Lesion Characterization Using Optical Coherence Tomography to Guide Percutaneous Coronary Intervention

Case report

A 61-year-old male with history of coronary artery disease, peripheral arterial disease, diabetes mellitus, hypertension, and dyslipidemia initially presented to the hospital with crescendo angina. His coronary history included two separate coronary artery bypass graft surgeries, as well as multiple coronary stents. The patient reported unrelenting chest pain over the prior 12 hours with associated shortness of breath. Physical examination was unremarkable. Electrocardiogram revealed non-specific T-wave changes, but laboratory analysis demonstrated elevated serum troponin. Subsequent coronary angiography revealed a discrete hazy lesion within a previously placed stent in the mid right coronary artery (RCA), suggestive of a segment of eccentric in-stent restenosis (Figure 1).  

The ostium of the RCA was engaged using a 6 French JR 4.0 Launcher guiding catheter (Medtronic). The lesion was crossed easily with a 0.014” Balanced Middle Weight (Abbott Vascular) guide wire. Optical coherence tomography (OCT) imaging was performed using a Dragonfly (St. Jude Medical), which characterized the lesion as a large thrombus within a segment of previously placed under-expanded stent (Figure 2). Since this lesion proved to be thrombotic in nature, with the potential of embolization during percutaneous coronary intervention (PCI), a SpiderFX 4.0 mm distal embolic protection device (Covidien) was deployed in the distal RCA (Figure 3). Balloon angioplasty was performed within the lesion using a 3.25 x 12 mm non-compliant balloon. Repeat OCT imaging revealed improved apposition of the stent with mild residual thrombus in the distal segment of the stent. A 3.0 x 20 mm non-compliant balloon was used to further dilate the distal RCA and subsequent OCT images confirmed an improved result (Figure 4). Upon removal, the filter demonstrated small amounts of thrombotic debris. Final angiogram revealed an excellent angiographic result with brisk flow into the distal RCA (Figure 5).

Discussion

The most frequent underlying cause of acute coronary syndromes is spontaneous rupture of atherosclerotic plaques and subsequent thrombosis. These vulnerable plaques have been identified by histology to have several characteristics, including a large lipid pool, thin fibrous caps (<65 µm), and activated macrophages.^1,2 Identification of these types of vulnerable lesions may guide PCI and optimize lesion management.

Intravascular coronary imaging has been performed using various modalities, including coronary angioscopy (CAS), intravascular ultrasound (IVUS), and optical coherence tomography (OCT). Each technique has its individual applications and limitations for detecting vulnerable plaques.³

CAS uses projected white light through thin, flexible glass fibers incorporated into catheters in order to see the color of the arterial surface through a clear saline injection, allowing diagnosis of thrombus, and yellow or white plaques.⁴ However, the inability to see through blood because of its opaque nature and the need to remove blood from the visual field remain the primary obstacles to the widespread use of CAS to evaluate plaque morphology.³

IVUS is a catheter-based imaging modality that provides high-resolution cross-sectional images of the coronary arterial walls, allowing qualitative measurements of luminal and vessel areas in vivo.⁵ Plaque morphology by ultrasound is often characterized by the intensity of the signals that correspond to tissue, calcium, and fibrosis.⁶ The major limitation of IVUS is insufficient spatial resolution:  at frequencies in the 20-40 MHz range, it has an axial resolution of 100-200 µm and a lateral resolution of 250 µm.⁷  

OCT is a catheter-based imaging system that utilizes near-infrared light, instead of white light or ultrasound, to produce high-resolution in vivo images of the coronary artery, lesion characteristics and deployed stents. The OCT light source operates on a wavelength ranging from 1,250 to 1,350 nm, which provides a tissue penetration of 1 to 3 mm compared to IVUS, which has a penetration of 4 to 8 mm.⁸ OCT has been shown to identify microstructural features of coronary lesions. One study of 357 grossly diseased arterial segments obtained from cadavers, and evaluated by histology and OCT imaging, showed that OCT was able to demonstrate, from various image criteria, the presence of several characteristics of each lesion, including the presence of thin or fibrous caps, lipid pools and calcification.⁹ Several others have shown that OCT can identify specific features of plaque morphology, including vulnerable plaques, that correspond to clinical presentations of acute coronary syndromes.  

The case herein demonstrates the ability of OCT to identify the characteristics of plaque morphology and the resulting impact on decisions regarding the intervention of the culprit lesion. We identified that the lesion was indeed thrombotic in nature, in the setting of poor apposition of the original stent placed in the mid RCA. This led to the utilization of an embolic protection device, as disruption of the thrombus with angioplasty may have likely induced embolization with drastic consequences. Thus, the use of high-resolution intracoronary imaging for plaque characterization may help guide PCI.  

Disclosure: Dr. George reports he is a consultant for Boston Scientific Corporation and Covidien. Dr. Shaw and Dr. Selvaraj report no conflicts of interest regarding the content herein.

The authors can be contacted via Dr. Jon George at georgej@deborah.org.

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