Nineteenth century "Traube's pulse" and current "Cardiac alternans": significant features in the history of cardiology.

Pulsus alternans is nowadays considered, in the third millennium, a clinical finding indicative of decreased myocardial contractility and an effective expression of ventricular dysfunction. In recent years, clinical scientific studies have evidenced the relevant connections between cardiac alternans and the risk of heart arrhythmias. Pulsus alternans was described in detail for the first time in its meaning as clinical sign of cardiac disease by Ludwig Traube in 1872. Traube had great competence in physical semeiotics and, besides being considered one of the founders of experimental pathology, this German internist accurately presented a situation characterised by a succession of higher and lower pulses. It is not by chance that one of the current synonyms of pulsus alternans is precisely Traube's pulse. The present clinical-historical approach has been selected not only for diachronic purposes, but also to illustrate, on epistemological grounds, the notable articulation and considerable complexity of an only apparently straightforward concept such as that of pulsus alternans. Its comprehension has undergone progress and its definition evolution, and the expression has included through time different physiologic, pathophysiologic and pathologic phenomena. Although now a century and a half old, the concept of pulsus alternans remains extremely modern and fascinating.