Principal Developer: J. Lam
Secondary Developers: R. Cote, A. Roussin

Thrombosis in Atrial Fibrillation

Atrial Fibrillation (AF) creates hemodynamic disturbances which lead to stasis in the atria. This in turn may lead to thrombus formation.
Thromboembolism is a major complication of AF and may result in TIA, stroke or ischemia of an internal organ or an extremity.

Epidemiology of AF

AF is frequent (1). It is, in fact, the most common pathological tachycardia. The prevalence increases with age: 0.2% below age 30 and over 12% at age 75 (2). Heart failure, hypertension and coronary artery disease are the predisposing factors most often associated with AF. Other strong associations are cardiomyopathies, mitral valve disease and hyperthyroidism.
The risk of stroke is approximately 4-5 % per year in non-rheumatic atrial fibrillation (3).

What is Lone AF ?

Lone atrial fibrillation is AF without structural disease, hypertension, diabetes or previous stroke.
The risk of embolization is low in patients below 65 with lone AF.

Paroxysmal / Chronic AF

Intermittent or paroxysmal AF and chronic AF have the same risk for thromboembolic events and therefore they should both be considered for antithrombotic therapy.(3)

Atrial Fibrillation: Potential Candidates for Warfarin

• lone AF above age 65
• paroxysmal (intermittent) AF
• chronic AF
• thyrotoxicosis
• congenital heart disease
• valvular disease
• planned cardioversion

Age Alone Not Necessarily an Exclusion Criteria

The risk of stroke increases with age while the rate of bleeding of warfarin therapy is poorly correlated with age, below 80. In five trials, the overall bleeding complications with warfarin in older patients were similar to aspirin or placebo.(5)
A patient should not be denied anticoagulation because of age alone.

Poor Candidates for Warfarin

• contraindications to oral anticoagulation
• prone to fall
• unreliable/uncooperative

These patients should be considered for aspirin therapy although protection may be suboptimal

Major Bleeding is Rare

Major bleeding occurs in less than 2% of the anticoagulated AF patients per year, when target INR is monitored and maintained. The risk of bleeding is associated with the intensity of anticoagulation, concomitant use of aspirin and underlying disorders.

Prevention of stroke in AF

For every patient with AF, the treatment options include:

• electrical or pharmacologic conversion to sinus rhythm versus control of heart rate
• prevention of stroke using warfarin or aspirin.

Treatment must be individualized and based on estimates of patient benefit versus risk.
In an overview of the randomized trials, warfarin reduced the annual risk of stroke by 68% and aspirin reduced the risk by 36%.(5)

Initiation Made Easier...

• Initiate with maintenance dose of warfarin
• Maintain target INR 2.5 (range 2.0 to 3.0)
• If INR value outside therapeutic range and no signs or symtoms of thromboembolic complications or bleeding, have PT done again in 3 days. If necessary, then adjust the dosage +/- 1mg.
• Monitor regularly, about once every 4-6 weeks, when anticoagulation level is stable.

Safety of Warfarin Therapy (4)

Bleeding is the most important complication of anticoagulant therapy. The intensity of anticoagulation, the concomitant use of ASA, NSAIDs and the underlying clinical disorder, are major factors influencing the risk of bleeding.
Skin rash and alopecia are uncommon adverse effects and may be managed by changing oral anticoagulants.
Skin necrosis is a rare complication and usually appears within a few days of the start of oral anticoagulation therapy.
Drug interactions are the commonest cause of significant change in the INR value. Patients should be advised not to change any medication without a physician's or pharmacist's advice. Adequate monitoring is the key to a successful and safe warfarin therapy. Please refer to the T.I.G. brochure on warfarin therapy.

References:

1. Kannel et al.NEJM.1982;306,:1018-22
2. Phillips et al.Mayo Clinic Proc.1990;65:344-59.
3. Albers et al.Chest.2001;119 (Suppl) 194S-206S.
4. Laupacis et al. Arch Intern Med. 1994