Loose Fibrin Clot Structure and Increased Susceptibility to Lysis Characterize Patients with Central Acute Pulmonary Embolism: the Impact of Isolated Embolism

Background Prothrombotic fibrin clot properties are associated with higher early mortality risk in acute pulmonary embolism (PE) patients. It is unknown whether different types of PE are associated with particular clot characteristics. Methods We assessed 126 normotensive, noncancer acute PE patients (median age: 59 [48-70] years; 52.4% males), who were categorized into central versus peripheral PE with or without concomitant deep vein thrombosis (DVT). Plasma fibrin clot permeability ( K-s ), clot lysis time (CLT), thrombin generation, platelet-derived markers, and fibrinolytic parameters were measured on admission. Plasma fibrin clot morphology was assessed by scanning electron microscopy (SEM). Results Patients with central PE ( n =76; 60.3%) compared with peripheral PE ( n =50; 39.7%) had 17.8% higher K-s and 14.3% shortened CLT (both p <0.01 after adjustment for potential confounders including fibrinogen), with no differences between segmental and subsegmental PE. SEM analysis demonstrated larger fibrin fiber diameter and pore size in central PE compared with peripheral PE (both p <0.01). For isolated PE, there was 23.3% higher K-s in central PE than in peripheral PE ( n =24; 19%) with no differences in other variables. Central PE combined with DVT ( n =45; 35.7%), as compared with central isolated PE ( n =31; 24.6%), was associated with shortened CLT (all p <0.05). Conclusion Our findings suggest that looser fibrin networks composed of thicker fibers with increased susceptibility to lysis characterize patients with central PE, suggesting that fibrin clot phenotype affects the size of thrombi occluding the pulmonary arteries, highlighting the role of fibrin structures in thrombus formation and stability.