Atrial and His bundle stimulation with an accessory nodo-ventricular connection.

A 39-year-old man with a history of frequent paroxysmal tachycardias for 27 years was referred for electrophysiology study. His resting electrocardiogram showed left bundle branch block, which persisted during paroxysmal tachycardia. Electrophysiology study demonstrated the presence of a right-sided accessory nodo-ventricular connection. The case is of particular importance as it illustrates the diagnostic value of QRS normalization with left atrial pacing and the therapeutic use of rapid His bundle pacing to terminate the tachycardia.