ECHOES-CHD

At the Montreal Children’s Hospital, we are embarking on an important study to better understand how newborns with congenital heart defects (CHD - abnormal heart anatomy at birth) adjust to life outside the womb. This transition is crucial as it involves important changes in how blood flows occur through the heart and lungs once the baby is disconnected from the mother and the placenta. For infants with heart defects, these changes can complicate their already vulnerable condition, potentially leading to brain injuries and developmental issues. 

Our recent investigations have shown that specific patterns in blood flow can severely affect how blood reaches the brain. To delve deeper, we have gathered a group of newborns with heart defect immediately after birth and followed them for their first week after birth using daily imaging of their heart with ultrasound ("echocardiogram"). We will be analyzing these echocardiograms with advanced imaging techniques such as 3D echocardiography reconstruction and speckle tracking (a method to track the motion of the heart during its contraction and relaxation). These technologies allow us to visualize and quantify the heart's  function with unprecedented detail, enabling a precise assessment of how the heart muscle moves and pumps blood. This might reveal subtle and important abnormalities that conventional scans cannot detect, and how this occurs during the first week after birth, while these infants are experiencing an important transition. 

We have collected comprehensive data on 62 newborns with heart defect, including both 2D and 3D echocardiography-derived images/clips ("videos"). This dataset now must be analyzed using these advanced techniques, which requires resources, expertise and time. This will help us understand the trajectory of the underlying heart function in these newborns and to assess the impact of this critical transition after birth during which disturbances (previously not studies) may affect how important organs are getting nourished in blood and oxygen. 

By analyzing this detailed data, our goal is to pinpoint how these heart defects affect newborns in their first week of life, aiming to improve how we manage and treat these vulnerable patients. Our findings could lead to interventions that are tailored specifically to their needs right after birth, potentially improving their chances of a healthier life. Insights from this study will also guide future research and interventions aimed at preventing complications in newborns with CHD, supported by partnerships with major health foundations.

Rationale: Newborns with a congenital heart defect (CHD) undergo the usual post-natal adaptation with a drop in pulmonary vascular resistance (PVR) and an abrupt increase in systemic vascular resistance (SVR) upon placental disconnection. This transition may be accompanied by altered systemic/pulmonary blood flow due to the presence of shunts and adverse underlying cardiac performance, which may lead to compromised cerebral blood flow (CBF). Vulnerabilities during the early cardiovascular transition elevate the risk of brain injuries, potentially contributing to long-term neurodevelopmental challenges1, 2. Newborns with CHD have signs of brain injury prior to surgical correction or palliation 3-6. Decreased preoperative CBF has been described in the CHD population and has been associated with increased incidence of acquired brain injuries and cerebral dysmaturation7, 8. It remains unclear how the underlying cardiac performance differs based on the type of cardiac lesion during this postnatal transitional period 9-11. 

We recently analyzed a cohort of neonates with CHD in a study that assessed Doppler ultrasound profiles of CBF relative to their underlying cardiac physiology in the first week of life 12. We observed that infants exhibiting retrograde flow in the post-ductal arch on the final day of monitoring—a sign of systemic steal into the pulmonary circulation—also demonstrated a marked increase in resistive index of the anterior cerebral artery (ACA), indicating heightened resistance to CBF. Preliminary findings (unpublished, poster 1675766 at PAS 2024) from 34 infants in this cohort who underwent both ACA Doppler and near infrared spectroscopy (NIRS) monitoring, revealed a correlation between cerebral saturation (Csat), an indirect measure of cerebral perfusion, and simultaneous Doppler measurements. Additionally, preliminary data on 49 newborns with CHD and NIRS monitoring showed that retrograde post-ductal aortic flow was linked to reduced CSat, increased cerebral oxygen extraction compared to pre-ductal systemic saturation, and lowered renal saturation in the first week of life (unpublished, poster 1678552 at PAS 2024). These observations suggest that in the pre-interventional and immediate postnatal period, infants with CHD experience flow disturbances detectable by ultrasound and NIRS, influenced by persistent shunts facilitating a steal effect from the systemic to the pulmonary circulation. However, it remains unclear whether changes in underlying cardiac performance contribute to these phenomena, or if specific cardiac performance profiles could potentially modulate these flow parameters as effect modifiers to prevent organ hypoperfusion in the future. 

New echocardiography techniques, such as speckle tracking (STE) and 3D-echocardiography allow the assessment of deformation of the global heart and its circumscribed segments, as well as, cardiac volumes, possibly uncovering subtle performance abnormalities previously undetectable by conventional imaging (Figure). Strain rate by STE correlates with LV peak elastance, a load-independent parameter of systolic function, derived from cardiac catheterization on an animal model 13. This was validated in a CHD pediatric population by catheterization13. Circumferential strain by echocardiography in the adolescent single ventricle population was found to be associated with transplant-free survival and to be more discriminative than clinical assessment 14. Another value of STE is the correlation between 2D-echocardiography longitudinal strain and ejection fraction by magnetic resonance imaging in the single ventricle population15. Hence, there is growing evidence outlining the usefulness of STE analysis of cardiac function in the CHD population 16. However, there is a need for high quality data on the evolution of cardiac performance once PVR drops in the neonatal CHD population. The use of STE and 3D echocardiography will allow refinement of our understanding of the impact of CHD physiologies on cardiac performance. This approach will uncover performance anomalies previously undetected by conventional echocardiographic tools.