Differences in automaticity between Purkinje strands from right and left dog ventricle

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Cardiac Conduction System

Background:

• Previous in situ studies suggest differences in pacemaker rates between left and right ventricular conduction systems.
• Understanding the automaticity of Purkinje fibers is crucial for comprehending cardiac rhythm regulation.

Purpose of the Study:

• To characterize and compare the automaticity of peripheral right and left canine Purkinje fibers in vitro.
• To investigate the functional dissimilarities in the intrinsic rate and response to various ionic and hormonal stimuli.

Main Methods:

• Utilized standard microelectrode techniques for in vitro electrophysiological recordings.
• Measured intrinsic rates (IR) of paired right (RPF) and left (LPF) canine Purkinje fibers.
• Assessed responses to changes in extracellular potassium (K0+) concentration and epinephrine stimulation.

Main Results:

• Control intrinsic rate was significantly higher in LPF (24.8 beats/min) compared to RPF (11.5 beats/min).
• High K0+ (5.4 mM) reduced IR more in RPF (-78%) than in LPF (-58%).
• Epinephrine (10(-6) M) increased IR, with LPF > RPF, though the chronotropic response was more pronounced in RPF.

Conclusions:

• Canine right and left Purkinje fiber automaticity are functionally dissimilar.
• Differences in intrinsic rate and response to K+ and epinephrine highlight regional specialization within the cardiac conduction system.