Characteristics and Catheter Ablation of Focal Atrial Tachycardia Originating From the Interatrial Septum

BackgroundAblation of focal atrial tachycardia (AT) originating from the interatrial septum (IAS) is challenging because of its complex anatomy.MethodsWe studied the electrocardiographic and electrophysiologic characteristics of focal, septal AT in seven patients who underwent successful ablation.ResultsThe site of successful ablation was at the site of earliest activation on the right side of the IAS in three patients and on the left side in four patients, >1 cm away from the centre of the fossa ovalis in the septum secundum. A negative or +/- versus a positive or -/+ P wave in lead V1 during AT accurately predicted a right- versus left-sided origin of the AT, respectively. In the four left septal AT cases, right atrial activation mapping opposite the site of successful ablation revealed the presence of a small, low-frequency potential followed by a larger, high-frequency potential. In contrast, a high-frequency potential was not preceded by a low-frequency potential in the three right septal AT cases.ConclusionsSeptal AT may originate from either side of the septum secundum. The P wave polarity in lead V1 accurately predicted the side of the IAS that the AT originated from. Left septal AT is characterised by the recording of double potentials reflecting far-field activation of the left-sided IAS, followed by near-field activation of the right-sided IAS, when recording from its right side, opposite the AT origin. These observations are particularly relevant when mapping an apparent right septal AT.