A Case Report of Irregular Narrow Complex Tachycardia: Atrioventricular Nodal Re-entrant Tachycardia with a Lower Common Pathway Wenckebach.

Figures

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  Figure 1:. Electrocardiogram and intracavitary electrograms: Baseline and induction of tachycardia.

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  Figure 2:. Electrocardiogram and intracavitary electrograms: Tachycardia and ventricular entrainment suggestive of typical atrioventricular nodal re-entrant tachycardia.

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  Figure 3:. Electrocardiogram and intracavitary electrograms: Narrow complex tachycardia in the index patient (spontaneous transition from a regular narrow QRS tachycardia [NCT] to an irregular NCT exhibiting Wenckebach periodicity).

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  Figure 4:. Electrocardiogram and intracavitary electrograms: In the cardiac cycle immediately preceding the dropped beat, the His-bundle (HB) potential (HBP) was consistently observed after the atrial deflection. This configuration signifies a maximal atrio–His (AH) interval prolongation, which was sufficient to place the HBP subsequent to the retrograde atrial activation. This sequence suggests that the maximum possible A–H delay had been achieved before the conduction failure. The observed progressive A–H interval prolongation, which defines the Wenckebach periodicity, must be attributed to a conduction decrement within the lower common pathway (LCP) rather than the antegrade slow pathway (SP). Had the Wenckebach phenomenon occurred in the antegrade SP, the resultant block would have interrupted the forward limb of the re-entrant circuit, thereby terminating the tachycardia. The sustained nature of the rhythm, despite the progressively delaying conduction, confirms that the site of block lies distally in the LCP (infranodal, suprahisian Wenckebach), allowing the re-entrant circuit to persist despite having an LCP block. Immediately following this LCP block, the HBP timing reverted,…