The Relationship between Refractory Period and Conduction Time of the AV Node under Various Cycle Lengths in the Canine Heart. The Significance of Wavelength and Excitable Gap in Reentrant Tachycardia.

To evaluate the significance of the refractory period and conduction time of the AV node for reentrant tachycardias incorporating the AV node, the effective refractory period of the AV node (ERP) and AH interval (AH) during atrial pacing at various cycle lengths were measured in 12 anesthetized dogs after verapamil administration. ERP-AH tended to be constant in each dog at different cycle lengths and increased as the AV node was suppressed. In reentrant tachycardia incorporating the AV node, assuming that the conduction time outside of the AV node is constant, the excitable gap decreases as ERP-AH increases and disappears if ERP-AH is prolonged up to the conduction time outside of the AV node. ERP-AH was calculated as an index of the excitable gap. On the other hand, ERP/AHs were significantly correlated with cycle lengths and tended to be similar at the same cycle length among the different dogs. ERP/AH is considered to be an index of the wavelength which is expressed as the product of refractory period and conduction velocity. However, because ERP was always longer than AH, ERP/AH was not applicable as an index of the wavelength in the AV node. The length through which the wavefront ran during the refractory period of the AV node was also dependent on ERP-AH. In conclusion, prolonging ERP-AH played an important role in suppressing reentrant tachycardias incorporating the AV node.