Atrial dissociation and double atrial arrhythmias.

Two independent sets of P waves have occasionally been observed in the electrocardiograms of experimental animals and attributed to dissociated activity of the two atria (Condorelli, 1929; Scherf and Siedek, 1934). The studies of Marcel and Exchaquet (1938) on the human fetus strongly suggest that atrial dissociation occurs in man, and electrocardiograms have also been illustrated and reported to show this phenomenon. The evidence in clinical cases was, however, not considered as conclusive by Lewis (1925), Katz (1946), White (1951), and Scherf and Schott (1953) because the possibility of artefacts could not be ruled out. Deitz et al. (1957) who reviewed the reported cases recently, considered some of the illustrations (Bay and Adams, 1932; Lombardini and Aviles, 1939; Moreira, 1951; Bellet, 1953) to be good or convincing examples of atrial dissociation, and reported three cases observed by them. Even in one of their three cases, however, artefact has been considered a reasonable possibility by Diamond and Hayes (1958). In almost all the cases reported to show atrial dissociation, the voltage of the secondary set of P waves has been very small and sometimes appreciable only on magnification. The purpose of this paper is to present electrocardiograms of a patient showing a clear secondary set of P waves with a voltage as high as 12 mm., undoubtedly demonstrating the phenomenon of atrial dissociation.