Hierarchy of ventricular pacemakers

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Cardiac Anatomy

Background:

• The ventricular specialized conduction system (VSCS) coordinates heart rhythm.
• Understanding pacemaker dominance is crucial for cardiac electrophysiology.

Purpose of the Study:

• To characterize pacemaker dominance within the VSCS.
• To investigate shifts in pacemaker location and rate after myocardial infarction.

Main Methods:

• Localization and quantification of escape ventricular pacemakers in vivo and in vitro.
• Utilized His bundle electrograms, electrocardiographic limb leads, and isolated VSCS preparations.
• Employed extra- and intracellular recordings for pacemaker identification.

Main Results:

• In normal hearts, dominant pacemakers were located in the proximal VSCS (His bundle/left bundle branch) at ~43 bpm.
• Myocardial infarction shifted pacemaker dominance to the infarct zone (peripheral left bundle branch) at ~146 bpm.
• Beta-adrenergic blockade did not alter pacemaker location but reduced rates in normal hearts.

Conclusions:

• Pacemaker dominance is normally in the proximal VSCS.
• Myocardial infarction causes a significant shift in pacemaker dominance to the infarct area.
• Pacemaker distribution is not influenced by sympathetic activity.