Thread by @ZiadIssaMD

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The mimicry of second-degree AV block (2°AVB)

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ECG patterns that mimic 2°AVB are often related to atrial ectopy, concealed junctional ectopy, or AVN echo beats. Distinguishing physiologic from pathologic AVB is important.

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In 2°AVB, sinus P-P interval is fairly constant (except for some variation caused by ventriculophasic arrhythmia), the nonconducted P wave occurs on time as expected, and P wave morphology is constant. With ectopy, P waves occur prematurely & often have different morphology.

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Early PACs can arrive at the AVN during the refractory period and conduct with long PRI or block (physiologic rather than pathologic block) and can mimic Mobitz I or Mobitz II 2°AVB.

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Atrial bigeminy, with failure of conduction of the PACs, can be misinterpreted as 2:1 AVB.

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Atrial trigeminy, with failure of conduction of the PACs, can be misinterpreted as Mobitz II AVB.

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PACs can partially penetrate the AV conduction system (concealed conduction) precipitating AVB during subsequent atrial complexes.

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The mere occurrence of PACs (even when conducted) in a trigeminal or quadrigeminal pattern can produce group-beating patterns mimicking Wenckebach periodicity.

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Apparent Mobitz type II AV block can also be caused by concealed junctional extrasystoles (confined to the specialized conduction system and not propagated to the myocardium) and junctional parasystole.