Transmembrane potentials of canine AV junctional tissues

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Comparative Anatomy

Background:

• The atrioventricular (AV) junction, critical for cardiac impulse propagation, includes the AV node, His bundle (HB), and specialized paranodal fibers (PNF).
• Understanding the precise conduction pathways and properties within the AV junction is essential for elucidating mechanisms of cardiac arrhythmias and conduction delays.

Purpose of the Study:

• To investigate a potential novel internodal pathway along the base of the septal cusp of the tricuspid valve (SCTV) in canine hearts.
• To characterize the electrophysiological properties, specifically maximum upstroke velocity (Vmax), of different components of the AV junctional tissues.

Main Methods:

• An in vitro, dissection-exposed canine right atrial (RA), transitional fiber (TF), and AV junctional preparation was utilized.
• Electrical impulse propagation was monitored from the RA through the TF, PNF, AV node, and HB.
• Transmembrane potentials and Vmax were measured in the PNF, AV node, and HB.

Main Results:

• A functional conduction pathway, termed the septal cusp pathway, was identified along the base of the SCTV, connecting the RA to the AV node via TF and PNF.
• Paranodal fibers (PNF) exhibited the lowest Vmax (2.5 V/sec), significantly lower than the AV node (7.0 V/sec) and His bundle (33 V/sec).
• The PNF demonstrated the slowest conduction velocity among the studied AV junctional tissues.

Conclusions:

• The septal cusp pathway represents a significant internodal conduction route in the canine heart.
• The paranodal fibers, not the AV node, are the primary site of slowed conduction within this pathway, contributing to AV conduction delay.
• This study enhances the understanding of AV conduction mechanisms and potential targets for therapeutic interventions in cardiac conduction disorders.