Infant with 2:1 atrioventricular block after surgery for congenital heart disease: What’s the mechanism?

Figures

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  Figure 1. Postoperative telemetry recordings: A: Sinus rhythm with normal PR intervals and bundle branch block pattern. B: Sinus with 2:1 AV block. C: Sinus rhythm interrupted by frequent premature junctional complexes (∗) and blocked premature atrial complexes (∗∗).

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  Figure 2. A: Sustained tachycardia with QRS complexes similar to sinus rhythm, abrupt onset and termination, and stable rate ∼180 beats per minute. B: Premature atrial complex (∗) induces tachycardia, sinus P waves are not readily apparent, and there was no clear VA dissociation.

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  Figure 3. Background sinus rhythm and His bundle extrasystoles (HBEs). A: During sinus rhythm, an HBE conducts retrograde to the atrium and antegrade to the ventricles. B: HBE conducts retrograde to atria but blocks antegrade to the ventricles, causing a blocked premature atrial complex. C: HBE conducts to ventricles but blocks retrograde in atrioventricular node, resulting in an isolated premature junctional complex. D: HBE blocks in both retrograde and antegrade directions, not affecting sinus node automaticity yet blocking conduction of a sinus impulse to the ventricles. Star indicates His bundle extrasystole. SAN = sinoatrial node.