ECG Challenge

ECG Section Editors

Authors: Víctor Expósito, Susana González-Enríquez, Felipe Rodríguez-Entem

UNCOMMON CAUSE OF SYNCOPE IN WPW SYNDROME CASE PRESENTATION – QUESTION:

A 38-year-old man was referred with transient episodes of syncope over a period of 2 years. Attacks occurred at rest and were non-related to exercise.  He denied previous episodes of tachyarrhythmia or palpitations preceding loss of consciousness.  He had no relevant past medical history and was not receiving any antiarrhythmic drug. Family history was unremarkable for cardiovascular diseases. An ECG showed intermittent WPW syndrome with right antero-septal pattern. Holter monitoring during an event demonstrated prolonged periods of complete heart block, with no ventricular escape (figure 1).

2nd-ECG-Challenge_WPW-block-(1)
Based on this rhythm strip, what is the most likely mechanism of the arrhythmia?*

References:

  1. Li HG, Klein GJ, Yee R, et al. Fatigue phenomenon in accessory pathways. J Cardiovasc Electrophysiol 1994; 5: 818-823
  2. Coumel P, Gourgon R, Slama R, Bouvrain Y. Conduction auriculo-ventriculaire par des fibres de pré-excitation, associée à un bloc complet de la voie nodo-hissiene: ‘Etude electrocardiographique de quatre cas. Archives des Maladies du Coeur 1973; 66: 285-304
  3. Porto AG, Brun F, Severini GM, et al. Clinical spectrum of PRKAG2 syndrome. Circ Arrhythm Electrophysiol 2016; 9: e003121