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Background: Increased coagulation activity has been established in paroxysmal atrial fibrillation (PAF), but data on the anticoagulant system are scarce. Purpose: To examine the protein C anticoagulant pathway in the early hours of the disease. Materials and Methods: Fifty-one patients (26 men and 25 women; mean age 59.84 + 1.60 years) and 52 controls (26 men and 26 women; mean age 59.50 + 1.46 years) were selected for the study. Protein C antigen and its activity, total protein S, free protein S and its activity, soluble forms of endothelial protein C receptor (sEPCR), and thrombomodulin (sTM) were examined in the plasma. Results: The indicators were studied in patients between the 2nd and the 24th hour after the onset of arrhythmia. Levels of protein C were significantly elevated in patients compared to controls (111.40% + 6.66% vs 94.83% + 4.47%; P ¼ .039). Protein C activity showed significant reduction in PAF (73.13% + 5.80% vs 103.3% + 3.80%; P < .001). Total protein S levels did not differ significantly (108.20% + 4.07% vs 102.40% + 3.65%; P ¼ .30). Free protein S (76.81% + 6.01% vs 122.10% + 3.97%; P < .001) and its activity (71.39% + 6.27% vs 119.50% + 6.54%; P < .001) were reduced in patients. Higher levels of sEPCR (203.10 + 10.33 vs 133.10 + 7.37 ng/mL; P < .001) and sTM (6.50+0.40 vs 4.48+0.28 ng/mL; P < .001) were measured in PAF. Conclusion: Protein C activity is reduced still in the first hours (until the 24th hour) of PAF clinical manifestation, determining reduced activity of the anticoagulant pathway as a whole. The established low levels of free protein S and its activity as well as low sEPCR and sTM levels are a possible explanation of the changes in protein C activity.

BackgroundData on coagulation changes in paroxysmal atrial fibrillation (PAF) are scarce. The aim of this study was to examine plasma antithrombin (AT) levels and activity as well as thrombin-antithrombin (TAT) complex levels in the early hours of the clinical manifestation of PAF.MethodsFifty-one patients (26 men and 25 women; mean age 59.84 ± 1.60 years) were consecutively selected with PAF duration < 24 hours, and 52 controls (26 men and 26 women; mean age 59.50 ± 1.46 years) matched the patients in terms of gender, age and comorbidities. Plasma levels and activity of AT and levels of the covalent TAT complex were studied once in each study participant.ResultsAT plasma levels in PAF patients were statistically significantly lower compared to controls (164.69 ± 10.51 vs. 276.21 ± 8.29 μg/mL, P < 0.001). Plasma activity of the anticoagulant was also significantly lower in PAF (71.33±4.87 vs. 110.72±3.09%, P < 0.001). TAT complex concentration in plasma was higher in the patient group (5.32 ± 0.23 vs. 3.20 ± 0.14 μg/L, P < 0.001).ConclusionWe can say that PAF is associated with significantly reduced AT levels and activity and increased levels of TAT complex during the first 24 hours after its manifestation. These changes indicate a reduced activity of AT anticoagulant system, which is a probable prerequisite for the established enhanced coagulation (high TAT complex levels).