RISK-BASED ANTICOAGULATION THERAPY IN PATIENTS WITH ATRIAL FIBRILLATION
Case presented by:
A 68-year-old woman with no prior medical history is referred because of atrial fibrillation (AF). She reports 3 prior episodes, which terminated on their own after 8 to 12 hours. The episodes are accompanied by shortness of breath and lightheadedness. During the third episode, she presented to the emergency department and was found to have AF. She presents to clinic following this emergency department visit to discuss her need for anticoagulation.
Question No. 1: Should this woman be anticoagulated chronically?
Discussion
AF is a common medical problem worldwide, with an estimated prevalence of 0.95% in the United States and an estimated affected population of 12 million to 15 million patients in 2050.1 Because hypertension, diabetes mellitus, obesity, and sleep apnea are increasingly prevalent in the US population and are risk factors for AF, controlling this rhythm and its associated morbidities is important.2 AF is associated with a two- to fourfold increase in morbidity, mediated predominantly by an increase in stroke risk.3 However, prevention of stroke, predominantly through anticoagulation, has its own risks. As newer antithrombotic methods become available, the risk–benefit ratio may change.
Risk of Stroke
AF confers at least a 1% annual stroke risk in patients younger than 60 years of age with lone AF. As risk factors increase, the risk of stroke increases, though not necessarily proportionately. As a result, numerous risk stratification scores have been developed to predict the annual chance of stroke based purely upon clinical factors. Whereas these algorithms are all effective predictors of risk, the CHADS2 schema is most frequently used due to its relative simplicity.
In the CHADS2 schema, one point is assigned for each risk factor as depicted in Table 50.1, expect for prior stroke or transient ischemic attack (TIA) of any cause, which gets 2 points. Annual stroke risk is estimated as roughly 1.9% for a score of 0, 3% for a score of 1, 4% for a score of 2, 6% for a score of 3, 8.5% for a score of 4, 12.5% for a score of 5, and 18.2% for a score of 6.4 A point total of ≥ 2 suggests a benefit to anticoagulation with warfarin, whereas a score of 1 indicates a neutral risk–benefit ratio. A score of zero indicates that the stroke risk is low. However, aspirin is recommended for stroke prophylaxis in these patients.
Table 50.1. Points per Risk Factor in the CHADS2 Risk Score
| Risk Factor | Point Score |
| Congestive heart failure | 1 |
| Hypertension | 1 |
| Age >75 years | 1 |
| Diabetes mellitus | 1 |
| History of stroke or TIA | 2 |
Judging the risk–benefit ratio for patients with scores of 1 can be difficult, as patient preference regarding personal views on risk–benefit ratios can be difficult to ascertain. Recently, the CHA2DS2-VASc risk score was developed. This system recognizes that female gender, vascular disease, and age <75 years convey higher stroke risk than previously recognized. The CHADS2 system is modified by incorporating 1 point each for ages 64 to 75 years, female gender, and vascular disease (including prior myocardial infarction, peripheral arterial disease, or aortic plaque), and 2 points for age >75 years. For patients with a score of zero, no stroke prophylaxis is recommended in either system. The CHA2DS2-VASc risk score moves many patients, especially women or those between the age of 55 and 74 years up from a CHADS2 score of 1 to a CHA2DS2-VASc score of ≥ 2, at which oral anticoagulation is required. However, uncertainty still remains for patients with a CHA2DS2-VASc score of 1 since oral anticoagulation is listed as preferred but aspirin is also an accepted option for these patients.
A retrospective evaluation of the CHA2DS2-VASc, CHADS2, and Framingham risk scores applied to a group of patients followed for one year after hospital discharge for AF validated the stroke prediction efficiency of the CHA2DS2-VASc score. Assuming that patients enrolled were not taking aspirin, the annual risk of thromboembolic events for each CHA2DS2-VASc score is demonstrated in Table 50.2. The CHA2DS2-VASc scoring system was a better predictor than the CHADS2 risk score though not as predictive as the Framingham scoring system. However, the Framingham scoring system is more difficult to use clinically than the CHADS2 and CHA2DS2-VASc scoring systems. Overall, the CHA2DS2-VASc score dropped the stroke risk for a score 1 from 3% to 0.7%, allowing better stroke prediction. The recent European Society of cardiology Guidelines for AF have switched to the CHA2DS2-VASc scoring systems.
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