Interaction of Transmembrane Potentials in Canine Purkinje Fibers and at Purkinje Fiber-Muscle Junctions

Abstract

Interactions between Purkinje fibers and ventricular muscle were studied in canine Purkinje-papillary muscle preparations. The change in duration of action potentials across the junctions between Purkinje fibers and papillary muscle was continuously graded, not abrupt. The transmembrane action potentials were longest in the false tendons and progressively shorter in more peripheral fibers. The responses of terminal Purkinje fibers and of neighboring muscle cells differed little in duration. The shortest action potentials were found in muscle fibers located in regions devoid of specialized tissue (tip of papillary muscle). These results suggest that the intercellular connections, including those at the junctions, offer relatively low resistance to current flow. During repolarization the current flowing between neighboring elements with intrinsically different repolarization times should therefore minimize the disparity in action potential durations on the two sides of the junctional site; a continuously graded change in duration would result. Because of this continuous gradation, premature ventricular responses initiated at the tip of the papillary muscle could be blocked, depending on the degree of prematurity, at various levels in muscle fibers functionally close to terminal Purkinje fibers or within the Purkinje system.

Relationship of Admission QRS Duration and Changes in QRS Duration With Myocardial Reperfusion in Patients With Acute ST Segment Elevation Myocardial Infarction (STEMI) Treated With Fibrinolytic Therapy

“…20 In experimental models of myocardial ischemia, demonstration of the association of QRS prolongation with Purkinje-ventricular conduction delay is further support for this mechanism. [24][25][26] Consistently, the correlation we detected between admission QRS duration and ischemia duration in our study group is in favour of the idea of ischemia as a mechanism of QRS prolongation. QRS prolongation might be a sign of extensive ischemia and a poor metabolic state, which was shown to worsen with the delay in reperfusion.…”

QRS Complex Duration is a Marker of Reperfusion in Patients Presenting with Acute ST Segment Elevation Myocardial Infarction

“…Prolongation of QRS that occurs during acute coronary obstruction is mostly due to slowing of conduction within the ischemic areas and this mechanism was proved in several experimental models and human studies [17][18][19][20]. In our study, we analyzed QRS complex duration changes on admission, at 60 and 90 min post reperfusion and we found that there is no significant difference between the two groups regarding the admission QRS but there is a significant prolongation of the QRS duration in 60 min and 90 min post reperfusion ECG in the group with impaired perfusion compared to group with a successful perfusion and our findings are in agreement with several published studies.…”

Modulation of the Purkinje-ventricular muscle junctional conduction by elevated potassium and hypoxia.

“…We found that this intervention has approximately equal effects on the two sequential steps involved in P-VM conduction. We then analyzed the increased delay from T cells and V cells on the basis of three hypothetical mechanisms: 1) increased coupling resistance, 2) decreased V cell excitability, and 3) decreased cellular responsiveness of the T cells. Our results show that the effects of elevated [K+J0 and hypoxia on T-VM delay can be accounted for by a decreased responsiveness of the T cells without any significant electrical uncoupling between T and V cells or decrease in VM excitability.…”