The natural history and epidemiology of venous thrombosis.

Epidemiologic studies over the past 30 years have provided much of the basis for the understanding of venous thromboembolic disease. There has been an evolution from simple descriptive studies using clinical diagnosis to various forms of comparative studies using objective diagnoses. Identification of high-risk cases in the hospitalized population has led to the development of both general and specific antithrombotic prophylactic regimens. This has occurred against a background of an increased understanding of the pathophysiology of venous thrombosis. Inhospital case interventions have allowed direct questions concerning pathophysiology to be addressed. Examples would include the use of certain types and dosages of anticoagulants and the use of mechanical devices to avoid stasis. Despite these advances, there are still areas that require further attention. One aspect of importance is to evaluate the thrombotic risk of new procedures. The possibility that a new procedure may be either less or more thrombotic than its predecessor should be addressed. In the case of the former, additional antithrombotic measures are needed. An example of this is the relatively disappointing results of regular low-dose heparin treatment in some orthopedic procedures. In the case of the latter, less severe measures may be indicated. Current antithrombotic methods are not without risks and may not be necessary with some of the new endoscopic surgical procedures. Another area of importance relates to the monitoring of compliance. The information on antithrombotic methods has been available for two decades, yet surveys of the application of these methods consistently show that antithrombotic protocols are used less in North America relative to their use in equivalent institutions in Europe. A third area that still needs further epidemiologic study is the incidence and effects of venous thrombosis in the general community. Despite the two recent descriptive studies cited above, relatively little, as compared with the in-patient perspective, is known about community risk factors and their prevention. With respect to the natural history of hospital-based cases it seems unlikely that much is to be gained from surveying the efficacy of heparin or heparin-like treatment for mortality end points. However, a large and still unsatisfactorily examined area is the true frequency and impact of the postphlebitic syndrome. This aspect is germane to both hospital- and community-acquired DVT and, with an aging population, clearly deserves a lot more attention.