Use of Anticoagulation in Elderly Patients with Atrial Fibrillation Who Are at Risk for Falls

Candice L Garwood, PharmD BCPS; Tia L Corbett, PharmD

Disclosures

The Annals of Pharmacotherapy. 2008;42(4):523-532. 

In This Article

Warfarin versus Aspirin for Atrial Fibrillation

Several studies have examined the efficacy of aspirin versus warfarin versus the combination of both in AF patients ( Table 3 ).[21,22,23,24,25,26,27,28] The AFI pooled data from 5 studies and came to the conclusion that warfarin reduces the risk of stroke by 68% in patients aged 65 years and older, with minimal increase in bleeding risk (1.3% with warfarin vs 1.0% with placebo).[16] When combining data from 3 trials of aspirin versus placebo in AF, the AFI found that the stroke risk reduction with aspirin use was 21%.[29] Another meta-analysis found that the relative risk reduction (RRR) in stroke was 52% for warfarin versus aspirin.[30] The SPAF III trial studied patients who were at high risk for stroke and were randomized to receive either adjusted-dose warfarin or low-intensity, fixed-dose warfarin with aspirin. The primary study endpoint, largely composed of stroke, showed an RRR of 77% (p < 0.0001) with adjusted-dose warfarin versus low-dose warfarin plus aspirin combination.[24]

In the EAFT (European Atrial Fibrillation Trial), patients with prior transient ischemic attack or stroke were assigned to receive an adjusted-dose vitamin K antagonist, aspirin, or placebo.[26] The RRR of the primary endpoint (composed of stroke, myocardial infarction, systemic embolism, and vascular death) using adjusted-dose vitamin K antagonist versus placebo was 47% (HR 0.53; 95% CI 0.36 to 0.79; p = 0.001), and vitamin K antagonist versus aspirin was 40% (HR 0.60; 95% CI 0.41 to 0.87; p = 0.008). Oral anticoagulation was more effective than aspirin in prevention of the primary outcome, largely because of greater efficacy in prevention of all strokes. The RRR for all strokes with adjusted-dose vitamin K antagonist versus placebo was 67% (HR 0.34; 95% CI 0.20 to 0.57; p < 0.001), and vitamin K antagonist versus aspirin was 47% (HR 0.38; 95% CI 0.41 to 0.87; p < 0.001). In addition, aspirin was no different than placebo for secondary stroke prevention (HR 0.86; 95% CI 0.64 to 1.15; p = 0.31). The EAFT study demonstrated that vitamin K antagonists such as warfarin have the same stroke risk reduction in high-risk patients in comparison with general AF study populations.[16,26] Patients 75 years of age and over with AF were studied to demonstrate the efficacy of adjusted-dose warfarin versus aspirin for primary stroke prevention in the BAFTA (Birmingham Atrial Fibrillation Treatment of the Aged) study.[25] Adjusted-dose warfarin illustrated a 52% RRR in the primary composite endpoint versus aspirin (p = 0.0027) and a 46% RRR in stroke versus aspirin (p = 0.003). There are some limitations of the BAFTA study. There was significant crossover between the treatment groups. Study enrollment was limited to patients greater than 75 years of age in whom there was clinical uncertainty regarding which of these 2 treatments should be chosen. By default, this would exclude the highest risk patients, with multiple risk factors, for whom warfarin would be a clear therapy choice.[25,31] Nevertheless, according to the ACCP guidelines, patients in the BAFTA study would be considered high risk.[2,25] The aspirin dose studied was 75 mg, which is lower than the dose in most AF studies.[21,24,26,32,33] However, the ACC/AHA/ESC guidelines recommend aspirin 81 mg as a therapeutic option in AF, and this dose is commonly considered in clinical settings for elderly patients.[5]

In elderly patients who are at high risk for falls, clinicians may consider aspirin as an effective alternative to warfarin. In examining the evidence for warfarin versus aspirin in AF, it appears that aspirin is only about half as effective at lowering stroke risk relative to warfarin.[25,26,30] We can deduce that, in patients with AF who are at high risk for stroke, aspirin may not be effective for stroke prevention.[26] Therefore, aspirin should not be considered the optimal therapeutic choice in high-risk elderly patients with AF.

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