Diagnosis, Unique Observations and Ablation of Atypical Fast-Slow Atrioventricular Nodal Reentrant Tachycardia Using...

Fast-slow atrioventricular nodal reentrant tachycardia incorporating an inferolateral left atrial slow pathway (inf-lat-LA-F/S-AVNRT) is an exceptionally rare variant of AVNRT. Data regarding its diagnosis, electrophysiological characteristics, and optimal ablation strategy remain limited.

We retrospectively analyzed three women (48 ± 15 years) who underwent electrophysiological study and successful ablation of inf-lat-LA-F/S-AVNRT presenting with a long RP configuration and earliest atrial activation along the mitral annulus at the 3, 4:30, or 6 o'clock position in the left anterior oblique view.

Atrial tachycardia was excluded using standard criteria. However, differentiation from AV reentrant tachycardia using a slowly conducting left-sided accessory pathway required a specific maneuver: absence of atrial resetting during two consecutive fully paced ventricular stimuli. Retrograde conduction via the inf-lat-LA slow pathway was not reproducibly demonstrated in one patient. Typical features of F/S-AVNRT, including double atrial response and presence of a lower common pathway, were observed. Novel findings included detectable retrograde activation of the inf-lat-LA slow pathway and spontaneous transition between distinct AVNRT circuits. Tachycardia was successfully eliminated by targeting the earliest atrial activation site or by a left-sided stepwise anatomical approach.

Inf-lat-LA-F/S-AVNRT is a rare AVNRT variant with distinctive diagnostic and electrophysiological features that may require an individualized ablation strategy.