Matthew Martinez, MD, FACC, discussed warfarin alternatives and newer mechanical and interventional strategies for the management of atrial fibrillation at Hospital Medicine 2013.
Warfarin alternatives and newer mechanical and interventional strategies were among the updates on management of atrial fibrillation discussed by Matthew Martinez, MD, FACC, at the Society for Hospital Medicine’s 2013 annual conference, held May 17-19 at the National Harbor’s Gaylord Nelson Convention Center in Ft. Washington, MD.
Atrial fibrillation, which affects approximately 2.3 million Americans, accounts for approximately 100,000 strokes per year. Its incidence is increasing, and atrial fibrillation is an independent predictor of mortality. The cost of atrial fibrillation increases with each recurrence, with hospitalization costs being the primary driver.
Consequences of atrial fibrillation include impaired hemodynamics, increased risk of thromboembolism (4.5-fold increased risk of stroke), increased hospitalizations, reduced quality of life, and a twofold increased risk of mortality independent of comorbid cardiovascular disease. Therapy for atrial fibrillation is aimed at reducing the individual and societal burden of disease: targets include fewer hospitalizations, improved quality of life, reduced incidence of sequelae and adverse effects of therapies, and improved survival. Treatment options for atrial fibrillation include rate control, maintenance of sinus rhythm, and stroke prevention.
For rate control, dronedarone presents an option with structural similarity and similar efficacy to amiodarone, but without the thyroid or pulmonary toxicity conferred on amiodarone by its iodine moiety. Dronedarone is effective at maintaining sinus rhythm, but only accomplishes conversion to sinus rhythm from atrial fibrillation in about 8% of patients. Ablation, long an option for selected individuals with atrial fibrillation, can now also be accomplished by means of cryoablation. Via cardiac catheterization, a balloon is deployed into the aperture of the pulmonary vein and an annular lesion is caused by cryocautery, “short-circuiting” aberrant conduction paths which cause atrial fibrillation.
Anticoagulation can also be a critical component of stroke prevention in patients with atrial fibrillation, for whom the incidence of all-cause stroke is 5%. Risk stratification via a tool such as the CHADS2 (which may be overly sensitive) or the CHA2DS2-VASc (gaining increasing acceptance in the US) can help delineate patients for whom anticoagulation is indicated. For stroke prevention, there are newer agents that may present alternatives to warfarin for some patients; dabigatran targets thrombin (Factor IIa), while rivaroxaban and apixaban target Factor Xa.
These newer agents have fixed dosing (except with reduced creatinine clearance), relatively short half-lives, minimal food and drug interactions and a wider therapeutic window. In comparison with warfarin in clinical trials, all show reduced risk of intracranial bleeding and less all-cause mortality.
However, none of the three agents has a viable antidote strategy. Additionally, dabigatran can cause considerable dyspepsia, and is associated with a slightly increased risk of myocardial infarction, perhaps because of overproduction of “upstream” products in the clotting cascade. Although insurance reimbursement for these agents is on the upswing, they are all very expensive medications, especially in contrast to warfarin. Finally, there are not yet head-to-head trials comparing the newer agents. Martinez advises physicians to familiarize themselves with these medications, and to continue watching the post-approval literature as more patient use data become available.
A novel method of mechanical prevention of thromboembolic events uses a left atrial appendage (LAA) occluder. This small parachute-like device, self-expanding with a thin layer of mesh, is deployed into the aperture of the LAA, and then becomes endothelialized. Once in place, this mechanical barrier which keeps clots within the LAA provides reduced risk of systemic embolism and cardiovascular stroke versus warfarin alone. The procedure is not yet widely available, but may represent a good treatment option, especially for patients who have not been successfully maintained on warfarin therapy.