How to Read an ECG | ECG Interpretation | EKG | OSCE Guide | UKMLA | CPSA | PLAB 2

Introduction

This tutorial provides a systematic approach to reading and interpreting an ECG (electrocardiogram). Understanding ECGs is essential for medical professionals, especially for those preparing for examinations like OSCE, UKMLA, CPSA, and PLAB 2. This guide will walk you through the key components of an ECG and how to analyze them effectively.

Step 1: Understand What an ECG Is

• An ECG is a test that measures the electrical activity of the heart over a period of time.
• It displays the heart's rhythm, rate, and other key parameters crucial for diagnosing cardiac conditions.

Step 2: Assess Heart Rate

• Calculate the heart rate using one of the following methods:
  1. Count the number of QRS complexes in a 10-second interval and multiply by 6.
  2. Use the formula: 300 divided by the number of large squares between two R waves.
• A normal heart rate ranges from 60 to 100 beats per minute.

Step 3: Evaluate Heart Rhythm

• Determine if the rhythm is regular or irregular by measuring the intervals between R waves.
• Identify the presence of any abnormal rhythms such as atrial fibrillation or ventricular tachycardia.

Step 4: Analyze Cardiac Axis

• The cardiac axis indicates the general direction of the heart's electrical activity.
• Use the limb leads (I, II, III) to assess the axis:
  • Normal axis: between -30° and +90°.
  • Left axis deviation: less than -30°.
  • Right axis deviation: greater than +90°.

Step 5: Examine P Waves

• P waves represent atrial depolarization.
• Check for:
  • Presence and shape: should be positive in lead II.
  • Duration: typically less than 0.12 seconds.

Step 6: Measure PR Interval

• The PR interval represents the time from the beginning of atrial depolarization to the beginning of ventricular depolarization.
• Normal duration is between 0.12 and 0.20 seconds.
• Prolonged PR intervals can indicate a heart block.

Step 7: Analyze QRS Complex

• The QRS complex indicates ventricular depolarization.
• Check for:
  • Duration: should be less than 0.12 seconds.
  • Morphology: abnormal shapes can indicate conditions like bundle branch block (BBB).

Step 8: Assess the ST Segment

• The ST segment reflects the time between ventricular depolarization and repolarization.
• Look for:
  • Elevation or depression: these changes can indicate ischemia or myocardial infarction.

Step 9: Evaluate ECG Territories

• Different regions of the heart correspond to specific leads on the ECG.
• Identify leads associated with various myocardial regions to locate potential ischemic areas.

Step 10: Analyze T Waves

• T waves represent ventricular repolarization.
• Note the shape and direction:
  • Normal T waves are upright in most leads.
  • Inverted T waves can indicate ischemia or other cardiac conditions.

Step 11: Identify U Waves

• U waves, if present, follow the T wave and can indicate electrolyte imbalances or other conditions.
• They are often small and not always visible.

Step 12: Document the ECG Findings

• Create a systematic report including:
  • Heart rate and rhythm.
  • Axis information.
  • Observations on P waves, PR interval, QRS complex, ST segment, T waves, and U waves.
• Ensure clarity and completeness in your documentation for future reference.

Step 13: Review Case Studies

• Apply your learning by examining clinical cases.
• Analyze different ECGs to identify abnormalities and practice your interpretation skills.

Conclusion

Successfully interpreting an ECG involves a systematic approach, from assessing heart rate and rhythm to examining individual waveforms and segments. Regular practice with case studies will enhance your skills and confidence. For further learning, consider using additional resources or quizzes to test your knowledge.