Supernormal Conduction in the Anomalous Bundles of the Wolff-Parkinson-White Syndrome: An Overlooked Electrophysiologic Property With Potential Clinical Implications

Abstract

The anterograde refractory period (RP) of the accessory pathway (AP) is the main determinant factor of ventricular rate during atrial fibrillation in the Wolff-Parkinson-White (WPW) syndrome. We describe 3 examples of anterograde supernormal conduction (SNC) and 1 of retrograde SNC in APs. The paradoxical early recovery of propagation due to SNC, well inside a prolonged anterograde RP in the AP, may play a relevant role to determine the rate of ventricular response during atrial fibrillation, eventually leading to extremely fast ventricular rates, syncope, and even ventricular fibrillation in patients with WPW syndrome supposed a priori to be exposed to a low risk of sudden cardiac death. This may require very precise conditions, including an enhanced adrenergic influence on the heart. Retrograde SNC in APs may also participate in the mechanism of paroxysmal supraventricular tachycardias that are not easily induced by programmed cardiac stimulation.

A Narrow QRS Tachycardia with Unusual Electrophysiological Characteristics: What Is the Mechanism?

“…These findings could be explained by the hypothesis that retrograde conduction of the bypass tract is manifested only at a determined CL produced by supernormal conduction phenomenon. Supernormal conduction in AP has been well documented in antegrade conduction over APs but it is quite rare in retrograde conduction . It requires the presence of a very long refractory period of the AP and then, conduction at low CLs cannot be detected resulting in a block‐conduct only pattern .…”

“…Supernormal conduction in AP has been well documented in antegrade conduction over APs but it is quite rare in retrograde conduction. [1][2][3] It requires the presence of a very long refractory period of the AP and then, conduction at low CLs cannot be detected resulting in a block-conduct only pattern. 4 We can discard the possibility of pacing site-dependent block that justifies our findings because pacing from two different sites (RV apex and RV outflow tract) was similar.…”

An Unusual Case of Preexcitation Treated with a Pacemaker

“…This has been extensively investigated and demonstrated in the AV junction and His‐Purkinje system but has also been reported in APs during retrograde conduction . Supernormal anterograde AP conduction has also been reported, but AP “gap” physiology better explains the observation of a marked prolongation of the S2–V interval when AP conduction resumes in this case. To the best of our knowledge, this is the first reported example of anterograde “gap” in AP conduction.…”