Postoperative Morbidity and Interstage Hemodynamics Following Stage I Palliation in Patients with Turner Syndrome and Hypoplastic Left Heart Syndrome.

BACKGROUND: Turner syndrome (TS) is associated with left-sided cardiac lesions, including hypoplastic left heart syndrome (HLHS). Mortality as high as 80-90% has been reported following stage I single-ventricle palliation (S1P) in patients with TS and HLHS (TS + HLHS). The specific factors that relate to poor outcomes are not well understood. METHODS: This is a single-center, retrospective cohort study that includes 197 patients with HLHS who underwent S1P between 2008 and 2022. The clinical outcomes and interstage hemodynamics of TS + HLHS patients (N = 11) were compared with HLHS without TS (TS-HLHS), (N = 186). RESULTS: Of the 11 TS + HLHS patients, 10 underwent S1P; 4 underwent Glenn and 1 had hemodynamics considered prohibitive for Glenn; only 1 survived to Fontan palliation. Post-S1P mortality was higher in TS + HLHS (60 v 25%, p = 0.017). Following S1P, TS + HLHS had higher rates of postoperative ECMO (70 v 28%, p = 0.006), surgical necrotizing enterocolitis (20 v 3%, p = 0.007), peritoneal drain placement (70 v 31%, p = 0.012), urinary tract infection (30 v 9%, p = 0.035), and ICU readmissions (median 5 v 1, p = 0.035). Interstage hemodynamics demonstrated higher right ventricular end diastolic, (11 v 8mmHg, p = 0.033), mean pulmonary artery (20 v 13mmHg) (p = 0.002), and left atrial pressures (9 v 6mmHg, p = 0.047) in TS + HLHS. CONCLUSION: High mortality rates are described in TS + HLHS patients following S1P. In our cohort, despite most surviving more than 30 days post-S1P, long-term survival remained poor. Interstage catheterization data suggest poor physiologic candidacy for subsequent stages of single-ventricle palliation. Understanding the clinical and hemodynamic factors related to poor outcomes in TS + HLHS will help inform management for this population.

Effects of cohort, genotype, variant, and maternal ß-blocker treatment on foetal heart rate predictors of inherited long QT syndrome.

AIMS: In long QT syndrome (LQTS), primary prevention improves outcome; thus, early identification is key. The most common LQTS phenotype is a foetal heart rate (FHR) < 3rd percentile for gestational age (GA) but the effects of cohort, genotype, variant, and maternal ß-blocker therapy on FHR are unknown. We assessed the influence of these factors on FHR in pregnancies with familial LQTS and developed a FHR/GA threshold for LQTS. METHODS AND RESULTS: In an international cohort of pregnancies in which one parent had LQTS, LQTS genotype, familial variant, and maternal ß-blocker effects on FHR were assessed. We developed a testing algorithm for LQTS using FHR and GA as continuous predictors. Data included 1966 FHRs at 7-42 weeks' GA from 267 pregnancies/164 LQTS families [220 LQTS type 1 (LQT1), 35 LQTS type 2 (LQT2), and 12 LQTS type 3 (LQT3)]. The FHRs were significantly lower in LQT1 and LQT2 but not LQT3 or LQTS negative. The LQT1 variants with non-nonsense and severe function loss (current density or ß-adrenergic response) had lower FHR. Maternal ß-blockers potentiated bradycardia in LQT1 and LQT2 but did not affect FHR in LQTS negative. A FHR/GA threshold predicted LQT1 and LQT2 with 74.9% accuracy, 71% sensitivity, and 81% specificity. CONCLUSION: Genotype, LQT1 variant, and maternal ß-blocker therapy affect FHR. A predictive threshold of FHR/GA significantly improves the accuracy, sensitivity, and specificity for LQT1 and LQT2, above the infant's a priori 50% probability. We speculate this model may be useful in screening for LQTS in perinatal subjects without a known LQTS family history.

Mitral Valve Abnormalities Associated with Single-Ventricle Palliation, Cardiac Death or Transplant in Fetuses with Postnatally Confirmed Coarctation of the Aorta.

Predicting if a fetus with borderline left heart structures and coarctation of the aorta (CoA) will require single ventricle palliation (SVP) is challenging, partly due to the limitations of fetal echocardiography in defining valvar abnormalities. Fetal echocardiographic findings predictive of SVP, particularly in relation to the mitral valve (MV), are not well defined. We performed a retrospective review of fetuses with postnatally confirmed CoA from 2010 to 2020. Fetuses with complex congenital heart disease or unequivocal hypoplastic left heart syndrome were excluded. Data were compared between those who underwent biventricular repair (BVR) versus SVP, cardiac death or orthotopic heart transplant (OHT) to determine differences in fetal echocardiograms. Of 67 fetuses with 131 total echocardiograms, 62 (93%) underwent BVR and 5 (7%) experienced SVP, cardiac death or OHT. Fetuses with confirmed CoA who experienced SVP, cardiac death, or OHT, had fetal MV z-scores that were 2.03 lower, on average, than those who underwent BVR (z-score = - 3.98 vs. - 1.94, 95% CI - 2.93, - 1.13). The incidences of MV anomalies and left to right flow across the foramen ovale were higher in the SVP, cardiac death and OHT group. SVP, cardiac death or OHT in fetuses with confirmed CoA were associated with severe fetal MV hypoplasia, MV anomalies and left to right flow across the foramen ovale. These findings may help guide prenatal counseling about the likelihood of SVP, cardiac death or OHT in fetuses with CoA and borderline left heart structures.

Transient fetal atrioventricular block: A series of four cases and approach to management.

INTRODUCTION: Fetal atrioventricular block (AVB) is a failure of conduction from atria to ventricles. Immune- and nonimmune-mediated forms occur, especially in association with congenital heart disease. Second-degree (2°) AVB may be reversible with dexamethasone and intravenous immunoglobulin in immune-mediated disease. However, once third-degree AVB develops, it is deemed irreversible with need for a pacemaker and risk for cardiomyopathy. Rarely, 2° AVB is a transient, benign phenomenon in the immature conduction system. Few case series of transient AVB have been reported, but a management approach has not been defined. METHODS/RESULTS/CONCLUSION: We report four patients with self-resolving, nonimmune fetal AVB and outline a management strategy.

Prenatally diagnosed coronary artery abnormalities in hypoplastic left heart syndrome are associated with a higher probability of heart transplantation.

OBJECTIVE: Coronary artery abnormalities (CA) occur in patients with hypoplastic left heart syndrome (HLHS) and may be associated with higher mortality and heart transplantation (HT). We aimed to determine whether fetuses with HLHS and prenatal CA have a higher risk of death or HT. METHODS: We performed a retrospective review of fetal echocardiograms with HLHS from 2011 to 2018. We excluded fetuses with ventricular septal defects, elective termination, death in utero, planned postnatal non-intervention, or absent follow-up data. Presence or absence of CA was determined by review of serial fetal echocardiograms. Survival analysis was used to evaluate the relationship between prenatal CA and death or HT. RESULTS: Of 86 patients with fetal HLHS, 11 had prenatal diagnosis of CA. Of these, six required HT and five died (one after undergoing HT); only one remains alive without HT. Of those without prenatal CA (n = 75), 25 died and 7 underwent HT. Patients with prenatal diagnosis of HLHS and CA had a significantly increased likelihood of death or HT (p-value <0.05). CONCLUSION: Prenatal diagnosis of CA in our cohort of patients with HLHS was associated with increased risk of death or HT. These data have significance for prenatal counseling and postnatal management.

A Multi-Interventional Nutrition Program for Newborns with Congenital Heart Disease.

OBJECTIVE: To evaluate how outcomes changed in newborns undergoing surgery for congenital heart disease after implementation of a standardized preoperative and postoperative nutrition program. STUDY DESIGN: We performed a single-center cohort study of newborns who underwent cardiac surgery between September 2008 and July 2015. We evaluated growth and feeding outcomes in the 2 years of preprogram time (phase 0), in the 2 years after initiation of a postoperative feeding algorithm (phase 1), and in the 2 years following introduction of a preoperative feeding program (phase 2) using traditional statistics and quality improvement methods. RESULTS: The study included 570 newborns with congenital heart disease. Weight-for-age z-score change from birth to hospital discharge significantly improved from phase 0 (-1.02 [IQR, -1.45 to -0.63]) to phase 1 (-0.83 [IQR, -1.25 to -0.54]; P = .006), with this improvement maintained in phase 2 (-0.89 [IQR, -1.30 to -0.56]; P = .017 across phases). Gastrostomy tube use decreased significantly (25% in phase 0 vs 12% and 14% in phases 1 and 2; P < .001) and preoperative enteral feeding increased significantly (47% and 46% in phases 0 and 1 vs 76% in phase 2; P < .001) without increases in necrotizing enterocolitis, hospital stay, or mortality. CONCLUSIONS: Introduction of a multi-interventional nutrition program was associated with improved weight gain, fewer gastrostomy tubes at hospital discharge, and increased preoperative enteral feeding without increases in necrotizing enterocolitis, hospital stay, or mortality.

Mothers with long QT syndrome are at increased risk for fetal death: findings from a multicenter international study.

BACKGROUND: Most fetal deaths are unexplained. Long QT syndrome is a genetic disorder of cardiac ion channels. Affected individuals, including fetuses, are predisposed to sudden death. We sought to determine the risk of fetal death in familial long QT syndrome, in which the mother or father carries the long QT syndrome genotype. In addition, we assessed whether risk differed if the long QT syndrome genotype was inherited from the mother or father. OBJECTIVE: This was a retrospective review of pregnancies in families with the 3 most common heterozygous pathogenic long QT syndrome genotypes in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3), which occur in approximately 1 in 2000 individuals. The purpose of our study was to compare pregnancy and birth outcomes in familial long QT syndrome with the normal population and between maternal and paternal carriers of the long QT syndrome genotype. We hypothesized that fetal death before (miscarriage) and after (stillbirths) 20 weeks gestation would be increased in familial long QT syndrome compared with the normal population and that the parent of origin would not affect birth outcomes. STUDY DESIGN: Our study was a multicenter observational case series of 148 pregnancies from 103 families (80 mothers, 23 fathers) with familial long QT syndrome (60 with LQT1, 29 with LQT2, 14 with LQT3) who were recruited from 11 international centers with expertise in hereditary heart rhythm diseases, pediatric and/or adult electrophysiology, and high-risk pregnancies. Clinical databases from these sites were reviewed for long QT syndrome that occurred in men or women of childbearing age (18-40 years). Pregnancy outcomes (livebirth, stillbirth, and miscarriage), birthweights, and gestational age at delivery were compared among long QT syndrome genotypes and between maternal vs paternal long QT syndrome-affected status with the use of logistic regression analysis. RESULTS: Most offspring (80%; 118/148) were liveborn at term; 66% of offspring (73/110) had long QT syndrome. Newborn infants of mothers with long QT syndrome were delivered earlier and, when the data were controlled for gestational age, weighed less than newborn infants of long QT syndrome fathers. Fetal arrhythmias were observed rarely, but stillbirths (fetal death at >20 weeks gestation) were 8 times more frequent in long QT syndrome (4% vs approximately 0.5%); miscarriages (fetal death at ≤20 weeks gestation) were 2 times that of the general population (16% vs 8%). The likelihood of fetal death was significantly greater with maternal vs paternal long QT syndrome (24.4% vs 3.4%; P=.036). Only 10% of all fetal deaths underwent postmortem long QT syndrome testing; 2 of 3 cases were positive for the family long QT syndrome genotype. CONCLUSION: This is the first report to demonstrate that mothers with long QT syndrome are at increased risk of fetal death and to uncover a previously unreported cause of stillbirth. Our results suggest that maternal effects of long QT syndrome channelopathy may cause placental or myometrial dysfunction that confers increased susceptibility to fetal death and growth restriction in newborn survivors, regardless of long QT syndrome status.

Sedated Echocardiograms Better Characterize Branch Pulmonary Arteries Following Bidirectional Glenn Palliation with Minimal Risk of Adverse Events.

Patients post-bidirectional Glenn (BDG) operation are at risk of left and right pulmonary artery (LPA and RPA) hypoplasia. Transthoracic echocardiograms (TTE) in active children can miss essential elements of anatomy. Procedural sedation improves image quality but increases risk of adverse events. We hypothesized that echocardiograms performed with sedation in patients post-BDG would improve visualization of branch pulmonary arteries with minimal adverse events. Patients post-BDG between 2007-2016 were identified. Exclusion criteria were > 12 months of age, absence of complete TTE before discharge, death before discharge, conversion to shunt physiology, and prolonged post-operative course > 7 weeks. Of 254 post-BDG patients, 153 met inclusion/exclusion criteria. TTE reports were reviewed for visualization of LPA/RPA and hypoplasia of LPA/RPA. Blinded assessment of image quality was performed (scale of 1[poor] to 5[excellent]). Pertinent clinical data were recorded. Pearson's chi-squared and Wilcoxon Rank Sum tests used for statistical analysis. The median age at surgery and hospital stay were 4.8 months and 10 days. Twenty-three patients underwent sedated TTE (15%). Sedated TTE significantly improved visualization of the RPA (100% vs 82%, p = 0.029) and LPA, though this did not reach statistical significance (100% vs 91%, p = 0.129). Sedated TTEs has significantly better image quality (median of 4 vs 3, p < 0.001). There were no serious adverse events due to sedation. Sedated TTE early post-BDG is safe, improves visualization of the RPA and LPA, and improves overall image quality. Routine sedated TTE in these patients should be considered. Implications for long-term outcome need to be further analyzed.

Postnatal Outcomes of Fetal Supraventricular Tachycardia: a Multicenter Study.

Supraventricular tachycardia (SVT), the most common fetal tachycardia, can be difficult to manage in utero. We sought to better understand predictors of the postnatal clinical course in neonates who experienced fetal SVT. We hypothesized that fetuses with hydrops or those with refractory SVT (failure of first-line SVT therapy) are more likely to experience postnatal SVT. This was a retrospective multicenter cohort study of subjects diagnosed with fetal SVT between 2006 and 2014. Fetuses with structural heart disease were excluded. Descriptive comparative statistics and univariate analysis with logistic regression were utilized to determine factors that most strongly predicted postnatal SVT and preterm delivery. The cohort consisted of 103 subjects. Refractory SVT was found in 37% (N = 38) of the cohort with this group more likely to be delivered prematurely (median = 36 vs. 37.5 weeks, p = 0.04). Refractory SVT did not increase the risk of postnatal SVT (p = 0.09). Postnatal SVT was seen in 61% (N = 63). Of those, 68% (N = 43) had postnatal SVT at ≤2 days of age. Postnatal SVT was associated with a later fetal SVT diagnosis (median = 30 vs. 27.5 weeks, p = 0.006). We found a strong correlation between postnatal SVT and later gestational age at fetal SVT diagnosis. Subjects with refractory SVT or hydrops did not have a higher risk of postnatal SVT. We propose strong consideration for term delivery in the absence of significant clinical compromise. Further studies to assess whether outcomes vary for preterm delivery versus expectant management in those with refractory SVT should be performed.

Prenatal Diagnosis of Alveolar Capillary Dysplasia with Misalignment of Pulmonary Veins.

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV) is a rare, lethal cause of neonatal respiratory failure and persistent pulmonary hypertension. We present a presumptive prenatal diagnosis of ACDMPV based on chorionic villus sampling of a FOXF1 mutation in a fetus with extra-pulmonary anomalies often associated with ACDMPV.

Fetuses of Mothers with Thyroid Disease May Be at Higher Risk of Developing Supraventricular Tachycardia.

OBJECTIVE: Fetal tachyarrhythmias complicate 0.5% of pregnancies, with high morbidity and mortality. We hypothesized that maternal factors may predispose to fetal supraventricular tachycardia (SVT). STUDY DESIGN: We reviewed medical records of all 124 mothers who presented to the Vanderbilt Fetal Cardiology Clinic from 2004 to 2010 for fetal arrhythmias, excluding heart block. Maternal factors were compared between 28 fetuses with SVT and a control group of 112 fetuses screened for noncardiac conditions. The proportions were analyzed using chi-square or Fisher exact test for categorical variables and Wilcoxon rank sum test for continuous variables. RESULTS: Of maternal factors, thyroid disease was statistically significant compared with controls. Among mothers whose fetuses had SVT, 21% had thyroid disease (83% hypothyroidism) compared with 3% of controls (p < 0.001). CONCLUSION: In this cohort, the maternal thyroid disease was more common in fetuses with SVT compared with controls (odds ratio = 9.8, 95% confidence interval 2.3-42.3), suggesting closer screening for fetal arrhythmias and SVT in mothers with thyroid disease. Also, routine screening of thyroid functions and thyroid autoantibodies may be warranted in mothers of fetuses with SVT.

Pediatric prenatal diagnosis of congenital heart disease.

PURPOSE OF REVIEW: Fetal cardiology is a rapidly evolving field. Imaging technology continues to advance as do approaches to in-utero interventions and care of the critically ill neonate, with even greater demand for improvement in prenatal diagnosis of congenital heart disease (CHD) and arrhythmias. RECENT FINDINGS: Reviewing the advances in prenatal diagnosis of CHD in such a rapidly developing field is a broad topic. Therefore, we have chosen to focus this review of recent literature on challenges in prenatal detection of CHD, challenges in prenatal counseling, advances in fetal arrhythmia diagnosis, and potential benefits to patients with CHD who are identified prenatally. SUMMARY: As methods and tools to diagnose and manage CHD and arrhythmias in utero continue to improve, future generations will hopefully see a reduction in both prenatal and neonatal morbidity and mortality. Prenatal diagnosis can and should be used to optimize location and timing of delivery and postnatal interventions.

Diagnosis and Management of Fetal Arrhythmias in the Current Era.

Diagnosis and management of fetal arrhythmias have changed over the past 40-50 years since propranolol was first used to treat fetal tachycardia in 1975 and when first attempts were made at in utero pacing for complete heart block in 1986. Ongoing clinical trials, including the FAST therapy trial for fetal tachycardia and the STOP-BLOQ trial for anti-Ro-mediated fetal heart block, are working to improve diagnosis and management of fetal arrhythmias for both mother and fetus. We are also learning more about how "silent arrhythmias", like long QT syndrome and other inherited channelopathies, may be identified by recognizing "subtle" abnormalities in fetal heart rate, and while echocardiography yet remains the primary tool for diagnosing fetal arrhythmias, research efforts continue to advance the clinical envelope for fetal electrocardiography and fetal magnetocardiography. Pharmacologic management of fetal arrhythmias remains one of the most successful achievements of fetal intervention. Patience, vigilance, and multidisciplinary collaboration are key to successful diagnosis and treatment.

Low Baseline Fetal Heart Rate Leads to Diagnosis of Long QT Syndrome Type 1.

A low baseline fetal heart rate at 20 weeks' gestation was detected in a fetus without cardiac structural anomalies. Fetal echocardiography and magnetocardiography were used to diagnose congenital long QT syndrome. It was confirmed in the neonate, and the same pathogenic variant in KCNQ1 was subsequently identified in the mother.

Variation in prenatal surveillance and management of anti-SSA/Ro autoantibody positive pregnancies.

OBJECTIVE: To describe international surveillance and treatment strategies for managing anti-SSA/Ro autoantibody positive pregnancies. STUDY DESIGN: An electronic REDCap questionnaire was distributed to Fetal Heart Society and North American Fetal Therapy Network members which queried institution-based risk stratification, surveillance methods/frequency, conduction abnormality treatments, and postnatal anti-SSA/Ro pregnancy assessment. RESULTS: 101 responses from 59 centers (59% US, 17% international) were collected. Most (79%) do not risk stratify pregnancies by anti-SSA/Ro titer; those that do use varied cutoff values. Many pregnant rheumatology patients are monitored for cardiac abnormalities regardless of maternal anti-SSA/Ro status. Surveillance strategies were based on maternal factors (anti-SSA/Ro status 85%, titer 25%, prior affected child 79%) and monitoring durations varied. Most respondents treat 2° and 3° fetal atrioventricular block, commonly with dexamethasone and/or IVIG. CONCLUSIONS: Wide variation exists in current fetal cardiac surveillance and treatment for anti-SSA/Ro autoantibody positive pregnancies, highlighting the need for evidence-based protocols to optimize care.

Management of Ebstein Anomaly in the Current Era: The Story of One Fetus and the Collaboration of Many-A Case Report.

Collaborative multicenter research has significantly increased our understanding of fetal Ebstein anomaly, delineating risk factors for adverse outcomes as well as predictors of postnatal management. These data are incorporated into prenatal care and therapeutic strategies and inform family counseling and delivery planning to optimize care. This report details the translation of findings from multicenter studies into multidisciplinary prenatal care for a fetus with Ebstein anomaly, supraventricular tachycardia, and a circular shunt, including transplacental therapy to control arrhythmias and achieve ductal constriction, informed and coordinated delivery room management, and planned univentricular surgical palliation.

Mitral valve abnormalities associated with single-ventricle palliation, cardiac death or transplant in fetuses with postnatally confirmed coarctation of the aorta.

Introduction: Predicting if a fetus with borderline left heart structures and coarctation of the aorta (CoA) will require single ventricle palliation (SVP) is challenging, partly due to the limitations of fetal echocardiography in defining valvar abnormalities. Fetal echocardiographic findings predictive of SVP, particularly in relation to the mitral valve (MV), are not well defined. Methods: We performed a retrospective review of fetuses with postnatally confirmed CoA from 2010 to 2020. Fetuses with complex congenital heart disease or unequivocal hypoplastic left heart syndrome were excluded. Data were compared between those who underwent biventricular repair (BVR) vs. SVP cardiac death or orthotopic heart transplant (OHT) to determine differences in fetal echocardiograms. Results: Of 67 fetuses with 131 total echocardiograms, 62 (93%) underwent BVR and 5 (7%) experienced SVP, cardiac death or OHT. Fetuses with confirmed CoA who experienced SVP cardiac death, or OHT, had fetal MV z-scores that were 2.06 lower, on average, than those who underwent BVR (z-score = -3.98 vs. -1.92, 95% CI: -2.96, -1.16). The incidences of MV anomalies and left to right flow across the foramen ovale were higher in the SVP cardiac death and OHT group. Conclusion: SVP, cardiac death or OHT in fetuses with confirmed CoA were associated with fetal MV hypoplasia, MV anomalies and left to right flow across the foramen ovale. These findings may help guide prenatal counseling about the likelihood of SVP, cardiac death or OHT in fetuses with CoA and borderline left heart structures.

Congenitally Corrected Transposition of the Great Arteries: Fetal Diagnosis, Associations, and Postnatal Outcome: A Fetal Heart Society Research Collaborative Study.

Background Fetal diagnosis of congenitally corrected transposition of the great arteries (ccTGA) has been increasingly reported; however, predictors of clinical outcomes remain underexplored. We undertook a multicenter, retrospective study to investigate natural history, associated anomalies, and outcomes of fetal ccTGA. Methods and Results Fetuses with ccTGA diagnosed from January 2004 to July 2020 within 20 North American programs were included. Fetuses with severe ventricular hypoplasia thought to definitively preclude biventricular repair were excluded. We included 205 fetuses diagnosed with ccTGA at a median gestational age of 23 (interquartile range, 21-27) weeks. Genetic abnormalities were found in 5.9% tested, with extracardiac anomalies in 6.3%. Associated cardiac defects were diagnosed in 161 (78.5%), with atrioventricular block in 23 (11.3%). On serial fetal echocardiogram, 39% demonstrated a functional or anatomic change, most commonly increased tricuspid regurgitation (6.7%) or pulmonary outflow obstruction (11.1%). Of 194 fetuses with follow-up, 26 were terminated, 3 experienced fetal death (2 with atrioventricular block), and 165 were live-born. Of 158 with postnatal data (median follow-up 3.7 years), 10 (6.6%) had death/transplant before 1 year. On univariable analysis, fetal factors associated with fetal death or death/transplant by 1 year included ≥ mild tricuspid regurgitation, pulmonary atresia, aortic obstruction, fetal arrhythmia, and worsening hemodynamics on serial fetal echocardiogram (defined as worse right ventricular function, tricuspid regurgitation, or effusion). Conclusions Associated cardiac lesions and arrhythmias are common in fetal ccTGA, and functional changes commonly occur through gestation. Worse outcomes are associated with fetal tricuspid regurgitation (≥mild), any arrhythmia, pulmonary atresia, aortic obstruction, and worsening hemodynamics on serial echocardiograms. These findings can inform prenatal counseling and perinatal management planning.

SCN5A allelic expression imbalance in African-Americans heterozygous for the common variant p.Ser1103Tyr.

BACKGROUND: Heterozygous and homozygous carriers of SCN5A-p.Ser1103Tyr, a common genetic variant with functional effects among African-Americans, have an increased risk of sudden death. We hypothesized that some heterozygous carriers may have unequal expression of wild-type and variant alleles and secondarily that predominance of the variant gene copy could further increase risk for sudden death in this population. METHODS: We quantified allele-specific expression of SCN5A-p.Ser1103Tyr by real-time reverse-transcription polymerase chain reaction (RT-PCR) in heart tissue from heterozygous African-American infants, who died from sudden infant death syndrome (SIDS) or from other causes, to test for allelic expression imbalance. RESULTS: We observed significant allelic expression imbalance in 13 of 26 (50%) African-American infant hearts heterozygous for SCN5A-p.Ser1103Tyr, and a significant (p < 0.0001) bimodal distribution of log2 allelic expression ratios. However, there were no significant differences in the mean log2 allelic expression ratios in hearts of infants dying from SIDS as compared to infants dying from other causes and no significant difference in the proportion of cases with greater expression of the variant allele. CONCLUSIONS: Our data provide evidence that SCN5A allelic expression imbalance occurs in African-Americans heterozygous for p.Ser1103Tyr, but this phenomenon alone does not appear to be a marker for risk of SIDS.