EKG Basics Lecture Notes

Introduction

• Overview of the lecture on basics of EKG.
• Importance of understanding physics and physiology before reading EKG cases.

EKG Fundamentals

Physics and Physiology of Heart Tissue

• Ventricular Myocardium: Considered for understanding electrical properties.
• Electrodes: Placed on tissue to measure electrical activity.
  • Positive electrode (right side) and negative electrode (left side).
• Depolarization:
  • Triggered by electrical stimulus.
  • Positive ions (calcium, sodium) flow in, causing a change in charge.
  • Electrical signal propagates through cells via gap junctions.

Charge Movements and Deflections on EKG

• Positive Charge Toward Electrode: Causes upward deflection on EKG.
• Positive Charge Away from Electrode: Causes downward deflection on EKG.
• Negative Charge Toward Negative Electrode: Causes upward deflection.
• Isoelectric Line: Indicates no net electrical activity or activity perpendicular to the lead axis.

Lead II EKG Waveform Analysis

• Lead II Setup:
  • Negative electrode on right arm, positive electrode on left leg.
• Atrial Activity:
  • SA node generates action potentials, depolarizing atria towards AV node.
  • P Wave: Indicates atrial depolarization, upward deflection.
  • PR Segment: Flat line indicating delay at the AV node (no net movement).
• Ventricular Activity:
  • Q Wave: Indicates septal depolarization, downward deflection.
  • R Wave: Positive deflection caused by left ventricular depolarization.
  • S Wave: Downward deflection as depolarization moves to the bases of ventricles.
  • T Wave: Indicates ventricular repolarization, upward deflection.

EKG Waveforms and Segments

• P Wave: Atrial depolarization.
• PR Segment: Atrial activity with no net movement; signifies AV node delay.
• Q Wave: Septal depolarization.
• R Wave: Indicates left ventricular depolarization.
• S Wave: Depolarization towards the bases of the ventricles.
• ST Segment: Entire ventricular myocardium remains depolarized (isoelectric).
• T Wave: Ventricular repolarization.

Understanding EKG Strips

• Large Box: 5 mm width, equals 0.20 seconds.
• Small Box: 1 mm width, equals 0.04 seconds.
• Height of Boxes: 5 mm in large box = 0.5 mV; 1 mm in small box = 0.01 mV.

Key Measurements

• PR Interval: Normal < 0.20 seconds.
• QRS Complex: Normal < 0.12 seconds, wide if > 0.12 seconds.
• QT Interval: Normal < 430 ms in males, < 460 ms in females; prolonged QT increases risk of arrhythmias.

Conclusion

• Recap of EKG basics and importance of understanding waveforms and leads.
• Preparation for analyzing EKG strips and identifying abnormalities.