Supernormal conduction in the accessory pathway of patients with overt or concealed ventricular pre-excitation

Abstract

It was recently shown that supernormal conduction in the diseased His-Purkinje system is more common than previously thought, and is always associated with prolongation of refractoriness. To assess whether supernormal conduction could also occur in the accessory pathway of patients with ventricular pre-excitation, 21 patients with manifestly prolonged refractoriness in the accessory pathway were studied. Under these conditions, programmed atrial stimulation revealed a phase of supernormal conduction in 16 (76%) of the 21. Therefore, what was believed to be a nonexistent or exceptional physiologic event was shown to be a rather common finding, at least under certain circumstances. Supernormal conduction occurred in all 7 patients with an anterograde refractory period of 480 to 980 ms, and in 5 of 10 patients with a refractory period greater than 1.0 second or with no anterograde conduction. Supernormal conduction could not be demonstrated in four patients with a refractory period less than or equal to 440 ms, but appeared in all four patients after the refractory period was prolonged by a rapid rate of stimulation or administration of ajmaline. The electrophysiologic changes underlying the occurrence of supernormal conduction in the accessory pathway are similar to those previously reported for the bundle branch system. The demonstration of supernormal conduction in the accessory pathway may uncover the presence of concealed ventricular pre-excitation. Supernormal conduction over the accessory pathway may facilitate a rapid ventricular response during atrial fibrillation, even if the refractory period is prolonged.

Linking in accessory pathways. Functional loss of antegrade preexcitation.

“…10 Nevertheless, a strong correlation existed between the observed paced cycle length of linking onset and the antegrade effective refractory period of the accessory pathway (r=0.97, see Figure 5). The observed linking window ranged from 70 to 290 msec.…”

Clinical and Experimental Evidence of Supernormal Excitability and Conduction

“…The occurrence of supernormal conduction in the accessory pathway was first reported by Mc Henry et al [40] followed by few articles describing the same phenomenon [41-47]. The occurrence of supernormal conduction in patients with ventricular pre-excitation was systematically investigated by Przybylski et al .…”

“…The occurrence of supernormal conduction in patients with ventricular pre-excitation was systematically investigated by Przybylski et al . whenever the refractory period of the anomalous pathway was clearly prolonged [41]. This study included 21 patients with a history of intermittent ventricular pre-excitation, a fact that obviously implied a prolonged anterograde refractory period in the accessory pathway.…”

“…In 4 out of the 21 patients with a relatively short refractory period (300 to 420 ms), refractoriness was intentionally prolonged with ajmaline to unmask the supernormal phase. Programmed atrial stimulation unveiled a supernormal phase of conduction in 16 of 21 cases during premature atrial stimulation [41]. The refractory period of the anomalous bundle was scanned with premature impulses introduced at progressively shorter intervals by 10 ms steps after eight sinus or paced beats at a cycle length slightly shorter than the sinus cycle length.…”

“…It has been pointed out that the duration of the refractory period of the accessory pathways is the main factor determining the ventricular response and the risk of ventricular fibrillation and sudden cardiac death in patients with pre-excitation during atrial fibrillation [41-47]. However, the existence of a supernormal phase of conduction in patients with anomalous pathways and a marked prolongation of the refractory period may be clinically relevant whenever sustained rapid propagation through the supernormal period of the pathway may cause extremely fast ventricular responses during atrial tachycardia, atrial flutter or atrial fibrillation.…”