Atrial Dissociation and Uniatrial Fibrillation

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Abstract
Independent rhythms occurring in the atria of animals has been known since 1900. Due to its rarity few clinical reports have appeared in the literature. There are two possible explanations; each atrium may be separately autonomous or a part of the atrial muscle may be discharging impulses independently. Interrupting atrial pathways by various methods indicate that the former may be an explanation. The latter explanation presupposes that the dissociated area must be protected by "entrance" and "exit" blocks. The co-existing atrial rhythms offer a convenient four group classification. One ecg shows a secondary set of atrial waves independent of the P waves. Another case presents the appearance, acceleration and decay of an ectopic atrial focus. The atrial focus starts slowly, accelerates to 150-200/ minute (atrial tachycardia) and then reaches 750/minute (atrial fibrillation). One other case shows diminutive "p" waves occurring at any time initiating short bursts (0.10 - 0.32 seconds) of rapidly occurring waves (1500/minute) of low amplitude (0.01 - 0.05 mv). In all these illustrations sinus node activity continues uninterrupted and controls the ventricular rate.