Cyanosis is the most common manifestation of symptomatic cardiovascular disease in the newborn infant. Moreover, cyanosis in the absence of significant respiratory distress is almost always caused by structural cardiovascular disease because pulmonary disease severe enough to cause cyanosis is usually associated with severe respiratory distress. Congenital cardiovascular defects that cause primarily cyanosis in newborn infants are reviewed in this chapter. Infants who have decreased systemic perfusion as the primary symptom, even if cyanosis is also present, are discussed in Chapter 8.
Adequate oxygen delivery to meet metabolic needs is essential for healthy survival. The amount of oxygen delivered to the tissues is dependent on systemic blood flow, hemoglobin concentration, and hemoglobin oxygen saturation (Table 6-1). At birth, oxygen consumption increases nearly threefold to meet the energy costs of breathing, feeding and digestion, and thermoregulation. Immediately after birth, systemic blood flow at least doubles, and systemic arterial oxygen saturation increases from about 75% to 95% (reviewed in Chapter 3). Thus, despite the increase in oxygen consumption, oxygen delivery increases similarly, and the reserve to extract oxygen remains large in normal infants. The fractional extraction of oxygen is about 30% so that the mixed venous saturation is about 65% to 70%. In contrast, newborn infants with cyanotic congenital heart disease cannot increase systemic arterial oxygen saturation, and, in fact, oxygen saturation often falls precipitously soon after birth. These infants are therefore at risk for inadequate systemic oxygen delivery, which, if untreated, may result in anaerobic metabolism, metabolic acidosis, and death.
Decreased pulmonary blood flow (Table 6-2) and malposition of the aorta over the systemic venous ventricle (transposition complexes) are the two main pathophysiological mechanisms responsible for severely decreased systemic arterial saturation in newborn infants with cyanotic heart disease. In the normal postnatal circulation, all of the poorly saturated systemic venous blood is directed through the right heart structures to the pulmonary arteries; the oxygen saturations of the blood in the systemic veins and pulmonary arteries are therefore equal. This blood becomes nearly fully saturated as it takes up oxygen in the pulmonary capillary bed and returns to the heart via the pulmonary veins. Pulmonary venous blood then passes through the left heart structures to the aorta. Thus, the oxygen saturations in the pulmonary veins and systemic arteries are the same, and pulmonary blood flow is equal to systemic blood flow (Table 6-1).
| Anatomic level | Structural defect |
|---|---|
| Tricuspid valve | Tricuspid valve regurgitation Tricuspid valve stenosis or atresia Ebstein anomaly |
| Right ventricle | Hypoplastic right ventricle Tetralogy of Fallot (subpulmonic stenosis with ventricular septal defect) |
| Pulmonary valve | Pulmonary valve stenosis or atresia with intact ventricular septum Pulmonary valve stenosis or atresia with ventricular septal defect (± single ventricle, malposed aorta, or aortopulmonary collateral vessels) Absent pulmonary valve syndrome |
| Pulmonary artery | Supravalvar pulmonary artery stenosis Branch pulmonary artery stenosis |
In conditions of decreased pulmonary blood flow (Table 6-2), systemic venous blood returns to the right atrium, but some of this desaturated blood does not reach the pulmonary arteries for oxygen uptake. Rather, a portion passes to the left heart structures and aorta, where it mixes with pulmonary venous blood, resulting in decreased systemic arterial saturation. In addition, a portion of pulmonary venous blood often returns to the lungs (eg, via a ductus arteriosus) and does not contribute to oxygen uptake. “Effective pulmonary blood flow” is defined as the volume of systemic venous blood delivered to the pulmonary arteries for oxygen uptake and is directly proportional to the oxygen saturation in the aorta (Table 6-1). In conditions of malposition of the aorta over the systemic venous ventricle (transposition complexes), cyanosis also occurs; in this situation, however, pulmonary blood flow is normal or even increased. For example, when the aorta is malposed over the ventricle that receives the systemic venous return (typically the right ventricle), most of the systemic venous blood is ejected into the aorta. Depending on the position of the pulmonary artery and the presence or absence of a ventricular septal defect, varying amounts of pulmonary venous blood are ejected into the aorta and pulmonary artery. In the most common defect in this category—d-transposition of the great arteries with intact ventricular septum (Figure 6-1A)—all of the pulmonary venous blood flows back to the pulmonary arteries if there is no communication between the two sides of the heart. The volume of pulmonary blood flow is normal, but it never reaches the systemic circulation—this is not compatible with survival. Survival is dependent on at least some of pulmonary venous blood entering the aorta. This must occur at the atrial level (eg, from the left atrium across the foramen ovale into the right atrium, right ventricle, and then the aorta), the arterial level (the ductus arteriosus), or both. Patency of the foramen ovale or ductus arteriosus is essential to survival. In the presence of both, left-to-right flow through the ductus arteriosus increases pulmonary blood flow so that left atrial volume and pressure increase, which in turn increases the left-to-right atrial shunt.
FIGURE 6-1.
A. Simple d-transposition of the great arteries (ventricular-arterial discordance). The immediate postnatal circulation shows pulmonary venous blood returning to the pulmonary artery and systemic venous blood returning to the aorta, causing severe cyanosis. The shunt through the foramen ovale, if present, passes in a left-to-right direction. The shunt through the ductus arteriosus is mixed, with a small right-to-left shunt in early systole and a much larger left-to-right shunt in diastole. Red arrows indicate oxygenated blood, and blue arrows indicate desaturated blood. Abbreviations: LA, left atrium; LV, anatomic left ventricle; RA, right atrium; RV, anatomic right ventricle.
Transposition of the great arteries is called ventricular-arterial discordance because the ventricles connect to the wrong arteries. In simple d-transposition of the great arteries, there is atrial-ventricular concordance because the right atrium connects normally to the anatomic right ventricle through a tricuspid valve, and the left atrium connects normally to the anatomic left ventricle through a mitral valve. However, atrial-ventricular discordance can also occur. In that case, the right atrium connects via the mitral valve to the left ventricle, and the left atrium connects via the tricuspid valve to the right ventricle (Figure 6-1B). If both atrial-ventricular discordance and ventricular-arterial discordance are present together, blood flow patterns are normal. Thus, this condition is often called “corrected” transposition of the great arteries. l-transposition of the great arteries is a more appropriate term because the embryologic abnormality is failure of the primitive heart tube to rotate to a rightward (d-looped) position. Instead, rotation is to the left (l-looping). As an isolated anomaly, l-transposition of the great arteries does not cause symptoms in infants, but associated cardiovascular defects are commonly present (see following text).
FIGURE 6-1.
B. l-transposition of the great arteries (atrial-ventricular and ventricular-arterial discordance). The immediate postnatal circulation shows systemic venous blood returning normally to the right atrium and then flowing to the anatomic left ventricle and pulmonary artery. Pulmonary venous blood returns to the left atrium and then flows to the anatomic right ventricle and aorta. Aortic saturation is normal, and there is a small left-to-right ductal shunt. The aorta arises anteriorly and to the left (l-loop) and ascends to the right. Red arrows indicate oxygenated blood, and blue arrows indicate desaturated blood. The abbreviations are the same as for Figure 6-1A.
Cyanosis is a critically important clinical finding to detect in the newborn infant. It is the primary presentation of cardiovascular disease that manifests symptomatically in the newborn infant. If cyanosis due to congenital cardiovascular disease is not recognized, the neonate may experience rapid and severe cardiovascular decompensation. Evaluation of cyanosis is discussed in Chapter 5, but the critical features of cyanotic congenital cardiovascular disease are the following:
Systemic arterial hypoxemia is manifested clinically by central rather than peripheral cyanosis.
Cyanosis is often not present immediately after birth, particularly in infants who have defects that cause decreased pulmonary blood flow, because the ductus arteriosus is still widely patent.
Cyanosis is not evident until a significant amount of reduced hemoglobin is present. If an infant has a systemic arterial oxygen saturation above 85%, cyanosis may be quite difficult to detect by visual inspection. Oxygen saturation should be measured by pulse oximetry in all newborn infants as a screening test and at any time that there is concern that central cyanosis may be present.
Oxygen saturation may differ between the upper and lower body. The ascending and descending aorta may be perfused by different ventricles if the ductus arteriosus is patent. Pulse oximetry should be performed on the right hand, which receives blood from the ascending aorta in the normal aortic arch, and on either foot, which receives blood from the descending aorta. Certain conditions are associated with different relationships in oxygen saturation between the upper and lower body; defining the relationship may be very helpful to identify the specific defect causing cyanosis (Table 6-3). It should also be remembered that, rarely, the right subclavian artery arises from the descending aorta and does not reflect ascending aorta saturation (Chapter 5).
Infants with cyanotic heart disease are hypoxemic and thus breathe rapidly. However, they rarely have respiratory distress (ie, no retractions or nasal flaring), and arterial CO2 levels are usually decreased because of hyperventilation. Thus, these defects are rarely confused with primary lung disease.
| Lower body oxygen saturation (relative to upper) | Defect groups possible | Defect groups excluded |
|---|---|---|
| Same | Decreased pulmonary blood flow Transposition complexes Pulmonary hypertension | None |
| Higher | Transposition complexes | Decreased pulmonary blood flow Pulmonary hypertension |
| Lower | Pulmonary hypertension | Decreased pulmonary blood flow Transposition complexes |
Obstruction to blood flow within the right heart or pulmonary arteries or severe regurgitation of the tricuspid or pulmonary valve causes decreased pulmonary blood flow (Table 6-2). Obstructive defects are far more common than defects in which valvar regurgitation is the dominant problem. In all of these situations, a portion of the systemic venous blood is shunted from the right atrium through the foramen ovale to the left atrium, where it mixes with pulmonary venous blood, resulting in systemic arterial desaturation. In certain defects, a right-to-left shunt across a ventricular septal defect is also present. Because obstruction or regurgitation almost always occurs proximal to the ductus arteriosus, upper and lower body saturations are always similar in this group of defects, even if the ductus arteriosus is patent. This is a very important finding that differentiates this group of newborns from those with transposition complexes or persistent pulmonary hypertension of the newborn (Table 6-3).
During fetal life, inflow or outflow obstruction to the right ventricle without a ventricular septal defect causes a large portion of blood that would otherwise enter the right ventricle to cross the foramen ovale into the left atrium. In the extreme case of either tricuspid atresia or pulmonary atresia with intact ventricular septum (Figure 6-2), all systemic venous return passes through the foramen ovale. Thus, the foramen ovale is extremely large in utero. Postnatally, a significant interatrial communication is usually present. This defect is essentially a stretched foramen ovale in which the flap does not fully close the foramen after birth. The interatrial communication is almost always nonrestrictive after birth, and systemic venous return to the left heart is unobstructed. However, in rare cases, the opening in the atrial septum is too small, and an emergency atrial septostomy is necessary to maintain systemic output.
FIGURE 6-2.
Pulmonary atresia with intact ventricular septum and right ventricular hypoplasia. Fetal flow patterns show systemic and umbilical venous return passing through the foramen ovale, causing it to be a large communication. The ascending aorta receives all of the ventricular output so that the aortic arch and isthmus are large and the ductus arteriosus, in which flow is reversed, is vertically oriented and small. Red lines indicate oxygenated blood, and blue lines indicate desaturated blood. The intermediate purple arrows illustrate mixing of the venous return so that systemic blood has decreased oxygen saturation. Abbreviations: LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
In these conditions, the left ventricle receives much more of the combined venous return because of the increased blood flow into the left atrium across the foramen ovale. The coronary and upper body circulations receive a normal amount of combined ventricular output so that the excess output passes through the aortic arch and isthmus to the descending aorta. This enlarges the aortic isthmus so that coarctation of the aorta does not occur. This is another important finding that differentiates these defects from the transposition complexes, in which coarctation of the aorta may be present.
Flow across the foramen ovale is not increased in the group of infants with obstruction to pulmonary blood flow who have a ventricular septal defect. For example, in patients with tetralogy of Fallot, venous return passes normally to the right ventricle, but rather than passing entirely into the main pulmonary artery, some of the right ventricular output is diverted into the ascending aorta through a subaortic ventricular septal defect (Figure 6-3). Thus, blood flow through the ascending aorta and aortic arch is increased (as in patients without a ventricular septal defect), and again coarctation of the aorta is not present.
FIGURE 6-3.
Tetralogy of Fallot. Fetal flow patterns show normal venous return to the right and left ventricles, but some right ventricular output is directed to the ascending aorta, enlarging the aortic arch and causing the ductus arteriosus to shunt left to right. Red lines indicate oxygenated blood, and blue lines indicate desaturated blood. The intermediate purple arrows illustrate mixing of the venous return so that systemic blood has decreased oxygen saturation. Abbreviations: LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
An extremely useful clinical finding in infants with cyanosis is the quality of the right ventricular impulse. Normally, the right ventricle is easily palpated along the lower sternum or in the subxiphoid area. This is because the right ventricle is the dominant ventricle during fetal life and is anteriorly positioned and the sternum is relatively pliable. The right ventricular impulse is either normal or increased in patients with right ventricular outflow tract obstruction, transposition complexes, or persistent pulmonary hypertension of the newborn. However, if inflow obstruction is present, the right ventricle does not fill normally and thus does not contract to a normal extent. The right ventricular impulse is decreased in such patients. Thus, the presence of a decreased right ventricular impulse in a newborn infant with cyanosis quickly limits the differential diagnosis to the few defects in which right ventricular inflow obstruction is present (Table 6-2), the two most common of which are described next.
In tricuspid atresia, the tricuspid valve fails to form normally, resulting in an atretic valve with total obstruction of inflow to the right ventricle from the right atrium. Consequently, all of the systemic venous blood crosses the foramen ovale to the left atrium and ventricle. The degree of right ventricular hypoplasia is variable. In the large majority of these infants, a ventricular septal defect is present, promoting the development of a small right ventricle as blood flows from the left ventricle through ventricular septal defect to right ventricle and pulmonary arteries in utero. The great arteries are usually normally related, but d-transposition of the great arteries is present in a small percentage of infants. When the great arteries are transposed, pulmonary blood flow is increased because the pulmonary valve arises directly from the left ventricle, whereas systemic blood flow depends on the size of the ventricular septal defect so that coarctation of the aorta may occur.
Physical examination reveals increasing cyanosis as the ductus arteriosus closes (except in the presence of a large VSD and unobstructed pulmonary blood flow), and the oxygen saturations are similar in all extremities. Tachypnea may be present, but respiratory distress is absent. The peripheral pulses and perfusion are normal, and the remainder of the noncardiac examination is usually noncontributory. The right ventricular impulse is decreased, an important finding directing the clinician to consider this diagnosis. Even more specific is a thrill, which may be present when blood flows anteriorly from the left ventricle to the right via a restrictive ventricular septal defect. This is pathognomonic of tricuspid atresia in a cyanotic newborn infant; in all other cyanotic defects with a ventricular septal defect, blood flows from the right ventricle posteriorly to the left so that a thrill is not present. The first heart sound is normal. No extra sounds or clicks are heard. The second heart sound depends on associated defects. It is usually single but will be split if the flow across the ventricular septal defect and pulmonary valve is large. However, at the normal rapid heart rates present at birth, a split second heart sound is difficult to appreciate. If the great arteries are transposed, the aortic component of the second heart sound may be loud. A murmur may be heard as a result of flow through a ventricular septal defect or right ventricular outflow tract obstruction.
Based on clinical findings alone, it is usually possible to limit the differential diagnosis in these infants to cyanosis caused by defects that result in right ventricular inflow obstruction (Table 6-2). Simple ancillary tests usually can then differentiate tricuspid atresia from pulmonary atresia with intact ventricular septum and determine whether there is associated d-transposition of the great arteries:
The chest radiograph shows a narrow mediastinum when the arteries are transposed and a normal mediastinum when they are normally related.
The electrocardiogram usually shows right atrial enlargement and decreased right ventricular forces in all of these defects, but the axis is inferior with a normal clockwise loop in pulmonary atresia with intact septum, whereas it is superior (0 to –60 degrees) with a counterclockwise loop in tricuspid atresia and normally related great arteries. Infants with tricuspid atresia and d-transposition of the great arteries may have a similar axis to those with pulmonary atresia (0 to +90 degrees).
Echocardiography is definitive. No tricuspid valve tissue is seen in the atrioventricular groove, between the right atrium and the right ventricle. Obligatory flow across the foramen ovale (or secundum atrial septal defect) into the left atrium is present and is often directed by a large eustachian valve in the right atrium. The size of the atrial communication, the presence of a ventricular septal defect, the size of the right ventricle and right ventricular outflow tract, the relationship of the great arteries, and the patency of the ductus arteriosus should all be evaluated.
These infants are considered to have a functional single ventricle because the right ventricle will never function as an adequate pumping chamber in the absence of an adequate inlet. Most infants require a systemic-to-pulmonary artery shunt shortly after birth because of severe cyanosis. Some centers are providing pulmonary blood flow by transcatheter placement of a stent in the ductus arteriosus rather than via a surgical aorto-pulmonary shunt. Subsequently a bidirectional Glenn shunt (superior cavopulmonary connection) and then a modified Fontan operation are performed (see following text). Infants who have a relatively well developed right ventricle and pulmonary valve because of the presence of a ventricular septal defect are only minimally cyanotic and may not need a systemic-to-pulmonary artery shunt. Occasionally, if pulmonary blood flow is very high, a pulmonary arterial band may be needed. Even more uncommon is when the pulmonary obstruction allows for an appropriate amount of pulmonary blood flow under low perfusion pressure so that no surgery in the first months of life is necessary. After the newborn period, these infants progress through staged single-ventricle palliation as described below. Infants with transposed great arteries often develop functional subaortic obstruction (restrictive bulboventricular foramen) and may need a Damus-Kaye-Stansel operation (see following text) to be performed at the time of either the bidirectional Glenn shunt or modified Fontan operation.
A second category of right ventricular inflow obstructive defects occurs when the tricuspid valve is present but is severely hypoplastic. This is associated with hypoplasia of the right ventricle and atresia of the pulmonary valve. After birth, pulmonary blood flow is entirely dependent on patency of the ductus arteriosus. The systolic pressure in the right ventricle is usually much greater than the systemic systolic pressure because of the right ventricular outflow tract obstruction. As a result of the very high pressure within the right ventricular cavity, embryonic connections of the right ventricular cavity with coronary arteries may persist as coronary sinusoids (Figure 6-4). These connections may perfuse the myocardium with poorly saturated blood and may not communicate with the proximal coronary system, or they may connect to the coronary arteries but with severely stenotic openings. In these situations, part of the coronary arterial circulation is dependent on perfusion from the right ventricle (“right ventricle–dependent coronary circulation”), which increases the risk of death because of myocardial ischemia.
FIGURE 6-4.
Pulmonary atresia with intact ventricular septum and right ventricular hypoplasia. A right ventricular angiogram demonstrating a very hypertrophied diminutive ventricle with extensive filling of both coronary arterial systems by sinusoidal communications with the hypertensive ventricle. Abbreviation: RV, right ventricle.
On physical examination, the infant is cyanotic within a few hours after birth and has similar oxygen saturations in all extremities. The peripheral pulses and perfusion are normal. Important noncardiac findings are rarely present. Although the right ventricle is usually generating systolic pressures that greatly exceed systemic pressure, the right ventricular impulse is often decreased because the right ventricle usually receives and ejects only a very small amount of blood. The first heart sound is normal. No extra sounds or clicks are heard. The second heart sound is single and of normal intensity. Murmurs are only occasionally present and reflect either a narrow ductus arteriosus or tricuspid valve regurgitation.
The chest radiograph shows a small cardiac silhouette and normal mediastinum, similar to that seen in tricuspid atresia with normally related great arteries.
The electrocardiogram shows decreased, normal, or increased right ventricular forces, depending on the mass of the right ventricular wall. In contrast to patients with tricuspid atresia, the axis is in the left inferior quadrant (+60 to 90 degrees); this is an important differentiating point.
The echocardiogram usually shows a small tricuspid valve annulus and a markedly hypertrophied right ventricle with little contraction and often evidence of endocardial fibrosis. The size of the tricuspid valve and right ventricle should be defined. There usually is no apparent right ventricular outflow tract, and there is a unidirectional right-to-left atrial shunt. Color Doppler echocardiography may demonstrate flow in the coronary arterial sinusoids within the myocardial wall. Evaluation of whether the coronary arterial circulation is dependent on the right ventricle is mandatory, and cardiac catheterization may be necessary to resolve this issue.
Treatment of these patients must be individualized and is often difficult and complicated. The major question is whether the tricuspid valve and right ventricle can grow enough to support some or all of the pulmonary circulation if right ventricular outflow obstruction is relieved or whether the patient must be treated as a functional single ventricle. In many of these patients, the very small tricuspid valve precludes its use in the circulation. However, there is a continuum between these patients and those with pulmonary valve atresia and a normal-size right ventricle (see below); in those patients with a moderately hypoplastic tricuspid valve and right ventricle, creation of continuity between the right ventricle and pulmonary artery may result in remarkable growth of the tricuspid valve and right ventricle. Placement of a systemic-to-pulmonary artery shunt may be necessary in addition to right ventricular outflow tract reconstruction to ensure adequate pulmonary blood flow, at least in the short term. Patients with an extremely hypoplastic right ventricle, right ventricle–dependent coronary circulation, or a right ventricle that fails to grow adequately after relief of right ventricular outflow tract obstruction are treated as functional single ventricles. They require a systemic-to-pulmonary artery shunt (or a stent in the ductus arteriosus) and later are candidates for a bidirectional Glenn shunt and modified Fontan operation (see following text).
Pulmonary atresia with an intact ventricular septum is not necessarily associated with a hypoplastic right ventricle. When the right ventricular cavity is well formed, the tricuspid valve is usually of nearly normal size but may be severely insufficient. Coronary arterial sinusoids do not develop, likely in part because the right ventricle cannot generate high pressures because of the tricuspid regurgitation. Additionally, by the time the outflow obstruction develops during fetal life, the embryonic sinusoids may have already regressed. Interestingly, the pulmonary arteries are usually normally developed despite the fact that they receive only a small amount of the fetal combined ventricular output through the ductus arteriosus.
The infant is cyanotic within a few hours after birth with similar oxygen saturations in all extremities. Mild tachypnea is present, but respiratory distress is absent. The peripheral pulses and perfusion are normal, and the noncardiac examination is unremarkable. Unlike the infant with the hypoplastic right ventricle, however, the large volume of blood passing into the right ventricle is associated with a normal to increased right ventricular impulse. The first heart sound is normal or may be obscured by the tricuspid regurgitation murmur. No extra heart sounds are present. The second heart sound is single. An early, blowing systolic murmur heard best at the left lower sternal border and radiating toward the right anterior chest is caused by the tricuspid valve regurgitation.
The chest radiograph usually shows an enlarged right atrium because of tricuspid insufficiency, and the central blood vessels are of normal size.
The electrocardiogram is similar to that seen in pulmonary atresia with a hypoplastic tricuspid valve, except that right ventricular hypertrophy is more common and right atrial enlargement may be especially pronounced.
The echocardiogram shows a nearly normal tricuspid valve annulus. The z score, a measure of the number of standard deviations from the normal mean diameter, is usually greater than –2. Severe tricuspid regurgitation with an enlarged right atrium is present. The right ventricle, which is well formed (inflow, body, and outflow components are all present), contracts normally, and endocardial fibroelastosis is not seen. The pulmonary arteries and pulmonary valve are normal in size, and the pulmonary circulation is exclusively from blood passing through the ductus arteriosus.
These infants require administration of prostaglandin E1 to maintain adequate pulmonary blood flow through the ductus arteriosus. Pulmonary valvuloplasty performed in the cardiac catheterization laboratory is the procedure of choice. Access to the pulmonary artery from the right ventricle usually is achieved by radio-frequency perforation of the atretic valve, and then a balloon valvuloplasty is performed. Many infants do very well after this procedure. However, sometimes the oxygen saturation is quite low because the hypertrophied and noncompliant right ventricle cannot accept an adequate amount of systemic venous return even after a successful valvuloplasty. In these cases, it is necessary to continue prostaglandin E1 administration after the procedure or to perform a systemic-to-pulmonary artery shunt. The ventricle, though, often rapidly remodels, and the prostaglandin E1 infusion or the shunt may be necessary for only a short period of time.
Critical pulmonary valve stenosis is very similar to pulmonary atresia with a normal-size right ventricle and is likely caused by similar events during cardiovascular development. Instead of an imperforate pulmonary valve, forward flow of blood is present. The distinction between critical and severe stenosis is based on a systemic arterial desaturation below some arbitrary level, usually about 90% to 92%, in the absence of a patent ductus arteriosus. Both critical and severe stenosis of the pulmonary valve cause right ventricular systolic pressures to be at or, most often, higher than systemic levels. If the degree of stenosis is critical, the ventricle cannot eject the entire systemic venous return across the pulmonary valve. In these cases, some of the systemic venous return crosses the foramen ovale to the left atrium, causing systemic arterial desaturation.
The clinical presentation of infants with critical pulmonary valve stenosis is similar to that of infants with pulmonary atresia. The right ventricular impulse may be increased if there is a large amount of tricuspid regurgitation. The second heart sound is single. Although there is forward flow across the pulmonary valve, it is so minimal that it cannot be heard, and the limited valve opening is not associated with an ejection click. A murmur of tricuspid regurgitation is usually present.
The chest radiograph and electrocardiogram are similar to those seen in pulmonary atresia.
Echocardiography is also similar to that seen in pulmonary atresia, except there is flow across the pulmonary valve and coronary sinusoids are rarely present. Forward flow may be so limited that it cannot be distinguished from the turbulence in the main pulmonary artery caused by ductal flow striking the atretic valve. Thus, definitive evidence of valve patency is often a small jet of pulmonary regurgitation visualized by color Doppler in the right ventricular outflow tract (Figure 6-5).
FIGURE 6-5.
Critical pulmonary stenosis. Two-dimensional echocardiography demonstrates a well-developed pulmonary valve that does not appear to open (A). Color Doppler demonstrates a narrow jet of pulmonary insufficiency (B, see arrow), indicating that the pulmonary valve is critically obstructed rather than atretic. The flow distal to the pulmonary valve represents not flow crossing the valve but rather ductal flow toward the valve (red) and reversal of that flow toward the branch pulmonary arteries (blue). Abbreviations: PA, pulmonary artery; RV, right ventricle.
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