Lecture Notes: ECG Interpretation

Introduction

• Presenter: Olivia from Geeky Medics
• Objective: Learn a structured approach to ECG interpretation
• Reminder: Check video on how to record an ECG
• At the end: Practice with a case study

Basic Principles of an ECG

• Records electrical activity of the heart
• Identifies and locates pathology
• Uses electrodes on the patient, conductive pads
• 12-lead ECG: produces 12 graphs but only 10 electrodes used

Components of an ECG Cycle

• P Waves: Atrial depolarization, precedes each QRS complex
• PR Interval: Time for electrical activity from atria to ventricles
• QRS Complex: Ventricular depolarization (Q, R, S waves)
• ST Segment: Time between depolarization and repolarization
• T Wave: Ventricular repolarization
• QT Interval: Time for ventricles to depolarize and repolarize

Pre-Interpretation Checks

• Confirm patient details (name, DOB, ECG details)
• Check date, time, and calibration of ECG
• Understand clinical context (symptoms like chest pain/breathlessness)

Calculating Heart Rate

• Normal: 60-100 bpm
• Tachycardia: >100 bpm
• Bradycardia: <60 bpm

Methods:

• RR Interval Method (for regular rhythms):
  • Count large squares in one RR interval, divide 300 by the count
• QRS Complex Method (for irregular rhythms):
  • Count QRS complexes on 10-second ECG strip, multiply by 6

Assessing Heart Rhythm

• Regular vs Irregular
• Regularly Irregular: Recurrent patterns
• Irregularly Irregular: No clear pattern (e.g., atrial fibrillation)

Cardiac Axis

• Represents direction of electrical activity
• Normal range: -30° to +90°
• Positive deflection indicates net electrical activity towards lead

Abnormalities:

• Right Axis Deviation: +90° to +180°, often due to right ventricular hypertrophy
• Left Axis Deviation: -30° to -90°, often due to left ventricular hypertrophy

P Waves

• Check presence, followed by QRS complex, and normal appearance
• Absent P waves: Look for atrial activity (flutter, fibrillation)

PR Interval

• Normal: 120-200 ms
• Prolonged PR: AV delay or block
  • 1st Degree AV Block: Prolonged PR, no dropped QRS, asymptomatic
  • 2nd Degree Type 1 (Mobitz 1): Progressive PR prolongation, dropped QRS
  • 2nd Degree Type 2 (Mobitz 2): Consistent PR, intermittent QRS drop, pathological
  • 3rd Degree/Complete Block: No electrical communication between atria and ventricles

Wolff-Parkinson-White Syndrome

• Accessory pathways lead to premature ventricle excitation
• ECG Features: Shortened PR interval, delta wave, widened QRS

QRS Complex

• Represents ventricular depolarization
• Check width, height, and morphology
• Broad QRS: Indicates abnormal depolarization (e.g., bundle branch block)

Bundle Branch Blocks:

• Right Bundle Branch Block: RSR’ pattern in V1 (M shape), broad S wave in V6 (W shape)
• Left Bundle Branch Block: Deep S wave in V1 (W), broad M-shaped R wave in V6

ST Segment

• Indicates ischemia or infarction
• ST Elevation: Indicates myocardial infarction (STEMI)
• ST Depression: Indicates myocardial ischemia (NSTEMI)

T and U Waves

• T Waves:
  • Tall: Hyperkalemia or hyperacute STEMI
  • Inverted: Normal variants or pathology
• U Waves: Seen in electrolyte imbalances, hypothermia

Case Study Example

• Demonstrates irregularly irregular rhythm (atrial fibrillation)
• No P waves, QRS normal, no ST elevation, normal T waves

Conclusion

• ECG interpretation is challenging, follow structured approach
• Document interpretation with details and impressions
• Further resources available at Geeky Medics website and textbook