To review normal blood flow configuration, oxygen-depleted blood is returned to the right ventricle (RV) of the heart, pumped to the lungs via the pulmonary artery (PA), oxygenated, returned to the left ventricle (LV), and pumped to the body via the aorta. In transposition of the great vessels (TGV) and congenitally corrected transposition of the great vessels (CCTGV), the major arteries of the heart are reversed.
The cause of congenital heart defects is unknown. Development of the fetal heart happens early in the pregnancy; usually during the fourth to fifth week. It has been hypothesized that gestational diabetes, excessive use of alcohol during pregnancy, mothers older than age 40, or poor nutrition may be a contributing factor. Pesticides used to control rats and mice, herbicides, and antidepressants may also be risk factors for the development of TGV in infants.
A & P of TGV
In TGV, the PA and the aorta—the two main arteries going out of the heart—are reversed or transposed. The PA is connected to the LV and the aorta is connected to the RV. This reversal causes poorly oxygenated blood to return to the body and well- oxygenated blood to return to the lungs via the PA (see Picturing TGV). In effect, this forms two separate circulatory systems.
Blood enters the lungs from the RV, is oxygenated, and returns to the lungs without circulating throughout the body. At the same time, poorly oxygenated blood is pumped to the body and returns to the left side of the heart without cycling through the lungs. Most babies born with TGV are cyanotic and extremely ill at birth. Surgery to correct the anatomic position of the aorta, PA, and coronary arteries, and restore normal circulatory function (known as arterial switching), must be performed as soon as possible.
Common defects associated with TGV are pulmonary outflow tract obstruction, coarctation of the aorta, ventral septal defect, and failure of the foramen ovale and the ductus arteriosus to close. These defects complicate TGV; if they're also present, the TGV is considered to be complex.
The primary nursing goal in infants with TGV is to identify the cardiac defect early. Symptoms, including cyanosis, shortness of breath, and poor feeding, usually appear at birth or shortly thereafter.
Getting to know CCTGV
In CCTGV, the two ventricles and the valves associated with them are reversed, with the weaker RV serving as the pump to the body and the stronger LV serving as the pump to the lungs so that oxygenated blood is pumped to the body but via the weaker pump. These babies aren't cyanotic at birth and may not have symptoms until adulthood.
Some patients have no symptoms with CCTGV and live very normal lives, whereas others become symptomatic over time. Major problems that can arise in the long-term care of patients who haven't undergone surgery to correct the defect are heart failure and electrical conduction defects (tachycardias, bradycardias, and blocks) that occur in the enlarged heart. Heart failure is due to the long-term overwork of the RV trying to support systemic circulation and common conduction abnormalities arising from the atrioventricular (AV) node.
If not diagnosed in childhood, these patients often present in their 30s to 50s with symptoms along the continuum from tricuspid valve leakage and problems with pump function to abnormal heart rhythms. Heart failure, cardiomyopathy of the right side of the heart, and pulmonary hypertension are common diagnoses in adults with CCTGV. Additionally, these patients may present with significant tricuspid regurgitation because of an overloaded RV, which is trying to act in the position of the LV, and high pressure on the tricuspid valves.
Because heart block is also common in these patients, angiotensin-converting enzyme inhibitors are often used empirically. Caution should be exercised with the use of beta-blockers, which may exacerbate AV block and precipitate bradycardia. Pacemaker implantation can be challenging in these patients due to the complex anatomy of the heart. Ventricular arrhythmias are uncommon in the pediatric setting but can be found in adult patients with the development of ventricular overload and failure.
Antibiotic prophylaxis before invasive procedures, such as dental procedures, is dependent on the specific heart defect and treatment. The American Heart Association recommends antibiotic prophylaxis only for unrepaired cyanotic heart disease, patients with repairs that use prosthetic materials or devices during the first 6 months following a procedure or patients with repairs that have residual defects that inhibit endothelialization, and valve replacement or valve disease in heart transplant patients.
When medical management fails, the adult with symptomatic CCTGV can be offered cardiac transplantation if the advanced disease or any surgical correction hasn't caused contraindications to transplant.
Living longer, stronger
Because of the advances in surgical and medical treatment, more children are living into adulthood with congenital heart conditions. Medical specialties to treat patients with congenital heart defects are growing to serve these patients. Your knowledge can make you a valuable member of your patient's healthcare team.
Learn more about it
Martins P, Castela E. Transposition of the great arteries. Orphanet J Rare Dis. 2008;3:27.
Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation. 2007;116(15):1736–1754.