When done during pregnancy, an echocardiogram — a noninvasive measurement of heart function that uses sound waves — may help doctors predict pulmonary hypertension in newborns, a study in China suggests.
An echocardiogram can show how well the heart’s right ventricle, one of its bottom pumping chambers, will push blood through to the lungs without becoming too stressed. According to researchers, prenatal echocardiogram results strongly predicted the likelihood of a baby being diagnosed with persistent pulmonary hypertension of the newborn (PPHN) after birth.
The study, “Perinatal changes of right ventricle-pulmonary artery coupling and its value in predicting persistent pulmonary hypertension of the newborn,” was published in the journal Clinical Physiology and Functional Imaging.
Before birth, a baby’s lungs are filled with amniotic fluid, the liquid that surrounds the fetus in the womb. Circulating blood bypasses the lungs by flowing through special passageways, and gas exchange occurs across the placenta, which also nourishes the fetus with nutrients and carries away wastes.
But within minutes after birth, some major changes occur. The baby’s first few breaths clear the amniotic fluid from the lungs and allow them to fill with oxygen. The special passageways close and pulmonary vascular resistance goes down. This means that the blood vessels of the lungs need to relax to allow the blood to flow through.
Sometimes, pulmonary vascular resistance remains high, and the right ventricle needs to work harder to be able to push the blood through the pulmonary artery that supplies the lungs.
Over time, when this occurs, the right ventricle becomes weaker, and the blood gets shunted from the right to the left side of the heart. When this happens in newborns, it is called persistent pulmonary hypertension or PPHN.
An echocardiogram is a scan that looks at the structure of the heart and the surrounding blood vessels, and how blood flows through them. It uses a transducer, similar to a microphone, to send out sound waves.
Predicting PPHN in newborns
While an echocardiogram can help diagnose PPHN, it is unclear whether it could help predict pulmonary hypertension in newborns before birth.
A team of researchers in China wondered whether there is any measurement in an echocardiogram that could help doctors predict PPHN.
“Right ventricle-pulmonary artery (RV-PA) coupling is an independent predictor of outcome in pulmonary arterial hypertension in adults,” they wrote.
RV-PA coupling refers to how well the right ventricle’s ability to contract matches its afterload, which typically includes the pressure it must work against while it pushes blood through to the lungs. And it can be measured on an echocardiogram.
To find out whether RV-PA coupling also may predict PPHN before or shortly after birth, the researchers drew on data from 1,196 babies who had an echocardiogram taken as part of a screening for heart defects. Their mothers ranged in age from 24 to 43 years.
“To the best of our knowledge, this is the first report on the perinatal changes in RV‐PA coupling and its predictive value for PPHN,” the researchers wrote.
The screening was done three times: first during the second trimester, at 24–27 weeks of gestation, and then in the third trimester, at 34–37 weeks. The third screen was done within 14 days after birth.
To measure RV-PA coupling, the researchers calculated the ratio of tricuspid annular plane systolic excursion (TAPSE), a measure of right ventricle function, divided by the mean pulmonary artery pressure (mPAP).
Six fetuses received a diagnosis of PPHN, which makes nearly five cases per 1,000 live births.
In healthy fetuses, TAPSE increased but mPAP decreased from the second to the third trimester, and then after birth. As a result, RV‐PA coupling also increased from the second trimester up to after birth (from 0.12 to 0.23 mm/mmHg or millimeters per millimeter of mercury).
RV‐PA coupling correlated positively with gestational age, meaning that the greater the RV‐PA coupling, the farther along the pregnancy went.
In fetuses with PPHN, both TAPSE and MPAP decreased from the second to the third trimester. Then, they increased after birth.
When their ratio was calculated, it was found that it decreased from the second trimester up to after birth (from 0.18 to 0.17 mm/mmHg). A reduced RV‐PA coupling means that the right ventricle continues to contract even if against too high an afterload.
To determine whether RV‐PA coupling may tell how likely pulmonary hypertension is to occur in newborns, the researchers calculated a measure called area under the curve. They found that it predicted PPHN more accurately during the second trimester than during the third (0.989 vs. 0.536).
The value above which babies were more likely to have PPHN was 0.16 mm/mmHg, with a sensitivity of 100%, a specificity of 96.36% and an accuracy of 97.73%. Sensitivity refers to a test’s ability to correctly identify people with a certain condition, whereas specificity is the ability to identify those without the condition.
This suggests RV-PA coupling as “a strong predictor of PPHN,” the team wrote.
The researchers noted one limitation was the small number of babies with PPHN in the study.
However, they concluded that “assessment of RV‐PA coupling during perinatal period by using TAPSE/MPAP ratio obtained by means of conventional echocardiography may give us a new idea about the development state of pulmonary vascular bed in fetuses.”