Warfarin associated with better 1-year outcomes for patients with CKD who experience acute MI with afib

Giving warfarin to acute myocardial infarction (MI) patients with atrial fibrillation who have chronic kidney disease (CKD) was associated with better 1-year outcomes than not giving warfarin, a study found.

Swedish researchers used national registry data from 2003-2010 to conduct an observational, prospective cohort study on 24,317 patients, all consecutive survivors of an acute MI with atrial fibrillation and known serum creatinine. They used estimated glomerular filtration rate (eGFR) to classify chronic kidney disease stages and prescription data from the registry to determine warfarin treatment (dosage information was not available). Outcomes were a composite end point of death, readmission from MI, or ischemic stroke within a year of discharge; readmission due to bleeding within a year of discharge; and the aggregate of the first 2 outcomes. Results were published March 5 by JAMA.

Twenty-two percent of patients (n=5,292) were prescribed warfarin at discharge, and 52% of patients had chronic kidney disease (CKD) of stage 3 or higher (eGFR <60 mL/min/1.73 m²). Compared with those not prescribed warfarin, patients who took warfarin had a lower risk of the first composite outcome in each CKD stratum for event rates per 100 person-years, as follows:

• eGFR >60: event rate, 28.0 for warfarin vs. 36.1 for no warfarin; adjusted hazard ratio (HR), 0.73 (95% CI, 0.65 to 0.81);
• eGFR 30-60: event rate, 48.5 for warfarin vs. 63.8 for no warfarin; HR, 0.73 (95% CI, 0.66 to 0.80);
• eGFR 15-30: event rate, 84.3 for warfarin vs. 110.1 for no warfarin; HR, 0.84 (95% CI, 0.70-1.02); and
• eGFR ≤15: event rate, 83.2 for warfarin vs. 128.3 for no warfarin; HR, 0.57 (95% CI, 0.37-0.86).

The reduced risk in the composite outcome was driven largely by a lower mortality risk. The crude absolute risk differences were 5.8% for death, 2.2% for MI, and 1.8% for stroke in the entire cohort. Warfarin in each stratum was associated with lower hazards of the aggregate outcome, and the risk of bleeding (n=1202 events) was not significantly higher in patients treated with warfarin in any CKD stratum, measured by event rates per 100 person-years.

The results “may suggest not denying warfarin to patients with atrial fibrillation after a myocardial infarction because of compromised renal function,” the authors wrote, but they added that the results are observational and thus don't offer conclusive guidance.

Editorialists agreed and added that confounding due to indication for selecting warfarin is especially relevant to a post-MI cohort. As well, they noted that Sweden has excellent international normalized ratio (INR) quality control, and warfarin benefits might be attenuated in countries with inferior INR control, such as the U.S. “These data support the use and continuation of warfarin therapy among patients with CKD with excellent INR control,” they concluded.