Prenatal Diagnosis of Hypoplastic Left Heart Syndrome: Can We Optimize Outcomes?

The capacity to diagnose congenital heart disease (CHD) through echocardiography before birth has revolutionized the practice of congenital heart care. The term “birth defect” of the heart is now a misnomer, as “birth” is but an arbitrary point in time in the temporal spectrum of care for these conditions. Fetal diagnosis is currently the most common means for first entry into the system of care of CHD. In the past, it was the acute presentation of a symptomatic newborn or detection of a murmur that would prompt inquiry and diagnosis of a cardiac structural abnormality. Today, screening obstetric ultrasound and fetal echocardiography as early as the first trimester of pregnancy are common and allow a wealth of benefits. Counseling and education of families can take place, allowing both physical and psychological preparation for the delivery and future care needs of a child with CHD. Knowledge of the presence of a heart defect allows the creation of a smooth transition from prenatal to postnatal life when the cardiovascular system is at risk. Identification of a congenital heart defect on fetal echocardiography provides the opportunity to avoid deleterious manifestations at birth such as severe hypoxemia or cardiovascular collapse, through the immediate initiation of management. Furthermore, prenatal diagnosis provides the opportunity to contemplate fetal treatment and to entertain strategies that may either alter the natural history of the anomaly and modify cardiac structure or perhaps improve the postnatal outcome, either short or long term.

In complex CHD, such as hypoplastic left heart syndrome (HLHS), prenatal diagnosis specifically enables practitioners to provide a seamless transition to extrauterine life by initiating prostaglandin medication at birth to maintain patency of the ductus arteriosus, thus avoiding instability. Numerous studies have highlighted the benefit of prenatal diagnosis on postnatal morbidity and mortality for HLHS. In the current issue of the Journal of the American Society of Echocardiography , Markkanen et al. demonstrate the benefits of prenatal diagnosis on postnatal right ventricular (RV) myocardial performance. They retrospectively reviewed a consecutive cohort of 66 infants with HLHS born in Finland between 2003 and 2010, 25 of whom were prenatally diagnosed. Prenatally diagnosed subjects were all delivered at Helsinki University Hospital and were not routinely intubated for mechanical ventilation or administered inotropic support. In contrast, infants who were postnatally diagnosed were transported to Helsinki University Hospital after diagnosis elsewhere and then stabilized for surgical intervention. Study parameters included lowest arterial pH; highest lactate, alanine aminotransferase, and creatinine levels; and early mortality to 30 days after the first stage of surgical palliation, the Norwood procedure. RV myocardial performance was evaluated by calculation of the postnatal global and segmental RV fractional area change (FAC), strain rate, and myocardial velocity from an apical four-chamber view using Velocity Vector Imaging (syngo USWP 3.0; Siemens Healthcare, Erlangen, Germany). The investigators found that prenatally diagnosed infants had better cardiac function before surgery compared with postnatally diagnosed infants (RV FAC 28% vs 21%), although there was no difference in RV FAC between surgical survivors and nonsurvivors. Infants diagnosed prenatally also had less acidosis and better end-organ function as determined by lower alanine aminotransferase and creatinine measures.

The Delivery Process for Complex Congenital Heart Disease

This study has a number of important implications. The authors found that infants prenatally diagnosed with HLHS are in a much better state as they embark upon a series of complex operations, but the question is why. Infants in this study were delivered with relatively strict controls. In Finland, all fetuses with prenatal diagnoses of HLHS were delivered at Helsinki University Hospital to avoid postnatal transportation from a different center, which may be hundreds of miles away. Control of the management decisions before, during, and immediately after delivery was possible, thereby reducing practice variability. Unfortunately, at many centers around the world, even with prenatal diagnoses of critical CHD, neonates are often transported from the birth center to a different site for congenital heart care via either ground or air ambulance. To stabilize for transport, neonates with underlying HLHS are often intubated and undergo mechanical ventilation. This practice places infants at risk for overventilation or underventilation. Those who are underventilated may incur significant lung atelectasis, furthering hypoxemia, whereas those who are overventilated may develop pulmonary overcirculation as a consequence of lowered pulmonary vascular resistance, ultimately leading to insufficient systemic blood flow, hypotension, and acidosis. Indeed, experience shows that it is not uncommon after a period of transport for an infant to be identified upon intensive care unit arrival to be significantly acidotic, often requiring resuscitation. Such ongoing acidosis may be an unavoidable consequence of spending a period of time in a moving vehicle or air ambulance, when there is less than optimal capacity for a high level of scrutiny. Markkanen et al. ‘s study suggests that neonatal transport may be a source for myocardial or end-organ dysfunction in patients with HLHS.

The concept of avoiding neonatal transport and optimizing care for both mother and fetus when carrying a fetus with CHD has led many centers to consider integration of obstetric and delivery services into a single care model for the fetus, mother, and newborn when there is a prenatal diagnosis of CHD. Ideally, a fetus with complex CHD should be delivered within an obstetric center that houses, or is adjacent to, a specialist congenital heart center. University hospitals or large multidepartmental medical centers often fulfill this criterion. Close collaboration across the disciplines of obstetrics and pediatric cardiology is mandatory in this scenario and is one of the hallmarks of the most successful programs. At our own institution, mothers carrying fetuses with prenatal diagnoses of complex CHD likely to require postnatal surgical intervention in the neonatal period are cared for by a combined obstetric and fetal cardiology team and offered delivery at our Special Delivery Unit, an obstetric service within a children’s hospital. The unit is specifically dedicated solely for delivery of mothers carrying fetuses with congenital anomalies. Building such a unit and all of the support personnel necessary allows the development of a single, unified team approach with specific protocols and clinical pathways targeted toward optimizing care for this unique mother-fetus dyad. This model has been replicated now at a number of centers around North America.

Integration of joint prenatal and delivery services between maternal fetal medicine specialists and fetal cardiologists allows the best opportunity for improved outcomes. When clinical care goals are shared and health care team members are geographically juxtaposed in one unit, common objectives can be more easily achieved. Familiarity with the nuances of obstetric care and the intricacies of complex congenital heart conditions by both sets of experts allows mutual understanding and optimal care planning. This collaboration has resulted in an improved understanding of what is important in the prenatal assessment of a fetus with HLHS. For example, through a joint clinical practice, we have been able to identify prenatal risk factors for HLHS, such as prematurity, underlying extracardiac congenital anomaly, underlying genetic syndrome or chromosomal abnormality, severe tricuspid regurgitation, restrictive or intact atrial septum, or diminished RV function. Current first-stage Norwood procedure surgical survival rates for prenatally diagnosed fetuses with HLHS at our center, in the absence of these risk factors, are as high as 92%. Conversely, survival for high-risk fetuses with any of the aforementioned risk factors ranges from only 20% to 50%. Risk factors are now scrupulously investigated during comprehensive obstetric and fetal cardiologic evaluations, and families are counseled accordingly. Greater focus on modifying prenatal risk factors when possible, or on designing risk-specific postnatal strategies, may provide for improved outcomes in this group. A joint obstetric and fetal cardiology team also allows investigational research in novel areas of care. One such example in our group is the interest in the psychological impact of prenatal diagnosis of CHD on maternal stress and the potential negative effects on fetal physiology through elevation in maternal cortisol levels. A single team, interdisciplinary collaboration that focuses its energies on answering complex maternal-fetal questions, is intuitively an ideal scenario and one that we think contributes to overall improved patient satisfaction and neonatal outcomes.

Prenatal diagnosis also ensures that the most appropriate team to care for a child with underlying CHD is assembled for the delivery. Knowledge of the presence of CHD allows either subtle, or at times extensively orchestrated, delivery room actions, which accrue benefit to newborns. Actions such as closer monitoring and staffing by expert nurses and neonatologists who are comfortable in the management necessary, and in the identification of trouble when it arises, can be quite helpful. For example, newborns with transposition of the great arteries require careful evaluation as to the potential need for mixing and creation of an interatrial communication through balloon atrial septostomy. The sooner a restrictive foramen ovale in a severely cyanosed infant with transposition is identified, the faster an atrial opening can be created, oxygen delivery improved, and end-organ function preserved. Performing a balloon atrial septostomy within minutes after birth in those with restrictive foramen ovale may diminish the hypoxemic time and consequently the likelihood of neonatal brain injury in the form of periventricular leukomalacia, a common finding noted in neonates with transposition of the great vessels. Furthermore, there are some forms of CHD for which neonates can be predicted, on the basis of prenatal assessment, to do very poorly as soon as separated from maternal support via placental circulation. Examples include fetuses with HLHS and intact atrial septum in which there is severe obstruction to pulmonary venous egress into the left atrium with resultant profound hypoxemia, or fetuses with complete heart block in need of urgent postnatal pacing. Such conditions require immediate action at birth if there is to be any hope of a successful outcome. Through an organizational mechanism we refer to as an “IMPACT procedure,” one can offer immediate postpartum access to cardiac therapy (IMPACT) by caesarian section delivery directly in a cardiac venue, either an operating room or a catheterization laboratory. A team of specialists, including fetal cardiologists, echocardiographers, cardiac anesthesiologists, and either cardiac catheterization specialists or cardiac surgeons, attends to the delivery providing whatever urgent service is necessary at the earliest moments of life.

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Jun 1, 2018 | Posted by in CARDIOLOGY | Comments Off on Prenatal Diagnosis of Hypoplastic Left Heart Syndrome: Can We Optimize Outcomes?

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