Paradoxical Increased Risk of Thrombosis after Initiation of Vitamin K Antagonists in Thromboembolic Disease

Vitamin k Antagosnist Oral Anticoagulants (VKA) are effective in the primary and secondary prevention of venous thromboembolism, in the prevention of systemic embolism and stroke in patients with prosthetic heart valves or atrial fibrillation. In patients with thromboembolic disease Low Molecular Weight Heparin (LMWH) and oral VKA are started at diagnosis. LMWH is than stopped once the International Normalised Ratio (INR) values are in the therapeutic range. The timing of stopping LMWH is important since its discontinuation too soon after a therapeutic INR has been achieved may paradoxically increase the risk of thrombosis. In a recent study, only 20% of the patients met the currently recommended treatment guideline of 4 days or more of heparin and warfarin overlap, until the international normalized ratio is greater than 2.0 for 2 consecutive days [1]. The manuscript will discuss the mechanisms behind the increased risk of thrombosis after initiation of oral anticoagulation therapy and how to avoid these risks.