Left Septal Atrial Tachycardias: Electrocardiographic and Electrophysiologic Characterization of a Paraseptal Focus

OBJECTIVE: The objective was to characterize the electrocardiographic and electrophysiological features of focal atrial tachycardia (FAT) originating from the left septum (LS). BACKGROUND: FAT is recognized to occur at predefined anatomic locations rather than randomly throughout the atria. We describe the ECG and EP features of ATs originating from the LS as an important site for apparent perinodal tachycardias. METHODS: Nine patients presenting with LS FAT from a consecutive series of 384 underwent EP/RFA for symptomatic FAT. RESULTS: The mean age was 56 ± 12 years; 7 female with symptoms for 36 ± 28 months. P wave morphology (PWM) was negative/positive in lead V1 and across the precordial leads and negative or negative/positive in inferior leads in all patients. Tachycardia was incessant in 6 out of 9 patients with a mean tachycardia cycle length 421 ± 56 milliseconds. His A was ahead of P wave in all patients (mean -15 ± 5 milliseconds) and earlier than CS proximal (mean 4 ± 9 milliseconds). Successful acute focal ablation achieved at a mean of 31 ± 12 milliseconds ahead of P wave with no recurrences at a mean follow-up of 30 ± 28 months. CONCLUSION: Although the left septum is an uncommon site for focal AT an awareness of this location for harboring foci is particularly important when mapping apparently right-sided septal tachycardias.