Basics of EKGs

Introduction

• Importance of understanding physics and physiology before interpreting 12-lead EKGs.
• Systematic approach to reading EKGs.

Basics of EKG Physics and Physiology

• Depolarization in Myocardium: Positive ions like sodium and calcium flow into cells, causing positive charge.
• Electrodes: Positive and negative electrodes create upward and downward deflections on EKGs.
  • Positive charges move towards a positive electrode → Upward deflection
  • Positive charges move away from positive electrode → Downward deflection
  • Negative charges move toward a negative electrode → Upward deflection
  • No net movement or perpendicular movement → Isoelectric line

Understanding Deflections

• Lead II: Commonly used in rhythm strips.
  • Starts in SA node, spreads through atria to AV node.
  • Atrial depolarization generates the first upward deflection (P wave).
  • PR Segment: Represents the time the AV node holds electrical activity.
  • Q Wave: Indicates septal depolarization, moving away from positive electrode.
  • R Wave: Ventricular depolarization, strong positive deflection.
  • S Wave: Depolarization at the base of ventricles, downward deflection.
  • ST Segment: Ventricles are fully depolarized, isoelectric line.
  • T Wave: Ventricular repolarization, upward deflection.

EKG Waveforms and Segments

• P Wave: Atrial depolarization.
• PR Segment: AV node holding electrical charge.
• QRS Complex: Ventricular depolarization (includes Q wave, R wave, and S wave).
  • Q Wave: Septal depolarization, negative.
  • R Wave: Main ventricular depolarization, positive.
  • S Wave: Depolarization moving toward the base, negative.
• ST Segment: Full ventricular depolarization, isoelectric line.
• T Wave: Ventricular repolarization, positive.

Twelve-Lead EKG Overview

• Limb Leads: Lead I, II, III.
• Augmented Leads: aVR, aVL, aVF.
• Precordial Leads: V1 to V6.
  • Each lead gives a different perspective of the heart's electrical activity.
  • Lead I: High lateral wall of left ventricle.
  • Lead II & III: Inferior wall.
  • aVR: Right ventricle, basal septum.
  • aVL: High lateral wall of left ventricle, similar to lead I.
  • aVF: Inferior wall of the heart.

Precordial Leads Details

• Placement: V1 to V6 across the chest.
• Horizontal/Transverse Plane: Observes the heart from a horizontal plane.
• R Wave Progression: R wave should increase from V1 to V6.
• S Wave: Should decrease from V1 to V6.

EKG Components and Measurements

• Large Box: 5 mm, equivalent to 0.20 seconds, and 0.5 millivolts.
• Small Box: 1 mm, equivalent to 0.04 seconds, and 0.01 millivolts.
  • Measurement for determining if intervals and segment lengths are within normal limits.

Key Intervals and Their Norms

• PR Interval: Less than 0.20 seconds (one large box).
• QRS Complex: Less than 0.12 seconds (three small boxes).
• QT Interval: Less than 430 ms for males and 460 ms for females (varies by heart rate).

Conclusion

• Understanding basic physics, physiology, and systematic approach to interpreting EKGs is crucial.
• Apply knowledge of vectors, deflections, and segment lengths to interpret 12-lead EKGs.

Future Discussion Topics

• Detailed discussion on reading real EKGs.
• Advanced EKG patterns, pathologies, and their clinical significance.