Risk of Thromboembolism after Short-Term Interruption of Warfarin.

Background: Significant uncertainty exists for patients who must discontinue warfarin prior to an invasive procedure. In part, the controversy results from the lack of published information about the risk of thromboembolism associated with short-term warfarin interruption. The aim of this observational study was to assess the frequency of thromboembolism and bleeding among a large cohort of patients whose warfarin was temporarily withheld before and after an outpatient invasive procedure.

Methods: A prospective cohort of patients taking warfarin was assembled from 101 sites with personnel designated as warfarin managers across the United States during the period August 2000 to December 2001; 98 sites were community-based physician office practices. All episodes of warfarin interruption among the 6,761 patients in the cohort were identified by investigator review of provider-generated progress notes. Surgical procedures (including cardiovascular interventions) that required hospitalization and cases in which follow-up INR values were not available for at least 30 days post-procedure were excluded. The primary outcomes (30 day follow-up) were

1. thromboembolism and

2. clinically significant hemorrhage.

For each patient, the following data were also recorded: type of procedure, number of days warfarin was withheld, presence or absence of bridging therapy (e.g. low molecular weight heparin [LMWH]).

Results: 1,024 unique patients (1,293 episodes of warfarin interruption) were included in our analysis. The mean age was 71.9 years; 43% were female. The most common procedures were colonoscopy (n=324), oral surgery (n=323), and ophthalmic surgery (116). Other common reasons for withholding warfarin were: epidural injection, prostate biopsy, breast biopsy, and dermatologic procedures. Perioperative heparin or LMWH was used in only 8.3% of cases. The duration of warfarin interruption was variable; however, more than 80% of patients had warfarin withheld for 5 days or fewer. Seven patients (0.7%) suffered post-procedure thromboembolism within 30 days (4 arterial, 3 venous). None of the 7 patients who experienced thromboembolism received peri-procedural bridging therapy; 3 of these thromboembolic events were associated with warfarin interruption ≥ 7 days. Twenty-three patients (2.3%) suffered clinically significant hemorrhage - of these, 14 had received peri-procedural heparin or LMWH.

Conclusion: For many chronically anticoagulated patients who need to undergo a minor, outpatient intervention, a brief (5 or fewer days) peri-procedural interruption of warfarin is associated with a low risk of thromboembolism. The risk for clinically significant bleeding, even among outpatients undergoing minor procedures, should be considered prior to the administration of bridging therapy.