CAT: Atrial Fibrillation: Warfarin summary

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ATRIAL FIBRILLATION - WARFARIN PREVENTS STROKES

Clinical Bottom Line

Warfarin decreases the risk of stroke in patients with NVAF, with an increase in major bleeding episodes. Patients with NVAF who are <65, without a history of hypertension, previous stroke or TIA or diabetes are at a low risk of stroke, even if not treated.

Citation: Atrial Fibrillation Investigators. Risk factors for stroke and efficacy of antithrombotic therapy in atrial fibrillation. Arch Intern Med 1994;154:1449-57.

Clinical Question: In a patient with NVAF, does warfarin decrease the risk of stroke compared with no therapy?

Search terms: atrial fibrillation and anticoagulation in MEDLINE

The Study

pooled analysis of data from 5 randomised trials comparing warfarin or ASA with placebo in pts with NVAF (AFASAK, SPAF-1, BAATAF, CAFA, SPINAF)
AFASAK - 75 mg ASA, SPAF-1 - 325 mg ASA and both trials double blind
CAFA/SPINAF double blind, BAATAF open
warfarin - 3 studies used PTs and 2 used INRs
lowest target intensity, PT of 1.2-1.5 and highest target intensity INR of 2.8-4.2
inclusion/exclusion criteria similar except AFASAK/SPINAF didn’t enrol pts with intermittent a fib
mean length of follow-up 1.2-2.3 yrs
mean age of pts 69

The Evidence

Outcome	ARR	NNT
Stroke	0.031	32
Death	0.018	55
Major haemorrhage	0.003	NNH 333

Risk Categories	CER (%)	EER	ARR	NNT
Age < 65 no risk factors = 1 risk factor	1 (0.3 to 3) 4.9(3 to 8.1)	1(0.3 to 3) 1.7(0.8 to 3.9)	0 0.032	- 33
Age 65-75 no risk factors = 1 risk factor	4.3(2.7 to 7.1) 5.7(3.9 to 8.3)	(0.4 to 2.8) 1.7 (0.9 to 3.4)	0.032 0.040	33 25
Age > 75 no risk factors = 1 risk factor	(1.6 to 7.7) 8.1(4.7 to 13.9)	1.7(0.5 to 5.2) 1.2 (0.3-5.0)	.018 .069	55 15

Comments:

from this analysis, efficacy of ASA not clear
few pts > 75 enrolled in these trials (20%), yet 70% of individual with NVAF are between the ages of 65 and 85, see Arch Intern Med 1995;155:469-73.

Appraised by: Straus, 1997; Expiry Date: Sept 1999

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