Congenital Heart Disease I

Symptoms and signs of ASD

Murmur at a few years of age Left parasternal budge cause of enlarged right ventricle Large S1, split S2 (delayed pulmonary valve) Systolic murmur over the pulmonary artery, and diastolic murmur over the lower left sternal border due to increased tricuspid flow Pulmonary vascularity increased, right side dilated due to increased flow, oxygen saturation of right side increased Can close spontaneously if less than 7mm diameter

Right-to-left shunt causes a mixture of

unoxygenated blood from the right heart (systemic venous return) with oxygenated blood returning from the pulmonary circulation. The oxygen content of the systemic arterial blood falls in proportion of the volume of systemic venous blood mixing with the normal pulmonary venous return. With the reduced oxygen content, even with an increased left ventricular output, tissue oxygen delivery falls and the work capacity of the muscles is limited.

Some congenital cardiac malformations (e.g. coarctation of the aorta and congenital aortic stenosis) produce narrowing of the left ventricular outflow tract, semilunar valves or great arteries. An obstruction in any of these pathways increases

ventricular afterload. Ventricular hypertrophy occurs in response, which results in thicker chamber walls, normal systolic performance but reduced chamber compliance and higher filling pressures in the atrium. With severe noncompliance, left-sided heart failure may occur (pulmonary venous congestion, pulmonary edema) or right-sided heart failure (systemic venous congestion) may occur (jugular venous distension, liver enlargement, ascites and peripheral edema).

Ostium secundum defect is the most common yet least serious type of

ASDs (75% of all ASDs). Ostium secundum defects are located near the fossa ovalis in the center of the septum. This defect presumably results from excessive fenestration or resorption of septum primum, underdevelopment of septum secundum, or some combination of the two conditions.

Clinical symptoms of PAPVR are similar to those triggered by

ASDs. Depending on the shunt volume, patients are either asymptomatic (single anomalous vein) or show pulmonary hypertension, dyspnea on exertion and cardiomegaly by chest radiography in the adult age.

VSD Catheterization studies

Catheterization studies show an increase in oxygen saturation at the right ventricular level reflecting the left-to-right ventricular shunt. With small defects the right ventricular and pulmonary artery pressures are normal. With large defects these pressures are increased up to near the systemic levels and the mean left atrial pressure may be elevated to the range of 10-15 mm Hg (normal left atrial pressure is about 8 mm Hg).

Lab findings PDA

(B) Chest radiograph. Chest radiograph shows cardiac enlargement, a prominent main pulmonary artery and pulmonary plethora (enlargement of blood vessels in the lungs. (C) Electrocardiogram (ECG). ECG shows left cardiac hypertrophy. (D) Echocardiogram. The echocardiogram is the procedure of choice to confirm the diagnosis and to characterize a PDA as silent, small, moderate, or large.

Moderate VSDs. A defect of moderate size allows a large left-to-right shunt (Qp/Qs of 1.4 to 2.2 : 1) which result in the following hemodynamic consequences:

(a) increased pulmonary vascular flow due to the left-to-right shunting; (b) increased volume load on left atrium and left ventricle leading to dilatation and eccentric hypertrophy; (c) excessive pulmonary blood flow leading to increased pulmonary artery pressure; and (d) decreased systemic cardiac output as blood is shunted through the VSD away from the aorta. Compensatory mechanisms are stimulated to maintain adequate organ perfusion, such as increased catecholamine secretion and salt/water retention by means of the renin-angiotensin system.

Blood flow pattern in an ASD

At birth, there is little or no shunt in either direction across an ASD because the compliance of the right and left ventricles is identical. The right ventricle gradually becomes thinner and more compliant than the left ventricle in response to the fall in neonatal pulmonary vascular resistance, so left atrial blood then flows across the ASD into the more compliant right ventricle. The magnitude of the shunt is usually described by the Qp/Qs ratio, where Qp is the pulmonary flow, and Qs is the systemic flow. Atrial septal defect is considered significant when it is > 5 mm in diameter. In this case the Qp/Qs ≥ 1.5 : 1.0, i.e. the volume of blood going to lungs is at least 1.5 times larger than the volume of blood going to aorta.

PDA Complications.

Infective ductus arteriosus endarteritis. During the pre-antibiotic era, infective endarteritis (IE) was a fatal complication and the most common cause of death (45%) in patients with PDA. Wide use of antibiotics and surgical closure of PDA has reduced significantly the incidence of IE. IE is an equivalent of infective endocarditis, characterized by fever associated with positive blood cultures or echocardiographic vegetations. Vegetations usually occur on the pulmonary artery end of the ductus, and embolic events are usually of the lung rather than the systemic circulation

Adult SX of ASD

Right-sided congestive heart failure. Adult patients complain of progressive shortness of breath with exertion. The mechanism of congestive heart failure is a volume overload in the right ventricle and pulmonary arteries in combination with an inefficient left ventricle because of a continuously reduced preload. (B) Atrial arrhythmias. Atrial fibrillation results from stretching of the conduction system in the enlarged atrium. (C) Paradoxical embolism. Stroke is caused by paradoxical embolization of thrombus from the venous system through the defect. Although patients have a net left-to-right shunt through the defect, virtually all have transient flow reversal with Valsalva maneuver. (D) Pulmonary vascular obstructive disease and pulmonary arterial hypertension. A fraction of individuals with uncorrected ASD that become symptomatic in their middle age go on to develop pulmonary vascular obstructive disease, sustained increase in pulmonary vascular resistance, pulmonary artery hypertension and shunt reversal, cyanosis and erythrocytosis (Eisenmenger syndrome).

Continual production of vasodilator prostaglandin E2 (PGE2) by the ductus and placenta is responsible for keeping

the ductus patent during gestation. Normally, the ductus begins to close with the first gasping respiration, and in a matter of hours, the ductus may be functionally closed. The mechanism of ductal closure is a complex interaction of the level of arterial oxygen and circulating prostaglandins.

The membranous septum is a small translucent structure located in the angle between the posterior and right aortic cusps. Membranous VSDs are located in

the membranous septum; they lie in the left ventricular outflow tract just below the aortic valve. Because the membranous septum is a small area, most defects extend into the immediately adjacent infundibular region, hence the term perimembranous VSD that is often used. Membranous VSD is the most common type of VSDs occurring in 75-80% of cases.

A small VSD offers a large resistance to flow, it is accompanied by a small shunt (Qp/Qs of <1.4) and the infant is asymptomatic. This type of defect imposes little physiologic burden on the heart, although patients are always at risk for infective endocarditis. The clinical presentation:

The defect is small in most cases and the left-to-right shunting is minimal to cause symptoms. These infants are brought to the cardiologist's attention because a murmur is detected during routine examination. A holosystolic murmur with a thrill along the lower left sternal border is characteristic for these infants. Weight gain usually is not affected.

CLINICAL PRESENTATION OF MEDIUM-SIZED DEFECTS. VSD

The size of the defect may diminish over time and spontaneous closure may occur, although less frequently than with small VSDs. The shunted blood is ejected into the pulmonary arteries, and then returned to the left atrium and the left ventricle. Both the right and left ventricles are volume overloaded. The right ventricle does not fail due to the low pressures in the pulmonary circulation and low pulmonary vascular resistance. Frequent respiratory infections may occur due to the high pulmonary blood flow. It is the left ventricle that is more overloaded because close to 50% of the systolic volume recirculates constantly from the left ventricle through the right heart and pulmonary arteries into the left heart again, with eventual development of left-sided congestive heart failure. Most cases respond to medical therapy, and pulmonary vascular resistance usually does not increase in these patients.

PFO Pathogenesis

The superior and leftward aspects of the septum primum (the flap) can open into the left atrium when right atrial pressure exceeds that of the left (e.g., Valsalva maneuver, cough, or mechanical ventilation). This process allows for transient right-to-left interatrial shunting with the potential for transmission of paradoxic emboli. Because it is present in all newborns, PFO technically is not a "congenital" defect.

There are rare cases in which there is only a common atrium, the atrial septa do not develop at all. Another name for this uncommon anomaly is

cor triloculare biventriculare. The right-sided portion of the common chamber has features of a morphologic right atrium (crista terminalis, pectinate muscles, right atrial appendage) and receives the superior and inferior vena cavae and coronary sinus. The left-sided portion of the common chamber has features of a morphologic left atrium (smooth nontrabeculated walls, a left atrial appendage) and receives the pulmonary veins. Absence of the atrial septum necessarily includes an atrioventricular canal defect associated with a common atrioventricular valve.

Most infants with ASD and significant shunt (Qp/Qs > 1.5 : 1.0) are

asymptomatic; they tolerate the large volume load on the right heart and pulmonary circuit quite well for a long time. The right ventricle readily adapts to volume overload and ejects its increased stroke volume into the low resistance pulmonary vascular bed. Right ventricle undergoes dilatation and hypertrophy and its function is maintained through the fourth decade. Years later, with normally decreasing left ventricular compliance with age and exacerbated by systemic hypertension, there is a further increase in the left-to-right shunt. Therefore atrial septal defects are associated with increasing left-to-right shunting as the patient gets older. This explains why individuals with ASD appear in adulthood with pulmonary vascular obstructive disease or right-sided congestive heart failure but no history of congenital heart disease in childhood.

Subpulmonary (infundibular or supracristal) VSDs are located under

the pulmonary valve when viewed from the right ventricle. Subpulmonary VSDs account for 5% of isolated VSDs in the United States

Small PDA

When the shunt is small (Qp:Qs <1.5 to 1), the only abnormality may be the presence of a continuous murmur often referred to as a "machinery" murmur. The murmur is loudest in the left infraclavicular area. There are no respiratory symptoms, and there is no evidence of cyanosis

A left-to-right shunt allows

a portion of the pulmonary venous return (i.e. oxygenated blood) to escape back to the right heart rather than being pumped to the aorta, thereby reducing cardiac output by the amount of the shunted volume. Tissue oxygen delivery is reduced.

Large VSD. A defect of large size (equal or greater than the aortic valve orifice) is

accompanied by a large shunt (Qp/Qs > 2.2 : 1). Left-sided congestive heart failure with pulmonary congestion is common and usually occurs within the first month of life. Long standing pulmonary congestion evolves toward pulmonary hypertension and ultimately leads to right-ventricular hypertrophy and dilation. Eisenmenger syndrome with shunt reversal and cyanosis characterizes the terminal stages of large VSDs.

A ventricular septal defect (VSD) is a

congenital abnormal opening in the ventricular septum that allows communication of blood between the left and right ventricles. Ventricular defects may be located anywhere in the ventricular septum, may be single or multiple, and may be of variable size and shape. VSD can occur as an isolated lesion or in combination with other congenital cardiac anomalies. The discussion in this section will refer to isolated VSD.

A large ASD with very significant shunt (Qp/Qs > 2.0 : 1.0) may cause

congestive heart failure and failure to thrive in an infant or child.

In general patients with PFO are never identified clinically because they have no symptoms. Transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE), and transcranial Doppler (TCD) can all be used to detect PFO. Right to left shunting at the atrial level has been implicated as a contributing factor to

cryptogenic stroke (via paradoxic embolism). Approximately 40% of ischemic strokes and transient ischemic attacks have no clear etiology and are therefore termed cryptogenic. One study of 60 adults under 55 years of age with ischemic stroke compared contrast echocardiographic examinations with 100 normal subjects. Patent foramen ovale prevalence was significantly higher in the stroke group (40%) than in controls (10%). Patent foramen ovale was found in 26 stroke patients (54%) with no other identifiable cause, and the study concluded that PFO-induced paradoxical embolism is a cause of stroke. Numerous studies have supported these findings. Patients with cryptogenic stroke in these studies were significantly younger (less than 45 years) with fewer risk factors for atherosclerosis, such as hypertension and smoking. The role of PFO as a risk factor for stroke is still debated.

Atrial septal defect (ASD) is characterized by a

defect in the interatrial septum allowing pulmonary venous return from the left atrium to pass directly to the right atrium. ASDs account for 10% of all congenital heart diseases. The female-to-male ratio of approximately 2:1. 2. Embryology. Atrial septation embryologically involves three structures: the septum primum, septum secundum, and atrioventricular (AV) canal septum.

In this defect, coronary sinus is located at a

distance to the left of its usual location in the left atrium. The atrial septum around the normal coronary sinus ostium disappears, leading to a communication between both atria.

Low oxygen tension is a factor in maintaining

ductal patency in the fetus, and the sharp increase in arterial oxygen saturation with the first breath is thought to be the initiating step in ductal closure.

A left-to-right shunt imposes a significant volume overload on the right heart, main pulmonary artery and pulmonary vasculature. The consequences are

enlargement of the right heart and main pulmonary artery. On the other hand the left ventricular output decreases because of the reduced preload. If the left ventricular output is not enough to meet the demands of the body, the patient will display growth retardation.

When the shunt is moderate in PDA (Qp:Qs between 1.5 and 2.2 to 1), patients may present with

exercise intolerance. In these patients, the moderate left-to-right shunt increases the volume load on the left atrium and ventricle, which results in left ventricular dilation and left-sided failure. The characteristic continuous murmur is louder than that associated with a small PDA, and is typically accompanied by a wide systemic pulse pressure and a dilated left ventricle associated with displaced left ventricular apex.

Atrioventricular canal (AV canal) defect arises from

faulty development of the embryonic endocardial cushions. In AV canal, a large primum atrial septal defect, a single atrioventricular valve annulus, a common atrioventricular valve (built-up of five leaflets), and a defect of the inlet ventricular septum are observed. AV canal is an uncommon congenital heart disease, accounting for about 4% of cardiac malformations. Approximately 50% of patients with AV canal have a chromosomal abnormality; of these 40% have Down syndrome (trisomy 21). AV canal defects result in increased pulmonary blood flow secondary to left-to-right shunting at the atrial and ventricular levels. This will eventually lead to pulmonary vascular obstructive disease, elevated pulmonary vascular resistance, and pulmonary hypertension. Pulmonary vascular obstructive disease can develop as early as several months of age. Patients with AV canal typically develop congestive heart failure, associated with pulmonary hypertension and complicated by insufficiency of the common atrioventricular valve in the first few months of life.

In partial anomalous pulmonary venous return (PAPVR) the blood flow is

from a few of the pulmonary veins returns to the right atrium instead of the left atrium. There are several anatomic variations of PAPVR. Usually, a single pulmonary vein is anomalous. The most common type of PAPVR is one in which a right upper pulmonary vein connects to the right atrium or the superior vena cava. PAPVR produces a left-to-right shunt. The volume of shunted blood depends on the number of anomalous pulmonary veins involved. Each normally connecting pulmonary vein contributes an average of 25% of the total pulmonary blood flow. A single anomalous vein is not usually hemodynamically significant and, hence, does not produce any symptoms.

Children with large-sized PDA are likely to eventually develop

irreversible pulmonary vascular disease secondary to long-standing high pulmonary blood flow and pulmonary hypertension. The right ventricle hypertrophies. Cyanosis indicate the development of shunt reversal and Eisenmenger syndrome.

Sinus venosus defect

is located in the upper portion of the atrial septum near the entry of superior vena cava. It gives rise to a superior vena cava connected to both atria. ASD

Infants with large VS defects develop

large left-to-right shunts in the first few weeks of life, resulting in signs of high pulmonary blood flow, congestive heart failure and failure to thrive. They present with tachypnea, tachycardia, pulmonary rales, hepatomegaly, sweating during feeding and recurrent respiratory infections. The systolic murmur is not prominent because there is no pressure gradient across the ventricular defect (thrills are uncommon). Unless surgery is performed in the first year of life, there is increasing likelihood that irreversible pulmonary vascular disease will develop leading to increased pulmonary vascular resistance, pulmonary hypertension and right ventricular hypertrophy (Eisenmenger syndrome), preventing successful repair.

The most important types of congenital heart disease causing right-to-left shunt are

tetralogy of Fallot, transposition of great arteries, persistent truncus arteriosus, tricuspid atresia, and Ebstein anomaly. These malformations are referred to as "cyanotic congenital heart disease". A right-to left shunt leads to severe hypoxemia, central cyanosis and clubbing. Right-to-left shunting does not respond to oxygen administration. The partial pressure of CO2 is normal as the patient increases minute ventilation to blow off CO2 derived from the shunt.

When the shunt is large in PDA (Qp:Qs >2.2 to 1), left ventricular volume overload develops initially. Then symptoms of

left-sided congestive heart failure and respiratory distress (tachypnea, shortness of breath, diaphoresis, recurrent pulmonary infections, poor feeding or growth failure) may be present, and the murmur may not be typical. The child with large PDA has bounding peripheral pulses, and wide pulse pressure, which is caused by the low diastolic pressure in the systemic circulation as blood runs off from the aorta into the pulmonary circulation. The cardiac impulse at the apex is hyperactive. These children are not cyanotic. Over time, there may be a progressive rise in pulmonary artery pressures, which, in the uncorrected patient, may lead to irreversible pulmonary vascular changes, increased pulmonary vascular resistance, pulmonary hypertension and right ventricular hypertrophy and Eisenmenger syndrome.

Ostium primum defect

located at the lower portion of the atrial septum, at the level of tricuspid and mitral valves. It is caused by incomplete fusion of septum primum with endocardial cushion.

Endocardial cushion VSDs

located beneath the tricuspid valve, extending to the tricuspid valve ring. About 5% of VSDs are of this type

PDA is also associated with what infection

maternal rubella infection during early pregnancy, a now uncommon occurrence. However, PDA is a common problem in premature infants, as the smooth muscle in the wall of the preterm ductus is less responsive to high PO2 and therefore less likely to constrict after birth. Conditions consisting of immature lungs are associated with persistent patency of the ductus. The factors involved are most likely inability of the immature lungs to clear the circulating prostaglandins that remain from gestation.

Muscular septum defects

may be located anywhere in the apical, mid, anterior, or posterior muscular septum and are often multiple. The term Swiss-cheese septum has been used to describe multiple muscular VSDs. These VSDs account for 10% of all defects.

PFO is also associated with what type of headache

migraine with aura. The mechanism of the migraine relationship to persistent foramen ovale remains unknown. A higher prevalence of PFO is found in migraineurs with aura compared to healthy controls: 54% vs. 24%. A postulated mechanism is that circulating substances, such as serotonin, for example, are removed by passage through the lungs in healthy people. In subjects with PFO serotonin is not removed during pulmonary circulation passage and can reach the cerebral blood flow. Serotonin lead to platelet activation and aggregation in the cerebral circulation and is thought to be the initiating trigger of migraines in susceptible individuals

A Qp/Qs ratio of < 1:1 indicates a

net right-to-left shunt. Right-to-left shunts are associated with left heart volume overload. Detection and localization of the shunt are accomplished by noting a decrease in O2 content as blood is sampled in the left heart chambers and aorta.

In ASD, the right atrium and ventricle are volume _______

overloaded and the left atrium and ventricle are volume underloaded. Chronic right ventricular overload has the potential for subsequent development of right ventricular dysfunction, right-sided heart failure or atrial arrhythmias

Patent ductus arteriosus (PDA) is a

persistent communication between the descending thoracic aorta and the pulmonary artery that results from failure of normal physiologic closure of the fetal ductus arteriosus. The ductus is functionally closed in about 90% of full term infants by 48 hours of age. Persistent patency for up to 10 days after birth is considered abnormal.

A left-to-right shunt from the aorta to the pulmonary artery leads to what in PDA

pulmonary overcirculation and left heart volume overload. This results in increased left ventricular stroke volume and, in time, compensatory left ventricular hypertrophy. The increased pulmonary flow from the ductal shunting leads to increased pulmonary fluid volume. Pulmonary edema is uncommon but may occur in premature infants owing to high pulmonary flow. On the other hand, the skin, bone, and skeletal muscle receive decreased blood flow due to a combination of decreased perfusion pressure and localized vasoconstriction. The next most likely organs to be affected by the decrease in organ perfusion are the gastrointestinal tract and kidneys. Some of the complications caused by PDA include necrotizing enterocolitis and decreased glomerular filtration rate.

Patients with moderate-sized PDA and with significant volume overload of the left heart and left ventricular dilation commonly

remain asymptomatic during infancy and childhood, but may develop congestive heart failure in adulthood, starting in the third decade.

The ductus arteriosus is a

remnant of the left sixth embryologic aortic arch and connects the origin of the left main pulmonary artery to the aorta, just distal to the left subclavian artery. During fetal life, the ductus is as large as the ascending aorta and carries outflow from the right ventricle to the descending aorta. Within hours of birth, the ductus closes, usually at the pulmonary end through muscular constriction. Later, there is obliteration of the lumen, initially by a pile up of endothelium and, finally, by complete occlusion through thrombosis, the ductus withering to a fibrous strand.

A patent foramen ovale (PFO) is a

slit or tunnel like passage in the interatrial septum formed by failure of postnatal fusion of the septum primum and septum secundum. PFO is a normal interatrial communication during fetal life. During fetal period, right-to-left flow occurs through the foramen because right atrial pressure exceeds that in the left. Everybody at birth has a patent foramen ovale. After birth, left atrial pressure increases with increasing pulmonary venous return, and the flap-valve of the foramen ovale functionally shuts owing to shifting of the left-sided septum primum against the septum secundum. Over a period of months, complete fusion between the 2 leaflets of the foramen ovale occurs in 75%-80% of individuals. The remaining 20%-25% of individuals have a persistently patent ('open') foramen ovale, which can continue to function indefinitely as a flap-valve allowing right to left flow whenever right atrial pressure exceeds left atrial pressure.

A Qp/Qs ratio of > 1:1 indicates

that pulmonary flow exceeds systemic flow and defines a net left-to-right shunt. The most important types of congenital heart disease causing left-to-right shunt are ventricular septal defect, atrial septal defect, and patent ductus arteriosus