Focal Atrial Tachycardia Focal AT is characterized as a fast rhythm from a discrete ori- gin, discharging at a rate that is generally regular, and con- ducting in a centrifugal manner throughout the atrial tissue. Focal AT represents approximately 3% to 17% of the patients referred for SVT ablation.49,122,186 The demographics of focal AT in the adult population will continue to change as SVTs are increasingly ablated at a younger age. Focal AT can be sustained or nonsustained. The atrial rate during focal AT is usually between 100 and 250 bpm.186 Presence and severity of symptoms during focal AT are vari- able among patients. Focal AT in the adult population is usu- ally associated with a benign prognosis, althoughAT-mediated cardiomyopathy has been reported in up to 10% of patients referred for ablation of incessant SVT.187,188 Nonsustained focal AT is common and often does not require treatment. The diagnosis of focal AT is suspected when the ECG criteria are met (Section 2). Algorithms have been devel- oped to estimate the origin of the focal AT from the P-wave morphology recorded on a standard 12-lead ECG.189,190 In general, a positive P wave in lead V1 and negative P waves in leads I and aVL are correlated to ATs arising from the left atrium. Positive P waves in leads II, III, and aVF suggest that the origin of AT is from the cranial portion of either atria. 