With aging, the prevalence of atrial fibrillation (AF) increases. In individuals aged 65 and older, the prevalence of AF is about 5%, and doubles to 10% in those aged 80 and older.1 Additionally, as the population ages, the number of people with AF is rising dramatically, with 5.6 million people in the United States projected to have AF by the year 2050. In this population, the risk of ischemic stroke is of primary concern; nonvalvular AF increases the risk of stroke by 5-fold and is responsible for approximately 24% of strokes in patients aged 80 to 89.1
A key challenge in the management of elderly patients with AF is balancing the need for anticoagulation to prevent stroke with the high risk of hemorrhage. While clinicians may opt to titrate anticoagulation to lower international normalized ratios (INRs) in the elderly, this approach has its downside--with evidence clearly demonstrating that an INR <2.0 results in a significantly higher risk of embolic stroke--without the expected reduction of the risk of hemorrhagic stroke (perhaps the most serious complication of warfarin therapy).2,3 Regardless, older patients remain more likely to be under-anticoagulated than their younger counterparts.4
As AF risk rises with increasing age, so does the risk of warfarin-related bleeding.1 In one study by Hylek and colleagues among elderly patients aged 80 and older, 13% had major bleeds in the first year of warfarin therapy. This was nearly 3 times the rate of major bleeds in younger patients. In this study, major bleed was defined as fatal, hospitalization with transfusion of 2 units of packed red blood cells, or involvement of a critical site (ie, intracranial, retroperitoneal, intraspinal, intraocular, pericardial, or atraumatic intra-articular hemorrhage).5
While increasing INR may be the most obvious risk factor for major hemorrhage, there are others. Prior stroke, prior GI bleed, hypertension, aspirin use, anemia, renal insufficiency, and malignancy have all been identified as risk factors. A risk factor-guided decision-making tool, such as the CHADS2 score, may be helpful in guiding the anticoagulation risk/benefit analysis for individual patients.6
Once a decision to anticoagulate an elderly patient has been made, and an appropriate INR target chosen, oral anticoagulation dosing in the elderly has special challenges. Studies have shown that required warfarin doses decline with age. In one study, patients aged 70 and older had a mean weekly maintenance dose of 5 mg. Additionally, mean maintenance doses decreased 0.4 mg for each year of increased age.7
The elderly may also require more frequent INR monitoring, as they have been shown to be more likely to experience fluctuations in their INR, and to take longer to return to the therapeutic range if found to be supratherapeutic.1 The American Geriatrics Society guidelines recommend monitoring INR daily until stable, and suggest that this be followed by testing 2 or 3 times weekly for 1 to 2 weeks, weekly for 1 month, and monthly thereafter.8 However, the increased frequency of such monitoring may represent a burden to the patient or caregivers.
Despite the complexities of anticoagulation in a challenging population like the elderly, the American Geriatrics Society recommends it unless it is specifically contraindicated.8