US-Doppler monitoring of asymptomatic distal deep vein thrombosis in patients given low-molecular-weight heparin at prophylactic doses after orthopedic surgery.

Objective: Many patients undergoing orthopedic surgery of the lower limbs h ave asymptomatic deep vein thrombosis. Unless they undergo a US-Doppler exp loration, these patients are not recognized and go untreated. The purpose o f this study was to examine the US-Doppler findings in patients with asympt omatic distal thrombosis given long term prophylaxis with low-molecular wei ght heparin in order to evaluate, under these conditions, the rate of US-Do ppler identified extension and look for possible factors predictive of exte nsion. Patients and methods: after a US-Doppler exploration performed systematical ly on day 8+3, patients with asymptomatic distal thrombosis (soleus, fibula r, posterior tibial, gastrocnemius) were informed of the choice between two practical attitudes: curative anticoagulant treatment for 2 to 3 months wi thout US-Doppler follow-up, or continuation of the prophylaxis (dalteparin 500 IU/d for three-quarters of the patients) for 5 to 6 weeks, depending on the results of a US-Doppler exploration performed 8 to 15 days later to ve rify the absence of extension of the existing thrombus. Extension at US-Dop pler exploration was defined as a mean increase in the size of the existing thrombus and/or development of a new localization. Curative treatment was given in case of extension. Results : Planned US-Doppler follow-up concerned 63 patients, 22 men and 41 women, mean age 67.5 +/- 13 years and 75.1 +/- 9 years respectively. An ex tension of the thrombus was observed in 11 cases (17.5%). None were symptom atic. In 2 cases, short femoral thrombi developed far from the initial sura l localizations. In the "extension" group, the number of arterial axes invo lved rose from 2.2 to 3.4 (mean) per patient and the mean diameter of these thrombi increased from 3.4 mm to 5.1 mm. In the "regression" group, the nu mber of arterial axes involved fell from 1.6 to 1.3 and mean diameter from 3.6 to 1.5 mm with complete disappearance in 12 cases between the first and third exploration. No factor predictive of extension could be identified. The number of axes involved at initial diagnosis, as well as mean age and n umber of knee prostheses, were slightly higher in the "extension" group. Conclusions: US-Doppler follow-up of patients with asymptomatic distal deep vein thrombosis after orthopedic surgery demonstrated that continuing prop hylaxis with low-molecular-weight heparin leads to a regression of the thro mbus in 80% of the casts. In case of extension, progression is slow and asy mptomatic. US-Doppler screening and follow-up of distal thrombosis could be an alternative to generalized continuation of prophylaxis.