Twelve-lead ECG interpretation in a patient with presumed left atrial flutter following AF ablation

The 12-lead ECG provides valuable clues to the mechanism and origin of organized tachycardias occurring in patients after catheter ablation of atrial fibrillation. Many of these patients have cavotricuspid isthmus-dependent flutter, and therefore it is important to be aware of variations from the norm of typical flutter. Left atrial reentrant tachycardias are, however, the most common arrhythmias encountered after catheter ablation of atrial fibrillation. The underlying circuits are typically formed around anatomic obstacles such as the PV ostia or the mitral valve, and facilitated by slow conducting, low voltage isthmuses through gaps through and bordering ablation lesions. They can be recognized by the presence of 12-lead synchronous iso-electric intervals separating flutter waves. Continuous activity ECGs (without 12-lead iso-electric intervals) are typical of larger size reentrant circuits not dependent on markedly slow conducting isthmuses. Delayed bystander activity can also however obscure iso-electric intervals. The integration of informed ECG analysis with a detailed knowledge of the index ablation strategy can provide an optimum platform for successful catheter ablation of these often very symptomatic arrhythmias.