Characteristics and catheter ablation of focal atrial tachycardia originating from the interatrial septum

Abstract

Background: Ablation of focal atrial tachycardia (AT) originating from the interatrial septum (IAS) is challenging because of its complex anatomy.

Methods: We studied the electrocardiographic and electrophysiologic characteristics of focal, septal AT in seven patients who underwent successful ablation.

Results: The 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, >1cm 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.

Conclusions: Septal 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.

Keywords: Atrial septum; Cardiac electrophysiology; Ectopic atrial tachycardia; Electrical catheter ablation; Electrocardiogram.