Study Sample Characteristics
After screening more than 7,500 potential cases of VTE, 1,567 Worcester residents were validated as a first time episode of possible, probable, or definite VTE. None of the remaining cases met our prespecified criteria for an acute venous thromboembolic event. The majority of these ineligible cases represented VTE occurring prior to the study year of interest (e.g., chronic DVT), cases in which VTE was suspected but ruled out, or simple misclassification.
The mean age of the study sample at the time of VTE diagnosis was 64.6 years and 55.9% were woman. Of the 1,567 patients, 1,310 had DVT (97.3% definite, 0.2% probable, 2.6% possible) and 465 had PE (52.0% definite, 22.6% probable, 25.2% possible) (208 patients had both DVT and PE). DVT was isolated to the calf in 127 (9.7%) and to the upper extremity in 186 (14.2%) of patients with DVT.
Incidence Rates of Venous Thromboembolism
The age-adjusted incidence rates of VTE in the greater Worcester population during the period under study (adjusted to 2000 U.S. Census data) was 114 per 100,000 population (95% C.I. 108, 120). The age adjusted incidence rates of DVT and PE, respectively, were 95 per 100,000 (95% C.I. 90, 101) and 34 per 100,000 (95% C.I. 31, 37), respectively. Age and sex-specific rates of VTE, DVT, PE, definite or probable DVT or PE, upper extremity DVT, and isolated calf DVT are provided in . The incidence rates within each category increased markedly with age (>7–10 fold from age <55 years to >75 years). The incidence rates of VTE in our various age strata were consistently higher in women than in men.
Incidence Rates* of Venous Thromboembolism
The annual age-adjusted incidence rate of VTE remained essentially unchanged between 1999 (109/100,000) and 2003 (117/100,000) as did the rates of DVT (94/100,000 to 98/100,000) (see ). The incidence rates of PE also remained relatively flat during the years under study (30/100,000 in 1999, 37/100,000 in 2001, and 34/100,000 in 2003). After excluding cases of VTE classified as “possible”, the annual incidence rates of DVT and PE remained relatively unchanged from 1999 to 2003. Incidence rates of VTE, DVT, and PE increased from 1999 to 2003 in younger patients (<65 years of age) but remained stable or slightly declined in patients > 65 years of age.
Incidence Rates* of Venous Thromboembolism by Study Year: The Worcester Venous Thromboembolism Study
Clinical Profile of Patients Developing Venous Thromboembolism
Between 1999 and 2003, the mean as well as median age of subjects with incident VTE declined (from 65.5 years to 62.7 years and 71.0 years to 65.0 years, respectively). The 5 most prevalent preexisting medical characteristics for VTE, in order of occurrence, included recent hospitalization, surgical procedure, malignancy, infection, and receipt of a central venous catheter (). The proportion of patients with a recent hospitalization or malignancy declined between 1999 and 2003.
Medical Characteristics of Patients with Venous Thromboembolism: The Worcester Venous Thromboembolism Study
Characterization of VTE Events
Approximately 72% of patients presented from the community to area hospitals with signs and symptoms suggestive of VTE (“community acquired”) (). This proportion did not change significantly between our 3 study years. Approximately 20% of all events were classified as unprovoked, 30% were thought to be related to malignancy, and 50% were considered to be provoked by other factors such as a recent hospitalization, surgery, trauma/fracture, or pregnancy. The proportion of patients with unprovoked events of VTE increased over time (17% in 1999 to 26% in 2003) whereas the proportion of patients with malignancy related events declined from 32% to 26%. The proportion of patients with VTE treated as outpatients increased from 22% in 1999 to 29% in 2003.
Diagnostic Modalities and Acute Treatment Practices
Of the 1,310 patients diagnosed with DVT, the vast majority underwent an ultrasound, whereas venograms were rarely performed (). In patients diagnosed with PE, the use of ventilation-perfusion scans declined markedly over time whereas the use of CT scans increased dramatically. Pulmonary angiography was utilized in only 2% of patients with PE.
Diagnostic and Treatment Strategies Utilized in Patients with Venous Thromboembolism
Between 1999 and 2003, the proportion of patients receiving unfractionated heparin decreased by more than one third whereas the proportion of patients receiving low-molecular weight heparin (LMWH) increased more than two-fold (). In approximately one quarter of patients, warfarin was not administered during their hospital encounter or was given entirely in the outpatient setting - this proportion did not change appreciably over time. An increasing proportion of patients were discharged on LMWH (alone or in combination with warfarin therapy) over time - 24.8% in 1999 to 47.5% in 2003. The placement of IVC filters as acute treatment for VTE occurred in approximately 1 in every 9 of patients with VTE during each study year.
Mean follow-up for the entire study cohort was 1,216 days. Long-term rates of recurrent VTE were 17.5%, 17.2% and 15.3% for the 1999, 2001, and 2003 cohorts respectively () After controlling for potentially confounding demographic and clinical differences between the 3 study cohorts, there was a trend towards reduced VTE recurrence in the 2003 cohort (O.R. 0.75, 95% CI 0.54, 1.04) (). Rates of major bleeding were approximately 12–13% for the 3 study cohorts and did not differ significantly by cohort year (, ). Long-term mortality decreased slightly between our initial study cohort of 1999 (43.3%) and the 2003 cohort (37.7%) but this difference was not statistically significant (, ). No significant changes in the rates of recurrent events of PE were detected over this period ().
Rate of recurrent VTE after initial VTE stratified according to year of diagnosis
Adjusted Odds of Selected Outcomes After the Diagnosis of VTE According to Study Year
Rate of major bleeding after initial VTE stratified according to year of diagnosis
Mortality after initial VTE stratified according to year of diagnosis