Can you interpret an electrocardiogram (ECG)?

ECG Interpretation Capability and Competency

As a medical consultant, I cannot personally interpret an ECG for you, but I can provide guidance on who should interpret ECGs and what competencies are required for accurate interpretation.

Who Should Interpret ECGs

Residency training in internal medicine, family medicine, or emergency medicine with Advanced Cardiac Life Support certification is sufficient for bedside interpretation of 12-lead ECGs in routine and emergency situations. 1

• Board certification and successful completion of residency training provide reasonable documentation of competency to interpret bedside ECGs 1
• Cardiologists demonstrate greater accuracy than noncardiologists, particularly when minimal clinical history is provided 1
• Noncardiologists are more influenced by patient history and clinical context when interpreting ECGs compared to cardiologists 1, 2

Current State of ECG Interpretation Accuracy

The accuracy of ECG interpretation varies significantly across training levels and even among experts:

• Medical students: 42.0% accuracy (95% CI, 34.3%-49.6%) 3
• Residents: 55.8% accuracy (95% CI, 48.1%-63.6%) 3
• Practicing physicians: 68.5% accuracy (95% CI, 57.6%-79.5%) 3
• Cardiologists: 74.9% accuracy (95% CI, 63.2%-86.7%) 3

First-year internal medicine residents demonstrate particularly low proficiency, with only 50% of ECGs read correctly overall 4. Critical diagnoses showed variable accuracy: acute MI (1.73/2.0), atrial flutter (1.5/2.0), ventricular tachycardia (1.11/2.0), and complete heart block (0.23/2.0) 4.

Systematic Approach to ECG Interpretation

When interpreting ECGs, follow this algorithmic framework 5, 2:

Step 1: Technical Quality Assessment

• Verify proper electrode placement, particularly precordial leads 5, 2
• Ensure adequate filtering settings (minimum 150 Hz high-frequency response for adults) 5, 2
• Identify any technical artifacts that may affect interpretation 5

Step 2: Rate and Rhythm Analysis

• Calculate heart rate: count QRS complexes in 6-second strip × 10, or use 300 ÷ number of large boxes between R waves 5, 2
• Identify underlying rhythm: confirm P wave before each QRS with consistent PR interval for sinus rhythm 5, 2
• Normal sinus rhythm: 60-100 bpm; bradycardia <60 bpm; tachycardia >100 bpm 5, 2
• Note irregularities: premature beats, pauses, or completely irregular patterns suggesting atrial fibrillation 5, 2

Step 3: Interval Measurements

• PR interval: normal 120-200 ms (assess AV conduction) 5, 2
• QRS duration: normal <120 ms (identify ventricular conduction delays) 5, 2
• QTc using Bazett's formula: normal <450 ms (men), <460 ms (women) 5, 2

Step 4: Axis Determination

• Normal axis: both leads I and aVF positive (+90° to -30°) 5, 2
• Left axis deviation: lead I positive, aVF negative (-30° to -90°) 5, 2
• Right axis deviation: lead I negative, aVF positive (+90° to +180°) 5, 2

Step 5: Ischemia/Injury Assessment

• ST elevation: >0.1 mV in limb leads or >0.15-0.2 mV in precordial leads indicates acute injury 5, 2
• Pathological Q waves: >0.04 seconds or >25% of R wave amplitude suggests MI 5, 2
• T-wave abnormalities: inversion, hyperacute changes, or flattening 5, 2
• Note location to determine affected coronary territory 5, 2

Critical Pitfalls to Avoid

Never interpret ECGs in isolation without clinical context—this is the single most important principle. 5, 2

• Do not over-rely on computer interpretation without physician verification, as errors remain common 5, 2
• Computer interpretations are helpful adjuncts but not substitutes for physician interpretation 1, 2
• Cardiologists as primary readers are more accurate (94%) than overreading cardiologists lacking clinical information (72%) 6
• Always compare with previous ECGs when available to identify dynamic changes 5, 2
• Electrode misplacement, particularly precordial leads, can lead to false diagnoses 5, 2

Maintaining Competency

Continuing medical education through seminars or self-assessment programs is encouraged for physicians who read ECGs infrequently. 1, 5

• Interpretation skills vary greatly even among expert electrocardiographers 1, 5
• Periodic self-study or continuing medical education ensures skills remain current 1, 5
• No specific yearly minimum number of ECG interpretations has been established to maintain competency 1

Special Circumstances

When interpreting ECGs without knowing the patient's clinical status:

• Additional experience or standardized testing beyond residency training may be desirable 1
• Cardiologists perform better than other specialists on standardized ECG examinations when minimal patient history is provided 1
• Clinical context significantly affects interpretation accuracy, particularly for noncardiologists 1, 2