The anatomy of the conduction system: implications for the clinical cardiologist

Area of Science:

• Cardiac Anatomy
• Electrophysiology
• Histology

Background:

• Over 100 years ago, the specialized cardiomyocytes responsible for the cardiac impulse were identified.
• Histological criteria for locating these cells in human hearts were established shortly after.
• Traditional histological methods remain valuable but can be augmented by modern molecular and immunohistochemical techniques.

Purpose of the Study:

• To review the current understanding of the anatomical arrangement and histological specialization of cardiac impulse-generating tissues.
• To integrate traditional histological findings with contemporary molecular and immunohistochemical data.
• To clarify the histological specialization of various cardiac structures, including nodes, conduction pathways, and potential arrhythmogenic substrates.

Main Methods:

• Review of historical and contemporary literature on cardiac anatomy and histology.
• Integration of findings from molecular and immunohistochemical studies.
• Evaluation of histological evidence for specialized myocardium in human hearts.

Main Results:

• Modern techniques enhance the identification and characterization of the sinus node, atrioventricular node, and atrioventricular conduction axis.
• Discovery of additional specialized myocardial areas, including the paranodal area of the terminal crest and atrioventricular ring tissues.
• Histological evidence does not support specialized myocardium in pulmonary venous sleeves, but provides insights into outflow tract tachycardia substrates.

Conclusions:

• Combined histological, molecular, and immunohistochemical approaches offer a more comprehensive understanding of cardiac specialized tissues.
• The study refines the anatomical and histological map of the cardiac conduction system and associated specialized tissues.
• Findings contribute to understanding the substrates for cardiac arrhythmias, particularly outflow tract tachycardias.