The supernormal phase of intraventricular conduction.

The supernormal phase of conduction is a short period of paradoxically improved conduction which may occur during an early phase of the recovery cycle of cardiac conducting tissue. The situation is paradoxical, for the improved conduction occurs during a short critical early period, while later impulses are blocked or have greater conduction delays. The term is, in a sense, a misnomer since conduction is not supernormal but merely a temporary improvement of a depressed state of conduction. Indeed, the supernormal phase of conduction does not occur in the normal heart but only when conductivity is depressed. The phase of supernormality is usually very short and only lasts a few hundredths of a second. Its position in the cardiac cycle is usually coincident with the U wave or the distal limb of the T wave. The supernormal phase of conduction has been demonstrated in the AV node, but could theoretically occur at any site with an actual or potential conduction delay. The following cases demonstrate the supernormal phase of intraventricular conduction.