Interatrial and sinoatrial block, with an illustrative case

Wenckebach phenomenon within the atria.

“…The PP inter-* vals showed a gradual decrease until one P wave was blocked. Scherf and Cohen (I964) commented on a case reported by Decherd, Ruskin, and Brindley in 1946. The electrocardiogram showed sinoatrial block and alternation between two peaks of a wide P wave.…”

Atrial Dissociation and Uniatrial Fibrillation

“…DISCIJSSION A variety of terms has been used to describe dissociation between the atria; intraauricular,4' 8 interauricular,9 12, 19 interatrial,20 atrial2' dissociation, and interatrial block. [20][21][22][23] There is clearly need for consistency and it would seem to us that the simplest, least ambiguous, and most acceptable term is atrial dissociation. Intra-atrial block refers to a distinct and different condition of abnormally widened and notched P waves, well exemplified by P-mitrale.…”

Sino-Auricular Block, Interference Dissociation, and Different Recovery Rates of Excitation in the Bundle Branches

“…The conducted beat of the interference dissociation sequence, if such premises were accepted, could then represent reciprocal rhythm. While a progressive increase in S-A time or a Wenckebach phenomenon has been claimed, on good evidence (Decherd et al, 1946) halving of the auricular rate, and all the objections of Lewis (1925) to the term and its implications still pertain. In the case reported herein, the disturbance in sinus rhythm resulting in marked auricular slowing allowed a lower rhythm centre to drive the ventricle and permitted the development of circumstances that give the picture of interference dissociation.…”