Basics of EKGs

Introduction

• Understanding EKGs starts with physics and physiology.
• Importance of knowing the physics before interpreting 12-lead EKG cases.

EKG Basics

• Positive and negative electrodes are used to stimulate heart tissue.
• Depolarization: Movement of positive ions (Calcium, Sodium) into cells causing electrical signals from cell to cell.
• EKG deflections:
  • Upward deflection: Positive charges moving towards a positive electrode.
  • Downward deflection: Positive charges moving away from a positive electrode.
  • Isoelectric line: No net movement of electrical activity or perpendicular movement to the axis of the lead.

EKG Waveform

Lead 2 Example

• P Wave: Atrial depolarization from SA node to AV node.
• PR Segment: Delay at the AV node, no net movement of charge.
• Q Wave: Septal depolarization, negative deflection as charges move away from the electrode.
• R Wave: Ventricular depolarization, positive deflection as charges move towards the electrode.
• S Wave: Ventricular depolarization towards the base, negative deflection.
• ST Segment: Ventricles fully depolarized, no net movement.
• T Wave: Ventricular repolarization, upward deflection as negative charges move towards the electrode.

EKG Leads

Limb Leads

• Lead 1: From right arm to left arm.
• Lead 2: From right arm to left leg, commonly used for rhythm strips.
• Lead 3: From left arm to left leg.
• Lead Direction: Positive electrode's view of the heart.

Augmented Unipolar Limb Leads

• aVR: Looks at right heart and basal septum, opposite waveform to lead 2.
• aVL: High lateral wall of the left ventricle.
• aVF: Inferior wall of the heart.

Precordial Leads

• V1-V6: Positioned on the chest to view the heart in a horizontal plane.
  • V1-V3: Right ventricle and basal septum.
  • V4: Transition point, larger R wave.
  • V5-V6: Lateral wall of the left ventricle.

EKG Interpretation

• Large Boxes: 5 mm height and width = 0.20 sec.
• Small Boxes: 1 mm height and width = 0.04 sec.
• PR Interval: <0.20 seconds, indicates atrial to ventricular conduction.
• QRS Complex: <0.12 seconds, indicates ventricular depolarization.
• QT Interval: Varies by gender, long QT can indicate risk of arrhythmias like Torsades de Pointes.

Summary

• Understanding EKGs requires knowledge of lead placement, waveforms, and how charges move through the heart.
• Proper interpretation involves knowing normal ranges for intervals and waveforms.