Despite its proven efficacy in reducing the risk of stroke in patients with abnormal heart rhythm, the blood thinner warfarin is less commonly given to racial minorities, even though their risk of stroke is higher than that of whites, a new study shows.
Furthermore, only about half of older patients in the United States hospitalized with abnormal heart rhythm, also referred to as atrial fibrillation, are prescribed warfarin when they are discharged, according to a report in the journal Stroke. Atrial fibrillation increases the risk of blood clot. By “thinning” the blood, warfarin can prevent the formation of these clots, which are the most common cause of strokes.
In a second journal paper, researchers found that physicians often don’t prescribe warfarin for patients over the age of 80 who have atrial fibrillation, even though their risk of stroke is high. Failure to prescribe the drug is frequently attributed to other existing conditions that would put the patient at risk for complications.
Dr. Brian F. Gage, from Washington University School of Medicine in St. Louis, and his associates created a National Registry of Atrial Fibrillation II data set. Their analysis included Medicare beneficiaries (i.e., at least 65 years old) hospitalized with atrial fibrillation between April 1998 and March 1999. The study consisted of 16,007 non-Hispanic whites, 797 blacks, and 468 Hispanic subjects.
Warfarin was prescribed for 49.1 percent of patients at discharge. Even among “ideal candidates” — those with a high risk of stroke and few reasons for not receiving the drug — warfarin was prescribed for only 64.6 percent.
Overall, warfarin was prescribed for 49.7 percent of whites, 43.2 percent of blacks, and 40.2 percent of Hispanics. Compared with whites, blacks and Hispanics who were prescribed warfarin were more likely not to be monitored during the first 90 days (9.7 percent, 21.3 percent and 16.7 percent, respectively) and at regular interval after 90 days.
Warfarin use was associated with a 35-percent reduction in strokes, which compares poorly to the 65-percent reduction observed in clinical trials, the authors note. The drug was even less effective in preventing stroke among minority patients.
Gage’s team suggests that poor follow-up probably contributes to warfarin’s reduced efficacy among blacks and Hispanics, as well as their increased risk of strokes unrelated to blood clots (for which warfarin provides less effective prevention) and their higher risk of diabetes and high blood pressure.
To determine the reasons why physicians don’t prescribe warfarin for patients with atrial fibrillation, Dr. Elaine M. Hylek at Boston University School of Medicine and her associates followed 405 patients age 65 or older who were admitted to a hospital for atrial fibrillation between 2001 and 2003.
They found that 51 percent of the patients were started on warfarin: 75 percent of those 65 to 69 years old, 59 percent of those 70 to 79, 45 percent of those 80 to 89, and 24 percent of those age 90 or older.
The most common reasons that physicians cited for not prescribing warfarin were hemorrhage (33 percent), falls (32 percent) and patient refusal or history of nonadherence (14 percent). Other reasons included mental impairment, alcohol abuse and advanced illness.
Approximately 75 percent of those not prescribed warfarin were put on aspirin or aspirin plus clopidogrel, which are less effective than warfarin at preventing stroke.
Strategies are needed to increase treatment eligibility of elderly patients, particularly reducing the risk of hemorrhage and falls, Hylek’s team maintains. They also call for research to find alternative stroke prevention strategies that don’t increase hemorrhagic risk.