Ventriculophasic modulation of atrioventricular nodal conduction in humans.

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Abstract
Background —Baroreceptor-mediated phasic changes in vagal tone have been hypothesized to cause ventriculophasic sinus arrhythmia (VPSA). The objectives of this study were to demonstrate ventriculophasic modulation of AV nodal conduction and to substantiate the role of the baroreflex on ventriculophasic AV nodal conduction (VPAVN) by pharmacological perturbation of parasympathetic tone. Methods and Results —Twelve patients with infra-Hisian second-degree heart block and VPSA were studied. Incremental atrial pacing was performed until AV nodal Wenckebach block at baseline, after phenylephrine infusion, and after atropine. AV nodal conduction curves were constructed for each phase and compared. At baseline, VPAVN was present in 9 of 12 patients on the steep portion of the AV nodal conduction curves. Phenylephrine increased systolic blood pressure from 149±33 to 177±22 mm Hg ( P P Conclusions —VPAVN was demonstrated in patients with infra-Hisian second-degree AV block. It was accentuated by phenylephrine and abolished by atropine, suggesting a baroreflex mechanism for VPSA and VPAVN.

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