Procoagulatory changes induced by head-up tilt test in patients with syncope: observational study

Orthostatic hypercoagulability is proposed as a mechanism promoting cardiovascular and thromboembolic events after awakening and during prolonged orthostasis. We evaluated early changes in coagulation biomarkers induced by tilt testing among patients investigated for suspected syncope, aiming to test the hypothesis that orthostatic challenge evokes procoagulatory changes to a different degree according to diagnosis.

One-hundred-and-seventy-eight consecutive patients (age, 51 ± 21 years; 46% men) were analysed. Blood samples were collected during supine rest and after 3 min of 70° head-up tilt test (HUT) for determination of fibrinogen, von Willebrand factor antigen (VWF:Ag) and activity (VWF:GP1bA), factor VIII (FVIII:C), lupus anticoagulant (LA1), functional APC-resistance, and activated prothrombin time (APTT) with and without activated protein C (C+/-). Analyses were stratified according to age, sex and diagnosis.

After 3 min in the upright position, VWF:Ag (1.28 ± 0.55 vs. 1.22 ± 0.54; p < 0.001) and fibrinogen (2.84 ± 0.60 vs. 2.75 ± 0.60, p < 0.001) increased, whereas APTT/C+/- (75.1 ± 18.8 vs. 84.3 ± 19.6 s; p < 0.001, and 30.8 ± 3.7 vs. 32.1 ± 3.8 s; p < 0.001, respectively) and APC-resistance (2.42 ± 0.43 vs. 2.60 ± 0.41, p < 0.001) decreased compared with supine values. Significant changes in fibrinogen were restricted to women (p < 0.001) who also had lower LA1 during HUT (p = 0.007), indicating increased coagulability. Diagnosis vasovagal syncope was associated with less increase in VWF:Ag during HUT compared to other diagnoses (0.01 ± 0.16 vs. 0.09 ± 0.17; p = 0.004).

Procoagulatory changes in haemostatic plasma components are observed early during orthostasis in patients with history of syncope, irrespective of syncope aetiology. These findings may contribute to the understanding of orthostatic hypercoagulability and chronobiology of cardiovascular disease.