How does aortic root diameter vary with age?

Aortic Root Diameter Variation with Age

The aortic root diameter increases with age in both men and women, with an approximate increase of 0.12 to 0.29 mm per year, though this relationship is stronger in younger individuals and weakens after age 40. 1

Normal Aortic Root Dimensions and Age-Related Changes

Age-Related Changes

• In adults, aortic root diameter increases with age in both genders:
  • Each 10-year increase in age is associated with an increase of 0.89 mm in men and 0.68 mm in women 1
  • The correlation between aortic root diameter and body size is:
    • Strong in children (r = 0.93)
    • Moderate in adults younger than 40 years (r = 0.71)
    • Weak in adults older than 40 years (r = 0.40) 2

Gender Differences

• Men have larger aortic root diameters than women at any given age (approximately 2.7 mm larger when adjusted for BSA and age) 3
• However, when indexed to body surface area (BSA), the dimensions are similar between genders, except for the ascending aorta where women tend to have greater indexed values 4

Normal Reference Values

According to the American College of Cardiology/American Heart Association guidelines, normal adult thoracic aortic diameters at the root level are 5:

• Root (female): 3.50 to 3.72 cm (SD 0.38 cm)
• Root (male): 3.63 to 3.91 cm (SD 0.38 cm)

Predictive Equations for Aortic Root Diameter

The most recent and comprehensive equation for predicting normal aortic root diameter (at the sinuses of Valsalva) is 3:

Expected aortic root size (cm) = 2.423 + (age [years] × 0.009) + (BSA [m²] × 0.461) - (sex [1 = man, 2 = woman] × 0.267)

• Standard error of estimate = 0.261 cm

Alternatively, a height-based equation can be used 3:

• Expected aortic root size (cm) = 1.519 + (age [years] × 0.010) + (height [cm] × 0.010) - (sex [1 = man, 2 = woman] × 0.247)
• Standard error of estimate = 0.215 cm

Age-Specific Nomograms

For different age groups, the European Heart Journal provides these formulas for predicting aortic root diameter at the sinuses of Valsalva 5:

• Children and adolescents (<18 years): 1.02 + (0.98 × BSA)
• Adults 20-39 years: 0.97 + (1.12 × BSA)
• Adults >40 years: 1.92 + (0.74 × BSA)

Clinical Implications

Measurement Considerations

• Measurements should be taken perpendicular to the axis of blood flow
• Include the largest measured aortic diameter (whether at sinuses of Valsalva or ascending aorta)
• Be aware that oblique imaging slices may overestimate the true aortic diameter 5
• Different imaging modalities may yield different measurements:
  • 2D echocardiographic measurements at the sinuses of Valsalva are typically larger than M-mode values 2
  • Using 2D values with M-mode nomograms may falsely diagnose aortic dilatation in 40% of normal children and 19% of normal adults 2

Factors Affecting Aortic Dimensions

Beyond age and gender, other factors influencing aortic root size include:

• Body size (BSA, height, weight) - strongly correlated with aortic dimensions
• Blood pressure - primarily affects the distal aorta 4
• Aortic stiffness - increases with age and should be considered when evaluating aortic diameter changes 4

Z-Score Calculation

For clinical evaluation, calculating the z-score is recommended 5:

• Z-score = (observed aortic root size - expected aortic root size) / 0.261

Surveillance and Management Implications

For patients with aortic root diameters exceeding normal ranges:

• Regular surveillance with appropriate imaging is recommended:
  • Aortic diameter 3.5-4.4 cm: imaging every 12 months
  • Aortic diameter 4.5-5.4 cm: imaging every 6 months
  • Aortic diameter ≥5.5 cm: consider surgical intervention 6

The upper normal limit for indexed aortic diameter at the sinuses of Valsalva is 2.1 cm/m² for both men and women, providing 98% specificity for detecting aortic dilatation 2.