Synonyms and Keywords: Isorhythmic AV dissociation Overview An atrioventricular dissociation characterized by independent and equally beating atrial and ventricular pacemakers, in the absence of a retrograde conduction from the ventricular depolarization to the atria is called as isorhythmic AV dissociation. Isorhythmic dissociation is not common in the general population and it is the most innocent type of AV dissociation. Pathophysiology Isorhythmic AV dissociation is a AV dissociation initiated by slowing of SA node due to sinus arrhythmia, sinus bradycardia , sinus arrest , or sinoatrial block. This allows an independent ventricular pacemaker response like either junctional rhythm giving a normal or near normal QRS appearance and duration or idioventricular rhythm with a more bizarre, wide QRS to take over the ventricles. In the presence of some degree of antegrade and retrograde atrioventricular block , there is a synchronization of independently beating sinus or atrial pacemaker with the junctional or ventricular pacemaker such that each discharges in the absolute refractory period of the other. Both the independent atrial and ventricular rates are bradycardic and nearly identical, in contrast to other types of AV dissociation.
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AV dissociation, electrocardiogram, junctional rhythm, retrograde P waves. The authors report no conflicts of interested for the published content. Manuscript received June 2, , final version accepted June 28, E-mail: adam. She denied any recent symptoms of cardiac ischemia or failure. There was no history of cardiac disease in her past. This represents an accelerated junctional rhythm with isorhythmic atrioventricular AV dissociation. A repeat ECG Figure 1B performed a few minutes later demonstrated sinus rhythm at 70 bpm with resting ST segment depression in the inferolateral leads.
A transthoracic echocardiogram performed at the time revealed normal left ventricular size and systolic function with no regional wall motion abnormalities and no significant valvular disease. Figure 1: A Electrocardiogram ECG on presentation demonstrating an accelerated junctional rhythm with isorhythmic atrioventriculardissociation.
Points to ponder AV dissociation is most commonly associated with third-degree or complete AV block. However, AV dissociation, in which two separate rhythms exist concurrently within the heart, can occur in other conditions. It can also occur when there is a pathologically high junctional or ventricular rate such as ventricular tachycardia VT with absence of retrograde VA conduction.
In our patient, the rhythm was initially misdiagnosed as an accelerated junctional rhythm with retrograde atrial activation. This is not correct as the P waves that follow the QRS complexes are positive in the inferior leads II, III, avF indicating an inferior axis; this indicates they must be originating in the high right atrium.
If these P waves were due to retrograde conduction, the RP intervals would be constant. In our patient, her flu-like illness was associated with enhanced automaticity of the junctional pacemaker focus resulting in an accelerated junctional rhythm. The rare conditions of the sinus node beating at a similar rate, and both pacemaker sites discharging near simultaneously have occurred to allow interference isorhythmic AV dissociation to exist Figure 2.
Eventually, the slight difference in rates between the two pacemaker sites allows one site to discharge early enough to capture the other site, breaking the cycle and resulting in return to sinus rhythm.
References Jacobson C. Atrioventricular dissociation. Am J Emerg Med ; —
AV Dissociation Masquerading as an Accelerated Junctional Rhythm with Retrograde Atrial Activation
Accelerated junctional rhythm, isorhythmic atrioventricular dissociation, and hidden P waves
Isorhythmic A-V dissociation