Chapter 31: Deep Venous Thrombosis

INTRODUCTION

Deep venous thrombosis (DVT) is a common disease with potentially serious consequences such as pulmonary embolism (PE). Although the risk without prophylaxis of all venous thromboembolism (VTE) was 15% in one study of medical inpatients, the rate of clinically symptomatic DVT was only 6% (n = 188). VTE represents a potentially fatal disease process with a clinical presentation that is often silent or nonspecific. A substantial number of patients remain at risk as a result of the demographics of an aging population and the ability of modern medicine to treat patients with chronic disease. During the past decade, many of the long-standing controversies surrounding the natural history, diagnosis, and therapy of patients with VTE have been partially or completely reconciled, resulting in substantial changes in the diagnostic and therapeutic approach to the disease. In the evaluation of patients with suspected VTE, an understanding of what is unknown can prove invaluable to the decision-making process.

EPIDEMIOLOGY

The age-adjusted incidence of first lifetime thrombosis is 1.92 per 1000 person-years, which translates into nearly 190,000 noted thromboses each year in persons ages 45 years or older in the United States.¹ DVT is especially common in hospitalized patients and may constitute the greatest mortality risk in some inpatient populations. The overall incidence of a first VTE seems to be similar among men and women, but the risk is higher among women of childbearing age than among men in the same age group. This gender difference likely relates to the association of VTE with pregnancy or the use of oral contraceptives. In contrast, the risk of thromboembolism among older women is substantially lower than that among men in the same age group.^2,3 The 28-day fatality rate after a first thrombosis is 11%, with cancer conferring an increased mortality risk. The 2.2-year recurrence rate after a first thrombosis is substantial at 7.7% per year.² Thrombosis rates increase with age and are more than twofold higher in those older than age 65 years. The relatively low incidence of VTE in Asians and Hispanics has not been explained but may relate to a lower prevalence of genetic factors predisposing to VTE, such as factor V Leiden, in Asian populations (0.5%) compared with whites (5%).²

The proportion of patients with VTE categorized as idiopathic falls in the range of 26% to 47% of first-time cases; the exact figure depends partly on the definitions of idiopathic and secondary VTE.² The majority of calf vein thrombi resolve spontaneously, and PE is uncommon. About 20% to 30% of DVTs propagate to the popliteal, femoral, or iliac veins, and 10% to 20% of all DVTs occur in proximal veins without prior calf involvement. Iliofemoral thromboses appear to be the source of most clinically apparent pulmonary emboli (Figure 31-1).