Functional properties of the human atrioventricular and intraventricular conduction system during premature atrial stimulation

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Abstract
Premature atrial stimulation combined with His bundle and local ventricular electrograms was used in three patients to analyse complex AV conduction patterns resulting from variable degrees of delayed or enhanced propagation within the atria, A-V node, and ventricular specialized conducting system. The St1-St2 intervals were plotted against the corresponding responses at the low right atrium (LRA), His bundle, intitial site of ventricular depolarization (V), right ventricular apex (RVA), and posterosuperior wall of left ventricle (LV). The electrophysiological effects of a β-blocking agent, Alprenolol, were studied in two patients. This drug, at a dose of 0·2 mg/kg, increased the effective and functional refractory periods of the atria and AV node. In the presence of bifascicular blocks the effective refractory period of the ventricular specialized conducting system was also lengthened. Different grades of functional bilateral bundle branch block were detected in one case. The amount of delay in each bundle branch block could not be determined from the surface leads alone. A supernormal phase of intra-atrial conduction occurred in one patient. These studies extend the usefulness of intracardiac recordings in understanding otherwise complex electrophysiological phenomena in the human heart.

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