The ladder diagram (a 100+ year history).

The ladder diagram (also called a laddergram) remains a popular visual aid when graphically representing the mechanism of arrhythmia. It disentangles atrial and ventricular electrical activity and gives explicit representation to the sinoatrial and atrioventricular nodes. More than 100 years after the first published ladder diagrams, this report reviews their origins, development, and limitations. Ladderlike diagrams have existed since 1885, first applied to venous and arterial pulsation timing or waveform tracings and later in 1920 alongside electrocardiograms to explain the generation and propagation of electrical impulses in the heart. Two examples are presented in which the underlying mechanism of arrhythmia either was predicted by a ladder diagram and later confirmed by intracardiac recordings (atrioventricular nodal reentrant tachycardia) or underwent evolution of its ladder diagram depiction as the pathophysiology became better understood (atrial flutter). In general, the ladder diagram represents well abnormalities of impulse conduction but is less explicit with abnormalities of impulse formation. In conclusion, the surprising scarcity of major changes since the introduction of the ladder diagram testifies to its power to deal with a range of arrhythmogenic mechanisms that were unknown at the time of its development.