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Cardiac Defects & Associated Congenital Disorders
We'll learn about two broad categories: acyanotic and cyanotic; be aware that this is a simplification scheme that we use to organize defects. As we'll see, the severity of the defect influences the degree of cyanosis present, and cardiac defects often co-occur.
We use echocardiogram to diagnose cardiac defects.
Blood travels through the lungs to receive oxygenation.
These defects produce increased pulmonary blood flow and/or pressure or volume overload of the heart, which can eventually lead to pulmonary hypertension and heart failure.
These defects are characterized by reduced oxygen concentration in systemic blood, which leads to hypoxemia and cyanosis (hence, these are referred to as the "blue babies" defects).
Acyanotic Defects
High pulmonary blood flow: Left to Right Shunts
Let's start with defects characterized by high pulmonary blood flow due to left to right shunts; this group includes septal defects and patent ductus arteriosus.
Ventricular Septal defects (VSD)
In ventricular septal defects (VSD), an opening in the interventricular septum allows blood to move from the left to right ventricle; instead of entering the systemic circulation, this blood is pushed through the pulmonary trunk.
Over time, left-to-right shunting increases pulmonary blood flow and leads to left-sided volume overload.
Children with small VSD are typically asymptomatic with normal growth. However, if the VSD is larger, signs of heart failure start to appear when pulmonary vascular resistance falls at approximately 4-6 weeks old. Signs include respiratory distress, poor weight gain, and fatigue after feeding.
VSDs are the most prevalent congenital cardiac anomaly in children.
VSDs are associated with DiGeorge, Down, and Holt-Oram, and CHARGE syndromes; maternal health and environmental factors.
A high-pitched "harsh" holosystolic murmur is typically audible at the lower left sternal border shortly after birth (suggestive of VSD).
Chest x-ray and ECG are supportive; diagnosis via echocardiography.
Defects may close spontaneously or require surgical repair.
Treatments include medical therapy for heart failure (diuretics, digoxin, ACE inhibitors). Surgical repair is required for larger VSDs; smaller VSDs often spontaneously close during first few years of life.
Subtypes of VSD: perimembranous (aka conoventricular) (most common), trabecular muscular, subpulmonary outlet, inlet (AV septal or canal).
If left untreated, a reversal in the shunt, called Eisenmenger syndrome, can occur.
Atrial Septal Defects
Atrial septal defects are characterized by openings in the interatrial septum that allow left to right shunting and volume overload of the right atrium and ventricle.
Over time, increased blood flow can lead to right-sided dilation and increased blood pressure in the pulmonary vasculature.
Although children with small defects are typically asymptomatic, the risk for pulmonary hypertension, heart failure, atrial arrhythmias, and paradoxical emboli increases in adulthood. As in ventricular septal defects, Eisenmenger syndrome can develop.
ASDs can be spontaneous, or associated with Holt-Oram, Noonan, and Down syndromes, genetic mutations.
Soft midsystolic murmur at upper left sternal border, wide fixed splitting of S2 is common.
Chest and x-ray can indicate ASD; echocardiogram is diagnostic.
Most defects between 3-8 mm close spontaneously by age 3; larger ASDs require transcatheter closure or surgical repair.
Subtypes of ASD include ostdium secondum (a defect in fossa ovalis), sinus venosus, ostium primum (a form of atrioventricular septal defect).
Patent ductus arteriosus
Patent ductus arteriosus is characterized by a persistent connection between the aorta and pulmonary artery.
During gestation, this connection allows fetal circulation to bypass the lungs; it usually closes after birth as a result of increased PaO2 (partial pressure of oxygen in the arterial blood) and a decline in prostaglandin concentration.
Because of pressure changes after birth, the patent ductus arteriosus shunts blood from the aorta to the pulmonary artery; this can lead to left sided heart dilation with pulmonary hypertension and high pulmonary vascular resistance.
When pulmonary vascular resistance exceeds systemic vascular resistance, the shunt reverses, resulting in Eisenmenger syndrome.
Failure to thrive, poor feeding, tachycardia, and tachypnea are worse in preterm infants, who may also present with respiratory distress, apnea, and necrotizing enterocolitis.
Obstructive Defects
Now, let's consider two acyanotic obstructive defects that cause blood to remain in the heart.
Coarctation of the aorta
Coarctation of the aorta is characterized by localized narrowing of the aorta, usually just distal to the origin of the left subclavian artery.
Narrowing in this location induces volume overload proximally, with upper extremity hypertension and left ventricular hypertension. Depending on the severity, patients present with headache, chest pain, leg claudication, heart failure, and shock.
Typically, we'll hear a soft bruit over the site of coarctation.
Diagnosis can involve echocardiography, CT, MR angiography.
Treatment options include balloon angioplasty with stent placement and surgical correction.
Stenosis
Congenital aortic or pulmonary artery stenosis causes ventricular outflow obstruction. Symptoms include exercise intolerance, syncope, angina, and dyspnea.
Cyanotic Defects
Reduced pulmonary blood flow: Left to Right Shunts
These are characterized by right to left shunts, in which blood bypasses the lungs.
Tricuspid Atresia
In patients with tricuspid atresia, agenesis of the right atrioventricular valve prevents communication between the right atrium and ventricle. As a result of reduced blood flow, the right ventricle is often hypoplastic.
Interatrial communication is maintained by atrial septal defects or a patent foramen ovale; other defects are also common, including pulmonary obstruction or transposition of the great arteries (which we'll learn about soon).
Tetralogy of Fallot
Tetralogy of Fallot comprises four defects:
A large ventricular septal defect, pulmonary artery obstruction, right ventricular hypertrophy, and an "overriding" aorta that is shifted to the right and connects to both ventricles.
The ventricular septal defect is often due to a misaligned conal septum that protrudes into the pulmonary outflow tract, producing pulmonary artery obstruction. Neonates with severe obstruction present with cyanosis and dyspnea during feeding with poor weight gain; if the obstruction is mild, cyanosis may be absent during rest.
Hypercyanotic spells are characterized by onset of hyperpnea and increased cyanosis; incidence peaks between 2-4 months
Eisenmenger syndrome
Chronically high blood pressure from untreated left to right shunts induces pulmonary vascular remodeling and pulmonary arterial hypertension. Eventually, pulmonary vascular resistance exceeds systemic vascular resistance, and the shunt reverses.
Mixed Flow Defects
In mixed flow defects, cardiac anomalies allow blood with high and low levels of oxygen to combine.
Transposition of the great arteries (TGA)
In TGA, the aorta arises from the right ventricle and the pulmonary artery arises from the left.
In the absence of atrial or ventricular septal defects, TGA causes severe neonatal cyanosis soon after birth, and poor tissue perfusion leads to metabolic acidosis; the condition is incompatible with life. If septal defects are present, cyanosis is less pronounced, but heart failure can still occur.
Persistent truncus arteriosus
Persistent truncus arteriosus occurs when the aorticopulmonary septum fails to separate the outflow tracts; ventricular septal defects are common co-defects.
As a result, both oxygenated and deoxygenated blood enter systemic, pulmonary, and coronary circulations.
Neonates present with mild cyanosis and signs of heart failure with poor feeding, diaphoresis, and tachypnea.
Patients have a continuous "machine-like" murmur heard at the upper left sternal border; bounding pulses are common.
Diagnose with echocardiography.
Treatment includes fluid restriction, diuretic. Approximately 1/3 of cases will spontaneously close; otherwise, surgical or catheter-based correction is needed.
Sometimes preterm infant treatment with COX inhibitor closes the PDA (only appears to be affective in preterm infants).
Total anomalous pulmonary venous return
In total anomalous pulmonary venous return, the pulmonary veins drain oxygenated blood into systemic venous circulation, where it mixes with deoxygenated blood.
In many cases, an associated atrial septal defect allows the mixed blood to move from the right to left atrium, then to the left ventricle and into the systemic circulation.
There are four subtypes of total anomalous pulmonary venous return based upon the level or location of the connection:
Cardiac subtypes connect the pulmonary veins directly to the right atrium, as we've shown in our diagram, or to the coronary sinus.
Supracardiac subtypes connect the pulmonary veins to the left brachiocephalic, SVC, or azygos vein.
Infracardiac subtypes connect the pulmonary veins to the portal or hepatic veins or to the IVC.
In mixed subtypes, we find a combination of the above types.
Neonates can have partial anomalous pulmonary venous return; this is similar to an atrial septal defect, which allows oxygenated blood to recirculate through the pulmonary vessels.