How should left ventricular dimensions be measured and indexed to body mass index (BMI)?

How to Measure LV Dimensions by BMI

Left ventricular dimensions should NOT be indexed to BMI directly; instead, measure LV mass and dimensions using standard echocardiographic techniques and index to body surface area (BSA), with consideration for indexing to height^2.7 in overweight and obese patients to avoid misclassification of left ventricular hypertrophy. 1

Standard Measurement Approach

The 2015 ASE/EACVI guidelines establish the definitive framework for LV quantification 1:

Linear Measurements

• Measure LV internal dimensions in the parasternal long-axis view at end-diastole
• Position measurements perpendicular to the LV long axis at or immediately below the mitral valve leaflet tips
• Use 2D-guided measurements rather than blind M-mode to avoid oblique sections
• Measure interventricular septum (IVS), LV internal diameter (LVID), and posterior wall thickness (PWT)

LV Mass Calculation

For normally shaped ventricles, use the cube formula:

• LV mass = 0.8 × 1.04 × [(IVS + LVID + PWT)³ − LVID³] + 0.6 g 1

For abnormally shaped ventricles or asymmetric hypertrophy, 2D or 3D methods are superior as they accommodate regional variations 1, 2

Critical Indexing Strategy

This is where BMI becomes relevant—not for direct indexing, but for choosing the appropriate normalization method:

Standard Indexing (BSA)

Index LV mass to BSA for most patients 1:

• Upper limits of normal (linear method): 95 g/m² (women), 115 g/m² (men)
• Upper limits of normal (2D method): 88 g/m² (women), 102 g/m² (men)

Alternative Indexing for Overweight/Obese Patients

The critical caveat: BSA indexing underestimates LVH prevalence in overweight and obese individuals 3, 4.

For patients with BMI ≥25 kg/m², consider indexing to height^2.7 3, 4:

• Upper limits: 49 g/m^2.7 (men), 45 g/m^2.7 (women) 1
• This method better identifies LVH and has superior prognostic value in obesity 4

Research demonstrates that in obese hypertensives, LVH prevalence is 69.7% when indexed to height^2.7 versus only 53.9% when indexed to BSA 4. The opposite pattern occurs in lean patients (19.8% vs 34.3%), where BSA indexing may overestimate LVH 4.

Geometric Pattern Assessment

Calculate relative wall thickness (RWT) regardless of body habitus 1:

• RWT = (2 × posterior wall thickness) / LV internal diameter at end-diastole
• RWT >0.42 = concentric pattern
• RWT ≤0.42 = eccentric pattern

This allows categorization into:

• Normal geometry (normal LV mass, RWT ≤0.42)
• Concentric remodeling (normal LV mass, RWT >0.42)
• Concentric hypertrophy (increased LV mass, RWT >0.42)
• Eccentric hypertrophy (increased LV mass, RWT ≤0.42)

Common Pitfalls

1. Never index LV dimensions directly to BMI—this is not validated and will produce erroneous results
2. Patients at extremes of height or BSA may be misclassified; consider both indexing methods 1
3. In obese patients with BMI ≥30, using BSA alone risks missing significant LVH 4, 5
4. 3D echocardiography provides the most accurate LV mass in asymmetric hypertrophy but lacks established reference values 1, 2

Practical Algorithm

1. Measure standard LV dimensions (IVS, LVID, PWT) at end-diastole
2. Calculate LV mass using appropriate formula
3. If BMI <25: Index to BSA
4. If BMI ≥25: Index to both BSA AND height^2.7, report both values
5. Calculate RWT to determine geometric pattern
6. Consider 3D echo if ventricle is asymmetrically hypertrophied

The Body Roundness Index (BRI) shows promise for identifying LVH risk in hypertensive patients 6, 5, but this is for risk stratification, not for indexing LV measurements themselves.