A 37-year-old woman with Wolff-Parkinson-White syndrome had experienced atrioventricular re-entrant tachycardias for 3 years. The standard ECG showed a shortened PQ interval, a positive delta wave in leads I, II and aVF and a negative delta wave in V1, suggesting a parahisian AP location ( Fig. 1 A) . A first electrophysiological procedure confirmed this location with the earliest ventricular activation during antegrade conduction recorded in the His-bundle area anteriorly on the His-bundle catheter. The patient was treated with antiarrhythmic drug therapy, but after several months, she remained symptomatic, so a second electrophysiological study was performed, confirming the parahisian location.
Cryoablation was applied without a prior transient cryomapping test as is usually recommended in such procedures. One application of cryoenergy at −70 °C caused a sudden loss of ventricular pre-excitation ( Fig. 1 B). The initial pre-excitation completely disappeared but, surprisingly, we observed a persistent short atrioventricular delay. The ECG showed a shortened PQ interval, a positive delta wave in leads I and aVL and a negative delta wave in leads III, aVF and V1, suggesting a dormant posteroseptal AP location ( Fig. 2 A and B ). The earliest site of ventricular activation during antegrade conduction was recorded in the posteroseptal region on the coronary sinus catheter. One application of direct cryoenergy at −70 °C abolished the shortened PQ interval after 9 s ( Fig. 2 C). No complication occurred. The patient left the hospital 1 day later in sinus rhythm, with a PR interval of 130 ms and without any pre-excitation on the ECG ( Fig. 3 ).
