Primary Criteria for Assessing Cardiac Function on ECG
The primary criteria for assessing cardiac function on an electrocardiogram (ECG) include heart rate and rhythm, intervals (PR, QRS, QT), axis determination, chamber enlargement/hypertrophy assessment, and evaluation for ischemia, infarction, and repolarization abnormalities. 1
Basic Components of ECG Assessment
Rate and Rhythm Assessment
- Evaluate heart rate (normal: 60-100 bpm)
- Identify rhythm (sinus vs. non-sinus)
- Assess for arrhythmias including:
- Supraventricular tachycardias
- Atrial fibrillation/flutter
- Ventricular tachycardia
- Bradyarrhythmias 2
Conduction Assessment
- PR interval (normal: 120-200 ms) - evaluates AV nodal conduction
- QRS duration (normal: <120 ms) - evaluates intraventricular conduction
- QT/QTc interval (normal: <440 ms in men, <460 ms in women) - evaluates ventricular repolarization
- Presence of conduction blocks (bundle branch blocks, fascicular blocks, AV blocks) 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° 1
Chamber Enlargement/Hypertrophy Assessment
- Left ventricular hypertrophy criteria:
- Sokolow-Lyon criterion: SV1 + RV5 or RV6 >35 mm
- Cornell voltage criterion: SV3 + RaVL >28 mm (men), >20 mm (women)
- Romhilt-Estes point score system 1
- Right ventricular hypertrophy criteria
- Atrial enlargement criteria 1
Ischemia and Infarction Evaluation
- ST-segment elevation or depression (≥1 mm in ≥2 contiguous leads)
- T-wave inversion (≥1 mm in depth in ≥2 contiguous leads)
- Q waves (pathological: ≥40 ms duration or ≥25% of R wave amplitude)
- Loss of R wave progression in precordial leads 1, 2
Advanced Assessment Criteria
Repolarization Abnormalities
- Early repolarization patterns
- Brugada patterns
- Long QT syndrome patterns
- Short QT syndrome patterns 1, 2
Electrolyte Abnormalities
- Hyperkalemia: tall, peaked T waves
- Hypokalemia: U waves, ST depression, flattened T waves
- Hypercalcemia: shortened QT interval
- Hypocalcemia: prolonged QT interval 1
Pericardial Disease
- Diffuse ST elevation with PR depression (pericarditis)
- Electrical alternans (pericardial effusion)
- Low voltage (large effusion) 1
Integration with Clinical Context
The American College of Cardiology/American Heart Association Task Force emphasizes that ECG interpretation should always be integrated with clinical data, as the same ECG pattern may be recorded in patients with different structural and pathophysiologic states 1. This explains the frequent low specificity of the ECG for determining the etiology and anatomy of cardiovascular disease.
Common Pitfalls to Avoid
- Relying solely on a single normal ECG to rule out cardiac causes of symptoms
- Failing to obtain appropriate rhythm monitoring when arrhythmia is suspected
- Not comparing with previous ECGs when available
- Overlooking subtle signs of ischemia or conduction abnormalities
- Misinterpreting normal variants as pathological findings 2
Special Considerations
Age-Related Changes
- QRS voltages tend to decline with increasing age
- Age-specific criteria should be applied, particularly in pediatric patients 1
Athlete's Heart
- Sinus bradycardia, first-degree AV block, and early repolarization are common normal findings
- Specific criteria exist for differentiating physiologic from pathologic findings in athletes 1
For accurate ECG interpretation, all computer ECG interpretations should be verified by a qualified physician, as automated systems may not correctly identify all rhythm disturbances, ischemia, or infarction patterns 1. The integration of clinical data and comparison with previous ECGs are essential for proper diagnostic accuracy.