Retrograde Activation of the His Bundle During Intermittent Paired Ventricular Stimulation in the Human Heart

Abstract

Intermittent paired ventricular pacing was performed in five patients, one of them with Wolff-Parkinson-White (WPW) syndrome. Retrograde activation of the His bundle and of the atria was observed in all patients. Bipolar leads with interelectrode distances of 1 mm seemed to be slightly better than the conventional ones (10 mm apart) for the identification of His (H) deflections buried inside the QRS complexes. Diagnosis of retrograde atrial activation was enhanced by the use of a high bipolar right atrial lead. In cases 1 and 2, V ₂ -A ₂ and V ₂ -H ₂ intervals consistently lengthened as the V ₁ -V ₂ interval was reduced. In two other patients, previously present retrograde P waves disappeared as the V ₁ -V ₂ interval was reduced. Yet at even shorter intervals, retrograde conduction to the His bundle and to the atria was seen. Ventricular echoes occurred in two cases, and reciprocating tachycardia in one. In these instances the His bundle was engaged in both retrograde and forward conduction. Finally in the patient with WPW syndrome A ₂ preceded H ₂ at a given coupling interval, suggesting retrograde atrial pre-excitation through an extra-Hisian pathway.