Background Intravascular imaging modalities are used clinically to investigate ambiguous angiographic coronary lesions, guide and optimise stent deployment, and assess stent-related complications. Both intravascular ultrasound (IVUS) and optical coherence tomography (OCT) facilitate characterisation of plaque components, although a lack of adequate spatial resolution and depth of penetration, respectively, limit their clinical application. Adaptation of the existing technologies and novel techniques are in development but require further validation. We have developed an ex-vivo whole heart cadaveric model that facilitates multi-modality imaging and accurate comparison with histology.
Methods We have developed a model for fluoroscopic and invasive assessment of coronary arteries within “whole heart” cadaveric specimens. Hearts are provided by the West of England heart valve bio-bank, following harvesting of valves for homograft production. The coronary ostium is dissected and mobilised to allow cannulation with a modified 6F coronary guiding catheter (Abstract 023 figure 1A), secured with sutures. The cadaveric specimen is held within a purpose-built perspex container, with adaptors on both sides of the container's lid allowing connection of the guide catheter internally, and a Y-connector and pressure/injector manifold externally, see Abstract 023 figure 1 panel B. Cadaveric specimens undergo angiography (see Abstract 023 figure 1C,D), placement of a 0.014″ guide wire and imaging catheter manipulation with the artery held at physiological temperature and pressure. In collaboration with the Department of Bioengineering, Erasmus MC, Rotterdam, we are using this model for assessment and validation of optical attenuation analysis as a tool to accurately delineate areas of macrophage infiltration, a major marker of plaque vulnerability. Optical attenuation governs the signal drop-off associated with tissue penetration. It is derived by fitting the following functional relation to the OCT data, I(z) = I0 exp(- μt z), where μt(z) is the local optical attenuation, the parameter of interest. The local signal intensity, I0, is also a free parameter in the fit, but is currently not analysed. The data are fitted in windows of 200 μm length, after appropriate processing to reduce speckle noise.
Results Comparison of OCT, IVUS, and VH-IVUS against histology confirm the challenges in characterising plaque (Abstract 023 figure 2A–D: arrows indicate calcium). Analysis of optical attenuation appears to correlate with areas of macrophage infiltration (arrows in Abstract 023 figure 2E–H).
Conclusions Our ex-vivo whole heart cadaveric model facilitates accurate comparison of imaging modalities against histology. Developments in the imaging technologies are necessary to facilitate plaque characterisation as a clinical application. Optical attenuation may offer additional information regarding the macrophage content and “vulnerability” of plaque, validation work using our cadaveric model is ongoing.
- Optical coherence tomography
- intravascular ultrasound