Heart Conduction System and EKG Analysis

Overview of the Heart and Its Electrical System

  • The analogy of the heart and a basement:
      - Just as we prevent water from flooding a basement, we ensure the heart continues to function properly.

Structure of the Heart

Sides of the Heart

  • Right Side of the Heart:
      - Primarily contains the conduction system.

  • Left Side of the Heart:
      - Responsible for the blood-pumping action.

Functions

  • Left Ventricle:
      - Pumps blood through the aorta, generating blood pressure.
      - Normal blood pressure is often described in systolic and diastolic terms.

Automaticity of the Heart

  • Definition: Refers to the intrinsic ability of the heart to continue beating independently.

  • Backup Systems:
      - Each component of the heart has a backup, ensuring that if one part fails, another can take over.
        - SA Node (Sinoatrial Node):
          - Considered the "mothership" of the heart’s electrical activity.
          - Normal heart rate: 60 to 100 beats per minute.
        - AV Node (Atrioventricular Node):
          - Backup for the SA node.
          - Automaticity: 40 to 60 beats per minute.
        - Bundle of His:
          - Leads to left and right bundle branches.
        - Purkinje Fibers:
          - Lower backup with automaticity: 20 to 40 beats per minute.

Electrical Impulses of the Heart

  • Automaticity:
      - Operates independently of conscious thought; governed by the autonomic nervous system.

  • Tracking Electrical Impulses:
      - Originates from the SA node and travels through various pathways:
        - Internodal pathways, leading to AV node, Bundle of His, right and left bundle branches, and then Purkinje fibers.
      - Atrial Kick: Refers to the contraction of the atria that fills the ventricles with blood before they contract.

Heart Contraction and Relaxation

  • Contraction:
      - Electrical activity: Depolarization.
      - Mechanical action: Systole.

  • Relaxation:
      - Electrical activity: Repolarization.
      - Mechanical action: Diastole.

Electrocardiograms (EKGs)

  • Purpose:
      - Measure the electrical activity of the heart, not the mechanical activity.

  • Components of EKG:
      - P wave: Atrial depolarization.
      - QRS complex: Ventricular depolarization.
      - T wave: Ventricular repolarization.
      - QT interval: Time from the start of ventricular depolarization to the end of ventricular repolarization.
      - PR interval: Time from the start of atrial depolarization to the start of ventricular depolarization.

Arrhythmias and Heart Rhythms

  • Normal Sinus Rhythm:
      - Heart rate between 60 to 100 beats per minute.

  • Dysrhythmias:
      - Disruptions in the normal conduction system.

Special Rhythm Conditions

  1. Bradycardia:
       - Definition: Heart rate less than 60 beats per minute.
       - Causes: Hypothermia, medications, athletic conditioning.
       - Symptoms: Potential instability, can lead to various issues.
       - Treatment: Atropine, dopamine, or transcutaneous pacing.

  2. Tachycardia:
       - Definition: Heart rate greater than 100 beats per minute.
       - Symptoms: Can be stable (no symptoms) or unstable (dizziness, hypotension).
       - Treatment: Varies based on symptoms; beta blockers, calcium channel blockers or vasovagal maneuvers used for symptom relief.
     

Atrial Fibrillation and Flutter

  • Atrial Flutter:
      - Characterized by organized electrical activity; can appear as "sawtooth" waves.
      - Treatment aims to stabilize heart rate and rhythm.

  • Atrial Fibrillation:
      - Irregular and chaotic electrical activity; no distinguishable P waves.
      - High risk for stroke.

Heart Blocks

  1. First Degree AV Block:
       - Prolonged PR interval (>0.2 seconds).

  2. Second Degree AV Block:
       - Type I (Wenckebach): Progressive prolongation of PR until a dropped beat.
       - Type II: Dropped beats without progressive PR lengthening.

  3. Third Degree AV Block:
       - Complete block; atria and ventricles beat independently.

Emergency Responses and Treatments

V-Tach and V-Fib

  1. Ventricular Tachycardia:
       - Defined as heart rate >100, regular but no P waves.
       - Treatment depends on stability; may involve medication, cardioversion, or defibrillation.

  2. Ventricular Fibrillation:
       - Life-threatening; requires immediate defibrillation and CPR.

Pacemakers and ICDs

  • Pacemakers:
      - Regulate heart rhythm in cases of bradycardia or AV blocks.

  • Implantable Cardioverter Defibrillators (ICDs):
      - Detect life-threatening tachyarrhythmias and deliver shocks if necessary.

Clinical Management and Evaluation

  • Assess symptoms, treat underlying causes, and proper rhythm evaluation.

  • Use antiarrhythmic medications/adjunct therapies as needed.

Conclusion

  • Understanding the heart's conduction system, the significance of automaticity, and proper monitoring techniques is critical in managing various arrhythmias and ensuring patient safety in clinical settings.