Table 3.1-5. Risk stratification of venous or arterial thromboembolism in patients receiving long-term VKA treatment

Indications for VKA treatment

Estimated risk of thromboembolism




Mechanical heart valve

Mechanical bileaflet aortic valve with no additional stroke risk factors

Mechanical bileaflet aortic valve and one of the following risk factors: atrial fibrillation, history of stroke/TIA, hypertension, diabetes mellitus, congestive heart failure, age >75 years

– Mechanical mitral valve; old-type mechanical aortic valve (caged-ball, tilting-disc)

– History of stroke or TIA in prior 6 months

Atrial fibrillation

CHADS2 score 0-2 and no history of stroke or TIA

CHADS2 score 3-4

– CHADS2 score 5-6

– History of stroke or TIA in prior 3 months

– Rheumatic heart disease


History of one VTE event >12 months ago, currently no other risk factors for VTE

– History of VTE in prior 3-12 months or recurrent VTE

– Milder forms of thrombophilia (eg, heterozygotes for prothrombin G20210A gene or factor V Leiden)

– History of VTE in prior 3 months

– Severe thrombophilia (eg, antithrombin, protein C or protein S deficiency, APS, several coexisting conditions)

– Cancer (treatment in prior 6 months or palliative therapy)

CHADS2 score: see table 3.4-2.

APS, antiphospholipid syndrome; TIA, transient ischemic attack; VKA, vitamin K antagonist; VTE, venous thromboembolism.