Cardiac Biometry

Dr. Omneya Nagy ElmakhzangySpecial Fetal Care Unit Ain Shams University

• Current practice guidelines for fetal echocardiography are largely based on a qualitative assessment of heart structures using standardized procedures that may include anatomic measurements for suspected growth problems.

Sklansky M 2011

Statistical methods for determing normal cardiac parameters

Percentiles

• A percentile (or a centile) is a measure used in statistics indicating the value below which a given percentage of observations in a group of observations fall

Z-score

• A Z-Score is a statistical measurement of a score's relationship to the mean in a group of scores. A Z-score of 0 means the score is the same as the mean. A Z-score can also be positive or negative, indicating whether it is above or below the mean and by how many standard deviations.

Percentile or z-score?

• From a practical perspective, it is much easier to interpret an aortic valve diameter that is2.5 standard deviations (SDs) below the mean as opposed to simply knowing that measurement is less than the 5th percentile for somatic size or MA.

Normalization according to what?

• In fetal life, centiles are usually normalized to gestational age. However, as the size of the fetus can vary hugely with a several-fold difference by late pregnancy.

• Interpretation of the size of the various cardiac structures requires normalization against some parameter of fetal size.(BPD, FL )

Components of Cardiac Biometry .How to measure ? And How to

interpret?

Aortic and pulmonary valve annulus

• When? During ventricular systole • Where ? Just below the level of the cusps of

the valve• Normal: Aortic valve is equal to or slightly

smaller than pulmonary valve

Long-axis view of the leftventricle showing the aortic valve

Short-axis view, showing the pulmonary valve

Aortic Valve Pulmonary valve

Tricuspid and Mitral valve annulus

• When ? During ventricular Diastole• Where? Just below the level of the cusps• Normal : Mitral valve is equal to or slightly

smaller than tricuspid valve

Right and left ventricular length

• Should be equal . The length is measured above levels of the cusps

•

Cardiothoracic circumference ratio

• Measured in the standard 4 chamber view • The CT circumference ratio should be always

less then 0.5 throughout gestation. It slowly increased through gestation

• ~ 11 weeks: 0.38• ~ 17-20 weeks: 0.45• term: 0.5

Aortic arch and isthmus diameter

Main pulmonary artery and ductus arteriosus measurements

End-diastolic ventricular diameter

• Where? just inferior to the atrioventricular valve leaflets

Thickness of the ventricular free walls and interventricular

septum• Where? just inferior to the atrioventricular

valves.

• Additional measurements if warranted, including:

• ο Systolic dimensions of the ventricles;• ο Transverse dimensions of the atria; and• ο Diameters of branch pulmonary arteries.

Determining the standard Deviation (z-score)

The Lee. et al study (2009)

• A retrospective cross-sectional study of 2735 fetuses was performed for standard biometry (biparietal diameter (BPD) and femoral diaphysis length (FDL)) and an assessment of menstrual age (MA).

• The goal :The main goal was to develop new z-score reference ranges for common fetal echocardiographic measurements

Parameter Slope Intercept

Correlation coefficient

Femoral diaphysis lengthAortic valve end-systolic diameter 0.0054 0.239 0.904Pulmonary valve end-systolic diameter 0.0103 0.150 0.994Left ventricular end-diastolic diameter 0.0135 0.395 0.991Right ventricular end-diastolic diameter 0.0138 0.466 0.952End-diastolic cardiac circumference 0.145 0.700 0.990

Menstrual ageAortic valve end-systolic diameter 0.0165 0.064 0.948Pulmonary valve end-systolic diameter 0.0253 −0.048 0.990Left ventricular end-diastolic diameter 0.0394 0.059 0.993Right ventricular end-diastolic diameter 0.0394 0.132 0.962End-diastolic cardiac circumference 0.341 −1.456 0.992

Biparietal diameterAortic valve end-systolic diameter 0.0063 0.111 0.940Pulmonary valve end-systolic diameter 0.0091 0.0338 0.988Left ventricular end-diastolic diameter 0.0125 0.248 0.974Right ventricular end-diastolic diameter 0.0147 0.198 0.988End-diastolic cardiac circumference 0.118 −0.178 0.994

Forget about tables• In summary : 2 tables were developed

• 1-Linear models for prediction of fetal cardiac dimensions based on femoral diaphysis length, menstrual age and biparietal diameter

• 2-Linear models for predicted standard deviations of fetal cardiac dimensions based on femoral diaphysis length, menstrual age and biparietal diameter

• Somehow put these two together you get an equation to calculate the z-score

• Once u got your z-score you now can know the standard deviation of your measurement from the mean value for this measurement .

• Clinical example for z-score calculation• Femoral diaphysis length (FDL) = 30 mm• Aortic valve (Ao) diameter = 3.5 mm

• From Table 1• Predicted Ao diameter = (0.119 × 30) − 0.577 = 3.0 mm

• From Table 2• Predicted SD = (0.0054 × 30) + 0.239 = 0.4 mm• z =Aoobserved − Aopredicted = 3.5 − 3.0 = 1.25 Predicted SD 0.4• The aortic diameter z-score is +1.25 SDs above the predicted mean for this femur length and therefore is within the normal range.

Do I need to do this??

• Luckily “NO”• All what you need is to get your

measurements and a software on your machine will do the math.