Average LVOT Diameter in Adults
The average left ventricular outflow tract (LVOT) diameter in adults is approximately 20-22 mm, with a normal range of 17-27 mm depending on body size and sex.
Normal Reference Values from Guidelines
The most authoritative reference values come from the 2015 ASE/EACVI chamber quantification guidelines, which provide specific measurements for the right ventricular outflow tract (RVOT) that can inform LVOT assessment 1:
- RVOT PLAX diameter: 25 ± 2.5 mm (normal range: 20-30 mm) 1
- RVOT proximal diameter: 28 ± 3.5 mm (normal range: 21-35 mm) 1
- RVOT distal diameter: 22 ± 2.5 mm (normal range: 17-27 mm) 1
While these are RVOT measurements, the LVOT diameter typically falls within a similar range of 20-25 mm for average-sized adults 2.
Body Size Adjustment
LVOT diameter correlates linearly with body surface area (BSA), independent of sex 3:
- The relationship follows the equation: LVOTd = 5.7 × BSA + 12.1 3
- This correlation (r = 0.55, P < 0.0001) allows for size-adjusted reference values 3
- For an average adult with BSA of 1.7-2.0 m², the expected LVOT diameter ranges from 21.8 to 23.5 mm 3
Clinical Measurement Considerations
Measurement Technique
The European Society of Cardiology recommends measuring LVOT diameter in a zoomed parasternal long-axis view in mid-systole from the inner edge of the septal endocardium to the anterior mitral leaflet, parallel to the aortic valve plane 2. The measurement should be taken 0.5-1.0 cm proximal to the aortic valve annulus 2.
Shape Heterogeneity
The LVOT is elliptical rather than circular in most patients, which can lead to underestimation of the true area when assuming a circular geometry 1, 4, 5:
- The proximal LVOT (left ventricular side) is more elliptical 5
- The distal LVOT (aortic side) is more circular 5
- Planimetric LVOT area is significantly larger than area calculated from diameter measurements (4.7 ± 1.0 cm² vs 3.3 ± 0.7 cm², P < 0.0001) 4
Measurement Accuracy
Transthoracic echocardiography (TTE) measurements correlate well with transesophageal echocardiography (TEE) 3, 6:
- TTE vs TEE: 23 ± 2 mm vs 23 ± 2 mm (P = 0.26, r = 0.95) 3
- In aortic stenosis patients: 24 ± 2 mm vs 24 ± 3 mm (P = 0.15, r = 0.92) 3
- Inter-observer variability: 4.8 ± 4.1% for TTE vs 4.2 ± 3.1% for TEE (P = 0.4) 6
Clinical Significance
Small LVOT Diameter Threshold
An LVOT diameter ≤17 mm is considered abnormally small and increases risk for LVOT obstruction 2, 7:
- Indexed LVOT diameter ≤2.5 cm/m² is associated with higher risk of LVOT obstruction (OR 5.41,95% CI: 1.15-25.39) 7
- In transcatheter procedures, neo-LVOT area <2 cm² is a risk factor for obstruction 2
Measurement Error Impact
LVOT diameter is squared in the continuity equation, making it the greatest potential source of error in aortic valve area calculations 1, 2: