An Unusual Case of A-v Nodal Rhythm with Varying A-v Block.

In the human electrocardiogram, A-V block prolongs the P-R interval to values exceeding 02 sec., while nodal rhythm is characterized by P-R intervals ranging from approximately plus 0-12 to minus 0-19 sec. (R-P intervals). The simultaneous occurrence of both A-V block and nodal rhythm may produce P-R intervals within normal range (0d12 to 0-2) ; however, this condition can be recognized by the characteristic retrograde P wave pattern (inversion of P II and P III), as recently shown by Langendorf, Simon, and Katz (1944). As the authors point out, this does not exclude the presence of A-V block with P-R intervals between plus 012 and minus 019. Since delay or even complete blockage of the A-V nodal impulse may occur on its way to the ventricles (antegrade block) as well as to the auricles (retrograde block) (Lewis, 1914; Lewis, White, and Meakins, 1914; Drury, 1924; and Scherf, 1926), any combination of P-R or R-P interval is compatible with the simultaneous existence of A-V block and nodal rhythm. The relation between P and R depends on the site of impulse formation and the site and the degree of the block. It is possible that in partial A-V block the site of impulse formation and that of the block are such that the antegrade impulse to the ventricles arrives simultaneously or earlier than the retrograde impulse to the auricles. This has been illustrated by Langendorf et al. (1944) in a scheme, but, naturally, this can not be easily demonstrated in actual tracings. The authors present cases with P-R intervals greater than 0-12 sec. The case presented in this paper is a further contribution to this problem because it illustrates a type of arrhythmia, apparently rare, since we have not seen it reported in recent years.