How to go about normal values for echocardiographic measurements?

How to go about normal values for echocardiographic measurements?

Normal values for echocardiographic measurements will vary with age, body surface area and the population being evaluated. It is almost impossible to memorize the normal values for the numerous echocardiographic measurements in use. Various national guidelines have provided posters and pocket guides for use whenever needed. EchoCalc is a mobile application from the British Society of Echocardiography which is available for download from the Apple App Store and GooglePlay [1].

There are a few useful tips for visual assessment during routine echocardiography. Most of the chamber sizes are checked in diastole except the left atrial diameter which is measured in systole. Of course, left ventricular dimensions are measured in both diastole and systole. In general, left atrial and aortic diameters are roughly equal when seen from the parasternal long axis view. So it is easy to make out enlargements, though this does not apply when both are dilated!

The size of a ventricular septal defect (VSD) is compared to the diameter of the aortic annulus. If it is more than half of the aortic annulus, it is considered as a large VSD. There is another classification into small, medium and large depending on VSD size being less than one third, one third to two thirds and more than two thirds of aortic size.

The Normal Reference Ranges for Echocardiography (NORRE) study enrolled 734 healthy volunteers from 22 institutions across Europe, USA, UAE and Japan [2]. Free full text is available online from the European Heart Journal Cardiovasc Imaging website. Normal reference values from the British Society of Echocardiography guidelines is also available online with free full text access from PubMed Central [1].

EchoNoRMAL Study was another project which used data from 22,404 adults [3]. They have given normal ranges for different regions like European, East Asian and South Asian. Full text of that article is also open access.

While assessing right sided chambers, the effect of respiration and hydration status should be noted. Sizes of right sided chambers and Doppler velocities will be lower in a hypovolemic state. Normal inferior vena cava collapses in inspiration, while absence of inspiratory collapse is a feature of right heart congestion.

The significant level of gradient across the tricuspid valve will be just 2 mm Hg for tricuspid stenosis while it is 5 mm Hg for mitral stenosis. This is because tricuspid valve has a larger area and is in the low pressure pulmonary circulation. Gradients will be higher across normal valves in the presence of an abnormally increased flow like left to right shunts and hyperdynamic circulatory states. This is applicable to diagnosis of associated pulmonary stenosis in atrial septal defect and aortic stenosis in aortic regurgitation. Flow rate is also important while assessing severity of stenosis. In a low flow state, even severe stenosis can have low gradient. The classical example is a low flow low gradient severe aortic stenosis.

In pediatric age group, measurements should always be compared with a nomogram. For example, coronary diameters in a suspected case of Kawasaki disease is very important in diagnosis and treatment. Another measurement is pulmonary artery size in cyanotic congenital heart disease with low pulmonary blood flow. In all these situations, z-score is important. Z-score is measured in terms of standard deviations from the mean. Simply put, it is the number of standard deviations by which the observed value differs from the population mean.

References

1. Harkness A, Ring L, Augustine DX, Oxborough D, Robinson S, Sharma V; Education Committee of the British Society of Echocardiography. Normal reference intervals for cardiac dimensions and function for use in echocardiographic practice: a guideline from the British Society of Echocardiography. Echo Res Pract. 2020 Feb 24;7(1):G1-G18. doi: 10.1530/ERP-19-0050. Erratum in: Echo Res Pract. 2020 Mar 20;7(1):X1. PMID: 32105051; PMCID: PMC7040881.
2. Kou S, Caballero L, Dulgheru R, Voilliot D, De Sousa C, Kacharava G, Athanassopoulos GD, Barone D, Baroni M, Cardim N, Gomez De Diego JJ, Hagendorff A, Henri C, Hristova K, Lopez T, Magne J, De La Morena G, Popescu BA, Penicka M, Ozyigit T, Rodrigo Carbonero JD, Salustri A, Van De Veire N, Von Bardeleben RS, Vinereanu D, Voigt JU, Zamorano JL, Donal E, Lang RM, Badano LP, Lancellotti P. Echocardiographic reference ranges for normal cardiac chamber size: results from the NORRE study. Eur Heart J Cardiovasc Imaging. 2014 Jun;15(6):680-90. doi: 10.1093/ehjci/jet284. Epub 2014 Jan 21. PMID: 24451180; PMCID: PMC4402333.
3. Echocardiographic Normal Ranges Meta-Analysis of the Left Heart Collaboration. Ethnic-Specific Normative Reference Values for Echocardiographic LA and LV Size, LV Mass, and Systolic Function: The EchoNoRMAL Study. JACC Cardiovasc Imaging. 2015 Jun;8(6):656-65. doi: 10.1016/j.jcmg.2015.02.014. Epub 2015 May 14. PMID: 25981507.