Extracardiac Recordings of His-Purkinje Activity During Conduction Disorders and Junctional Rhythms

Previous investigations have demonstrated a surface recording technique using signal averaging to detect electrical activity during the "isoelectric- P-R segment. Various physiological and pharmacological in-terventions suggest that the source of these potentials is the His-Purkinje system (HPS). In order to assess the sensitivity of averaged recordings to changes in HPS activation, i.e., conduction defects in the HPS, recordings were made directly from the heart surface using a bipolar, anterior-posterior epicardial lead in 15 dogs which underwent thoracotomy. The signal was amplified, filtered and averaged using a digital com-puter for purposes of signal enhancement. The epicardial averaged lead (EAL) contained activity coincident with HPS depolarization and similar to those recorded by leads on the body surface of intact dogs from previous studies. The standard ECG and His bundle electrogram from an electrode catheter served as references in localizing and assessing several conduction disorders experimentally produced by traumatic and ischemic injury. Among the disorders produced were: 1) atrioventricular (A-V) nodal block which resulted in loss of recorded activity in the EAL following the P wave. 2) First and second degree intra-His bundle block produced by anterior septal artery ligation showed split 1-is potentials in the HBE (10) and 2:1 conduction with block in the His bundle (20). In the blocked beats the EAL showed a reproducible portion of the activity coincident with proximal His bundle activity of the split His potentials in both cases. 3) I