Incidence and Determinants of Traumatic Intracranial Bleeding Among Older Veterans Receiving Warfarin for Atrial Fibrillation

Abstract

Importance: Traumatic intracranial bleeding, which is most commonly attributable to falls, is a common concern among health care professionals, who are hesitant to prescribe oral anticoagulants to older adults with atrial fibrillation.

Objective: To describe the incidence of and risk factors for traumatic intracranial bleeding in a large cohort of older adults who were newly prescribed warfarin sodium.

Design, setting, and participants: Retrospective cohort study at the US Department of Veterans Affairs (VA). Participants included 31 951 veterans with atrial fibrillation 75 years or older who were new referrals to VA anticoagulation clinics (for warfarin therapy) between January 1, 2002, and December 31, 2012. The dates of the core analysis were March 2014 through May 2015, and subsequent ad hoc analyses were performed through December 2015. Patients with comorbid conditions requiring warfarin were excluded.

Main outcomes and measures: The primary outcome was hospitalization for traumatic intracranial bleeding. Secondary outcomes included hospitalization for any intracranial bleeding or ischemic stroke. We used International Classification of Diseases, Ninth Revision, Clinical Modification codes to identify the incidence rates of these outcomes after warfarin initiation using VA administrative data (in-system hospitalizations) and Medicare fee-for-service claims data (out-of-system hospitalizations). Clinical characteristics, laboratory results, and pharmacy data were extracted from the VA electronic medical record. For traumatic intracranial bleeding, Cox proportional hazards regression was used to determine predictors of interest selected a priori based on prior known associations.

Results: The study population comprised 31 951 participants. The mean (SD) patient age was 81.1 (4.1) years, and 98.1% were male. Comorbidities were common, including hypertension (82.5%), coronary artery disease (42.6%), and diabetes mellitus (33.8%). During the study period, the incidence rate of hospitalization for traumatic intracranial bleeding was 4.80 per 1000 person-years. In unadjusted models, significant predictors of traumatic intracranial bleeding included dementia, fall within the past year, anemia, depression, abnormal renal or liver function, anticonvulsant use, labile international normalized ratio, and antihypertensive use. After adjusting for potential confounders, the remaining significant predictors for traumatic intracranial bleeding were dementia (hazard ratio [HR], 1.76; 95% CI, 1.26-2.46), anemia (HR, 1.23; 95% CI, 1.00-1.52), depression (HR, 1.30; 95% CI, 1.05-1.61), anticonvulsant use (HR, 1.35; 95% CI, 1.04-1.75), and labile international normalized ratio (HR, 1.33; 95% CI, 1.04-1.72). The incidence rates of hospitalization for any intracranial bleeding and ischemic stroke were 14.58 and 13.44, respectively, per 1000 person-years.

Conclusions and relevance: Among patients 75 years or older with atrial fibrillation initiating warfarin therapy, the risk factors for traumatic intracranial bleeding are unique from those for ischemic stroke. The high overall rate of intracranial bleeding in our sample supports the need to more systematically evaluate the benefits and harms of warfarin therapy in older adults.

Figure 1. Derivation of the study cohort

Of 99,552 patients initially identified through administrative data, 31,951 were included in the final sample.

Figure 2. Kaplan-Meier plot for traumatic intracranial bleeding events over time

Based on the Weibull distribution (Weibull shape = 1.28, 95% CI 1.27–1.29), there was a modest increase in the hazard of traumatic intracranial bleeding over time.

Figure 3. Rate of traumatic intracranial bleeding and stroke, stratified by CHA2DS2-VASc score

The observed rate of stroke increased as CHA2DS2-VASc score increased, while the rate of traumatic intracranial bleeding remained relatively constant across CHA2DS2-VASc categories. PY = person-years.