This case demonstrates that true 2:1 AV block in congenital LQTS can be localized to the Purkinje network due to dynamic changes in refractoriness.
Suggests Purkinje refractoriness drives 2:1 AV block in congenital LQTS; hypothesis-generating and should not yet change practice.
INTRODUCTION: Conduction abnormalities associated with long QT syndrome (LQTS) have been reported as "pseudo 2:1 AV block" due to sinus intervals shorter than ventricular refractoriness. METHOD AND RESULTS: We report the electrophysiologic characteristics of a patient suffering from congenital LQTS with episodes of true 2:1 AV block. Induction of 2:1 infra-Hisian blocks and return to 1:1 conduction were observed using single atrial and ventricular extrastimuli. The block was located in the Purkinje network but not in the myocardium. CONCLUSION: The His-Purkinje system of our LQTS patient displayed dynamic properties with a strong increase in refractoriness for short-long sequences and a decrease for long-short sequences that triggered intermittent 2:1 AV blocks.
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Pruvot et al. (1999) studied this question.
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