Lesson 2: EKG

Lesson 2: EKG

  • P wave: Atrial depolarization begins

  • PR interval: Atrial depolarization complete

  • QRS complex: Atrial repolarization + ventricular depolarization

  • ST segment: Ventricular depolarization complete

  • T wave: Ventricular repolarization begins

Correlation with Cardiac Action Potential

  • Match phases of ventricular action potential to EKG components:

    • Phase 0: QRS complex

    • Phase 2: ST segment

    • Phase 3: T wave

Ventricular Action Potential

  • Key events and EKG correlation:

    • Phase 0: Depolarization (Na+ in) → QRS

    • Phase 1: Initial repolarization (Cl- in, K+ out) → QRS

    • Phase 2: Plateau (Ca2+ in) → ST segment

    • Phase 3: Final repolarization (K+ out) → T wave

    • Phase 4: Resting phase (K+ leak) → End of T wave, start of QRS

  • Absolute refractory period: No stimulus can depolarize myocyte.

  • Relative refractory period: Larger stimulus required for depolarization.

Electrical Activity in Cardiac Cycle

  • Electrical events trace:

    • Atrial Depolarization: P wave

    • Ventricular Depolarization: QRS

    • Atrial Repolarization: Within QRS complex

    • Ventricular Repolarization: T wave

Integrating EKG with Cardiac Cycle

  • Electrical events precede mechanical events briefly.

  • Key mechanical events:

    • Isovol. Contraction

    • Rapid Ejection

    • Reduced Ejection

    • Isovol. Relaxation

    • Diastole: Includes rapid filling, reduced filling, atrial systole

  • Consider impacts of cardiac dysrhythmias on heart's mechanical functions and physiologic consequences.