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Approach to Congenital Defects

TSRA Primer - Congenital

TSRA Content:


Author: Hannah McMullen, MD

This is a revision and update from the previous edition of the TSRA Primer in Cardiothoracic Surgery written by Eric Griffiths, MD.

Congenital heart defects represent a diverse array of anatomic malformations. The resulting clinical presentation is reflective of the underlying physiology that leads to obstruction, left to right shunting, or right to left shunting.

Obstruction

Congenital heart defects can result in obstruction of blood flow at many different levels including inflow and outflow of each chamber of the heart, the aorta, or the pulmonary artery. These obstructive lesions result in a pressure load on the respective ventricle, giving way to concentric ventricular hypertrophy and elevated filling pressures that may lead to diastolic and/or systolic ventricular dysfunction. If the pressure load persists, the ventricle decompensates, ultimately leading to dilatation and failure. The severity of the symptoms is based on the degree and duration of the obstruction.

High-grade, left-sided, (systemic) lesions include LV outflow tract obstruction (LVOTO), aortic stenosis, and coarctation of the aorta. The infant will present with low cardiac output, cool clammy skin, poor capillary refill, fluid retention, feeding intolerance, easy fatigability, chest pain, syncope, pulmonary edema, and other signs of congestive heart failure. Low-grade obstructions can be relatively asymptomatic, only manifesting symptoms after progression to ventricular dysfunction.

Right-sided obstructions involve obstruction between the right atrium and right ventricle, or obstruction of the right ventricular outflow. Tricuspid atresia and Ebstein’s anomaly, which describes downward displacement of the tricuspid valve with atrialization of the right ventricle, cause inflow resistance of blood into the heart and subsequent “backup” that results in increased central venous pressure. The right ventricular (RV) outflow-level obstructions include RV outflow tract obstruction (RVOTO), tetralogy of Fallot (TOF), pulmonary stenosis, and hypoplastic pulmonary arteries. Severely obstructing right-sided lesions require right-to-left shunts through a ventricular or atrial communication for adequate circulation; the presentation of these obstructions are typically the manifestations of the shunt, discussed in more detail below. Moderate obstructions may also be associated with concomitant right-to-left shunts, and thus decreased pulmonary blood flow resulting in low oxygen saturation. The thin-walled right ventricle is susceptible to pressure overload, hypertrophy, and progression to dilatation and failure.

Post-cardiac obstruction can also occur with narrowing or disruption of the aorta. Coarctation of the aorta describes narrowing with intact continuity. The most common location of coarctation is referred to as “juxtaductal” and is found in close proximity to the ductus arteriosus in neonates (ligamentum arteriosum in adults). Upon closure of the ductus arteriosus shortly after birth, affected patients possess a circulatory system with a greater percentage of blood flow directed proximal to the coarctation, with decreased flow distally. If undetected in the neonatal period, this often manifests by young adulthood with lower extremity claudication, differential 4-extremity blood pressures, and decreased pulses in the lower extremities. A holosystolic murmur upon interscapular auscultation is a characteristic finding.

Interrupted aortic arch refers to a spectrum of defects characterized by luminal discontinuity of the aortic arch. This can occur between the innominate artery and the left common carotid artery (Type C), between the left common carotid and left subclavian artery (Type B), or distal to the left subclavian artery (Type A). Type B is the most common subtype and is often associated with other congenital defects such as DiGeorge syndrome, aberrant right subclavian artery, and bicuspid aortic valve.

Left-To-Right Shunts

Left-to-right shunts result in oxygenated blood crossing a pathologic defect and mixing with deoxygenated blood in the right heart. The size of the defect and the extent of pulmonary vascular resistance determine the amount of blood that is shunted, thus influencing the clinical presentation. The most common left to right shunts are: atrial septal defect (ASD), ventricular septal defects (VSD), and patent ductus arteriosus (PDA). These are often described either as "nonrestrictive" or “restrictive” based on whether their size is adequate to allow free flow and equalization of pressures on both sides of the defect or not. Large, nonrestrictive VSDs or PDAs lead to a large volume of blood shunted from left to right, resulting in pulmonary over-circulation and pulmonary edema. The increased volume load from the pulmonary veins returning to the left ventricle leads to dilatation and ultimately congestive heart failure (Gallery 2.1).

Large ASDs lead to shunting from the left atrium to the right atrium, resulting in volume overload of the right ventricle. This, in turn, may lead to pulmonary hypertension (HTN) in early adulthood and right ventricular failure. The remodeling of pulmonary vasculature is eventually irreversible; this fatal condition is called Eisenmenger syndrome. This is characterized by perip.

Clinically, babies with a left-to-right shunt may present with tachypnea, pulmonary edema, failure to thrive, and frequent respiratory tract infections. In children and adolescents, symptoms include decreased exercise tolerance, and multiple respiratory tract infections. Endocarditis and bacteremia may also develop from the turbulent flow through the defect.

Right-To-Left Shunts (Cyanotic Lesions)

Right-to-left shunts allow deoxygenated blood to bypass the lungs and mix with the systemic circulation, decreasing the oxygenation of the blood delivered to the body, leading to cyanosis. This is encountered in two important clinical scenarios:

1. Obstruction of pulmonary blood flow with an escape route through an ASD or VSD, seen in Tetralogy of Fallot and Pulmonary Atresia (PA)

2. Direct access to the aorta from the RV through a large patent ductus arteriosus (PDA) with proximal systemic obstruction, seen in hypoplastic left heart syndrome (HLHS), double-outlet right ventricle (DORV), and d-transposition of the great arteries (dTGA)

The oxygen saturation and degree of cyanosis depend on the amount of mixing between venous and arterial blood. Patients may be relatively asymptomatic or may experience fatigue, failure to thrive, and/or hypoxia. Many of these lesions rely on the right-to-left shunt to prevent cardiovascular collapse. In addition, some of these lesions such as d-TGA, tricuspid atresia, and pulmonary atresia also rely upon a left-to-right shunt to ensure some degree of oxygenated blood eventually reaches end-organ tissues. Maintenance or creation of these shunts is essential to temporize or palliate the patient until surgical repair can be accomplished.

Conclusion

The clinical presentation of patients with congenital heart defects is an illustration of underlying pathology in conjunction with physiological compensation. Understanding the pathophysiology and interpreting the severity and duration of the lesions is critical for optimal perioperative management and determining the ideal timing for operative intervention.