Widespread distribution and rate differentiation of the atrial pacemaker complex

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology

Background:

• The origin of the P wave in electrocardiography is traditionally attributed to the sinus node.
• Rate-related changes in the P wave suggest a complex underlying mechanism.

Purpose of the Study:

• To investigate the basis of rate-related changes in the canine electrocardiographic P wave.
• To determine if the atrial depolarization wave originates from a unifocal or multicentric source.

Main Methods:

• Electrophysiological study in dogs.
• Mapping of atrial excitation origins using multiple pacemaker sites.

Main Results:

• A multicentric origin of the atrial depolarization wave was identified, involving 3-5 pacemaker sites.
• These sites were spatially distributed over a 30-40 mm area, significantly larger than the sinus node.
• Each pacemaker site dominated excitation within specific heart rate ranges, with shifts occurring at rate limits.
• Pacemaker centers were consistently located at the superior vena caval-right atrial junction.

Conclusions:

• Dogs possess a widely distributed atrial pacemaker complex beyond the sinus node.
• These specialized atrial pacemaker centers are functionally differentiated for specific heart rate ranges.
• The findings suggest a complex system of coordinated atrial activation involving multiple pacemakers.