Abstract 16169: Individual and Regional Determinants of Time in Therapeutic Range Among Patients Randomized to Warfarin in the ROCKET AF Trial of Rivaroxaban
Background: Time in the therapeutic range (TTR) of INR 2-3 is a common measure of warfarin anticoagulation quality. We explored individual and regional determinants of TTR among patients randomly allocated to warfarin in the ROCKET AF double-blind trial of rivaroxaban vs. warfarin in patients with atrial fibrillation.
Methods: ROCKET AF enrolled patients with prior stroke/TIA or multiple stroke risk factors (mean CHADS2 score = 3.5). This analysis includes patients assigned to warfarin while on treatment. Patient features were assessed at study entry. INRs were performed via standardized point-of-care devices at least every 4 weeks or more frequently, as indicated. Local investigators managed warfarin. Patient TTR was calculated using the Rosendaal technique for a strict range of INR 2-3 and modeled via multiple linear regression.
Results: 6,983 patients were followed for a median of 1.7 years on warfarin (IQR: 1.1-2.2 years). The median TTR was 58% (IQR: 43-71%). Multiple patient features were significantly related to TTR and included heart failure which exerted a strong negative effect, prior VKA use which had the strongest positive effect, followed by prior GI bleeding and older age, both positive effects (Table 1a). After adjusting for patient features, geographic site still exerted a dominant effect. Regions with lower patient TTR had lower median INR (Table 1b) and more frequent INRs below 2.0. Indeed, most of the differences in regional TTRs were due to time below INR 2.0 (data not shown). Precision in INR targeting, assessed by interquartile range, was lowest in the lowest TTR region but generally similar across regions (Table 1b).
Conclusions: Prior warfarin use and common patient features, such as heart failure, are associated with patient TTR but the strongest single independent determinant of TTR in the ROCKET trial was geographic site. Our results suggest implicit targeting of lower INRs, within the INR range of 2.0-3.0, in the regions with the lowest TTRs.
- © 2011 by American Heart Association, Inc.