Patients with limited postoperative AF are at increased risk of recurrence; however, further research is needed to identify which patients would benefit from long-term anticoagulation. CLINICAL STATEMENTS AND GUIDELINES Kleindorfer The safety of oral anticoagulation in the setting of cerebral amyloid angiopathy and in the presence of microhemorrhages remains unclear and merits fur- ther study. The efficacy of left atrial appendage closure com- pared with DOACs is unknown. The DOAC efficacy in morbidly obese patients is unknown. 5.4.2. Valvular Disease Recommendations for Valvular Disease Referenced studies that support recommendations are summarized in online Data Supplements 33 and 34. COR LOE Recommendations In patients with ischemic stroke or TIA and valvular AF (moderate to severe mitral steno- sis or any mechanical heart valve), warfarin is recommended to reduce the risk of recurrent stroke or TIA.452 457 In patients with a mechanical mitral valve and a history of ischemic stroke or TIA before valve replacement, aspirin (75 100 mg/d) is recom- mended in addition to warfarin with an INR target of 3.0 (range, 2.5 3.5) to reduce the risk of thrombosis and recurrent stroke or TIA.458,459 In patients with ischemic stroke or TIA and native aortic or nonrheumatic mitral valve disease (eg, mitral annular calcification or mitral valve prolapse) who do not have AF or another indication for anticoagulation, anti- platelet therapy is recommended to reduce the risk of recurrent stroke or TIA. In patients with a bioprosthetic aortic or mitral valve, a history of ischemic stroke or TIA before valve replacement, and no other indication for anticoagulation therapy beyond 3 to 6 months from the valve placement, long-term therapy with aspirin is recommended in preference to long-term anticoagulation to reduce the risk of recur- rent stroke or TIA. 