Accelerated atrioventricular (AV) junctional discharge resulting in nonparoxysmal junctional tachycardia (NPJT)1,2 frequently produces AV dissociation and is an example of cause 2, namely, acceleration of a subsidiary pacemaker.3 In Fig 1, NPJT actively usurped control of the ventricles but failed to capture the atria retrogradely and, as a consequence, ie, secondarily, AV dissociation resulted. Note also that as the P wave moved in front of QRS (Fig 1, top right), the atrial rate slightly exceeded the ventricular rate. Atrioventricular dissociation persisted because the timing of both rhythms permitted mutual extinction of each wave front to prevent capture. Because of this interference in impulse transmission, there exists no evidence in this example of complete AV dissociation to postulate any degree of either anterograde or retrograde AV block; physiologic refractoriness prevented impulse transmission through the AV junction. The failure to conduct does not necessarily mean pathologic block. Figure 2 illustrates
Zipes DP, Fisch C. Atrioventricular Dissociation. Arch Intern Med. 1973;132(1):130–133. doi:10.1001/archinte.1973.03650070116020
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