How long should someone with atrial fibrillation be anticoagulated before DC cardioversion, and how long should this be continued afterwards?

For years, the rationale for a period of anticoagulation prior to cardioversion was that the anticoagulation would either stabilise or abolish any thrombus, the assumption being that thromboemboli associated with cardioversion occurred when effective atrial contraction was restored, dislodging pre-existing thrombus. Furthermore, it was assumed that recent onset atrial fibrillation was not associated with left atrial (LA) or left atrial appendage (LAA) thrombus and could therefore be safely cardioverted without anticoagulation. Although this has become standard clinical practice it is not evidence-based and not without hazard. With anticoagulation most thrombus appears to resolve rather than to organise. In patients with non-rheumatic atrial fibrillation most atrial thrombi will have resolved after four to six weeks of anticoagulation but persistent thrombus has been reported. Left atrial thrombus is present in a significant proportion of patients with recent onset atrial fibrillation and the associated thromboembolic rate is similar to that found in patients with chronic atrial fibrillation. Furthermore, cardioversion itself is associated with the development of spontaneous contrast and new thrombus and, in the absence of anticoagulation, even those patients who have had thrombus excluded using transoesophageal echocardiography have subsequently developed symptomatic thromboemboli.

For most patients a period of 4 to 6 weeks of anticoagulation and a transthoracic echocardiogram prior to cardioversion will be sufficient. Patients at high risk of thrombus (e.g. those with cardiomyopathy, mitral stenosis or previous thromboembolism) should undergo a transoesophageal study prior to cardioversion. In certain patients there may be cogent arguments for minimising the period of anticoagulation. In these patients transoesophageal echocardiography can be undertaken and provided no thrombus
is identified will abolish the need for prolonged anticoagulation prior to cardioversion. However, all patients with atrial fibrillation need to be fully anticoagulated at the time of cardioversion and for a period thereafter.

The duration of post-cardioversion anticoagulation should be dictated by the likely timing of the return of normal LA/LAA function and the likelihood of maintaining sinus rhythm. If atrial fibrillation has been present for several days only, normal atrial function will usually be re-established over a similar period and intravenous heparin for a few days post-cardioversion is probably adequate. Where the duration of AF is longer or unknown a period of anticoagulation with warfarin for 1–3 months is advised (reflecting a slower time course of recovery of atrial function).