• To determine the relationship between postoperative myocardial dysfunction and morbidity [ Time Frame: 24 hours ] [ Designated as safety issue: No ]
• To determine the effects of prophylactic NAC on postoperative morbidity [ Time Frame: 24 hours ] [ Designated as safety issue: No ]

• To determine the relationship between postoperative myocardial dysfunction and morbidity
• To determine the effects of prophylactic NAC on postoperative morbidity

The purpose of this study is to determine whether intravenous N-acetylcysteine (also known as Acetadote), an antioxidant medication that has been used for years to treat Tylenol overdose, helps prevent heart dysfunction in the early postoperative period following congenital heart surgery. Children undergoing major heart surgery, such as the arterial switch operation, routinely develop temporary heart dysfunction in the first 12-24 hours after surgery. This heart dysfunction may be severe and contributes to an increased risk for death or prolonged hospitalization. Current standard treatments include intravenous medications such as dopamine, epinephrine, and vasopressin that support your child's blood pressure and heart function. Unfortunately, high doses of these medications have the potential to cause severe side effects including loss of fingers and toes, liver and kidney dysfunction, and heart rhythm abnormalities. Our goal is to find a way to reduce heart dysfunction after major heart surgery in order to promote a smoother postoperative period, and reduce the risks associated with heart operations in children.

This is a randomized, placebo-controlled, blinded study of intravenous N-acetylcysteine (NAC) for the prevention of postoperative myocardial dysfunction and apoptosis in infants undergoing arterial switch for D-transposition of the great arteries. Subjects will be age 0-3 months, and no distinctions will be made based on gender or race. Infants operated before 36 weeks post-conceptional age or with birth weight less than 1.8 kilograms will be excluded. Informed consent will be obtained from the patient's parent by one of the investigators in the hospital before the infants undergo surgery.

Subjects will be randomized based on a block randomization scheme to receive placebo or NAC infusion, starting with a loading dose 1 hour prior to surgery. If there is any concern by the ICU physician that the patient is developing toxicity to the medicine, the study drug will be discontinued and the patient removed from the study. Patients will have a thermodilution catheter placed during surgery for postoperative direct measurement of cardiac output. Endomyocardial biopsy will be performed by the surgeon pre- and post-bypass for measurement of markers of apoptosis. Postoperatively, patients will continue to receive an infusion of IV NAC for 24 hours. Blood draws will be through existing arterial and central venous catheters. Serum labs collected will include serial lactate values (already collected routinely), liver and renal function tests, CK-MB and troponin-I levels as a marker of myocardial injury, and S100b level as a marker of brain injury. Total additional blood removed for research purposes will be less than 15 mL. Cardiac output will be measured serially by thermodilution. Serial transthoracic echocardiography will be used to determine left ventricular function. Inotropic score, duration of mechanical ventilation, length of ICU stay, and length of hospitalization will be recorded.

• Transposition of Great Vessels
• Congenital Heart Disease

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Inclusion Criteria:

• All patients transferred to or born at C.S. Mott Children's Hospital between 0 and 3-months-old undergoing ASO for d-TGA or anatomic variants (including double-outlet right ventricle with transposition physiology).

Exclusion Criteria:

• Less than 36-weeks post-conceptional age at the time of enrollment
• Birth weight less than 1800 grams;
• Evidence of significant renal, hepatic, or neurological dysfunction
• Additional significant cardiac lesions other than patent ductus arteriosus, isolated ventricular septal defect, simple coarctation, and/or atrial septal defect
• Preoperative extracorporeal membrane oxygenation (ECMO).