Impulses of S-A block area

Area of Science:

• Cardiovascular physiology
• Cardiac electrophysiology

Background:

• Sino-atrial (S-A) block affects heart rhythm.
• The precise anatomical site of S-A conduction and block has been debated.

Purpose of the Study:

• To pinpoint the specific anatomical location responsible for sino-atrial conduction.
• To investigate the relationship between this location and the development of S-A block.

Main Methods:

• Micro-electrode recordings were performed on 13 excised rabbit hearts.
• Specific areas, including the connection between the sinus node and the right branch of the crista terminalis, were surgically altered (cut).
• Conduction times and block degrees were observed after these interventions.

Main Results:

• The fastest S-A conduction was consistently found in the area connecting the sinus node and the right branch of the crista terminalis.
• Cutting this specific area induced transient first, second (Wenckebach), and third-degree S-A blocks.
• Further cutting of the surrounding caval area in hearts with existing blocks resulted in complete S-A block.
• Intervention in the caval area, excluding the critical connection, did not alter conduction time.

Conclusions:

• The dominant pathway for sino-atrial conduction is the connectable area between the sinus node and the right branch of the crista terminalis.
• Impairment of this specific anatomical region is essential for the development of any degree of S-A block.