Tolga D. Dittrich, MD
Mechanical thrombectomy (MT) for acute stroke has made remarkable advances over the last few years. Despite technological improvements, revascularization still is not successful in a considerable fraction of treated patients. This inevitably raises the question of why MT is so difficult in some patients and how we might treat them better in the future.
An important starting point could be a more comprehensive understanding of the biological composition of thrombi and their mechanical properties. Experimental studies have shown that increasing thrombus stiffness is associated with unsuccessful or incomplete recanalization. For example, particularly stiff platelet-rich thrombi could not be removed by aspiration alone or combined with a stent retriever in an animal model.
Boodt and colleagues addressed the mechanical characterization of thrombi collected during MT in patients with acute ischemic stroke and examined their relationship to quantitative thrombus composition. For this purpose, 41 thrombi from 19 patients with acute stroke who received MT between July and October 2019 were examined. Mechanical stress sampling using compression was performed to measure thrombus stiffness (tangent modulus at 75% elongation, Et75), and a histological workup was performed. The relationship between histological composition and stiffness was analyzed using uni- and multivariable linear regression models. Fibrin and platelet content of the thrombi were strongly associated with increased thrombus stiffness (particularly from a platelet content of about 70%). For every 1% increase in fibrin/platelets and every ≈1% decrease in erythrocytes, stiffness increased by 9 kPa.
So does the same thrombectomy device work equally well for all types of thrombi? Existing evidence suggests that it does not, but it is too early to draw definitive conclusions as there is still little data. The results of Boodt et al. provide an essential basis for future research as they could inform the development of future thrombectomy devices. Thrombectomy techniques and devices tailored to the stiffer thrombi that are more difficult to penetrate by stent retriever are only one possible future field of application.
