Modern day treatment of acute deep venous thrombosis

Primary prophylaxis of venous thromboembolism in surgical patients

Venous thromboembolism is a major risk for surgical patients during the perioperative period. Prevention of perioperative venous thromboembolism remains a critical component of surgical patient care. The risk for venous thromboembolism in surgical patients can be stratified by their risk factors and by the type of operation. Pharmacological prophylaxis for venous thromboembolism includes unfractionated heparin, low-molecular weight heparin, fondaparinux, warfarin, antiplatelet therapy, and direct thrombin inhibitors. Mechanical devices such as graduated compression stockings, intermittent pneumatic compressions, and venous foot pumps are also effective modalities for venous thromboembolism prophylaxis. The optimal preventive measure of venous thromboembolism should be based on the degree of risk for venous thromboembolism with the intensity of prophylaxis while balancing potential treatment benefits and risks in each individual patient. The epidemiology of venous thromboembolism, the methods for achieving venous thromboembolism prophylaxis, and the approach to institute venous thromboembolism prophylaxis in surgical patients undergoing various operative interventions are reviewed in this article.

Pharmacokinetics of tissue plasminogen activator in an isolated extracorporeal circuit

PURPOSE

The aim of this study was to investigate the pharmacokinetics of tissue plasminogen activator (tPA) under the conditions of an isolated extracorporeal circuit.

METHODS

Plasma levels of tPA were measured in the perfusion solution and in central venous blood before, during, and after the perfusion in seven patients undergoing regional hyperthermic fibrinolytic perfusion with tPA in addition to surgical thrombectomy for extended deep venous thrombosis.

RESULTS

After 15 minutes of fibrinolytic perfusion, the level of tPA in the perfusion solution was 10,427 +/- 4432 ng/mL, and after 30 minutes the maximum level of 19,726 +/- 5630 ng/mL was reached. After 60 minutes when the perfusion was discontinued, tPA concentrations dropped to 15,931 +/- 4818 ng/mL. In central venous blood, tPA levels increased to a maximum of 230.7 +/- 89.6 ng/mL after 60 minutes of perfusion, which represented 1.4% of the concentration measured in the perfusion solution at the same time. With disconnection of the extracorporeal circuit, the tPA levels in central venous blood decreased rapidly and reached a level of 24.1 +/- 8.7 ng/mL after 120 minutes.

CONCLUSION

The use of regional hyperthermic fibrinolytic perfusion in the treatment of extended deep venous thrombosis makes it possible to achieve extremely high concentrations of tPA in the perfusion solution. At the same time, the entry of the fibrinolytic agent into the systemic circulation is minimized.

Vascular endothelial growth factor and basic fibroblast growth factor are found in resolving venous thrombi

OBJECTIVE

Resolution of venous thrombi is accompanied by an ingrowth of capillaries, which appears to be analogous to angiogenesis in other tissues. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are major regulators of angiogenesis. The aim of this study was to determine the temporal changes and the location of VEGF and bFGF expression in a rat model of venous thrombus resolution.

DESIGN AND METHODS

Thrombi were induced in the inferior venae cavae of rats by creating a stenosis to reduce blood flow by 80% to 90%. Thrombi, adjacent inferior vena cava wall, and systemic blood were collected at 1, 3, 7, 14, 21, and 28 days after thrombus generation (n = 9). Sham operations were performed (n = 5), and blood was collected at 1, 3, and 7 days. VEGF and bFGF were measured with specific immunoassays, and levels in tissues were expressed as picogram per milligram soluble protein. Tissues from two animals that were humanely killed 7 days after thrombus formation were prepared for histological examination. Immunohistochemistry was performed by the use of antibodies against VEGF, bFGF, and ED-1 (a monocyte/macrophage marker).

RESULTS

Laminated thrombi were reliably produced with a median weight at 1 day of 39 mg (range, 23-63 mg). There was a significant increase in thrombus VEGF concentration between 1 day (median, 247; range, 0-514) and 7 days (median, 556; range, 254-1741) (P =.02). There was no difference between the seventh day and subsequent days. There was a positive linear correlation between thrombus bFGF concentration and time (R = 0.74, P <.0001), with a more than 300-fold increase in bFGF concentration over the 28 days of the study. VEGF and bFGF concentrations in the adjacent vena caval wall did not change significantly with time. The serum VEGF was significantly raised at 1 day (median, 5520 pg/mL; range, 4040-7912 pg/mL) and 3 days (median, 3880 pg/mL; range, 2564-7232 pg/mL) compared with 7 days (median, 1790 pg/mL; range, 232-3228 pg/mL) (P <.0001). Similar changes in the serum VEGF also developed in the sham-operated animals. The serum bFGF (day 1 median, 15.5 pg/mL; range, 1-42 pg/mL) did not change with time. Immunohistochemistry showed that the VEGF antigen was localized to monocytes, endothelial cells, and spindle-shaped cells within the thrombus. The bFGF antigen was localized to mononuclear cells and spindle-shaped cells and was also present in the extracellular matrix.

CONCLUSION

VEGF and bFGF are found in organizing thrombi and have characteristic temporal expression patterns, which suggest that they have a role in thrombus resolution. Augmenting angiogenic growth factor expression may enhance thrombus recanalization, thus reducing long-term complications.

[Fibrinolytic therapy of deep vein thrombosis]

BACKGROUND

The most important complications of deep vein thrombosis are pulmonary embolism and postthrombotic syndrome. While the medicine of lethal pulmonary embolism is reduced to less than 2% by conventional anticoagulation, fibrinolytic therapy aims at a reduction of the greater than 50% incidence of postthrombotic syndrome. The optimal therapeutic regimen concerning risks and effect has not been established yet.

RESULTS

A review of 26 studies involving ultrahigh-dose streptokinase (UHSK), urokinase (UK), and tissue-type plasminogen activator (rt-PA) shows the highest success rate for UHSK (45% complete and 40% parital patency), whereas there are lower rates for UK (25% and 40%) and low-dose locoregionally applied rt-PA (22% and 44%). The studies were not directly comparative, however. Published data concerning complications range from 1.7% mortality for UHSK to 0.9% for UK and 0.0% for rt-PA. Success criteria, however, are varying and not well defined. The influence of fibrinolytic therapy on the incidence of postthrombotic syndrome has not been established prospectively, but a reduction by 40 to 50% can be assumed. Calf vein thromboses are not indication for lytic therapy. In patients with iliacal vein thromboses there is an increased risk of pulmonary embolism using UHSK.

CONCLUSIONS

UHSK can be regarded the standard concerning success rate in deep vein thromboses. DATA involving locoregional therapy with rt-PA are inconsistent and worse, but bleeding complications might be less frequent. Large prospective studies evaluating the impact on incidence and severity of the postthrombotic syndromes, which involve a controlled application of compression therapy are needed.