The patient described in the question stem has a mechanical heart valve and an INR of 3.1. INR of 2.5-3.5 is recommended for patients with a bileaflet mechanical aortic valve and atrial fibrillation.
The American College of Chest Physicians recommendations for anticoagulation in patients with prosthetic heart valves are as follows:
INR 2-3: bileaflet mechanical valve in aortic position
INR 2.5-3.5: mechanical valve in mitral position OR bileaflet mechanical aortic valve with atrial fibrillation
INR 2.5-3.5 + ASA: mechanical valve and history of systemic embolization
Warfarin is an oral anticoagulant that acts as a Vitamin K antagonist. It interferes with the hepatic synthesis of coagulation factors II, VII, IX, X, and proteins C and S. Anticoagulation with warfarin is monitored using the International Normalized Ratio, or INR, which reflects prothrombin time and the extrinsic coagulation pathway.
Gutierrez et al. review atrial fibrillation: "Atrial fibrillation is the most common cardiac arrhythmia. It impairs cardiac function and increases the risk of stroke. The incidence of atrial fibrillation increases with age. Key treatment issues include deciding when to restore normal sinus rhythm, when to control rate only, and how to prevent thromboembolism. Rate control is the preferred management option in most patients."
Ezekowitz discusses the guidelines outlined above in further detail. He also reviews the use of rapid anticoagulation: "Rapid anticoagulation can be achieved either with unfractionated heparin or with low-molecular weight heparin (LMWH). Heparin is initiated with an intravenous bolus of 80 U/kg bodyweight, and an infusion of 18 U/kg/h. The activated thromboplastin time should be 60-80s. An alternative to intravenous heparin is subcutaneous LMWH, which is prescribed in a mg/kg dose."
Answer 1: INR of 2-3 is indicated for a bileaflet mechanical aortic valve.
Answer 3: The presence of diabetes is not the most important factor determining the appropriate level of anticoagulation for this patient. Answer 2 is a better answer.
Answer 4: The presence of hypertension is not the most important factor determining the appropriate level of anticoagulation for this patient. Answer 2 is a better answer.
Answer 5: INR of 2.5-3.5 + ASA is indicated for a mechanical valve with a history of systemic embolization. The patient is not taking aspirin.
Gutierrez C, Blanchard DG. Atrial fibrillation: diagnosis and treatment. Am Fam Physician. 2011 Jan 1;83(1):61-8. Review.
PMID:21888129 (Link to Abstract)
Ezekowitz MD. Anticoagulation management of valve replacement patients. J Heart Valve Dis. 2002 Jan;11 Suppl 1:S56-60. Review.
PMID:11843522 (Link to Abstract)
Singer DE, Albers GW, Dalen JE, Fang MC, Go AS, Halperin JL, Lip GY, Manning WJ; American College of Chest Physicians. Antithrombotic therapy in atrial fibrillation: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008 Jun;133(6 Suppl):546S-592S.
PMID:18574273 (Link to Abstract)