Hypothesis: Does the time spent within the target INR range differ when patients are managed by AMD or IT models of anticoagulation care?

Experimental Design: The 36-month trial enrolled 192 eligible patients currently receiving chronic warfarin therapy at the William S. Middleton Memorial VA Hospital. Consenting patients are enrolled and randomized to 1 of 2 groups: usual clinic care with face-to-face visits every 4 weeks (AMS model) or clinic visits every 3 months with interim laboratory visits and telephone follow-up every 4 weeks (IT model). At study conclusion, the amount of time the INR is within target range will be compared between the two groups. Thromboembolic and bleeding event rates, patient knowledge, quality of life and healthcare utilization will also be analyzed.