Transoesophageal echocardiography (TOE) has become an essential tool in the management of patients with atrial fibrillation (AF) by enabling safe early cardioversion and helping to prevent perioperative strokes during AF ablation procedures. Visualisation of left atrial appendage (LAA) thrombus remains key to the decision to proceed to cardioversion or ablation. The justification for this approach comes from a multicentre, randomised, prospective trial of patients (n = 1222) with AF of more than 2 days’ duration, assigned to early TOE-guided cardioversion or delayed cardioversion following conventional anticoagulation.1 The study found no difference in the composite primary end point (cerebrovascular accident, transient ischaemic attack and peripheral embolism) at 8 weeks between the two treatment options. However, the TOE group had fewer haemorrhagic complications, although there was an embolic event rate (0.5–0.8%) in both groups. By 8 weeks, there were no significant differences between the two groups in the rates of death, maintenance of sinus rhythm or in functional status.

This study led to the use of TOE to exclude LAA thrombus, thereby allowing early cardioversion for many patients. However, this management strategy still exposes patients to a small but persistent stroke rate that requires further explanation. A possible cause is suboptimal anticoagulation after cardioversion and it is a reminder that thrombus formation is not a static process and a single “safe” TOE may not be sufficient …