Background: Anticoagulation therapy with warfarin is widely considered the standard of care for stoke prophylaxis in patients with atrial fibrillation who are at high risk of stroke. Community-based studies in the US have reported that the effectiveness of anticoagulation varies by management approach and that patients receiving warfarin have international normalised ratio (INR) values within the target therapeutic range less than half the time.
Objective: To estimate the lifetime societal costs and health benefits of warfarin therapy to prevent strokes, specifically in elderly patients (mean age 70 years) with atrial fibrillation who are at high risk of stroke, when anticoagulation is managed through usual care versus anticoagulation management services, where dedicated anticoagulation professionals (e.g. physician or pharmacist) monitor and oversee patients.
Methods: Semi-Markov decision model with a 30-day cycle length and 10-year time horizon (to reflect the mean life expectancy of the study population). Univariate sensitivity analyses and Bayesian second-order multivariate probabilistic sensitivity analysis using Monte Carlo simulation were performed. Outcomes measures were costs and QALYs. Most of the probability and outcome estimates included were derived from the recent SPORTIF (Stroke Prevention using ORal Thrombin Inhibitor in atrial Fibrillation) V trial. Utility values were derived from a large, nationally representative sample of individuals in the Medical Expenditure Panel Survey and were adjusted for age, sex, race, ethnicity, income, education and co-morbidity. Resource utilisation was based on experience at the University Medicine Group Practice Anticoagulation Clinic (University of Colorado, Denver, CO, USA) and costs ($US; 2004 values) included were for warfarin and aspirin (acetylsalicylic acid) use and those associated with major bleeding, treatment of primary events, routine INR and biochemistry monitoring, ECGs, and clinic visits. Costs and outcomes were discounted by 3% per annum.
Results: The anticoagulation management service improved effectiveness by 0.057 (95% credible interval 0, 0.36) QALYs and reduced costs by $US2100 (95% credible interval -$US19,800, $US300) [2004 values] compared with usual care. Results were sensitive to the extent of the increase in risk of primary events (all strokes and systemic embolic events attributable to usual care, but were robust to variation in other input variables). The anticoagulation management service was the dominant strategy in 91% of Monte Carlo simulations.
Conclusion: The anticoagulation management service appears to cost less and provide greater effectiveness than usual care. To enhance stroke prophylaxis among high-risk patients with atrial fibrillation, physicians and Medicare plans may wish to consider augmenting 'usual care' by the addition of patient-monitoring technology strategies such as formally organised anticoagulation monitoring programmes.