Systematic Approach to ECG Interpretation
Use the "RIRI" mnemonic (Rate, Intervals, Rhythm, Ischemia/Infarction) as your systematic framework for ECG interpretation—this structured approach ensures comprehensive analysis while reducing interpretation time and minimizing missed diagnoses. 1
The RIRI Method: Step-by-Step Approach
1. Rate Assessment
- Calculate heart rate using the 300 method: Divide 300 by the number of large boxes between consecutive R waves 2
- Alternatively, count QRS complexes in a 6-second strip and multiply by 10 2, 3
- Normal sinus rhythm: 60-100 bpm; bradycardia <60 bpm; tachycardia >100 bpm 2
2. Intervals Measurement
- PR interval (normal: 120-200 ms or 3-5 small squares): Assess AV conduction 2, 3
- QRS duration (normal: <120 ms or <3 small squares): Evaluate ventricular conduction 2, 3
- QTc interval: Use Bazett's formula; normal <450 ms (men), <460 ms (women) 2, 3
- Measure QRS duration in a lead with an initial Q wave for accuracy 2
3. Rhythm Analysis
- Identify P waves before each QRS: Confirms sinus rhythm 2
- Check R-R interval regularity—irregular patterns suggest atrial fibrillation or other arrhythmias 2, 3
- Examine P wave morphology: normally upright in leads I, II, aVF; biphasic in V1 3
- Note any premature beats, pauses, or completely irregular patterns 2
4. Ischemia/Infarction Detection
- ST-segment elevation: >0.1 mV in limb leads or >0.15-0.2 mV in precordial leads indicates acute injury 2
- Pathological Q waves: >0.04 seconds or >25% of R wave amplitude suggests myocardial infarction 2
- T-wave abnormalities: Inversion, hyperacute changes, or flattening 2
- Identify the coronary territory affected by noting which leads show abnormalities 2
Additional Systematic Elements
Axis Determination (Quick Method)
Chamber Enlargement Assessment
- Left ventricular hypertrophy: S in V1 + R in V5 or V6 >3.5 mV (Sokolow-Lyon criterion) 2, 3
- Evaluate P wave duration and amplitude for atrial enlargement 2, 3
Critical Pitfalls to Avoid
Technical Errors
- Never accept computer interpretation without physician verification—automated systems produce frequent errors, particularly with arrhythmias (0-94% accuracy) 4, 2, 3
- Verify proper electrode placement, especially precordial leads, as misplacement causes false diagnoses 2
- Check for adequate filtering settings to avoid waveform distortion 2
Interpretation Errors
- Always compare with previous ECGs when available—this identifies important changes that isolated interpretation misses 2
- Never interpret ECG findings without clinical context—the same pattern has different implications depending on symptoms 2, 3
- Recognize that interpretation varies even among expert electrocardiographers, so maintain humility in borderline cases 4, 2
Quality Assessment
- Evaluate recording quality before interpretation by checking for artifacts, electrical interference, and baseline stability 2
- Ensure minimum high-frequency response of 150 Hz for adults to maintain diagnostic precision 2
Competency Maintenance
Training requires knowledge of pathophysiology, skill in recognizing abnormal patterns, and clinical experience relating ECG findings to patient presentation 4. The American College of Physicians recommends periodic objective assessment rather than simply completing a minimum number of interpretations 4. Continuing medical education through seminars or self-assessment programs keeps skills current, especially for physicians who read ECGs infrequently 2.
Despite major interpretation errors occurring in 4-33% of cases, adverse patient outcomes from these errors occur in less than 1% of interpretations, emphasizing the importance of clinical correlation 4.