Interaction of vitamin K antagonists with heparin affect monitoring by activated clotting times.

Background: Unfractionated heparin is recommended during atrial fibrillation (AF) ablation to achieve activated clotting time (ACT) above 250-300 s to prevent clot. Many patients on therapeutic international normalised ratio (INR) undergo AF ablation procedures; however, it is unknown whether they require less heparin to achieve similar ACT levels.

Methods: During AF ablation, the ACT was measured before and 10 min after administration of i.