Interpreting an ECG accurately requires a systematic approach. Beginners often make predictable mistakes that can lead to missed diagnoses or unnecessary concern. Understanding these common pitfalls can help medical students, interns, and junior doctors develop confidence and improve diagnostic accuracy.
1. Not Following a Systematic Approach: The most common mistake is reading the ECG randomly. A structured sequence helps avoid missing important findings:
- Confirm patient details and calibration.
- Determine the heart rate.
- Assess rhythm.
- Evaluate the cardiac axis.
- Measure PR, QRS, and QT intervals.
- Examine P waves.
- Analyze QRS morphology.
- Assess ST segments and T waves.
- Compare with previous ECGs if available.
Using the same sequence every time significantly reduces interpretation errors.
2. Ignoring ECG Calibration: Check if ECG machine is calibrated as Paper speed: 25 mm/second and Voltage calibration: 10 mm = 1 mV
3. Miscalculating the Heart Rate:
A. For regular rhythms, 300 รท number of large squares between consecutive R waves.
B. For irregular rhythms: Count QRS complexes in 10 seconds and multiply by six.
4. Missing Lead Misplacement: Incorrect limb or chest lead placement can produce ECG abnormalities that resemble disease.
5. Confusing Normal Variants with Disease: Several normal ECG findings are often mistaken for pathology. Recognizing normal variants prevents unnecessary investigations.
6. Missing ST-Segment Changes: Many beginners focus only on dramatic ST elevation while overlooking subtle ischemic changes like ST depression, hyperacute T waves. Serial ECGs are often more informative than a single recording.
7. Overlooking QT Interval Prolongation: A prolonged QT interval increases the risk of life-threatening ventricular arrhythmias.
8. Misidentifying Bundle Branch Blocks: Beginners frequently confuse between RBBB, LBBB and ventricular rhythms.
9. Forgetting to Look at previous ECGs: A finding that appears abnormal may actually be chronic.
10: Ignoring the clinical picture: An ECG should never be interpreted in isolation. Always correlate ECG findings with the patientโs symptoms, examination, laboratory results, and imaging when appropriate.
ECG interpretation is a skill that develops through repetition and a systematic approach rather than memorization alone. A normal ECG does not rule out serious heart disease. Up to one-third of patients with an acute coronary syndrome may have a normal or non-diagnostic initial ECG, which is why serial ECGs and clinical assessment remain essential in emergency medicine.
MBH/DB