Residual Stroke Risk in AF Likely Not Anticoagulant Failure

Pam Harrison

May 10, 2016

SYDNEY, AUSTRALIA — The remaining stroke risk in patients with atrial fibrillation (AF) who are receiving either warfarin or other oral anticoagulants is probably not due to a failure of anticoagulant treatment, but rather to a baseline stroke risk that would be expected in the absence of AF in similar populations, a cohort study suggests[1].

"Residual stroke risk in anticoagulant-treated patients with AF is more likely to reflect the population-associated risk of noncardioembolic strokes in patients of similar age, sex, and comorbidity without AF, rather than anticoagulant treatment failure," according to Dr Ben Freedman (University of Sydney, Australia) and associates in their report in JAMA Cardiology. They say there remains an appreciable stroke risk of about 1.7% per year on warfarin and 1.4% per year on non-vitamin K antagonists over a 2.2 years of follow-up.

In their study, published online May 4, 2016, of 5555 patients in whom incident AF had been detected on ambulation, about 45% had been prescribed warfarin with or without an antiplatelet. About 29% of the group were taking an antiplatelet alone, while the remaining 26% of patients had received no antithrombotic therapy. They were compared with 24,705 controls matched by age and sex.

The adjusted cumulative stroke incidence over 1.5 years was 3.9% in untreated patients, 1.3% in those receiving warfarin, and 1.2% in the controls without AF (P=0.75), the group reports.

Hazard Ratios for Outcomes by AF Status vs Incidentally Detected Ambulatory AF Without Antithrombotic Therapy

Fatal stroke HR (95% CI)
Incidentally detected ambulatory AF, oral anticoagulant with or without antiplatelets 0.33 (0.16–0.66)
No AF 0.29 (0.19–0.44)
Nonfatal stroke HR (95% CI)
Incidentally detected ambulatory AF, oral anticoagulant with or without antiplatelets 0.56 (0.37–0.85)
No AF 0.33 (0.24–0.44)

As Freedman points out, the adjusted cumulative mortality at 1.5 years was 7.2% in patients in whom AF had been detected and who received neither anticoagulation nor antiplatelet therapy. This compares with 4.2% for patients receiving warfarin vs 2.5% among controls.

Even after adjustment for potential baseline confounders, the residual risk for mortality was significantly greater in the treatment group than in the control group (P=0.005), the group writes. In contrast, neither the incidence of stroke nor mortality was reduced by the use of antiplatelet therapy.

Freedman reported receiving research grants to conduct investigator-initiated studies from Bayer Pharma, Bristol-Myers Squibb/Pfizer, and Boehringer Ingelheim; personal fees from Bayer Pharma and Bristol-Myers Squibb/Pfizer, AstraZeneca, Gilead, and Servier; and nonfinancial support from Bayer Pharma and Boehringer-Ingelheim. Disclosures for the coauthors are listed in the article.

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