568 Imaging and quantitative estimation of thrombus burden in patients with ST elevation acute myocardial infarction (STEMI) with the use of micro-computed tomography-A methodological approach
Authors: Karagiannidis E , Konstantinidis N V , Sofidis G , Chatzinikolaou E , Sianos G 
Published: January 2020

Abstract

Funding Acknowledgements
Operational Program "Human Resources Development, Education and Lifelong Learning" - co-financed by the European Social Fund and Greek national funds

Background
Acute myocardial infarction with ST elevation (STEMI) remains one of the leading causes of mortality. High thrombus burden has been proven to be an independent risk factor for stent thrombosis and for Major Adverse Clinical outcomes. However randomized controlled trials concerning thrombus aspiration showed controversial results, providing no evidence of benefits for thrombus aspiration. A possible explanation is that aspiration was performed as a routine strategy, whereas these patients should be considered as a heterogeneous group and they should be risk-stratified. Thus, it is important to classify patients according to the volume of thrombus burden. The currently existing classifications of thrombus burden are based on visual assessment of angiographic characteristics and they are not reflecting the volume of the thrombi in actual numbers. To the best of our knowledge, never before has the exact volume of thrombus burden been quantified.

Purpose
The study aims to assess for the first time, through the application of innovative technologies (micro-Computed Tomography, micro-CT), important characteristics of aspirated thrombi (volume and density), which might be linked to certain clinical outcomes, in patients with STEMI.

Methodology
After being aspirated, thrombi are preserved in formalin. As they consist of soft tissue with low X-ray absorption, thrombi have to be stained using contrast enhancing chemicals prior to scanning; in particular a solution containing 0.3% phosphotungstic acid is used (Metscher protocol). The scanning procedure results into a series of projection images arranged in the form of image stacks which, in turn, are reformed in sections with the use of special software, which applies a modified algorithm of backward projection Feldkamp. The resulting sections are combined to create the 3D models which are further analyzed to extract useful measurements for the characteristics of the thrombi, such as volume and density.

Results
From January 2018 to May 2019, 66 patients were enrolled in the study. Mean age was 60.36 (±11.71) years and the majority of them (78.7%) were men. Revascularization was achieved in mean 358 ± 255 minutes from symptom onset. Distal embolization was observed in 27.5% of the patients and no-reflow phenomenon was seen in 11.6%. Angiographically evident residual thrombus burden was observed in 6 patients (8.7%). Micro-CT managed to effectively quantify the volume and the density of aspirated thrombi. Mean volume was 12.98 ± 10.84 mm3, mean density was 2992 ± 872 HU and mean surface was 0.206 ± 0.19.

Conclusion
Micro-CT can be used as a tool to effectively assess important characteristics of aspirated thrombi, which might be linked to certain clinical outcomes. This method could become the gold standard for the exact measurement of thrombus burden and could be used in larger, clinically-oriented trials to help stratify patients with thrombus burden according to their risk for adverse outcomes.
Abstract 568 Figure. Coronary thrombi as depicted on micro-CT