What is the clinical evidence from this study?

Study design: Observational. Population: Chronic atrial fibrillation (n=312). Intervention: Warfarin vs. Aspirin 325 mg daily. Primary outcome: Incidence of new thromboembolic stroke (p=<.001).

March 1, 1999Open Access

Incidence of New Thromboembolic Stroke in Persons 62 Years and Older with Chronic Atrial Fibrillation Treated with Warfarin Versus Aspirin

Q: What are the key findings of this study?

Warfarin significantly reduced the incidence of new thromboembolic stroke compared to aspirin in older patients with chronic atrial fibrillation (32% vs 65%; P<.001).

Key Result

Warfarin significantly reduced the incidence of new thromboembolic stroke compared to aspirin in older patients with chronic atrial fibrillation (32% vs 65%; P<.001).

Study Design

Type

Observational (n=312)

Multicenter

PICO

Population

Chronic atrial fibrillation (n=312)

Intervention / Comparator

Warfarin vs Aspirin 325 mg daily (Adjusted to maintain INR between 2.0 and 3.0)

Primary Outcome

Incidence of new thromboembolic stroke, p=<.001

Main Result

Absolute Event Rate: 32% vs 65%

p-value: p=<.001

Abstract

OBJECTIVE: To investigate the incidence of new thromboembolic (TE) stroke in older persons with chronic atrial fibrillation treated with oral warfarin versus aspirin. DESIGN: In an observational study of 312 older persons with chronic atrial fibrillation, long-term aspirin 325 mg daily was administered to 187 persons, and oral warfarin, in a dose adjusted to maintain the international normalized ratio (INR) between 2.0 and 3.0, was administered to 115 persons. The incidence of new TE stroke was analyzed in persons treated with warfarin versus aspirin at 36 +/- 17 months (1 to 99 months) follow-up. SETTING: A large, long-term healthcare facility. PATIENTS: The patients included 208 women and 104 men, mean age 84 +/- 7 years (range 62 to 101 years). MEASUREMENTS AND MAIN RESULTS: Four of 125 persons (3%) on warfarin stopped taking warfarin compared with four of 187 persons (2%) on aspirin who stopped taking aspirin because of adverse effects (P not significant). In persons with prior stroke, the incidence of new TE stroke was 40% (27 of 67) in persons treated with warfarin versus 81% (56 of 69) in persons treated with aspirin (P < .001). In persons with no prior stroke, the incidence of new TE stroke was 22% (13 of 58) in persons treated with warfarin versus 56% (66 of 118) in persons treated with aspirin (P < .001). The incidence of new TE stroke in all subjects was 32% (40 of 125) in persons treated with warfarin versus 65% (122 of 187) in persons treated with aspirin (P < .001). Cox regression analysis showed that persons taking warfarin had a 76% less chance of developing a new TE stroke than those taking aspirin after controlling the confounding effects of other risk factors. CONCLUSION: In an observational study of older persons with chronic atrial fibrillation, persons treated with oral warfarin to maintain an INR between 2.0 and 3.0 had a significantly lower incidence of new TE stroke than persons treated with oral aspirin 325 mg daily.