This chapter discusses common left-to-right shunt lesions such as atrial septal defect (ASD), ventricular septal defect (VSD), patent ductus arteriosus (PDA), endocardial cushion defect (ECD), and partial anomalous pulmonary venous return (PAPVR).
Atrial Septal Defect
Prevalence
Atrial septal defect (ostium secundum defect) occurs as an isolated anomaly in 5% to 10% of all congenital heart defects (CHDs). It is more common in females than in males (male-to-female ratio of 1:2). About 30% to 50% of children with CHDs have an ASD as part of the cardiac defect.
Pathology
- 1.
Four types of ASDs exist: secundum defect, primum defect, sinus venosus defect, and coronary sinus ASD. Patent foramen ovale (PFO) does not ordinarily produce intracardiac shunts (see Chapter 15 ).
- 2.
Ostium secundum defect is the most common type of ASD, accounting for 50% to 70% of all ASDs. This defect is present at the site of fossa ovalis, allowing left-to-right shunting of blood from the left atrium (LA) to the right atrium (RA) ( Fig. 12-1 ). Anomalous pulmonary venous return is present in about 10% of cases.
FIGURE 12-1
Anatomic types of atrial septal defects (ASDs) viewed with the right atrial wall removed. IVC, inferior vena cava; SVC, superior vena cava.
- 3.
Ostium primum defects occur in about 30% of all ASDs, if those that occur as part of complete ECD are included (see Fig. 12-1 ). Isolated ostium primum ASD occurs in about 15% of all ASDs. This is discussed in greater detail in the section on partial ECD.
- 4.
Sinus venosus defect occurs in about 10% of all ASDs. The defect is most commonly located at the entry of the superior vena cava (SVC) into the RA (superior vena caval type) and rarely at the entry of the inferior vena cava (IVC) into the RA (inferior vena caval type). The former is commonly associated with anomalous drainage of the right upper pulmonary vein (into the RA), and the latter is often associated with anomalous drainage of the right lung into the IVC (“scimitar syndrome”) (see Chapter 15 ).
- 5.
Coronary sinus ASD is a rare type of defect in which a defect is present in the roof of the coronary sinus. The LA blood shunts through the defect and empties into the RA through the coronary sinus orifice, producing clinical pictures similar to other types of ASD.
- 6.
Mitral valve prolapse (MVP) occurs in 20% of patients with either ostium secundum or sinus venosus defects.
Clinical Manifestations
History
Infants and children with ASDs are usually asymptomatic.
Physical Examination ( Fig. 12-2 )
- 1.
A relatively slender body build is typical. (The body weight of many is less than the 10th percentile.)
FIGURE 12-2
Cardiac findings of atrial septal defect. Throughout this book, heart murmurs with solid borders are the primary murmurs, and those without solid borders are transmitted murmurs or those occurring occasionally. Abnormalities in heart sounds are shown in black. Exp, expiration; Insp, inspiration.
- 2.
A widely split and fixed S2 and a grade 2 to 3 of 6 systolic ejection murmur are characteristic findings of ASD in older infants and children. With a large left-to-right shunt, a mid-diastolic rumble resulting from relative tricuspid stenosis may be audible at the lower left sternal border.
- 3.
Classic auscultatory findings (and electrocardiographic [ECG] and radiography findings) of ASD are not present unless the shunt is reasonably large (at least Qp/Qs of 1.5 or greater). The typical auscultatory findings may be absent in infants and toddlers, even in those with a large defect because the RV is poorly compliant.
Electrocardiography ( Fig. 12-3 )
Right axis deviation of +90 to +180 degrees and mild right ventricular hypertrophy (RVH) or right bundle branch block (RBBB) with an rsR′ pattern in V1 are typical ECG findings. In about 50% of patients with sinus venosus ASD, the P axis is less than +30 degrees.
Radiography Studies ( Fig. 12-4 )
- 1.
Cardiomegaly with enlargement of the RA and right ventricle (RV) may be present.
FIGURE 12-4
Posteroanterior and lateral views of chest roentgenograms from a 10-year-old child with atrial septal defect. The heart is mildly enlarged with involvement of the right atrium (best seen in the posteroanterior view) and the right ventricle (best seen in the lateral view with obliteration of the retrosternal space). Pulmonary vascularity is increased, and the main pulmonary artery segment is slightly prominent.
- 2.
A prominent pulmonary artery (PA) segment and increased pulmonary vascular markings are seen when the shunt is significant.
Echocardiography
- 1.
A two-dimensional echocardiographic study is diagnostic. The study shows the position as well as the size of the defect, which can best be seen in the subcostal four-chamber view ( Fig. 12-5 ). In secundum ASD, a dropout can be seen in the midatrial septum. The primum type shows a defect in the lower atrial septum; the SVC type of sinus venosus defect shows a defect in the posterosuperior atrial septum.
FIGURE 12-5
Diagram of two-dimensional echocardiography of the three types of atrial septal defects (ASDs). The subcostal transducer position provides the most diagnostic view. A , Sinus venosus defect. The defect is located in the posterosuperior atrial septum, usually just beneath the orifice of the superior vena cava. This defect is often associated with partial anomalous return of the right upper pulmonary vein. B, Secundum ASD. The defect is located in the middle portion of the atrial septum. C, Primum ASD. The defect is located in the anteroinferior atrial septum, just over the inflow portion of each atrioventricular valve. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
- 2.
Indirect signs of a significant left-to-right atrial shunt include RV enlargement and RA enlargement, as well as dilated PA, which often accompanies an increased flow velocity across the pulmonary valve. These findings indicate the functional significance of the defect.
- 3.
Pulsed Doppler examination reveals a characteristic flow pattern with the maximum left-to-right shunt occurring in diastole. Color-flow mapping enhances the evaluation of the hemodynamic status of the ASD.
- 4.
M-mode echocardiography may show increased RV dimension and paradoxical motion of the interventricular septum, which are signs of RV volume overload.
- 5.
In older children and adolescents, especially in those with overweight, adequate imaging of the atrial septum may not be possible with the ordinary transthoracic echocardiographic study. Transesophageal echocardiography (TEE) may be used as an alternative.
Natural History
- 1.
Earlier reports have indicated that spontaneous closure of the secundum defect occurs in about 40% of patients in the first 4 years of life (reported rates vary between 14% and 55% of patients). The defect may decrease in size in some patients. However, a more recent report indicates the overall rate of spontaneous closure to be 87%. In patients with an ASD smaller than 3 mm in size diagnosed before 3 months of age, spontaneous closure occurs in 100% of patients at 1½ years of age. Spontaneous closure occurs more than 80% of the time in patients with defects between 3 and 8 mm before 1½ years of age. An ASD with a diameter larger than 8 mm rarely closes spontaneously. Spontaneous closure is not likely to occur after 4 years of age.
It may be that “small ASDs” detected by color Doppler studies are not the true ASD; they may simply be incompetent foramen ovale which resolved to competent PFO without shunt. (Spontaneous closure of VSD is associated with high velocities across the defect with resulting platelet adhesion to a jet lesion on the septal leaflet of the tricuspid valve. Such hemodynamic abnormalities do not exist with ASD.)
- 2.
Most children with an ASD remain active and asymptomatic. Rarely, congestive heart failure (CHF) can develop in infancy.
- 3.
If a large defect is untreated, CHF and pulmonary hypertension begin to develop in adults who are in their 20s and 30s, and it becomes common after 40 years of age.
- 4.
With or without surgery, atrial arrhythmias (flutter or fibrillation) may occur in adults. The incidence of atrial arrhythmias increases to as high as 13% in patients older than 40 years of age.
- 5.
Infective endocarditis does not occur in patients with isolated ASDs.
- 6.
Cerebrovascular accident, resulting from paradoxical embolization through an ASD, is a rare complication.
Management
Medical
- 1.
Exercise restriction is unnecessary.
- 2.
In infants with CHF, medical management (with a diuretic) is recommended because of its high success rate and the possibility of spontaneous closure of the defect.
Nonsurgical Closure
Nonsurgical closure using a catheter-delivered closure device has become a preferred method, provided the indications are met. Several closure devices that can be delivered through cardiac catheters have been shown to be safe and efficacious for secundum ASD closure. In the United States, currently only the Amplatzer septal occluder (AGA Medical) and Helex septal occluder (W.L. Gore and Associates) are approved for secundum ASD closure. Currently, there are no transcatheter devices designed for closure of sinus venosus, primum, or coronary sinus ASDs.
The use of the closure device may be indicated to close a secundum ASD measuring 5 mm or more in diameter (but less than 32 mm for Amplatzer device and less than 18 mm for Helex device) and a hemodynamically significant L-R shunt with clinical evidence of RV volume overload (i.e., Qp/Qs ratio of 1.5:1 or greater or RV enlargement). There must be enough rim (4 mm) of septal tissue around the defect for appropriate placement of the device, although some newer devices no longer require a septal rim present along the entire margin of the defect. The size of the rim around the ASD can be estimated by two-dimensional echocardiographic study as diagrammatically shown in Figure 12-6 . The rim size is estimated in four directions: anterosuperior, anteroinferior, posterosuperior, and posteroinferior ( Magni et al, 1997 ).
The timing of the device closure for secundum ASD is not entirely clear. Considering the possibility of spontaneous closure, it is wise not to use the device in infancy unless the patient is symptomatic with heart failure. ASD closure devices can be implanted successfully in children younger than 2 years of age, although common practice suggests that a weight greater than 15 kg may offer some technical advantages and simplify the procedure ( Feltes et al, 2011 ). Closure rates are excellent with small residual shunts seen in fewer than 5% of patients at 1 year of follow-up.
Complications are extremely rare. The overall risk of the procedure is 7.2% with the major complication rate of 1.6%, including device embolism with surgical removal. Other reported complications may include the following.
- 1.
Early ECG abnormalities are common within the first 24 hours after implant, but most of these resolve quickly.
- 2.
Probably the most feared complication with the Amplatzer device (but not with the Helex device) is early or late erosion of the device into the aortic root, with subsequent pericardial tamponade and rare death. It may be related to the oversizing of devices and deficiency of the anterosuperior (or retroaortic) rim (see Fig. 12-6 ).
- 3.
Rarely thrombus formation in the right and left atrium occurs (2%–3%), but cerebral embolism is not more frequent than after surgical closure of the defect.
- 4.
Release of nickel from the device (with peak at 1 month after implant) is a rare cause of significant allergic reaction.
Advantages of nonsurgical closure include a complete avoidance of cardiopulmonary bypass with its attendant risk, avoidance of pain and residual thoracotomy scars, a less than 24-hour hospital stay, and rapid recovery. All of these devices are associated with a higher rate of small residual leak than is operative closure.
Postdevice Closure Follow-up
The patients are prescribed aspirin 81 mg per day for 6 months. Postprocedure echocardiographic studies check for a residual atrial shunt and unobstructed flow of pulmonary veins, coronary sinus, and venae cavae, and proper function of the mitral and tricuspid valves. If 1-month and 1-year follow-up echocardiographic findings are normal, yearly or biennial follow-up will suffice. Some cardiologists prescribe aspirin 81 mg for patients with residual shunt to prevent paradoxical embolization, but most cardiologists do not.
Surgical Closure
Indications and Timing
Surgical closure is indicated only when device closure is not considered appropriate. Therefore, most patients with secundum ASD are not candidates for surgical closure of the defect.
- 1.
A left-to-right shunt with a pulmonary-to-systemic blood flow ratio (Qp/Qs ratio) of 1.5:1 or greater is a surgical indication. Surgery is usually delayed until 2 to 4 years of age because the possibility of spontaneous closure exists.
- 2.
If CHF does not respond to medical management, surgery is performed during infancy, again if device closure is considered inappropriate.
- 3.
High pulmonary vascular resistance (PVR) (i.e., >10 units/m 2 , >7 units/m 2 with vasodilators) may be a contraindication for surgery (or device closure).
Procedure
For secundum ASD, the defect is traditionally repaired through a midsternal incision under cardiopulmonary bypass by either a simple suture or a pericardial or Teflon patch. Recently, so-called minimally invasive cardiac surgical techniques with smaller skin incisions have become popular, especially for female patients. For ASDs (including simple primum ASDs and sinus venosus defects), one of the following techniques can be used: midline short transxiphoid incision with minimal sternal split (preferred), transverse inframammary incision with vertical or transverse sternotomy, or small lower midline skin incision with either partial or full median sternotomy. The benefit of this technique appears to be an improved cosmetic result; it does not reduce pain, hospital stay, or surgical stress.
For a sinus venosus defect without associated anomalous pulmonary venous return, the defect is closed using an autologous pericardial patch. When it is associated with pulmonary venous anomaly, a tunnel is created between the anomalous pulmonary vein and the ASD by using a Teflon or pericardial patch. A plastic or pericardial gusset is placed in the SVC to prevent obstruction to the SVC. Alternatively, one may use the Warden procedure . In this procedure, the SVC is divided above the level of the pulmonary venous entry. The cardiac end of the SVC is oversewn, and a pericardial baffle is placed in such a way to drain the pulmonary venous blood through the sinus venosus ASD into the LA. The proximal SVC is sewn to the right atrial appendage to drain the SVC blood to the RA.
For coronary sinus ASD, the ostium of the coronary sinus is closed with an autologous pericardium with care to avoid conduction tissues, provided it is not associated with persistent left SVC. This will result in drainage of coronary sinus blood into the left atrium.
Mortality
Fewer than 0.5% of patients die; however, there is a greater risk for small infants and those with increased PVR.
Complications
Cerebrovascular accident and postoperative arrhythmias may develop in the immediate postoperative period.
Postoperative Follow-up
- 1.
Cardiomegaly on chest radiographs and enlarged RV dimension on echo as well as the wide splitting of the S2 may persist for 1 or 2 years after surgery. The ECG typically demonstrates RBBB (or RV conduction disturbance).
- 2.
Atrial or nodal arrhythmias occur in 7% to 20% of postoperative patients. Occasionally, sick sinus syndrome, which occurs especially after the repair of a sinus venosus defect, may require antiarrhythmic drugs, pacemaker therapy, or both.
Ventricular Septal Defect
Prevalence
Ventricular septal defect is the most common form of CHD and accounts for 15% to 20% of all such defects, not including those occurring as part of cyanotic CHDs.
Pathology
- 1.
The ventricular septum may be divided into a small membranous portion and a large muscular portion ( Fig. 12-7 , A ). The muscular septum has three components: the inlet septum, the trabecular septum, and the outlet (infundibular or conal) septum. The trabecular septum (also simply called the muscular septum) is further divided into anterior, posterior, mid, and apical portions. Therefore, VSD may be classified as a membranous, inlet, outlet (or infundibular), midtrabecular (or midmuscular), anterior trabecular (or anterior muscular, posterior trabecular (or posterior muscular), and apical muscular defect ( Fig. 12-7 , B ).
- a.
The membranous septum is a relatively small area immediately beneath the aortic valve. The membranous defect involves varying amounts of muscular tissue adjacent to the membranous septum (perimembranous VSD). According to the accompanying defect in the adjacent muscular septum, perimembranous VSDs have been called perimembranous inlet (atrioventricular [AV] canal type), perimembranous trabecular, or perimembranous outlet (tetralogy type) defects. Perimembranous defects are most common (70%).
- b.
Outlet (infundibular or conal) defects account for 5% to 7% of all VSDs in the Western world and about 30% in Far Eastern countries. The defect is located within the outlet (conal) septum, and part of its rim is formed by the aortic and pulmonary annulus. An aortic leaflet can prolapse through the VSD and cause aortic insufficiency (see later for further discussion). It has been called a supracristal, conal, subpulmonary, or subarterial defect.
- c.
Inlet (or AV canal) defects account for 5% to 8% of all VSDs. The defect is located posterior and inferior to the perimembranous defect beneath the septal leaflet of the tricuspid valve (see Fig. 12-7 , B ).
- d.
Trabecular (or muscular) defects account for 5% to 20% of all VSDs. They frequently appear to be multiple when viewed from the right side. A midmuscular defect is posterior to the septal band. An apical muscular defect is near the cardiac apex and is difficult to visualize and repair. The anterior (marginal) defects are usually multiple, small, and tortuous. The “Swiss cheese” type of multiple muscular defect (involving all components of the ventricular septum) is extremely difficult to close surgically.
FIGURE 12-7
Anatomy of ventricular septum and ventricular septal defect (VSD). A, Ventricular septum viewed from the right ventricular (RV) side. The membranous septum is small. The large muscular septum has three components: the inlet septum (I), the trabecular septum (T), and the outlet (or infundibular) septum (O). B, Anatomic locations of various VSDs and landmarks viewed with the RV free wall removed. a, outlet (infundibular) defect; b, papillary muscle of the conus; c, perimembranous defect; d, marginal muscular defect; e, central muscular defect; f, inlet defect; g, apical muscular defect.
(From Graham TP Jr, et al: Moss’s Heart Disease in Infants, Children, Adolescents. Baltimore, Williams & Wilkins, 1989.)
- a.
- 2.
The defects vary in size, ranging from tiny defects without hemodynamic significance to large defects with accompanying CHF and pulmonary hypertension.
- 3.
The bundle of His is related to the posteroinferior quadrant of perimembranous defects and the superoanterior quadrant of inlet muscular defects. Defects in other parts of the septum are usually unrelated to the conduction tissue.
- 4.
In an infundibular defect, the right coronary cusp of the aortic valve may herniate through the defect. This may result in an actual reduction of the VSD shunt but may produce aortic regurgitation (AR) and cause an obstruction in the RV outflow tract (RVOT). A similar herniation of the right or noncoronary cusp occasionally occurs through perimembranous defects.
Clinical Manifestations
History
- 1.
With a small VSD, the patient is asymptomatic with normal growth and development.
- 2.
With a moderate to large VSD, delayed growth and development, decreased exercise tolerance, repeated pulmonary infections, and CHF are relatively common during infancy.
- 3.
With long-standing pulmonary hypertension, a history of cyanosis and a decreased level of activity may be present.
Physical Examination ( Figs. 12-8 and 12-9 )
- 1.
Infants with small VSDs are well developed and acyanotic. Before 2 or 3 months of age, infants with large VSDs may have poor weight gain or show signs of CHF. Cyanosis and clubbing may be present in patients with pulmonary vascular obstructive disease (Eisenmenger’s syndrome).
FIGURE 12-8
Cardiac findings of a small ventricular septal defect. A regurgitant systolic murmur is best audible at the lower left sternal border; it may be holosystolic or less than holosystolic. Occasionally, the heart murmur is in early systole. A systolic thrill (dots) may be palpable at the lower left sternal border. The S2 splits normally, and the P2 is of normal intensity.
FIGURE 12-9
Cardiac findings of a large ventricular septal defect. A classic holosystolic regurgitant murmur is audible at the lower left sternal border. A systolic thrill is also palpable at the same area (dots). There is usually a mid-diastolic rumble, resulting from relative mitral stenosis, at the apex. The S2 is narrowly split, and the P2 is accentuated in intensity. Occasionally, an ejection click (EC) may be audible in the upper left sternal border when associated with pulmonary hypertension. The heart murmurs shown without solid borders are transmitted from other areas and are not characteristic of the defect. Abnormal sounds are shown in black. Insp, inspiration.
- 2.
A systolic thrill may be present at the lower left sternal border. Precordial bulge and hyperactivity are present with a large-shunt VSD.
- 3.
The intensity of the P2 is normal with a small shunt and moderately increased with a large shunt. The S2 is loud and single in patients with pulmonary hypertension or pulmonary vascular obstructive disease. A grade 2 to 5 of 6 regurgitant systolic murmur is audible at the lower left sternal border (see Figs. 12-8 and 12-9 ). It may be holosystolic or early systolic. An apical diastolic rumble is present with a moderate to large shunt (caused by an increased flow through the mitral valve during diastole) (see Fig. 12-9 ).
- 4.
With infundibular VSD, a grade 1 to 3 of 6 early diastolic decrescendo murmur of AR may be audible. This murmur may be caused by herniation of an aortic cusp.
Electrocardiography
- 1.
With a small VSD, the ECG findings are normal.
- 2.
With a moderate VSD, left ventricular hypertrophy (LVH) and occasional left atrial hypertrophy (LAH) may be seen.
- 3.
With a large defect, the ECG shows biventricular hypertrophy (BVH) with or without LAH ( Fig. 12-10 ).
FIGURE 12-10
Tracing from a 3-month-old infant with a large ventricular septal defect, patent ductus arteriosus, and pulmonary hypertension. The tracing shows biventricular hypertrophy with left dominance. Note that V2 and V4 are in ½ standardization.
- 4.
If pulmonary vascular obstructive disease develops, the ECG shows RVH only.
Radiography ( Fig. 12-11 )
- 1.
Cardiomegaly of varying degrees is present and involves the LA, left ventricle (LV), and sometimes RV. Pulmonary vascular markings increase. The degree of cardiomegaly and the increase in pulmonary vascular markings directly relate to the magnitude of the left-to-right shunt.
FIGURE 12-11
Posteroanterior and lateral views of chest roentgenograms of a ventricular septal defect with a large shunt and pulmonary hypertension. The heart size is moderately increased, with enlargement on both right and left sides of the heart. Pulmonary vascular markings are increased, with a prominent main pulmonary artery segment.
- 2.
In pulmonary vascular obstructive disease, the main PA and the hilar PAs enlarge noticeably, but the peripheral lung fields are ischemic. The heart size is usually normal.
Echocardiography
Two-dimensional and Doppler echocardiographic studies can identify the number, size, and exact location of the defect; estimate PA pressure by using the modified Bernoulli equation; identify other associated defects; and estimate the magnitude of the shunt. Because the ventricular septum is a large, complex structure, examination for a VSD should be carried out in a systematic manner to be able to specify the exact location and size of the defect. When possible, more than one view should be obtained, preferably a combination of the long- and short-axis views.
The cardiac valves serve as markers of specific types of VSDs except for the trabecular septum. The membranous VSD is closely related to the aortic valve, the inlet VSD to the tricuspid (or AV) valve, and the infundibular VSD to the semilunar valves. Figure 12-12 is a collection of selected views of parasternal, apical, and subcostal views, which are useful in locating the site of VSDs.
The membranous septum is closely related to the aortic valve. In the apical and subcostal “five-chamber” views, it is seen in the LV outflow tract (LVOT) just under the aortic valve ( Fig. 12-12 , C3 ). In the parasternal short-axis view at the level of the aortic valve, it is seen adjacent to the tricuspid valve ( Fig. 12-12 , B1 ). These are the best views to confirm the membranous VSD. The membranous VSD is not visible in the standard parasternal long-axis view, but by tilting the transducer slightly to the right, away from the aorta, the membranous VSD becomes visible. Figure 12-13 shows a membranous VSD imaged in the apical “five-chamber” view.
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