What is a step‑by‑step approach to interpreting a pediatric ECG, including assessment of heart rate, rhythm, axis, intervals, chamber size, QRS morphology, ST‑segment and T‑wave changes, and subsequent management based on the findings?

Step-by-Step ECG Evaluation

Evaluate every ECG systematically using a standardized sequence: rate, rhythm, axis, intervals (PR, QRS, QT), chamber enlargement, QRS morphology, ST segments, and T waves—this approach minimizes missed findings and ensures reproducibility. 1

1. Technical Quality and Artifact Recognition

Before interpretation, verify technical adequacy:

• Confirm proper electrode placement to avoid misdiagnosis—V1 and V2 belong in the 4th intercostal space (not the 2nd), and V5/V6 should align horizontally with V4 in the 5th intercostal space 1, 2
• Check for limb lead reversal and precordial lead misplacement, which are common errors that distort R-wave progression and can simulate anteroseptal infarction 1, 2
• Identify motion artifacts from tremors, shivering, or muscle activity—these create irregular baseline undulations but do not affect the intrinsic rhythm 1, 3
• Verify bandwidth settings: use ≥150 Hz sampling rate for pediatric ECGs and ≥250 Hz high-frequency cutoff to avoid amplitude distortion 1
• Ensure computer interpretation is physician-confirmed—automated readings require overreading for accuracy 1

2. Heart Rate

• Calculate rate using standard methods (300/number of large boxes between R waves, or count complexes in 6 seconds × 10) 1
• Apply age-appropriate normal ranges for pediatric ECGs:
  • Neonates 0-1 days: 93-154 bpm (mean 123) 1
  • 1-3 months: 121-179 bpm (mean 150) 1
  • Older children and adults: 60-100 bpm 1

3. Rhythm Assessment

• Identify P waves before each QRS complex to confirm sinus rhythm 1
• Measure P-wave axis: normal is +59° to +197° in neonates, narrowing to +31° to +114° by 1-3 months 1
• Evaluate P-wave morphology for atrial enlargement or ectopic rhythms 1
• Assess regularity of R-R intervals to detect arrhythmias 1

4. Axis Determination

• Calculate QRS axis using leads I and aVF:
  • Normal adult: -30° to +90° 1
  • Neonates: +59° to +200° is normal (right axis is physiologic) 1
  • By 1 month: upper limit falls to +160° 1
• Left axis deviation (−45° to −90°) suggests left anterior fascicular block if qR pattern in aVL with R-peak time ≥45 ms and QRS <120 ms 1
• Right axis deviation beyond age-appropriate norms warrants evaluation for right ventricular hypertrophy or congenital heart disease 1

5. Interval Measurements

PR Interval

• Measure from P-wave onset to QRS onset 1
• Normal ranges (age-dependent):
  • Neonates: 0.08-0.16 seconds (mean 0.11) 1
  • Adults: 0.12-0.20 seconds 1
• PR >0.20 seconds indicates first-degree AV block 1

QRS Duration

• Measure in lead with initial Q wave (typically V5) 1
• Age-specific normal values:
  • Neonates: 0.02-0.08 seconds (mean 0.05) 1
  • Children <4 years: <90 ms 1
  • Children 4-16 years: <100 ms 1
  • Adults: <120 ms 1
• Complete RBBB: QRS ≥120 ms (adults) with rSR' in V1/V2 and wide S in I and V6 1
• Complete LBBB: QRS ≥120 ms (adults) with broad notched R in I, aVL, V5, V6; absent q waves in I, V5, V6; R-peak time >60 ms in V5/V6 1
• Incomplete RBBB: QRS 110-119 ms (adults) with RBBB morphology—note that rSr' in V1/V2 with normal QRS duration is a normal variant in children 1

QT Interval

• Measure from QRS onset to T-wave end and correct for heart rate (QTc) 1
• Recognize measurement challenges with digital ECG systems—QT intervals differ from single-channel recordings 1
• Prolonged QTc (>440 ms in males, >460 ms in females) raises concern for long QT syndrome, especially in young patients 1

6. Chamber Enlargement

• Right ventricular hypertrophy in neonates: tall R waves in V1/V2 are normal due to physiologic RV dominance 1
• Left ventricular hypertrophy: increased R-wave amplitude in V5/V6 and S-wave depth in V1/V2 (use age-appropriate voltage criteria) 1
• Atrial enlargement: P-wave duration >0.12 seconds (left atrial) or amplitude >2.5 mm (right atrial) 1

7. QRS Morphology and R-Wave Progression

• Assess R-wave progression across precordial leads V1-V6 1
• Poor R-wave progression (failure to increase from V1 to V4) may indicate anterior infarction, but always consider lead misplacement first 1, 4, 2
• Early transition (R>S before V3) can be normal variant or suggest posterior infarction—requires correlation with clinical context and comparison to prior ECGs 4
• In neonates, QRS morphology may have more notches and direction changes than in adults—this is normal 1

8. ST Segments and T Waves

• Measure ST-segment deviation at the J-point (60-80 ms after QRS end) 1
• ST elevation ≥1 mm in two contiguous leads suggests acute injury 1
• ST depression ≥0.5 mm indicates ischemia or reciprocal changes 1
• T-wave inversions beyond V1 in adults or beyond V3 in children warrant investigation 1
• Beware of artifactual ST changes from inappropriate high-pass filtering (>0.05 Hz), which can create false J-point and ST-segment deviation 1

9. Conduction Abnormalities

• Nonspecific intraventricular conduction delay: QRS >110 ms (adults) without RBBB or LBBB criteria 1
• Bifascicular block: RBBB + left anterior fascicular block (RBBB with left axis deviation −45° to −90°) 1
• Peri-infarction block: QR complex in inferior or lateral leads with wide terminal QRS portion directed opposite to Q wave 1

10. Clinical Correlation and Management

• Compare with prior ECGs whenever available—serial changes are often more significant than isolated findings 4
• Consider patient age, symptoms, and risk factors when interpreting borderline abnormalities 1, 4
• In high-risk patients (elderly, alcohol use, known cardiac disease), pursue further evaluation with cardiac biomarkers, echocardiography, or stress testing for concerning findings 4
• Recognize that single screening ECGs have limitations—diseases like hypertrophic cardiomyopathy may develop over time with initially normal ECGs 1

Common Pitfalls to Avoid

• Never diagnose bundle branch blocks in children using adult QRS duration criteria—use age-specific cutoffs 1
• Do not overlook technical errors—electrode misplacement is extremely common (only 16% of cardiologists correctly identify V1 position in one study) 5
• Avoid misinterpreting normal pediatric variants as pathology (e.g., right axis deviation in neonates, rSr' pattern in children) 1
• Remember that computer measurements change with digital technology—established normal limits from analog era may not apply 1