Proper Procedure for Interpreting an Electrocardiogram (ECG)
A systematic approach to ECG interpretation must follow a structured algorithm that includes rate, intervals, rhythm, and ischemia/infarction assessment (RIRI approach), with mandatory physician overreading of all computer-generated interpretations to ensure accurate diagnosis and appropriate patient management. 1, 2
Technical Considerations Before Interpretation
- Verify proper lead placement and recording quality with standard calibration (10 mm/mV and 25 mm/s)
- Ensure adequate bandwidth (≥150 Hz for adults/adolescents, ≥250 Hz for children)
- Compare with previous ECGs when available
- Check for technical artifacts that may affect interpretation
Step-by-Step ECG Interpretation Algorithm
1. Rate Assessment
- Calculate heart rate (normal: 60-100 beats/min)
- Identify bradycardia (<60 beats/min) or tachycardia (>100 beats/min)
2. Interval Measurements
- PR interval (normal: 120-200 ms)
- QRS duration (normal: <120 ms)
- QT interval (corrected for heart rate using QTc)
- Normal QTc: <450 ms in men, <460 ms in women 1
3. Rhythm Analysis
- Identify P waves (normal duration <120 ms, amplitude <2.5 mm)
- Assess P-QRS relationship for AV conduction
- Classify as sinus rhythm or identify specific arrhythmias
4. Ischemia/Infarction Evaluation
- Examine for ST segment deviations:
- ST elevation ≥0.1 mV (1 mm) in two contiguous leads suggests myocardial injury
- Different thresholds for ST elevation in V2-V3 by gender and age:
- ≥0.2 mV (2 mm) in men ≥40 years
- ≥0.25 mV (2.5 mm) in men <40 years
- ≥0.15 mV (1.5 mm) in women 1
- Assess for pathological Q waves (>40 ms or >25% of R wave amplitude)
- Evaluate T wave morphology (inversions, hyperacute changes)
5. Chamber Abnormalities Assessment
- Left ventricular hypertrophy (using Sokolow-Lyon or Cornell criteria)
- Right ventricular hypertrophy (R in V1 >7 mm or R/S ratio in V1 >1) 1
6. Conduction Abnormalities Evaluation
- Bundle branch blocks
- Fascicular blocks
- AV blocks
Critical Considerations
Competency Requirements
- Physicians should interpret at least 500-800 ECGs under supervision to develop competency
- Maintain proficiency by interpreting at least 100 ECGs yearly
- Formal training in ECG interpretation during residency or fellowship is essential 1
Computer Algorithm Limitations
- Error rates up to 40.7% for acute myocardial infarction
- Only 0-94% of disorders classified correctly
- All computer-based reports require physician overreading 3, 1
Common Pitfalls to Avoid
- Misdiagnosis of mimicking conditions: Both cardiac and non-cardiac conditions can mimic acute myocardial infarction on ECG, including pericarditis, stress-induced cardiomyopathy, and post-ictal changes 4
- Relying solely on computer interpretation: Computer algorithms have significant limitations and should never replace physician interpretation 3, 1
- Failure to compare with previous ECGs: Serial comparison of ECGs should be done by trained observers regardless of whether the ECG program provides a serial comparison 3
- Isolated interpretation without clinical context: ECG findings must be integrated with clinical data and patient-specific context 1
Special Considerations
- Major interpretation errors are common (4-33%) even among trained physicians 1
- Time-dependent conditions require rapid and accurate ECG interpretation
- Periodic objective assessment of interpretation skills in clinical context is more important than completing a minimum number of interpretations 1
By following this systematic approach to ECG interpretation, clinicians can minimize errors, improve diagnostic accuracy, and ensure appropriate patient management based on accurate ECG interpretation.