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Left Atrial Thrombus Despite Anticoagulation: The Importance Of Homocysteine

Patients in atrial fibrillation may have left atrial thrombi or strokes despite adequate anticoagulation. It is important to consider elevated plasma total homocysteine (tHcy) as a treatable clotting factor that may explain such cases. Metabolic B12 deficiency is common even in patients with a “normal” serum B12.  Measurement of holotranscobalamin, methylmalonic acid or, in folate-replete patients, tHcy are necessary to diagnose metabolic B12 deficiency when the serum B12 is below 400 pmol/L.  Elevated tHcy quadruples the risk of stroke in atrial fibrillation, and is far more common than the usual clotting factors for which testing is commonly performed:  among patients attending a secondary stroke prevention clinic, tHcy > 14 mmol/L is present in 20% at age 40, and in 40% at age 80.  B vitamin therapy does reduce the risk of stroke;  key issues are renal impairment and adequacy of vitamin B12. This intervention should be considered routinely in patients with AF.

Credits: Dr. J. David Spence

Biosense Webster
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Introduction to AFib
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