From the Research
The normal diameter of the ventricular outflow tract in neonates ranges from approximately 5 to 8 mm for the right ventricular outflow tract (RVOT) and 5 to 7 mm for the left ventricular outflow tract (LVOT), with some variation based on the neonate's size, weight, and gestational age. These measurements are typically obtained using echocardiography, which is the preferred imaging modality for cardiac assessment in neonates. The RVOT connects the right ventricle to the pulmonary artery, while the LVOT connects the left ventricle to the aorta. These measurements are clinically important for diagnosing conditions such as pulmonary stenosis, aortic stenosis, or other congenital heart defects that may affect the outflow tracts. When evaluating a neonate's cardiac function, it's essential to consider that these values should be interpreted in the context of the patient's body surface area (BSA) or weight, as there is a direct correlation between body size and cardiac dimensions. Z-scores, which represent how many standard deviations a measurement is from the mean for a given BSA, are often used to determine if an outflow tract dimension is normal, as seen in studies such as 1. Key factors to consider when measuring the ventricular outflow tract diameter include:
- The location of measurement, with the sinotubular junction (STJ) and aortic valve (AV) hinges being common sites 2, 3
- The method of measurement, with 2D echocardiography being a commonly used technique 2, 1
- The patient's size and weight, as these can affect the normal range of ventricular outflow tract diameters 4 It's also important to note that the reproducibility and accuracy of left ventricular output (LVO) quantification by echo are better when aortic diameter is measured at the AV, as shown in a study published in 2022 1. Overall, when evaluating the ventricular outflow tract in neonates, it's crucial to consider these factors and use the most recent and highest-quality evidence to guide clinical decision-making.