

Figure 1

Intravascular ultrasound assessment of an intermediate left main coronary artery stenosis. Eccentric and calcified distal left main coronary artery (LMCA) lesion (A). Representative cross-sectional intravascular ultrasound (IVUS) images of the proximal reference segment with highlighted minimal luminal area (MLA) (highlighted blue) (C) and target lesion MLA (blue) highlighting eccentricity and superficial calcification (D). The calculated MLA (shaded blue) was 5.1 mm², which is below the safe deferral threshold of 6 mm² (B). Panel B reproduced from Jasti et al. Circulation, 2004 (32).

Figure 2

Hybrid use of intracoronary imaging and physiology to guide coronary revascularisation. Coronary angiography demonstrating intermediate distal left main coronary artery (LMCA) stenosis (A) with downstream severe disease in the mid left anterior descending (LAD) artery (B). Both fractional flow reserve (C) and resting full-cycle ratio (F) assessment confirm ischaemia within the LAD territory. Optical coherence tomography imaging demonstrates the minimal luminal area within the LMCA is 7.95 mm² (D), highlighting that targeted revascularisation of the proximal to mid LAD should be considered and precluding need for intervention of the LMCA.

Figure 3

Optical coherence tomography assessment of the distal left main coronary artery bifurcation. Intermediate angiographic distal left main coronary artery (LMCA) lesion (A), with cross sectional optical coherence tomography image (B) of the distal LMCA body with minimal luminal area (MLA) of 3.82 mm². Importantly, the MLA decreases significantly at the point of confluence (C), which illustrates a slit like orifice to the circumflex artery. Further OCT images of the proximal to mid LAD (D) then highlight concentric calcification, which may act to resist semi-compliant balloon dilatation.

Figure 4

Optical coherence tomography and fractional flow reserve. Intermediate lesion of the distal left main coronary artery (A), which extends into the proximal left anterior descending (LAD). Initial optical coherence tomography images (B) demonstrate a minimal luminal area of 2.64 mm², with evidence of a small intimal dissection (at 11 o’clock). Fractional flow reserve (FFR) assessment of the vessel (C) demonstrates that the lesion is highly haemodynamically significant (FFR 0.67).