The outstanding clinical feature of the cardiac arrhythmia now known to be associated with fibrillation of the auricles is irregularity of the ventricular beat. Before use of the electrocardiographic method made possible the recognition of the underlying disturbance in mechanism, the condition was termed pulsus irregularis perpetuus. The irregularity is not, however, invariably permanent. It may occur as paroxysms which terminate spontaneously; or a drug, such as quinidine, may be employed to restore sinus rhythm. It is also known that there may be complete heart block in auricular fibrillation, often the result of the therapeutic use of digitalis. As an accompaniment of A-V dissociation, regular idioventricular rhythm is established, usually at rates ranging from 30 to 40, though occasionally higher when the impulse is initiated in the junctional tissues.
More rarely it may be noted that, for varying periods, the ventricles, though beating at a rate of 60 or over,