How To Read An ECG: A Step-By-Step Guide
Introduction
Electrocardiograms (ECGs or EKGs) are essential tools in diagnosing heart conditions. Whether you’re a medical professional, a student, or just someone curious about heart health, learning how to read an ECG is a valuable skill. This guide will walk you through the basics of ECG interpretation.
Understanding the ECG Grid
An ECG printout consists of a grid of small and large squares.
- Small squares represent 0.04 seconds.
- Large squares (5 small squares) represent 0.2 seconds.
- The vertical axis measures voltage (mV), while the horizontal axis represents time.
The 12-Lead ECG
A standard ECG includes 12 leads, each providing a different view of the heart:
- Limb Leads: I, II, III, aVR, aVL, aVF
- Precordial (Chest) Leads: V1–V6 These leads help pinpoint the location of any heart abnormalities.
Step-By-Step ECG Interpretation
1. Check the Heart Rate
Count the number of R waves in a 6-second strip and multiply by 10, or use the 300-150-100-75-60-50 rule for large squares.
2. Assess the Heart Rhythm
- Regular rhythm: Consistent R-R intervals.
- Irregular rhythm: Varying R-R intervals (e.g., atrial fibrillation).
3. Evaluate the P Wave
- Normal P waves should be upright in leads I and II.
- Abnormal P waves may indicate atrial abnormalities.
4. Measure PR Interval
- Normal: 0.12–0.20 seconds.
- Prolonged PR interval suggests first-degree heart block.
5. Examine the QRS Complex
- Normal duration: <0.12 seconds.
- Prolonged QRS may indicate bundle branch block or ventricular hypertrophy.
6. Look at the ST Segment
- Elevated ST: Possible myocardial infarction.
- Depressed ST: Possible ischemia.
7. Analyze the T Wave
- Tall, peaked T waves: Hyperkalemia.
- Inverted T waves: Ischemia or past infarction.
8. Review the QT Interval
- Prolonged QT: Risk of arrhythmias (e.g., torsades de pointes).
- Shortened QT: Hypercalcemia.
Common ECG Abnormalities
- Atrial fibrillation: Irregularly irregular rhythm, no distinct P waves.
- Myocardial infarction: ST elevation, pathological Q waves.
- Ventricular tachycardia: Wide QRS, fast rate (>100 bpm).
- Heart blocks: PR interval abnormalities or dropped beats.
Conclusion
Reading an ECG takes practice, but following a structured approach helps simplify interpretation. Always consider the clinical context and, when in doubt, consult a cardiologist. By mastering ECG basics, you enhance your ability to detect and manage cardiac conditions efficiently.
