Can I Interpret an ECG?
Yes, you can and should interpret ECGs if you have completed residency training with Advanced Cardiac Life Support (ACLS) certification, which provides sufficient competency for bedside interpretation in routine and emergency situations. 1
Training Requirements for ECG Interpretation
- Residency training with ACLS certification is the minimum standard for independent ECG interpretation in clinical practice 1
- Continuing medical education through seminars or self-assessment programs is encouraged for physicians who read ECGs infrequently to maintain current skills 1
- The responsibility for correctly interpreting an ECG lies with the physician, who must be able to recognize patient-dependent errors, operator-dependent errors, and artifact 2
Computer Interpretation: Use With Caution
- Computer interpretations must always be verified by a qualified physician—they are helpful adjuncts but never substitutes for physician interpretation 1
- Computer programs provide accurate heart rate, intervals, and axes, but interpretations of rhythm disturbances, ischemia, or infarction require careful physician over-reading 1
- Do not over-rely on computer interpretation without physician verification, as errors remain common 1
Systematic Approach to ECG Interpretation
The American College of Cardiology recommends the following systematic framework 1:
Technical Verification
- Verify proper electrode placement and adequate filtering settings before interpretation, as misplaced precordial leads can significantly alter findings and lead to false diagnoses 1
- Ensure minimum high-frequency response of 150 Hz for adults to maintain diagnostic precision 1
Step-by-Step Analysis
- Calculate heart rate by counting QRS complexes in a 6-second strip and multiplying by 10, or using 300 divided by the number of large boxes between R waves 1
- Identify the underlying rhythm by confirming a P wave before each QRS complex with consistent PR interval for sinus rhythm 1
- Measure PR interval (normal: 120-200 ms) to assess AV conduction 1
- Evaluate QRS duration (normal: <120 ms) to identify ventricular conduction delays or bundle branch blocks 1
- Calculate corrected QT interval (QTc) using Bazett's formula; normal <450 ms for men, <460 ms for women 1
- Determine electrical axis using leads I and aVF: normal axis when both positive (+90° to -30°) 1
- Examine for ST-segment elevation (>0.1 mV in limb leads or >0.15-0.2 mV in precordial leads) indicating acute injury requiring emergent reperfusion 1
- Identify pathological Q waves (>0.04 seconds or >25% of R wave amplitude) suggesting prior myocardial infarction 1
Critical Integration With Clinical Context
- Never interpret the ECG in isolation—clinical signs and symptoms alone lack sufficient sensitivity (35-38%) and specificity (28-91%) to rule in or rule out acute coronary syndrome without ECG and biomarkers 1
- The ECG must be interpreted in conjunction with clinical presentation for diagnosis and triage, including destination decisions and cardiac catheterization laboratory activation 1
- A skilled physician must integrate clinical data, provide differential diagnosis, and compare with previous tracings, as the same ECG pattern may occur in different pathophysiologic states 1
Essential Pitfalls to Avoid
- Do not fail to compare with previous ECGs when available, as this can miss important dynamic changes 1
- Do not interpret findings without clinical context, which may lead to inappropriate management decisions and adverse outcomes 1
- Recognize that noncardiologists are more influenced by patient history than cardiologists when interpreting ECGs, making systematic approach even more critical 1
When to Obtain Expert Consultation
- Field-transmitted ECG for expert interpretation is reasonable if on-site interpretation is unavailable 1
- In the worst-case scenario, ECGs can always be faxed or transmitted for inter-consultation with a more experienced reader 2