Focal automaticity manifesting as incessant right atrial tachycardia

Abstract

A 75-year-old woman without structural heart disease presented with incessant regular monomorphic atrial tachycardia (AT). Spontaneous arrhythmia termination was repeatedly followed by a single sinus beat before reinitiation. Variations in tachycardia cycle length (CL) between 200 and 400 ms were frequently observed. The P-wave morphology was consistent with a focal origin from the crista terminalis; however, electroanatomic mapping (CARTO 3 system, Biosense Webster Inc., Diamond Bar, CA) demonstrated centrifugal activation of the right atrium originating from the atrial septal wall near the fossa ovalis. Further mapping at the site of the earliest atrial activation during AT revealed a rapid, regularly discharging focus (Figure 1, blue dot) at fixed 100-ms CL represented by the low-amplitude (0.17 mV) spike electrograms (↓) with an isoelectric interval between successive spikes. The accompanying local atrial potential (▼) during firing was clearly sharper, higher (0.75 mV), and well separated from the preceding spike at fixed 30-ms conduction delay but of lower amplitude (0.95 mV) than that during sinus beats (*). The recorded abnormal activity could not be detected when the catheter tip was moved a few millimeters. The initiation and termination of firing at the site of interest were recorded during catheter manipulation. The onset of AT on the surface electrocardiogram did not always coincide with the initiation of local, high-frequency activity but did terminate immediately with cessation of local firing. The first tachycardia P wave and subsequent discernible P waves were identical. Alterations in the degree of atrial capture by the focal activity (from 2:1 to