Proper Method for Reading Electrocardiograms (ECGs)
A systematic approach to ECG interpretation is essential for accurate diagnosis, with all ECGs requiring verification by a qualified physician regardless of computer interpretation, as incorrect readings can significantly impact patient morbidity and mortality.1, 2
Systematic Approach to ECG Interpretation
Step 1: Technical Assessment
- Verify proper lead placement and recording quality
- Check calibration (standard: 10 mm/mV, 25 mm/s)
- Identify artifacts, baseline wander, or improper filtering
- Ensure adequate bandwidth (high-frequency cutoff ≥150 Hz for adults/adolescents, ≥250 Hz for children) 1
Step 2: Rate and Rhythm Analysis
- Calculate heart rate (using R-R intervals)
- Determine if rhythm is regular or irregular
- Identify the basic rhythm (sinus, atrial, junctional, ventricular)
- Look for conduction abnormalities (blocks, pre-excitation)
Step 3: Axis Determination
- Calculate electrical axis using leads I and aVF
- Normal adult axis: -30° to +90°
- Identify axis deviations and their potential causes
Step 4: Interval Measurements
- PR interval (normal: 120-200 ms)
- QRS duration (normal: ≤120 ms)
- QT/QTc interval (normal: ≤450 ms men, ≤460 ms women)
- Identify prolonged or shortened intervals
Step 5: Waveform Analysis
- P wave morphology (atrial activity)
- QRS complex morphology (ventricular depolarization)
- ST segment evaluation (elevation, depression, or normal)
- T wave assessment (polarity, amplitude, symmetry)
- U wave presence or absence
Step 6: Integration with Clinical Context
- Compare with previous ECGs when available
- Interpret findings in context of patient's clinical presentation
- Consider differential diagnoses based on ECG findings
Critical Pitfalls to Avoid
Overreliance on Computer Interpretation
Computer algorithms have significant limitations with only 0-94% of disorders being correctly classified 2. Studies show computer interpretations are particularly problematic for:
- Arrhythmias (highest error rates) 3
- Acute myocardial infarction (40.7% error rate) 3
- High-degree AV blocks (75% error rate) 3
Technical Errors
- Misplacement of limb or precordial electrodes (especially V1/V2 placed too high) 1
- Inadequate bandwidth settings affecting waveform fidelity 1
- Failure to recognize artifacts that mimic pathology
Clinical Context Bias
- Misleading clinical history can reduce diagnostic accuracy by 5% for cardiologists and up to 25% for residents 4
- However, correct clinical history improves accuracy by 4-12% 4
- Always interpret the ECG first before applying clinical context to avoid premature diagnostic closure
Competency Requirements
The American College of Physicians and American Heart Association recommend that physicians interpreting ECGs should have:
- Formal training in ECG interpretation during residency or fellowship
- Understanding of cardiac electrophysiology and pathophysiology
- Experience relating ECG findings to clinical context
- Ability to identify technical artifacts 1, 2
Board certification, residency training, and Advanced Cardiac Life Support certification provide reasonable documentation of competency to interpret bedside ECGs in routine and emergency settings 1.
Maintaining Competency
- Continuing medical education through seminars or self-assessment programs is encouraged, especially for physicians who interpret ECGs infrequently 1
- Regular comparison of interpretations with expert overreads
- Periodic self-assessment and quality improvement activities
Remember that even with proper training, major interpretation errors occur in 4-33% of cases among trained physicians 2, highlighting the importance of a systematic approach and continuous improvement in ECG interpretation skills.