Atrial Tachysystole with Block

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Abstract
Two patients are reported who demonstrated bouts of rapid atrial activity with associated AV block at times unrelated to the administration of digitalis. The criteria of Lown and Levine for the differentiation of PAT with block from atrial flutter are examined. The application of atrial rate in the region of the arbitrary borderline is not a useful criterion. Determination of P-wave direction in leads II and III cannot be made in the presence of an undulating baseline. Identification, when possible, is not sufficient evidence for distinguishing the two arrhythmias. The appearance of the baseline may not warrant the decisive weight commonly given to it. A combination of recording instrument characteristics, the appearance of atrial repolarization at critical rates, as well as subjective factors may explain the undulatory baseline rather than denote a special electrocardiographic entity. Alternation of the P-P cycle length in PAT with block occurs inconstantly and is not an intrinsic property of the arrhythmia. Digitalis, which has a vagal effect, may contribute to the presence of this [see figure in the PDF file] phenomenon. The occurrence of ventricular premature contractions, response to carotid sinus pressure, and the AV ratio are nonspecific findings. The mode of termination of the arrhythmia may also lack specificity. Restoration of sinus rhythm following potassium administration will be, at times, coincidental. Moreover, the successful outcome of such a therapeutic trial is evidence of digitalis intoxication not proof of a specific arrhythmia. Experimental and clinical evidence has firmly established that digitalis is capable of producing an atrial arrhythmia attended by AV block. This report does not contest the observation. A critical review of the contrasting features of atrial flutter and PAT with block and an analysis of the data in the present cases suggest that the electrocardiogram does not provide a means for the clear-cut separation of atrial tachycardia from flutter in certain cases and questions the existence of such a division. The term atrial tachysystole with block is offered as a designation for such tracings.