Quantitative Estimation of Thrombus Burden in Patients With STEMI Using Micro-Computed Tomography (QUEST-STEMI)

Acute myocardial infarction with ST elevation (STEMI) remains one of the leading causes of mortality in developed countries, in spite of the important advances in pharmacological therapy and in mechanical reperfusion therapy. Having an important role in provoking ischemia, thrombus has been studied in many clinical trials and high thrombus burden has been proven to be an independent risk factor for stent thrombosis and for Major Adverse Clinical outcomes. However large randomized controlled trials concerning thrombus aspiration showed controversial results, providing as a whole no evidence of distinct benefits for thrombus aspiration. A possible explanation could be that aspiration was performed as a routine strategy in all of these trials, whereas these patients should be considered as a heterogeneous group and thus they should be risk-stratified. For this reason, it is of paramount importance to classify patients according to the volume of thrombus burden. The currently existing classifications of thrombus burden (the most important being those of Gibson and of Sianos) are based on visual assessment of angiographic characteristics and thus they are not reflecting the volume of the thrombi in actual, absolute numbers.

The main purpose of the study is to develop a methodology for the exact estimation of thrombus burden by measuring the volume and the density of aspirated thrombi in patients presenting with STEMI and referred for primary PCI. After being aspirated using dedicated catheters, thrombi will be preserved in formalin and their volume will be calculated with the use of micro-CT. The scanning procedure results into a series of projection images arranged in the form of image stacks which, in turn, are reformed in sections (cross section images) with the use of the NRecon (Bruker, Kontich, Belgium) software, which applies a modified algorithm of backward projection Feldkamp. The resulting sections will be combined to create the 3D models which will be further analyzed to extract useful measurements for the characteristics of the thrombi, such as for the volume and the elative density. Shape analysis on the surface and internal structure of the three-dimensional representations of the specimens will lead to the identification of the important features that can be used to estimate variability within samples and perform clustering for the significant differences between clots. In addition, possible differences in clot internal and external structure (e.g. architecture of the various cell types) will be assessed through the 3D models rendered from the stacks of images The Secondary end points of the study include the examination of the association of the aforementioned variables with the angiographic classification of thrombus burden (according to Sianos), with electrocardiographic and angiographic characteristics suggestive of poor patient prognosis and with major adverse cardiac events during the follow-up period of one year.

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.

Inclusion criteria

• Patients presenting with symptoms of myocardial ischemia lasting for more than 30 minutes
• Definite ECG changes indicating STEMI
• Patients undergoing primary PCI within 12 hours from symptom onset
• Possibility to perform thrombus aspiration
• Age>18 years
• Written informed consent prior to enrolment in the clinical trial

Exclusion criteria

• Treatment with fibrinolytic therapy for qualifying index STEMI event
• Patients with known intolerance to aspirin, ticagrelor or heparin
• Patients with active internal bleeding
• Patients with a recent history of intracranial hemorrhage