Prevalent digoxin use and subsequent risk of death or hospitalization in ambulatory heart failure patients with a reduced ejection fraction—Findings from the Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training (HF-ACTION) randomized controlled trial

Background: Despite more than 200 years of clinical experience and a pivotal trial, recently published research has called into question the safety and efficacy of digoxin therapy in heart failure (HF). Methods: HF-ACTION (ClinicalTrials.gov Number: NCT00047437) enrolled 2331 outpatients with HF and an EF ≤35% between April 2003 and February 2007 and randomized them to aerobic exercise training versus usual care. Patients were grouped according to prevalent digoxin status at baseline. The association between digoxin therapy and outcomes was assessed using Cox proportional hazard and inverse-probability weighted (IPW) regression models adjusted for demographics, medical history, medications, laboratory values, quality of life, and exercise parameters. Results: The prevalence of digoxin therapy decreased from 52% during the first 6 months of enrollment to 35% at the end of the HF-ACTION trial (P <0.0001). Study participants were 59± 13 years of age, 72% were male, and approximately half had an ischemic etiology of HF. Patients receiving digoxin at baseline tended to be younger and were more likely to report New York Heart Association functional class III/IV symptoms (rather than class II) compared to those not receiving digoxin. Patients taking digoxin had worse baseline exercise capacity as measured by peak VO₂ and 6-min walk test and greater impairments in health status as reflected by the Kansas City Cardiomyopathy Questionnaire. The association between digoxin and the risk of death or hospitalization differed depending on whether Cox proportional hazard (Hazard Ratio 1.03, 95% Confidence Interval 0.92–1.16; P =.62) or IPW regression models (HR 1.08, 95% CI 1.00–1.17; P =.057) were used to adjust for potential confounders. Conclusion: Although digoxin use was associated with high-risk clinical features, the association between digoxin therapy and outcomes was dependent on the statistical methods used for multivariable adjustment. Clinical equipoise exists and additional prospective research is required to clarify the role of digoxin in contemporary clinical practice including its effects on functional capacity, quality of life, and long-term outcomes.