Characterization of the Porcine Fibrinolytic System and Identifying its Temporal Changes in a Porcine Model of Cardiac Arrest

Abstract

Many initial survivors of cardiac arrest develop disability or die, stemming from post-cardiac arrest syndrome (PCAS), where the complications are secondary to acquired coagulopathy. Shock dysregulates both coagulation and fibrinolysis, but neither is directly treated during resuscitation. This study focuses on 1) characterizing the porcine fibrinolytic system, and 2) studying its temporal changes in a porcine model of cardiac arrest. The optimal conditions needed to generate and degrade porcine plasma clots were assessed. Plasminogen, fibrinogen and tissue-type plasminogen activator (tPA) of either human or porcine origin were tested in all possible permutations. Plasmin generation was monitored using a chromogenic substrate S-2251 and the rates were quantified using time-squared analysis. Porcine fibrin demonstrated preference toward porcine plasminogen and tPA over human counterparts. With human fibrin, all reactions were faster than all-porcine components and species-preference was no longer present. Ventricular fibrillation (VF) arrest was induced in Yorkshire pigs using a transvenous pacer. Blood samples were collected into citrate at five times: baseline (Pre), 1-min post VF (VF1), 8-min post VF (VF8), 5-min post return of spontaneous circulation (ROSC) and death (PM). Plasma was isolated and clot formation and lysis was performed using conditions above. Reactions were monitored by optical density (OD) to determine: 1) clot lysis time (CLT), 2) total OD change (ΔOD; implying clot structure), and 3) baseline OD (implying plasma composition). Transient fibrinolysis resistance was observed; CLT increased by approximately 3-fold at VF8 compared with Pre and decreased thereafter. Both ΔOD and baseline OD showed significant changes during VF compared with Pre, but normalized once ROSC was achieved. Fibrinolysis inhibition was normalized by increasing tPA, suggesting the defect is due to imbalance of the fibrinolytic system. Fibrinolysis can effectively be studied in porcine models. Direct intervention to normalize fibrinolysis during resuscitation may enhance ROSC and reduce reperfusion injury, which may improve outcomes from cardiac arrest.