Atrial Fibrillation
• Each year, in the US alone, atrial fibrillation causes >50,000 strokes and $12 billion in medical expenditure. Thus, safe and cost-effective stroke prevention is critical to the atrial fibrillation population.
• Atrial fibrillation (AF) is the most common arrhythmia (rhythm disorder) affecting 2.2 million Americans and accounting for about one-third of all hospitalizations related to cardiac rhythm problems. It’s a big public health issue with an annual cost per patient of approximately $3,600.1
• AF can arise from temporary (acute) causes such as alcohol consumption, heart attack, surgery, lung disease, or a metabolic disorder (such as an overactive thyroid gland) or long-term (chronic) conditions such as high blood pressure, diabetes, or heart failure.
• Overall, hospitalizations for AF have increased 66% in the last 20 years. This is due to various factors, including the aging of the population, a rise in chronic heart disease, and obesity.
• While AF is seen in only about 1% of the total US adult population, it affects about 4% of those older than 60 years and 9.0% of those older than 80 years. Up to 40% of patients with heart failure also experience AF, and patients with this combination of heart problems are at particularly high risk for cardiac death.
• The most common signs of AF are heart palpitations, chest pain, and shortness of breath. Up to one-third of patients with atrial fibrillation have no symptoms (silent AF), which is more common in the elderly.
• Several studies have reported a two- to three-fold lower prevalence of AF in blacks than whites. Since traditional risk factors for AF such as hypertension and diabetes are more common in blacks, the lower prevalence of AF in blacks than whites has been termed the ‘AF paradox.’2 However, only one third of blacks were as likely to be aware of the condition as whites.3 Besides, blacks were approximately one fourth as likely to be treated with warfarin as whites even when they were aware of AF.3
• AF can be occasional (paroxysmal, which self terminates) or ongoing (persistent). If it does not respond to an electric current that is used to reset the heart’s rhythm back to its regular pattern (called cardioversion), it can progress to permanent AF. Approximately 30% to 45% of cases of paroxysmal AF (when the AF lasts for 7 days or less) and 20% to 25% of cases of persistent AF (that lasts for more than 7 days) occur in young patients without any identifiable underlying disease. This is known as “lone AF.”
• If the heart’s atria are not contracting properly, blood can pool in the heart’s upper chambers. Such pooled blood can lead to the formation of blood clots within the atria, which in turn can cause strokes if the clots are carried into the blood stream and lodge in the arteries of the brain. About 15% to 20% of all strokes occur in people with AF, totaling about 70,000 strokes each year in the US and countless numbers worldwide.
• AF confers a 5-fold risk for stroke with greater or lesser risk depending on the number of concomitant risk factors. Just like there can be silent AF, strokes can be “silent” too. Elderly people with stroke, including silent stroke, have double the risk of dementia and a steeper decline in global cognitive function.
• Transient ischemic attacks (TIAs) are “warning strokes” that produce stroke-like symptoms but no lasting damage. TIA confers a 10-fold risk of stroke, therefore a history of TIA and AF is a combination that suggests a strong need for preventive therapy and stroke risk reduction.
• There are two approaches to treatment of AF: heart rate control or heart rhythm control, with therapies ideally achieving both goals. When medication is ineffective, AF treatments can include cardioversion, ablation therapy (that targets specific cells that are causing the AF), and open-heart or minimally-invasive surgery that also targets a specific area of the heart that is causing the problem.
• The two most common drugs used to prevent blood clot formation (and thus reduce the risk of stroke) are warfarin (commonly known as Coumadin) and aspirin. Although warfarin is more effective than aspirin for preventing stroke, it has more side effects especially bleeding.
• Aspirin is the standard treatment for patients without other risk factors for stroke who are also under 75 years of age. If you have only one moderate risk factor for stroke in addition to atrial fibrillation (such as hypertension, diabetes, or heart failure), either aspirin or warfarin may be considered to reduce stroke risk. If you have at least one high-risk factor (e.g., a previous stroke or TIA, age older than 75), you will likely receive warfarin.
• Because warfarin is a powerful blood thinner, it requires intense monitoring that involves regular blood tests to measure INR (International Normalized Ratio). For patients with AF, the target INR is usually 2.0 to 2.5. The frequency of INR measurements varies from individual to individual and is driven by how stable the measurements have been over time.
• While aspirin and warfarin can be very effective in reducing the risk of stroke (and heart attack), they are associated with a small risk of serious side effects. Most of the side effects are bleeding related. Patients at higher risk for injury (those with balance issues, those who abuse alcohol, and those who work in professions where falls are possible, etc.) may not be able to use warfarin, even if they would otherwise qualify for this therapy.
• Dabigatran etexilate (Pradaxa) was developed with the hope that it would be as effective as warfarin, but safer and easier to administer. It does not require INR monitoring. The Randomized Evaluation of Long Term Anticoagulation Therapy (RE-LY) found that dabigatran 150 mg twice daily was superior to warfarin in the prevention of ischemic stroke.
• The cost of Pradaxa is more than $5 per day which is about 50 times higher than generic warfarin. On the basis of results from several recent trials, Dabigatran 150 mg (twice daily) was cost-effective in AF populations at high risk of hemorrhage or high risk of stroke and poor control of INR with warfarin.4
Sources
1. CardioSmart. American College of Cardiology.
2. Gbadebo TD, Okafor H, Darbar D. Differential impact of race and risk factors on incidence of atrial fibrillation. Am Heart J. Jul 2011;162(1):31-37.
3. Meschia JF, Merrill P, Soliman EZ, et al. Racial disparities in awareness and treatment of atrial fibrillation: the REasons for Geographic and Racial Differences in Stroke (REGARDS) study. Stroke. Apr 2010;41(4):581-587.
4. Shah SV, Gage BF. Cost-effectiveness of dabigatran for stroke prophylaxis in atrial fibrillation. Circulation. Jun 7 2011;123(22):2562-2570.