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Updated: Jan 26, 2026
Robotic Ablation of Atrial Fibrillation
Published on: May 29, 2015
International normalized ratio control and subsequent clinical outcomes in patients with atrial fibrillation using
Patricia O Guimarães1, Renato D Lopes2, John H Alexander1
1Duke Clinical Research Institute, Durham, NC, 27705, USA.
Insights
Warfarin
Area of Science:
- Cardiology
- Pharmacology
Background:
- Warfarin is a common anticoagulant for atrial fibrillation (AF).
- Maintaining International Normalized Ratio (INR) within the therapeutic range is crucial for efficacy and safety.
- Predicting future INR stability and clinical outcomes remains a challenge.
Purpose of the Study:
- To investigate the association between INR measurements and clinical outcomes in AF patients on warfarin.
- To determine if historical INR data can predict future INR measurements and outcomes.
Main Methods:
- Analysis of data from the ARISTOTLE trial, including patients randomized to warfarin.
- Inclusion criteria focused on patients with documented events or sufficient warfarin exposure and INR measurements.
- Statistical analysis to assess the predictive ability of historical INR and time in therapeutic range (TTR).
Main Results:
- A significant proportion of patients experienced INR values outside the therapeutic range (e.g., <1.5 or >4.0).
- Last recorded INRs before major bleeding or ischemic stroke events were often outside the ideal range.
- Historical time in therapeutic range (TTR) showed weak association with future TTR (R²=0.212) and limited predictive ability (C-index=0.61).
Conclusions:
- Most bleeding events in AF patients on warfarin may not be preventable solely through INR monitoring.
- Routine INR measurements have limited predictive power for future TTR or clinical outcomes.
- Clinical interpretation of INR values may require re-evaluation to avoid over-reliance on their predictive capacity.
Abstract:
We explored associations between INR measures and clinical outcomes in patients with AF using warfarin, and whether INR history predicted future INR measurements. We included patients in ARISTOTLE who were randomized to and received warfarin. Among patients who had events, we included those with ≥ 3 INR values in the 180 days prior to the event, with the most recent ≤ 60 days prior to the event, who were on warfarin at the time of event (n = 545). Non-event patients were included in the control group if they had ≥ 180 days of warfarin exposure with ≥ 3 INR measurements (n = 7259). The median (25th, 75th) number of INR values per patient was 29 (21, 38) over a median follow-up of 1.8 years. A total of 87% had at least one INR value < 1.5; 49% had at least one value > 4.0. The last INRs before events (median 14 [24, 7] days) were < 3.0 for at least 75% of patients with major bleeding and > 2.0 for half of patients with ischemic stroke. Historic time in therapeutic range (TTR) was weakly associated with future TTR (R2 = 0.212). Historic TTR ≥ 80% had limited predictive ability to discriminate future TTR ≥ 80% (C index 0.61). In patients with AF receiving warfarin, most bleeding events may not have been preventable despite careful INR control. Our findings suggest that INRs collected through routine management are not sufficiently predictive to provide reassurance about future time in therapeutic range or to prevent subsequent outcomes, and might be over-interpreted in clinical practice.
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