Automaticity in atrioventricular valve leaflets of rabbit heart

Area of Science:

• Cardiac electrophysiology
• Heart valve function
• Autonomic nervous system control of the heart

Background:

• The sinoatrial node is the primary cardiac pacemaker.
• The role of cardiac valve structures in impulse generation is not well understood.
• Investigating alternative pacemaker sites is crucial for understanding cardiac arrhythmias.

Purpose of the Study:

• To investigate the electrophysiological properties of pacemaker fibers within rabbit atrioventricular valves.
• To determine the influence of intrinsic autonomic nerves on valve pacemaker activity.
• To explore the potential role of valve pacemakers in cardiac rhythm disturbances.

Main Methods:

• Microelectrode techniques were employed on isolated rabbit atrioventricular valve preparations.
• Spontaneously beating tricuspid and mitral valve leaflets were superfused with Tyrode solution.
• Action potentials and impulse conduction were analyzed, along with responses to pharmacological agents and electrical stimulation.

Main Results:

• Pacemaker activity was identified in fibers located on the valve leaflets.
• Impulse conduction from valve foci to the atrium was slow, with frequent exit block.
• Valve pacemaker action potentials differed from sinoatrial node cells but shared sensitivity to verapamil and insensitivity to tetrodotoxin.
• Endogenous neurotransmitters modulated valve pacemaker automaticity and conduction, potentially inducing pacemaker escape and extrasystoles.

Conclusions:

• Atrioventricular valve leaflets harbor cardiac fibers with intrinsic pacemaker capabilities.
• Intrinsic autonomic nerves innervating these valve fibers can significantly influence cardiac rhythm.
• These findings suggest a novel mechanism for cardiac rhythm generation and potential contribution to arrhythmias.