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Latex D-dimer Signal in In Situ Femoral Vein Thrombus in Swine and Effect of Minidose Exogenous Tissue Plasminogen Activator Bolus^*

^* From the Department of Medicine and Radiology (Dr. Robinson), Medical College of Georgia and Veterans Affairs Medical Center, Augusta, GA; Department of Internal Medicine (Dr. Pineda), University of South Carolina Medical Center and Veteran’s Affairs Medical Center, Columbia, SC; Department of Internal Medicine (Dr. Salah), Medical College of Georgia, Augusta, GA; Department of Pediatric Surgery (Dr. Pipkin), University of Alabama, Birmingham, AL; Department of Radiology (Mr. Corley), Medical College of Georgia, Augusta, GA; Department of Clinical Pathology (Ms. Jonah), Medical College of Georgia, Augusta, GA; and Department of Internal Medicine (Dr. Gossage), Medical College of Georgia and Veterans Affairs Medical Center, Augusta, GA.

Correspondence to: Vincent J. B. Robinson, MD, Medical College of Georgia, Section of Cardiology, BBR 6515A, Department of Medicine, Augusta, GA 30912; e-mail: vrobinso{at}mail.mcg.edu

Study objectives: We created in situ femoral vein thrombi in swine to investigate the response of the latex d-dimer signal to acute in situ venous thrombosis, and to determine the minimum dose of exogenous bolus tissue plasminogen activator (t-PA) required to significantly elevate the d-dimer signal.

Study design: We studied seven swine (20 to 22 kg) under pentobarbital anesthesia. A 6-cm segment of the proximal femoral vein was surgically exposed and briefly ligated. Thrombin, 250 U, was then injected into the isolated femoral vein segment to create an in situ clot. After clot formation was documented to be complete between the ligatures, they were then released. D-dimer levels were then measured every 15 min for 1 h before and 1 h after clot formation with ligatures released. Time-response curves to establish timing of peak t-PA effect were performed, and then escalating dose-response curves of d-dimer level to minidose t-PA were plotted.

Results: After formation of the clot, the release of ligatures resulted in no change in d-dimer levels over 1 h (p = 0.62) in all swine. When a time-response curve to exogenous t-PA bolus in the presence of femoral clot was plotted, there was a maximal increase in d-dimer signal at 30 min after bolus t-PA administration. The subsequent dose-response curves for escalating fivefold boluses of minidose t-PA showed an increase in d-dimer signal at doses of 0.8 mg (p = 0.03) and 4 mg (p = 0.003).

Conclusion: We conclude the following: (1) in situ femoral vein clot formation does not elevate d-dimer signal for 1 h after ligature release; (2) minidose t-PA boluses of 0.8 mg and 4 mg significantly elevated the latex d-dimer signal above baseline; and (3) there is a potential role of minidose t-PA in enhancing the d-dimer signal in in situ deep venous thrombosis.

Key Words: in situ clot • latex d-dimer signal • minidose tissue plasminogen activator