Computed Tomography-Based Left Ventricular Tissue Heterogeneity in Ischaemic Cardiomyopathy: Investigation of Adipose Tissue and Fibrosis with Extracellular Volume

Iulia Nazarov1, Luca Azzolin2, Aurel Neic3, Mohammad Kayyali1, Sri Kousthubha Allampalli1, Ursula Rohrer1, Ronak Rajani4, Fernando Campos5, Gernot Plank6, John Whitaker1, Martin Bishop1
1King's College London, 2Karlsruhe Institute of Technology, 3NumeriCor GmbH, 4Guy's and St Thomas' NHS Foundation, 5School of Biomedical Engineering and Imaging Sciences, King's College London, 6Medical University of Graz


Abstract

Background: Myocardial fibrosis presence is a known pro-arrhythmic substrate, though growing evidence points towards infiltrated myocardial adipose tissue as also playing an important arrhythmogenic role. On CMR imaging, however, distinguishing between the two can be challenging.    Aims: The primary aim of this study is to develop CT-based metrics to characterize the left-ventricle (LV) heterogeneity by identifying regions of adipose and thinning myocardium. A secondary aim is to compute the extracellular volume (ECVCT) to validate the CT-derived thresholds.  Methods: A late iodine enhancement CT protocol was carried out pre-procedurally for 10 VT ablations. A diastolic phase CT scan was used to automatically segment the heart anatomy and to define adipose based on the CT attenuation values of –180 to –5 HU. Personalized 3D models were constructed to include the layers of fat, and the LV wall thickness (WT) was calculated as the distance between the endocardium and the subepicardial fat. The distribution of the WT was modeled by three Gaussian mixture models that informed the cut-offs between thinning and healthy tissue. Pre-, post-contrast, and angiography CT scans were used to compute the ECVCT based on the difference in attenuation values.  Results: Analysis of the WT returned a 5.89±0.85 mm cut-off value between thinned and healthy myocardium. The median ECV in regions defined as healthy (29.82% [28.03-32.033]) was significantly different than the ECV in thinned (33.69% [32.17-35.29]) or adipose (23.37% [18.29-26.70]) myocardium. The high ECV values present in the thinning myocardial wall define the fibrotic tissue.  Conclusion: CT provides a comprehensive modality to computationally characterize the LV tissue and identify potential arrhythmogenic substrate in ICM patients.