New-onset atrial flutter and fibrillation require investigation to exclude underlying heart disease
and thyroid dysfunction. Transthoracic echocardiography should be performed, and cardiology input
sought. These arrhythmias are associated with a risk of thrombus formation within the left atrial
appendage, and a therapeutic dose of LMWH should be given instead of warfarin. If the onset is 24-h duration, 8 weeks of
adequate anticoagulation should be completed before DCCV to reduce the risk of stroke. If the
arrhythmia cannot be tolerated, then a transoesophageal echocardiogram (TOE)-guided cardioversion
may be considered, although small thrombi may not be detected, so the risk of stroke is still present
even if the TOE is reassuring.