Pediatric Cardiac Z-Score Reference¶
Quick reference for Z-score calculations and interpretation in pediatric cardiology.
Understanding Z-Scores¶
Z-score = (Observed value - Mean for BSA) / Standard Deviation
Interpretation¶
| Z-Score | Interpretation |
|---|---|
| -2 to +2 | Normal |
| +2 to +2.5 | Mildly dilated/enlarged |
| +2.5 to +5 | Moderately dilated |
| >5 | Severely dilated |
| <-2 | Small/Hypoplastic |
Coronary Artery Z-Scores (PHN/AHA)¶
Classification (Kawasaki Disease)¶
| Z-Score | Classification |
|---|---|
| <2.0 | Normal |
| 2.0 to <2.5 | Dilation only |
| 2.5 to <5.0 | Small aneurysm |
| 5.0 to <10.0 | Medium aneurysm |
| ≥10.0 OR ≥8mm absolute | Giant aneurysm |
PHN Coronary Z-Score Equations¶
Body Surface Area (BSA) using Haycock formula:
BSA (m²) = 0.024265 × Height(cm)^0.3964 × Weight(kg)^0.5378
Left Main Coronary Artery (LMCA):
Mean = 0.31747 × BSA^0.36008 - 0.02887
Z = (Observed - Mean) / (Mean × 0.10199 + 0.01602)
Left Anterior Descending (LAD):
Mean = 0.26108 × BSA^0.37893 - 0.02852
Z = (Observed - Mean) / (Mean × 0.12579 + 0.0127)
Right Coronary Artery (RCA):
Mean = 0.26117 × BSA^0.39992 - 0.02756
Z = (Observed - Mean) / (Mean × 0.18375 + 0.01323)
Online Calculators¶
- parameterz.com - Multiple Z-score systems
- zscore.chboston.org - Boston Children's calculator
- PHN coronary calculator in most echo reporting systems
Aortic Root Z-Scores¶
Aortic Annulus, Sinus of Valsalva, STJ, Ascending Aorta¶
Detroit/Pettersen equations commonly used
| Structure | Mean (cm) | SD |
|---|---|---|
| Aortic Annulus | 0.897 + 1.476 × BSA^0.5 | 0.12 |
| Sinus of Valsalva | 1.020 + 1.548 × BSA^0.5 | 0.15 |
| Sinotubular Junction | 0.857 + 1.296 × BSA^0.5 | 0.14 |
| Ascending Aorta | 0.742 + 1.587 × BSA^0.5 | 0.16 |
Marfan Syndrome Thresholds¶
| Z-Score | Interpretation |
|---|---|
| <2 | Normal |
| 2-3 | Mild dilation |
| 3-4 | Moderate dilation |
| >4 | Severe dilation |
| ≥5 cm absolute | Surgery consideration |
Left Ventricular Z-Scores¶
LV Internal Dimension (Diastole) - LVID d¶
Boston equations (commonly used)
Normal Z-score range: -2 to +2
| Z-Score | Interpretation |
|---|---|
| >2 | LV dilation |
| <-2 | Small LV |
LV Mass Z-Score¶
- Normal: <+2
- LVH: ≥+2
Shortening Fraction vs Z-Score¶
Note: SF is typically reported as percentage, not Z-score - Normal SF: 28-44% - Consider Z-score for LVEDD to assess chamber size
Right Ventricular Z-Scores¶
Tricuspid Annulus¶
Less standardized than LV measurements
Pulmonary Valve Annulus¶
Important for planning interventions (balloon valvuloplasty, TPV)
| Z-Score | Clinical Implication |
|---|---|
| <-2 | Hypoplastic; may need RVOT augmentation |
| -2 to +2 | Normal |
| >+2 | Dilated; consider regurgitation |
Mitral Valve Z-Scores¶
Mitral Annulus¶
| Z-Score | Interpretation |
|---|---|
| <-2 | Hypoplastic (consider MS evaluation) |
| >+2 | Dilated (often with MR) |
Pulmonary Artery Z-Scores¶
Main Pulmonary Artery (MPA)¶
| Z-Score | Interpretation |
|---|---|
| >+2 | Dilated (consider PH, shunt lesion) |
| <-2 | Hypoplastic |
Branch PA Z-Scores¶
Important for assessing branch PA stenosis
Practical Tips¶
When to Use Z-Scores¶
- Always for coronary arteries (Kawasaki)
- Always for aortic root (Marfan, BAV)
- Recommended for all chamber dimensions
- Essential for serial comparisons (growth-adjusted)
Common Pitfalls¶
- Using wrong BSA formula - Haycock preferred for most calculations
- Applying adult reference data - Always use pediatric-specific equations
- Single measurement reliance - Serial trending more valuable
- Ignoring measurement technique - Standardize approach (leading edge, inner edge)
BSA Formulas Comparison¶
| Formula | Equation | Best Use |
|---|---|---|
| Haycock | 0.024265 × H^0.3964 × W^0.5378 | Standard for Z-scores |
| DuBois | 0.007184 × H^0.725 × W^0.425 | Adults |
| Mosteller | √(H × W / 3600) | Quick estimate |
Age-Specific Considerations¶
Neonates¶
- Use PHN equations (validated 0-18 years)
- Consider premature infant-specific data if available
- Rapid growth affects serial comparisons
Adolescents/Young Adults¶
- Transition to adult reference data around 18 years
- Some overlap in pediatric vs adult equations
- Document which reference used
Reporting Standards¶
Required Elements¶
- Measurement in cm (or mm)
- Z-score value
- Reference equation used
- BSA at time of measurement
Example Report Language¶
Normal coronaries:
"Coronary arteries are normal in origin and course. LMCA 0.25 cm (Z = +1.2), LAD 0.21 cm (Z = +0.8), RCA 0.22 cm (Z = +1.0). Z-scores calculated using PHN equations with BSA 0.45 m²."
Kawasaki with aneurysm:
"LAD coronary artery aneurysm measuring 0.55 cm (Z = +6.8, medium aneurysm). RCA mildly dilated at 0.32 cm (Z = +2.8, small aneurysm). Z-scores per 2017 AHA Kawasaki guidelines using PHN equations."
Quick Reference Card¶
Kawasaki Coronary Risk Stratification¶
| Risk Level | Z-Score | Long-term Therapy |
|---|---|---|
| Level 1 (No involvement) | <2 at all times | ASA 6-8 weeks |
| Level 2 (Dilation) | 2.0-2.5 | ASA until normal |
| Level 3 (Small aneurysm) | 2.5-5.0 | ASA long-term |
| Level 4 (Medium aneurysm) | 5.0-10.0 | ASA + anticoagulation |
| Level 5 (Giant aneurysm) | ≥10.0 or ≥8mm | ASA + anticoagulation |
Aortic Surgery Thresholds¶
| Condition | Z-Score/Size Threshold |
|---|---|
| Marfan (no risk factors) | 5.0 cm |
| Marfan (with risk factors) | 4.5 cm |
| Loeys-Dietz | 4.0-4.2 cm |
| Turner syndrome | ASI ≥2.5 cm/m² |
| BAV (no risk factors) | 5.5 cm |
| BAV (with risk factors) | 5.0 cm |
Online Resources¶
- parameterz.com - Comprehensive Z-score calculator
- zscore.chboston.org - Boston Children's Hospital
- PHN Calculator - Integrated in Syngo, Tomtec
- ParameterZ mobile app - iOS/Android available
Always use standardized measurement technique and document reference equations used Z-scores enable growth-independent serial comparison