Plasma thromboxane B2 concentration in patients with ventricular septal defect and pulmonary hypertension.

Plasma thromboxane B2 (TXB2)-a stable metabolite of thromboxane A2 (TXA2)-conventional hemodynamic parameters, mean pulmonary input energy (input energy), and mean pulmonary output energy (output energy) were measured to assess platelet activation in 21 patients with pulmonary hypertension and a ventricular septal defect (VSD). The patients were divided into 2 groups: group A (normal range) and group B (high level). TXB2 levels were measured by radioimmunoassay. There was no relationship between plasma TXB2 concentrations and conventional hemodynamic parameters except the pulmonary-to-systemic pressure ratio. Output-to-input energy ratio was correlated logarithmically with the plasma TXB2 concentration. We concluded that patients with output/input energy ratio >0.15 had a high TXB2 concentration and activated platelets in pulmonary capillaries.