What are the major key findings in step 2 of ECG (Electrocardiogram) interpretation?

Major Key ECG Findings for Step 2 of ECG Interpretation

In step 2 of ECG interpretation, the key findings to assess are rate, rhythm, axis, intervals, and ST-T wave changes, which are critical for identifying life-threatening conditions that affect morbidity and mortality.

Rate and Rhythm Assessment

• Heart rate calculation: Determine if bradycardia (<60 bpm) or tachycardia (>100 bpm) is present
• Rhythm regularity: Assess for regular vs. irregular patterns
• P wave morphology: Evaluate for presence, consistency, and relationship to QRS complexes
• Rhythm abnormalities: Identify specific arrhythmias that may require immediate intervention 1

Conduction System Evaluation

• PR interval: Normal (120-200 ms) vs. prolonged (>200 ms, suggesting AV block) or shortened (<120 ms)
• QRS duration: Normal (<120 ms) vs. widened (>120 ms, suggesting bundle branch blocks or ventricular rhythms)
• QT interval: Assess for prolongation (risk of torsades de pointes) or shortening
• New conduction abnormalities: Compare with previous ECGs when available 1

ST-T Wave Analysis

• ST elevation: Assess for patterns consistent with STEMI (≥1 mm in two contiguous leads)
• ST depression: Evaluate for subendocardial ischemia
• T wave inversions: Note depth, distribution, and symmetry
• Repolarization changes: Differentiate between ischemic and non-ischemic causes 2

Chamber Abnormalities

• Left ventricular hypertrophy: Increased QRS voltage with associated ST-T changes
• Right ventricular hypertrophy: Right axis deviation with tall R waves in right precordial leads
• Atrial enlargement: P wave abnormalities (duration, amplitude, or morphology) 1

Axis Determination

• Normal axis: -30° to +90°
• Left axis deviation: -30° to -90°
• Right axis deviation: +90° to +180°
• Extreme axis deviation: -90° to -180° (northwest axis) 1

Clinical Correlation

The ECG findings in step 2 must be interpreted in the clinical context. ST elevation in a patient with active symptoms usually indicates acute occlusion of an epicardial artery requiring emergent reperfusion therapy 2. However, many patients have ST segment elevation due to non-ischemic causes, making clinical correlation essential.

Common Pitfalls to Avoid

• Over-reliance on computer interpretation: Computer programs have shown lower sensitivity than cardiologists in diagnosing key conditions like LVH (56.6% vs. 63.9%), anterior MI (77.1% vs. 84.9%), and inferior MI (58.8% vs. 71.7%) 3
• Missing subtle changes: Comparison with previous ECGs is crucial for detecting significant changes
• Failure to recognize high-risk patterns: Widespread ST depression with ST elevation in aVR may represent diffuse subendocardial ischemia from severe coronary disease requiring urgent intervention 4
• Ignoring clinical context: ECG interpretation accuracy improves significantly when combined with clinical assessment 5

Systematic Approach for Step 2

1. Calculate heart rate (normal: 60-100 bpm)
2. Assess rhythm regularity and P wave morphology
3. Measure intervals: PR, QRS, QT
4. Determine axis
5. Evaluate for chamber enlargement/hypertrophy
6. Analyze ST-T wave changes for ischemia/injury patterns
7. Look for conduction abnormalities
8. Compare with previous ECGs when available 1

This systematic approach to step 2 of ECG interpretation helps identify potentially life-threatening conditions that require immediate intervention, directly impacting patient morbidity and mortality outcomes.