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Understanding Cardiac Conduction and ECG

Apr 12, 2025

Lecture Notes on Cardiac Conduction System and ECG Interpretation

Overview

  • The heart's continuous beating is coordinated by the cardiac conduction system.
  • Key component: The Sinoatrial (SA) node, which acts as the heart's pacemaker.
  • Understanding the conduction system helps interpret ECG/EKG results.

Structure of the Heart

  • Right Side of Heart: Right atrium and ventricle with low oxygen blood.
  • Left Side of Heart: Left atrium and ventricle with high oxygen blood.
  • Blood Flow Path:
    • Blood enters right atrium via superior and inferior vena cava.
    • Passes through tricuspid valve to right ventricle.
    • Right ventricle pumps it to lungs via pulmonary artery.
    • Oxygenated blood returns via pulmonary veins to left atrium.
    • Passes through bicuspid (mitral) valve to left ventricle.
    • Left ventricle pumps it to the body via the aorta.

Cardiac Conduction System

  • Types of Tissue:

    • Cardiac Conduction Tissue: Non-contractile, conducts signals.
    • Cardiac Muscle Tissue: Contractile, pumps blood and conducts signals.
    • Fibrous Tissue: Non-conductive, separates atria from ventricles.

  • Key Components:

    • Sinoatrial (SA) Node: Pacemaker, sends rhythmical signals; influenced by brain but can function autonomously.
    • Internodal Pathway: Connects SA node to AV node; includes interatrial pathway to left atrium.
    • Atrioventricular (AV) Node: Delays signal ensuring atria contract before ventricles.
    • Bundle of His: Transmits signals rapidly; splits into right and left bundle branches.
    • Purkinje Fibers: Spread signals through ventricular muscle, enabling rapid contraction.

ECG/EKG Interpretation

  • P-Wave: Atrial depolarization.
  • PR Interval: Time for atrial contraction and AV node delay.
  • QRS Complex: Ventricular depolarization (and atrial repolarization, though less visible).
  • ST Interval: Ventricular contraction.
  • T-Wave: Ventricular repolarization.

Heart Sounds

  • First Heart Sound (S1): "Lub" - Tricuspid and mitral valves close at start of ventricular contraction.
  • Second Heart Sound (S2): "Dub" - Aortic and pulmonary valves close at ventricular relaxation.

Conclusion

  • The cardiac conduction system is crucial for coordinated heart function.
  • Understanding ECG components allows for monitoring electrical activity in the heart.

Additional Resources

  • Anatomage Virtual Dissection Table: For detailed anatomical exploration.
  • Patreon Supporters: Access to labeled/unlabeled diagrams.

These notes summarize key concepts regarding the cardiac conduction system and how it ties into ECG interpretation, providing a framework for understanding heart function and monitoring through medical imaging.

Full transcript