The Wenckebach phenomenon in sino-atrial block.

Abstract

Four cases are presented illustrating the diversity of the electrocardiographis presentation of sino-atrial Wenckebach conduction. All the patients had advanced heart disease and were receiving digitalis therapy. In one case the arrhythmia was precipitated by the intravenous injection of propranolol (inderal). The principles governing the arrhythmia are described and formulae are presented for the calculation of the true sinus cycle. Previous diagnostic criteria for this arrhythmia are critically reviewed. Sino-atrial Wenckebach conduction may masquerade as conspicuous sinus arrhythmia, and is not as uncommon as the paucity of published reports would suggest. A method of distinguishing sino-atrial Wenckebach conduction from the relatively benign sinus arrhythmia is described.