Pseudo atrioventricular block most likely caused by junctional extrasystoles mimicking Mobitz II second degree atrioventricular block: A case report

Figures

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  Figure 1. A 3-channel 24-hour Holter monitoring shows a first P wave conducted to the ventricles, followed by a second nonconducted sinus P wave that collides (black bars) with a retrograde ectopic junctional wavefront (first asterisk). The anterograde wavefront of the junctional beat depolarizes the ventricles. The third sinus P wave is blocked (black top horizontal bar), since the conduction system is recovering excitability from the previous beat (effective refractory period [ERP]) or eventually another retrograde wavefront of a junctional beat may have collided retrogradely with an anterograde sinusal wavefront. As the ectopic focus was reset and takes time to recover, the P/QRS relationship changes and then the QRS precedes the P wave. In the next beats, the atria are depolarized by the sinus node and the ventricles by the junctional focus.

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  Figure 2. A 3-channel 24-hour Holter monitoring with the first 2 P sinus waves depolarizing the ventricles. Then, a concealed ectopic beat from the atrioventricular junction (black asterisk) collides retrogradely with the sinus wavefront at the level of the atrioventricular junction (black top horizontal bar), avoiding the propagation of the first. The ectopic beat does not depolarize the ventricles (black bottom horizontal bar), as they are in the effective refractory period (ERP). The 2 subsequent sinus P waves depolarize the ventricles and then a retrograde junctional beat wavefront collides (black top horizontal bar) with an anterograde sinus one and simultaneously depolarizes the ventricles with aberrancy (red arrow). The preceding and post-P-wave blocked PR intervals are the same and could be misdiagnosed as a Mobitz II second-degree atrioventricular block.

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  Figure 3. Two blocked P waves in the fourth minute of a treadmill test in CM5 derivation. The PR interval before and after the 2 blocked P waves are the same:160 ms. The first 2 sinus P waves are conducted to the ventricles. The third P wave is blocked by a concealed junctional beat that collides retrogradely with the anterograde sinus wavefront (black top horizontal bar). The junctional beat does not depolarize the ventricles, since they are in the effective refractory period (ERP) (black bottom horizontal bar). From the fourth to the sixth sinus beats the impulses are normally conducted to the ventricles. The seventh QRS is probably generated by the junctional ectopic beat, since the PR interval shortens slightly abruptly. The tenth P wave is blocked by another concealed junctional extrasystole that collides retrogradely with the sinus beat (black top horizontal bar) but does not depolarize the ventricles because they are in the ERP (black bottom horizontal bar). The last beat is a junctional QRS (black asterisk) dissociated from the sinus P wave. It is worth noting that CM5 is recorded at a different time from the other leads that are simultaneously recorded. The third P wave recorded…