Clinical research study
Myocardial Ischemic Events in ‘Real World’ Patients with Atrial Fibrillation Treated with Dabigatran or Warfarin

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Abstract

Background

Dabigatran may provide less protection against myocardial infarction than vitamin K antagonists (VKAs) in patients with atrial fibrillation. This may be particularly evident among “switchers” to dabigatran from VKA, as a result of discontinuation effects.

Methods and Results

We identified in nationwide Danish registries a cohort of VKA-naïve “new starters” on dabigatran (110 mg twice daily [bid] and 150 mg bid dose regimes) or warfarin, and a cohort of prior VKA-experienced “switchers” to dabigatran or “continuers” on warfarin. Cohorts were followed for an average of 16.0 months. Adjusted Cox regression models were used to compare event rates. Relative to warfarin, there was a nonsignificant trend to lower myocardial infarction rates with dabigatran among VKA-naïve users (110 mg hazard ratio [HR] 0.71; 95% confidence interval [CI], 0.47-1.07; 150 mg HR 0.94; 95% CI, 0.62-1.41); however, there was a nonsignificant trend to increased myocardial infarction rates among prior VKA-experienced users (110 mg HR 1.45; 95% CI, 0.98-2.15; 150 mg HR 1.30; 95% CI 0.84-2.01). An increased myocardial infarction rate relative to warfarin among prior VKA-experienced users was clearly significant during the early follow-up period of <60 days (110 mg HR 3.01; 95% CI, 1.48-6.10; 150 mg HR 2.97; 95% CI, 1.31-6.73). Comparable results were obtained for a composite end point (myocardial infarction, unstable angina, or cardiac arrest) among both VKA-naïve and prior VKA-experienced users.

Conclusions

In this large-scale nationwide cohort study, we found that switching to dabigatran increased the risk of myocardial infarction compared with continued warfarin usage in the early period after switching. Caution may be warranted, especially when switching prior VKA-experienced patients with atrial fibrillation to dabigatran.

Section snippets

Methods

We used the civil registration number assigned to all Danish residents to link 3 nationwide databases: 1) the Danish National Prescription Registry,10 which records purchase date, Anatomical Therapeutic Chemical (ATC) classification code, and package size for every prescription purchase in Denmark since 1994; 2) the Danish National Patient Register11 established in 1977, which includes admission/discharge date, and discharge International Classification of Diseases (ICD) diagnoses for >99% of

Study Population Characteristics

During the inclusion period, we identified the VKA-naïve cohort from 4818 and 8133 eligible first-time purchases of dabigatran and warfarin, respectively. The VKA-experienced cohort was identified from 3379 eligible purchases defining a switch from warfarin to dabigatran, alongside 277,937 non-first-time warfarin purchases (among 49,868 unique current VKA users). There were a comparable number of 110-mg-bid users among dabigatran users in both the VKA-naïve (44.1%) and VKA-experienced cohort

Discussion

In this large nationwide cohort study, which included both “switchers” and “new starters” on dabigatran or warfarin, we showed that in the cohort of previously VKA-naïve users (ie, “new starters” on dabigatran or warfarin) there was a nonsignificant trend to lower myocardial infarction rates with dabigatran among VKA-naïve users for both the 110-mg-bid and the 150-mg-bid dose of dabigatran relative to warfarin. In the cohort of VKA-experienced users (“switchers” to dabigatran or “continuers” on

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    Funding: This study was funded by a grant from the Obel Family Foundation.

    Conflict of Interest: GYHL has served as a consultant for Bayer, Astellas, Merck, Sanofi, BMS/Pfizer, Daiichi-Sankyo, Biotronik, Portola, and Boehringer Ingelheim, and has served as a speaker for Bayer, BMS/Pfizer, Boehringer Ingelheim, Daiichi-Sankyo, and Sanofi Aventis. TBL has received investigator-initiated educational grants from Bayer Healthcare and Boehringer Ingelheim, and served as a speaker for Boehringer Ingelheim, Bayer Healthcare, and BMS/Pfizer. In addition, DAL is on the Steering Committee of a Phase IV apixaban study (AEGEAN). Both GYHL and DAL have participated in various clinical trials of stroke prevention in atrial fibrillation. TBL has served as an investigator for Janssen Scientific Affairs, LLC and Boehringer Ingelheim. TBL and LHR have been on the speaker bureaus for Bayer, BMS/Pfizer, Janssen Pharmaceuticals, Takeda, Roche Diagnostics and Boehringer Ingelheim. The other authors have no conflicts of interest to declare. MR is a full-time employee of the Danish Health and Medicines Authority. The views expressed in this article reflect her personal views and do not necessarily represent the position of the Danish Health and Medicines Authority.

    Authorship: TBL: original idea, wrote the first draft and made revisions; LHR, MR, DAL: interpreted data, edited and drafted revisions to the article; AGR, FS: analyzed the data, drafted and revised the paper; GYHL: co-wrote the first draft and made revisions. All authors had access to the data and a role in writing the manuscript.

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