The Electrocardiographic Footprints of Wenckebach Block.

In 1899, Karel Frederik Wenckebach described a cardiac arrhythmia with periodic dropped beats now referred to as a Wenckebach sequence. This was later shown to be due to a block in the atrioventricular node, but today, we identify Wenckebach sequences throughout the heart with most being recognised on the surface electrocardiograph as characteristic footprints. This manuscript will revisit Wenckebach atrioventricular block, the typical features of which only occur in about 15% of cases, with the remainder atypical. Earlier reports regarded Wenckebach atrioventricular sequences as rare as they are only occasionally seen on the surface 12-lead electrocardiograph. Today, however, with the increased use of ambulatory Holter monitoring, Wenckebach atrioventricular sequences occur in 4-6% of all traces and are particularly common at night in the young. Most, but not all cases are benign and the clinical spectrum will be reviewed. Atypical Wenckebach atrioventricular sequences are a complex group which will be analysed in detail with a broad range of illustrations. Outside the atrioventricular conducting system, such as in the sinus node, Wenckebach sequences may not be obvious as they are partially hidden from the electrocardiographic tracing. However, by understanding the sequence footprints, clues are available in interpreting tracing with periodic pauses. Dual chamber paced rhythms may show Wenckebach sequences due to electronic control of the atrioventricular delay. Rarely exit blocks at the cellular level in the atrium, ventricle or at the pacing electrode-tissue interface can demonstrate Wenckebach sequences recognised on the surface electrocardiograph.