Atrial Fibrillation Treatment Reduces Stroke Risk

At the Southern Hospital Medicine Conference, held November 7-9, 2013, in New Orleans, LA, Sammy Khatib, a cardiologist at the John Ochsner Heart and Vascular Institute, gave a presentation about stroke reduction management by treating atrial fibrillation (AF).

During his presentation, Khatib observed that AF is the most common sustained cardiac rhythm anomaly. The condition is estimated to increase the risk of stroke fivefold, and it is independently associated with a 50 to 90% increase in the risk of death. Symptoms include fatigue, heart palpitations, lightheadedness, and dyspnea, but patients can also be asymptomatic. The condition affects 2.2 million people in the United States alone, and its US prevalence is projected to rise to 4 million by 2030.

Current recommendations for stroke prophylaxis include aspirin, which reduces a patient’s risk by about 22%; vitamin K antagonists, which reduce risk by about 62%; and direct thrombin inhibitors such as dabigatran and Factor 10a inhibitors such as rivaroxaban and apixaban, though their ability to reduce stroke risk remains unknown.

Khatib discussed the results of several studies that compared the efficacy of novel anticoagulant (NOAC) therapy to warfarin in reducing stroke and systemic embolism in patients with AF. The 2009 RE-LY study, the 2011 ROCKET-AF study, and the 2011 ARISTOTLE study compared the efficacy of dabigatran, rivaroxaban, and apixaban to warfarin, respectively.

The researchers found that the NOACs were more convenient to use, caused less intracranial bleeding, and were not inferior to warfarin for the reduction of stroke and systemic embolism. Although apixaban had a lower rate of overall bleeding and reduced mortality, all 3 NOACs were associated with a higher rate of bleeding in patients with mechanical heart valves, as well as a higher rate of renal dysfunction, especially in patients with a creatinine clearance of less than 30.

Khatib also discussed the CHADS2, a risk stratification scheme for predicting stroke in patients with AF. To calculate that score, one point each is given for congestive heart failure (CHF), hypertension (HTN), age above 75, and diabetes mellitus (DM), while 2 points are given for previous stroke, transient ischemic attack (TIA), or thromboembolism. A score of 1 represents a stroke risk of 2.8% per year, while a score of 6 represents a stroke risk of 18.2%.

However, Khatib pointed out that CHADS2 is prone to some inaccuracies. For example, 30 to 50% of patients are classed as moderate risk, other risk factors for stroke are not taken into account, and low-risk patients are not identified.

In contrast, CHA2DS2-VASc score may be more accurate, especially for low risk patients. The assessment includes CHF, HTN, DM, stroke, vascular disease, female sex, and ages 65 and up. A score of 1 on the test translates to a stroke risk of 1.3%, 6 translates to a risk of 9.8%, and 9 translates to a risk of 15.2%.

Khatib then discussed the American College of Cardiology risk assessment tool AnticoagEvaluator, which is available as a mobile app to allow physicians to go through a checklist for patient characteristics, and then calculate individual risk for stroke, thromboembolism, and annual major bleeding event.

Other methods for stroke reduction in AF patients include devices that target the left atrial appendage (LAA), such as the Watchman device, which traps clots before they exit the LAA. The efficacy of the Watchman compared to warfarin was evaluated in the PROTECT AF study, which included AF patients with CHADS scores of 1 or more.

“A total of 86% of those with the implanted device were able to discontinue warfarin,” Khatib said. Major bleeding occurred in 3.5% of patients, and serious pericardial effusion in 4.8%. However, Khatib added that procedural safety-related to peri-implantation complications still need improvement. The Lariat device, a wire device that works by epicardial/endocardial LAA ligation, is still under active investigation.

Khatib emphasized that AF should be managed by rhythm control, which is based on symptoms, as well as stroke reduction, which is based on the underlying risk of stroke.