Background: With usual supplementation practices, most children are Vitamin D Deficient (VDD) following Congenital Heart Disease (CHD) surgery and alternative regimens need consideration. Methods/Results: i) A systematic review identified 88 pediatric trials of high dose vitamin D. Studies evaluating the Institute of Medicine (IOM) Tolerable Upper Intake Level (UL) did not rapidly normalize levels, while loading therapy (≥ 40000 IU) did so within 3 days. Hypercalcemia occurred more often with doses above 400000 IU. ii) A double blind RCT was designed to determine whether pre-operative administration of the IOM UL can prevent post-operative VDD. Results after the first 30 participants completed study procedures demonstrated it was possible to recruit (1.8 patients per month) and complete study procedures (i.e. blood collection). Unfortunately few participants (45%) received more than 30 doses of study drug. Conclusion: Prevention of post-operative VDD in the majority of CHD patients will require alternatives to the IOM recommendations.

Congenital heart disease (CHD) is characterized by structural defects of the heart and great vessels. It is the most common birth defect, affecting an estimated 1% of live births, and is the leading cause of mortality among birth defects. Despite recent progress in genetic research, more than 50% of CHD cases remain unexplained. An estimated 23% are due to aneuploidies and copy number variants and up to 30% has been attributed to de novo variation, though that number ranges between 3-30% depending on CHD complexity. The contribution of somatic mosaicism, or de novo genetic mutations arising after oocyte fertilization, to congenital heart disease (CHD) is not well understood due to limitations in sample size, detection method, and validation rate. Further, the relationship between mosaicism in blood and cardiovascular tissue has not been determined. We developed a computational method, Expectation-Maximization-based detection of Mosaicism (EM-mosaic), to analyze mosaicism in exome sequences of 2530 CHD proband-parent trios. EM-mosaic accurately detected 309 mosaic mutations in blood, with 85 of 94 (90%) candidates tested independently confirmed. We found twenty-five likely damaging mosaics in plausible CHD-risk genes, affecting 1% of our cohort. Variants in these genes predicted as damaging had higher variant allele fraction than benign variants, suggesting a role in CHD. The frequency of protein-coding mosaic variants detectable in blood was 0.122 or roughly 1 in 8 individuals. Analysis of 66 individuals with matched cardiac tissue available revealed both tissue-specific and shared mosaicism, with shared mosaics generally having higher allele fraction. CHD patients often present with comorbid cardiac and extracardiac anomalies that further their impact quality of life. Neurodevelopmental disorders (NDDs) are especially prevalent in CHD cases compared to the general population, yet the underlying genetic causes remain poorly explained. Further, patients with single ventricle defects undergoing surgery often later develop arrhythmias and experience worsening ventricular function. We used a statistical approach to dissect the association between de novo variation and these clinical outcomes and found that pleiotropic mutations contribute a large fraction of the risk of acquiring NDD and abnormal ventricular function phenotypes in CHD patients. We developed a proof-of-concept rare variant risk score that combines information from de novo, rare transmitted, and copy- number variants and show that prediction of outcomes such as NDD can be improved, especially in complex CHD cases.

A 36-year-old woman was seen with complaints of exertional chest pain and shortness of breath. Her medical history included atrial fibrillation and diabetes. Physical examination was unremarkable except for an irregular cardiac rhythm. Myocardial perfusion imaging revealed the presence of a large area of infarction involving the entire anterior and apical walls and part of the anteroseptal wall with minimal periinfarct ischemia. Computed tomography coronary angiogram revealed an anomalous left main coronary artery arising from the main pulmonary artery. Right and left heart catheterizations demonstrated moderate pulmonary hypertension with a slight step-up in oxygen saturation between the right ventricle and main pulmonary artery. Coronary angiography showed a large tortuous right coronary artery with collaterals to the left anterior descending artery that drained into the main pulmonary artery. She was referred for surgery. This case demonstrates a rare coronary artery anomaly in an adult where survival is dependent on collateral circulation.

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Tetralogy of Fallot (TOF) is the most common cyanotic congenital cardiac defect with a global annual incidence of 40,000 cases. Advances in surgery and perioperative care led to improvements in perioperative mortality and, thus, a growing number of survivors. TOF survivors often suffer from complications related to a failing right ventricle. Follow-up studies evaluating TOF repair strategies suggest an association between the type of surgical repair strategy and late right ventricular health. However, surgical practices remain unchanged and led by institution-level biases. The body of evidence addressing outcomes based on TOF surgical repair strategy is weak and controversies persists on the management of these patients.  This thesis comprises 6 chapters that form the foundation of a multi-centre research program on outcomes after TOF surgical repair. The program uses various methodologies to generate evidence with a vision to change surgical practices.  Chapter 1 is an introduction providing background on TOF and contemporary areas of controversy.  Chapter 2 presents the results of a retrospective analysis evaluating the use of early echocardiogram parameters in predicting late cardiac magnetic resonance imaging evaluation of the right ventricle.  Chapter 3 presents the results of a retrospective cohort exploring the association between TOF repair strategy and development of right bundle branch block.  Chapter 4 presents the results of a multinational survey aiming to explore contemporary biases in TOF surgical repair strategy selection.  Chapter 5 presents the background, rationale, design and baseline cohort characteristics of the Tetralogy of Fallot for Life (TOF LIFE) study. The study is a multi-centre inception cohort study with a follow-up period of 2 years.  Finally, Chapter 6 discusses the conclusion, limitations, and future implications of this research program. / Thesis / Doctor of Science (PhD)

The purpose of this literature review is to discuss the mechanisms of a cardiac arrest and how it contributes to the high-risk classification of congenital heart disease patients. While assessing the diagnoses process and types of treatments applied to cardiac arrest and congenital heart disease separately, we further explain this information’s significance by combining their incidence rates and analyzing their associations as it relates to surgical operations. A narrative review of studies is conducted in pediatrics and adults to reveal distinctions in lesion characteristics and interventions, as well as limitations that permit inconsistencies in data reports on health outcomes. There is not adequate research and data collection in reference to perioperative cardiac arrest in congenital heart disease patients and the aim of this paper is to highlight the need for further studies and to present current research that has been conducted to fill the gaps of this global health issue.

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