Preventing strokes in patients with atrial fibrillation: What’s the evidence?

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Atrial fibrillation (AFib or AF) is the most common abnormal heart rhythm, affecting an estimated one to two per cent of our population — that’s 350,000 Canadians living with AF. Its incidence increases with age, so numbers are likely to increase as our population continues to age.

AF can lead to serious complications. It increases the risk of stroke by three to five times; an estimated 20 per cent of all strokes are caused by AF. Medications called antithrombotic drugs help to prevent stroke, but also increase the risk of serious bleeding.

There are two types of antithrombotic drugs used to prevent stroke in people with non-valvular AF:

• anticoagulant drugs such as warfarin (Coumadin); and a newer class of oral anticoaulant drugs, called NOACs, which includes dabigatran (Pradaxa), rivaroxaban (Xarelto), and apixaban (Eliquis)

• antiplatelet drugs such as acetylsalicylic acid (ASA, Aspirin) and clopidogrel (Plavix).

Warfarin has been the mainstay of therapy for more than 60 years. It is effective in preventing strokes in patients with AF, but there are some challenges with warfarin therapy: diet restrictions, drug and food interactions, the need for regular international normalized ratio (INR) monitoring, and frequent dosing changes.

The newer drugs, NOACs, are given in fixed doses so routine blood tests and dose adjustments are not needed; however, these drugs are costly, long-term safety data and clinical experience is lacking, and unlike warfarin, there is no reversal agent in the event of a serious bleed.

Antiplatelet drugs are less effective than warfarin and the NOACs, but are sometimes used for patients considered to have a low risk of stroke. Given the changing landscape of available drug options for the prevention of stroke in patients with AF, the Canadian Agency for Drugs and Technologies in Health (CADTH) undertook systematic reviews of the scientific evidence for these drugs as well as an economic analysis.

The results:

• Compared with warfarin, the added benefit of NOACs in preventing stroke in patients with AF is small. The estimated number of patients who would avoid a stroke or other blood clot if treated with a new drug rather than warfarin was less than 10 people for every 1,000 patients treated per year.

• Bleeding risks for patients treated with the newer drugs compared with warfarin were similar overall, with a modest decrease in intracranial bleeding and a small increase in gastrointestinal bleeding.

• While warfarin can be reversed with vitamin K, there is no reversal agent or proven management strategy if bleeding occurs with the new drugs.

• The newer drugs were significantly more costly even when the cost of INR monitoring with warfarin was factored in, and the cost-effectiveness of the newer drugs was uncertain.

• Compared with anticoagulant drugs, people on antiplatelet drugs experience more strokes without any reduction in bleeding risk. Even though antiplatelet drugs are inexpensive, they are not cost-effective because the cost of treating additional strokes and bleeding events must be factored in.

An expert committee made recommendations based on CADTH’s systematic reviews and economic analysis to guide policy and clinical decisions.

The bottom line:

• Warfarin is the recommended first-line therapy for preventing stroke in patients with atrial fibrillation.

• NOACs are a second-line option for some patients with non-valvular atrial fibrillation who are not doing well on warfarin.

• If a new oral anticoagulant is prescribed, patients must be monitored.

• For people who are able to use an anticoagulant, anticoagulant drugs should be used in preference to antiplatelet drugs.

Improving warfarin management:

A structured plan of care can help to improve warfarin management in any care setting. This includes regularly scheduled patient follow-up, monitoring for adherence and side effects, regular INR monitoring, dose adjustments based on INR results using a dosing tool or nomogram, ongoing patient education, involving other health professionals in patient care and education, and engaging caregivers to ensure adherence to treatment and regular follow-up. For more evidence-based reports, tools, and other information from CADTH on the prevention of stroke in patients with AF, please visit www.cadth.ca/clots.

If you would like more information about CADTH, the AF project, or other topics we’re working on please visit www.cadth.ca.