Evaluation of post-repolarization refractoriness for conduction block in cardiac muscle - Studies in an artificial isthmus in the canine right atrium

Post-repolarization refractoriness (PRR) is an important factor in determin ing conduction block and is the difference between the effective refractory period (ERP) and the duration of the monophasic action potential (MAPD). I n the present study, conduction block in an artificial isthmus in the canin e atrium was evaluated and the coupling interval of a premature beat, which caused the block, was defined as the block coupling interval (BCI). The us efulness of this value was also evaluated. Radiofrequency linear ablation w as performed on the right atrial surface parallel to the atrioventricular g roove in 5 mongrel dogs, and an artificial isthmus (8-10mm wide and 25-30mm long) was created. Fourteen simultaneous unipolar recordings were performe d in the isthmus with a resolution of 1.2mm. Single extra-stimuli with basi c drive train were delivered to induce conduction block in the isthmus and when it occurred, the coupling interval at the recording site just proximal to the site of the block was defined as the BCI. At the site of the block, the ERP and MAPD at each drive cycle length were measured. The PRR was cal culated using 2 different formulae: (1) [ERP-MAPD], and (2) [BCI-MAPD]. It was found that each value was shortened in accordance with the shortening o f the basic drive cycle length. In all basic drive trains, BCI>ERP>MAPD, an d [ERP-MAPD] was always shorter than [BCI-MAPD]. In the shorter cycle lengt h of basic drives, the difference between [ERP-MAPD] and [BCI-MAPD] was mor e prominent. In the artificial isthmus model in the canine atrium, BCI was always longer than the ERP measured at the same site as the block. Because the ERP may not directly reflect the block phenomenon, the electrophysiolog ic evaluation should use the BCI instead, as in the PRR evaluation.