Preservation of pre-excitation despite acute myocardial infarction complicated by complete heart block.

In a 53-year-old man with ventricular pre-excitation (normal PR interval, QRS interval of 0.12 seconds and delta-waves) acute inferior wall myocardial infarction was complicated by, successively, first-degree atrioventricular block, second-degree atrioventricular block (Wenckebach type) and complete heart block. The QRS pattern of pre-excitation was preserved throughout these events. The classification of ventricular pre-excitation is reviewed and the correlation between the various electrocardiographic patterns (the Wolff-Parkinson-White syndrome and its variants and the Lown-Ganong-Levine syndrome) and the anomalous conduction pathways of Kent, James and Mahaim are discussed. In this case the best possible explanation for preservation of pre-excitation during complete heart block was the existence of accessory fibres of Mahaim.