Common congenital anomalies with a left to right shunt: Atrial septal defects (ASDs), Partial anomalous pulmonary venous return, Ventricular septal defects (VSDs), and Patent ductus arteriosus (PDA)
Atrial septum defect (ASD)
An atrial septal defect (ASD) is a congenital defect in the interatrial septum allowing a direct communication between the atria. It is common, about 10% of all congenital heart disease cases, more common in females. (male to female ratio of 1:2).
There are three main types of ASDs:
Secundum ASD, the most common type (70-75% of ASDs) is located in the central portion of the interatrial septum.
Primum ASD, about 20% of all ASDs, (or partial endocardial cushion defect ) is in the lower part of the septum, near the atrioventricular valves. This is the second most common type.
Primum ASDs are a part of the spectrum of endocardial cushion defects. They are often accompanied by a cleft in the anterior leaflet of the mitral valve, causing mitral regurgitation. A complete endocardial cushion defect (complete atrioventricular canal defect) is a more complex congenital anomaly consisting of a primum ASD, a ventricular septal defect of the inlet type, and anomalies of the atrioventricular valves (a common atrioventricular valve). Endocardial cushion defects are commonly seen in patients with trisomy 21 (Down syndrome).
Sinus venosus defect is located near the entrance of the superior vena cava (SVC) or the inferior vena cava IVC to the right atrium and is a less common type (about 5-10% of all ASDs), commonly associated with a partial anomalous pulmonary venous return.
Pathophysiology of atrial septal defects ( ASDs)
Clinical, electrocardiographic and echocardiographic findings in atrial septal defects
In case of a large ASD with a large L-R shunt, a mid-diastolic rumble may be audible at the left lower sternal border, i.e. at the tricuspid area due to the increased flow through the valve.
The typical auscultatory findings often are not present in infants and toddlers, even with a large defect, because at this age the right ventricle often is not compliant enough to allow a large L-R shunt.
The ECG usually shows a RBBB, or an incomplete RBBB with an rsR′ pattern in V1 (also see chapter The Electrocardiogram -ECG . In case of a moderate to large ASD, right QRS axis deviation (frontal axis between +90 to +180°) and/or other indications of right ventricular hypertrophy may be present, but in the case of an ostium primum defect, there is an RBBB pattern with a left QRS axis.
Chest radiographs if the shunt is moderate or large, show cardiomegaly (with right atrial and right ventricular enlargement), increased vascular markings in the lungs and a prominent main pulmonary artery (at the mid-left heart border).
Echocardiography in a patient with an atrial septal defect (ASD) shows the position and the size of the defect and the abnormal flow (shunt) through the interatrial septum. If the defect is moderate to large, echocardiography also shows a dilated right atrium, right ventricle, and pulmonary artery. The finding of dilated right heart chambers proves that the ASD is hemodynamically significant and is in favor of ASD closure.
Cardiac catheterization is not necessary for the diagnosis of an ASD, but it can be necessary in the case of significant pulmonary hypertension to decide if the defect should be closed.
2. Right ventricle (enlarged-compare with the left one)
5. A color jet passing through the midportion of the atrial septum with a direction from left to right. It is a left to right shunt of blood at the midportion of the atrial septum due to a secundum ASD. Closure of the defect is indicated because the L-R shunt is significant enough to result in right heart chamber enlargement. In this case, transcatheter device closure was successfully performed.
Natural history of atrial septal defects (ASDs)Spontaneous closure of an ASD often occurs in patients with secundum ASDs with a diameter < 8mm before the age of 1.5 years, but an ASD >8 mm rarely closes spontaneously.
After the age of 4 years, spontaneous closure is not likely to occur.
Spontaneous closure may occur only in secundum defects. It does not occur in primum or sinus venosus ASDs. If a large ASD is left without closure, pulmonary hypertension and signs of right heart failure can develop in the third or fourth decade of life.
Management of atrial septal defects
Children with a secundum atrial septal defect are usually observed without intervention for at least the first 3 years of life, due to the possibility of spontaneous closure.
A case (Video) showing the ECG and echocardiographic features of this condition
Partial anomalous pulmonary venous returnThis is a congenital anomaly, causing a L-R shunt. One or more (but not all) pulmonary veins drain into the right atrium directly or indirectly by draining into a systemic vein (e.g. into the superior vena cava , inferior vena cava, left innominate vein). The right pulmonary veins are more often involved. They may drain into the right atrium, or into the superior vena cava (in this case, often there is also an associated ASD of the sinus venosus type), or into the inferior vena cava in association with an intact atrial septum.
When the left pulmonary veins are involved, they drain into the left innominate vein or into the coronary sinus. Partial anomalous pulmonary venous return has many of the physiologic characteristics of an atrial defect (ASD) and it is also often associated with an ASD. Therefore, this condition is usually discussed in the same chapter with the ASD. Most often, there is an associated ASD, but in some cases, partial anomalous pulmonary venous return is present without an ASD.
The hemodynamics are those of an atrial defect, i.e. this condition also causes volume overload of the right atrium and the right ventricle and increases flow through the pulmonary circulation.
On clinical examination, a difference of an isolated partial anomalous pulmonary venous return from an ASD is the following: In the absence of a concomitant ASD, although the second heart sound (S2) can be widely split, this wide split of S2 is not fixed relative to respiration.
Similar to an ASD, often a midsystolic murmur (grade 2/6-3/6) is heard at the upper left sternal border, due to the increased flow through the pulmonary artery. Occasionally, a mid-diastolic rumble may also be present, resulting from increased flow through the tricuspid valve.
When there is an isolated partial anomalous pulmonary venous return without an ASD, this condition only rarely causes symptoms and the development of pulmonary hypertension is extremely rare.
ECG and radiographic findings are similar to those of an ASD: The ECG is normal or with RBBB or indications of right ventricular hypertrophy. The chest X-ray may demonstrate mild to moderate cardiomegaly due to the enlargement of the right heart chambers, prominence of the main pulmonary artery and increased vascular markings in the lungs.
Echocardiography should lead to the suspicion of partial anomalous pulmonary venous return when there is an enlargement of the right ventricle and atrium, without any other obvious cause and inability to visualize all four pulmonary veins. In normal infants and children, the suprasternal coronal "crab" view typically demonstrates the connection of the four pulmonary veins to the left atrium. The absence of any normal pulmonary venous connection to the left atrium should raise a suspicion of an anomalous pulmonary venous return. Transthoracic echocardiography (TTE) can demonstrate the dilated right ventricle and right atrium and it can often also demonstrate anomalous cardiac connections, but extracardiac connections may be difficult to identify on TTE. The demonstration of anomalous pulmonary venous return with extracardiac connections typically requires magnetic resonance imaging (MRI) or computed tomography (CT).
Partial anomalous pulmonary venous return is often found in patients with an ASD. The ASD can be of any type, although a sinus venosus ASD is most commonly associated with anomalous pulmonary venous return. A sinus venosus ASD often is associated with abnormal drainage of the right upper pulmonary vein. In the presence of diagnostic difficulties, cardiac MRI can establish the diagnosis of partial anomalous pulmonary venous return.
Treatment of partial anomalous pulmonary venous return.Surgery is indicated if there is a significant left-to-right shunt with a Qp/Qs ratio > 2:1. Surgery is also indicated if patients demonstrate evidence of right heart volume overload (dilated right heart chambers on echocardiography) or symptoms. Surgery, when needed, is performed at an age of 2 -5 years. When there is only an anomaly of one pulmonary vein, without an ASD, surgery is not undertaken.
Ventricular septal defects (VSDs)There are four anatomic types depending on the location of the defect.
Perimembranous or membranous VSD is the most common type (70%) and it involves the membranous septum, a small part of the septum immediately beneath the aortic valve. These defects usually also have an accompanying defect of the adjacent muscular septum and depending on the location of this defect they are further classified as perimembranous trabecular, perimembranous inlet or perimembranous outlet.
Another type of VSDs are inlet defects, which are located beneath the septal leaflet of the tricuspid valve.
Outlet VSDs, also called conal or supracristal, are located in close proximity to the annulus of the aortic valve and of the pulmonary valve. These two valve annuli form part of the defect's rim. A common complication of this defect involves herniation of the right coronary cusp of the aortic valve through the defect. This can cause a reduction of the shunt, but also it often causes progressive aortic regurgitation. It may also result in a degree of obstruction of the right ventricular outflow tract.
Trabecular (muscular) VSDs may be central or apical, depending on their location in the muscular interventricular septum.
Pathophysiology of ventricular septal defects (VSDs)The main pathophysiologic feature of a VSD is a left to right (L-R) shunt. The magnitude of the shunt depends on the size of the defect and the pressure difference between the two ventricles, which in turn depends on the pulmonary arterial pressure and thus, on the level of the pulmonary arterial resistance. The larger the size of the defect and the lower the pulmonary vascular resistance, the larger the L-R shunt.
A large VSD if left untreated will cause over the years a progressive rise of the pulmonary vascular resistance, due to progressive obstructive changes of the pulmonary arterioles. This leads to an elevated pulmonary arterial and right ventricular systolic pressure resulting in a reduction in the magnitude of the L-R shunt. This condition has also effects on the ventricles with the left ventricle decreasing in dimensions, whereas the size of the right ventricle increases. When the obstructive changes in the pulmonary vasculature become serious and irreversible, bidirectional shunt develops across the VSD (or even net right to left R-L shunt) and this leads to the development of cyanosis because unoxygenated venous blood from the right ventricle enters the left ventricle and the systemic circulation.
Symptoms and signs of a VSDIn infants and children, a small restrictive defect does not cause any symptoms and is diagnosed because of the auscultation of a murmur. A large non-restrictive VSD can cause dyspnea, failure to thrive and signs of congestive heart failure early, even at the age of 2-3 months, or later. In adults a small restrictive defect will be asymptomatic (and the only sign will be the murmur), a defect of a moderate size may cause dyspnea on exertion and palpitations due to the development of atrial fibrillation, whereas a large non-restrictive VSD can cause symptoms and signs of right heart failure and central cyanosis (Eisenmenger syndrome). Apart from cyanosis patients with Eisenmenger syndrome often have edema (due to the right-sided heart failure) and clubbing.
The murmur of a VSD is pansystolic (holosystolic, i.e. it is present during the whole duration of systole), grade 2/6-5/6, best heard at the lower left sternal border. The murmur can be accompanied by a palpable systolic thrill (also at the lower sternal border). The murmur occasionally can be early systolic in patients with small muscular VSDs.
Murmurs of increased flow may be audible if the shunt is moderate to large, such as a systolic murmur due to increased flow through the pulmonary valve, or an apical diastolic rumble due to increased flow through the mitral valve (The L-R shunt causes not only increased flow through the pulmonary valve and the pulmonary circulation, but also an increased flow through the mitral valve which also leads to volume overload of the left ventricle. This happens because as a result of the increased flow through the pulmonary circulation, there is also an increased pulmonary venous return of blood to the left atrium).
If pulmonary hypertension develops, the pulmonic component (P2) of the second heart sound becomes loud (generally a loud P2 is a sign indicative of pulmonary hypertension, regardless of the etiology). With the development of pulmonary hypertension the systolic murmur of a VSD becomes less prominent and if severe pulmonary hypertension develops the murmur usually disappears. This happens because in the presence of pulmonary hypertension there is a smaller pressure difference between the left and right ventricle resulting in a reduction in the flow of blood through the defect from the left into the right ventricle.
The ECG and the chest X-ray in patients with a VSDIn patients with a small restrictive VSD both the ECG and the chest X-ray are usually normal. In patients with a defect of moderate size the ECG will usually show features of left ventricular and left atrial hypertrophy and enlargement respectively and in a large non-restrictive defect left atrial enlargement with combined ECG features of left and right ventricular hypertrophy. In the case of pulmonary vascular obstructive disease with pulmonary hypertension the ECG usually shows features of isolated right ventricular hypertrophy.
The chest X-ray in the case of a VSD with a moderate or large shunt will show enlargement of the cardiac silhouette (due to dilation of the left atrium and ventricle and occasionally also the right ventricle). A moderate to large shunt will also result in increased pulmonary vascular markings (to a degree that is in direct proportion to the magnitude of the L-R shunt). If pulmonary vascular obstructive disease with significant pulmonary arterial hypertension has developed, the main pulmonary artery and its main branches at the hila of the lungs are dilated, while there are markedly reduced pulmonary vascular markings at the lung fields (this is a typical chest X-ray pattern of pulmonary arterial hypertension of any cause).
Echocardiography in a patient with a ventricular septal defectTransthoracic echocardiography can identify the presence of a VSD, from the turbulent jet of flow across the interventricular septum, and it can also demonstrate the location and size of the defect and it can provide information about its hemodynamic significance. An increased left ventricular and left atrial size (and also a Qp/Qs>1.5) indicates the presence of a significant (moderate or large) L-R shunt.
From the peak gradient across a VSD measured with continuous wave Doppler, by subtracting this gradient from the systolic arterial pressure, the right ventricular systolic pressure (RVSP) can be calculated. RVSP is equal to PASP (pulmonary artery systolic pressure) if there is no coexisting stenosis of the right ventricular outflow tract or the pulmonary valve.
A young woman with a harsh holosystolic murmur best heard at the mid-to lower left sternal border. Echocardiogram left parasternal long axis view. What is the cause of the patient's cardiac murmur ?
1. The jet of turbulent high velocity flow originating from the left ventricle just proximal to the aortic valve and entering the right ventricle is shown (with color flow Doppler) 2. left ventricle, 3. aorta, 4. left atrium.
Cardiac catheterizationCardiac catheterization is not needed for the diagnosis of a VSD, but only if there is pulmonary hypertension to calculate the pulmonary vascular resistance and in some cases where echocardiography does not fully clarify the anatomic diagnosis, or if there is a significant possibility of coronary artery disease. In a VSD with a L-R shunt cardiac catheterization will reveal an elevated oxygen saturation in the pulmonary artery, and this is also an indication that there is no severe pulmonary hypertension. In case that severe pulmonary hypertension has developed this will result in a significant reduction in the L-R shunt and so, much less oxygenated blood from the left ventricle will enter the right ventricle and the pulmonary artery. Therefore, in this case, the oxygen saturation in the pulmonary arterial blood will be low. In these cases, simultaneous comparison of the pulmonary arterial and systemic blood pressures is mandatory, as well as calculation of the pulmonary vascular resistance and assessment of its response to vasodilators. This assessment is necessary to demonstrate if pulmonary arterial hypertension is reversible or irreversible.
The natural history of ventricular septal defects (VSDs)Membranous and muscular VSDs can decrease in size with time, or close spontaneously. Until the age of 6 months spontaneous closure occurs in about 30-40% of these defects. On the contrary, inlet or infudibular defects do not decrease in size and thus they also do not demonstrate spontaneous closure.
In infants with large VSDs congestive heart failure can occur but usually after the first 6-8 weeks of life, because at that time the pulmonary vascular resistance has fallen enough to allow a large L-R shunt which can cause severe volume overload of the left heart chambers due to the increased pulmonary venous return.
Large VSDs can cause a slowly progressive elevation of the pulmonary arterial pressure. This is the result of progressive obstructive changes in the pulmonary arterioles as a reaction of the pulmonary arterial circulation to the chronically increased blood flow. Although pulmonary vascular changes may begin early, even at an age of 6-12 months, severe pulmonary arterial hypertension leading to a R-L shunt and the appearance of cyanosis usually does not occur before the second decade of life.
Another complication that can develop in some infants with a large VSD is infudibular stenosis, i.e. stenosis of the right ventricular outflow tract just below the pulmonary valve. This reduces the L-R shunt and in some cases it may even cause the development of a R-L shunt with cyanosis, a condition similar to the tetralogy of Fallot.
Treatment of the patient with a VSDIn infants with large defects usually medical treatment is given initially (furosemide, ACE inhibitor) to control heart failure, while waiting for the gradual spontaneous decrease in the size of the defect, but if this does not happen or if there is inadequate control of the manifestations of congestive heart failure then closure of the defect is decided.
In children and adults indications for VSD closure are the following: A VSD of a hemodynamically significant size, i.e a defect causing symptoms or dilation of the left ventricle, or a gradual worsening in left ventricular function, or Qp/Qs> 1.5:1 or an elevation in pulmonary arterial pressure > 50 mmHg but in the last case with a pulmonary vascular resistance <7 Wood Units. If the pulmonary vascular resistance > 7 Woods then the defect is closed if there is a shunt with a Qp/Qs> 1.5 : 1 or reactivity of the pulmonary circulation to vasodilators has been demonstrated (a fall in pulmonary vascular resistance and pulmonary arterial pressure with vasodilators). If there is irreversible pulmonary arterial hypertension and Eisenmenger syndrome then closure of any pathologic communication between the left and right circulation (such as a VSD or an ASD) is contraindicated.
Another indication for the closure of a VSD is related to the development of aortic regurgitation as a complication of an outlet VSD, which can be progressive. There is an indication for closure if such a VSD causes more than mild AR.
A video. Echocardiogram of a woman (age 22) with a small perimebranous ventricular septal defect. From the you tube channel
Patent ductus arteriosus (PDA)The ductus arteriosus is a vessel of the fetal circulation which forms a communication between the proximal descending aorta, just distal to the origin of the left subclavian artery and the bifurcation of the pulmonary artery. This vessel is open in the fetus, but it normally closes immediately after birth. The closed ductus after birth will normally form the ligamentum arteriosum.
A patent ductus arteriosus (PDA) is a congenital anomaly occurring when the ductus fails to close after birth, occurring in 1:2000 live births. It is more common in females. Factors increasing the risk for a PDA are premature birth, maternal rubella, birth at a high altitude and genetic factors.
A PDA causes a left to right ( L-R) shunt with a direction from the aorta to the pulmonary artery, because the pressure in the aorta is higher than that of the pulmonary artery.
A PDA (patent ductus arteriosus) is classified based on its size and the magnitude of the L-R shunt. A measure of the magnitude of the shunt is Qp/Qs (the ratio of pulmonary to systemic flow).
• A silent PDA: very small duct, no murmur on clinical examination, usually detected only on echocardiography
• A small PDA : A continuous murmur is present. Qp/Qs <1.5
• A moderate PDA: A continuous murmur is present. Qp/Qs between 1.5 and 2.2
• A large PDA: A continuous murmur is present. Qp/Qs > 2.2
• PDA with Eisenmenger syndrome: Significant pulmonary hypertension with reversal of the shunt direction (R-L, i.e., from the pulmonary artery to the aorta). This causes differential cyanosis (cyanosis in toes and not fingers). In this case, the murmur is only systolic or inaudible (not heard).
Pathophysiology of patent ductus arteriosusA patent ductus arteriosus (PDA), when it is of a moderate or large size, pathophysiologically causes:
1) Increased flow in the pulmonary circulation. This happens because, in addition to the normal flow of blood from the right ventricle through the pulmonary artery to the lungs to get oxygenated, an additional amount of blood enters the pulmonary circulation through the ductus.
2) Left ventricular volume overload. This is an important consequence and occurs in a PDA of a large or at least moderate size. The left ventricle (LV) is forced to accommodate and pump a larger volume of blood. This happens because the blood returning to the LV through the pulmonary veins and the left atrium, includes not only the cardiac output of the systemic circulation, that is, the amount of blood returning from the tissues to the right heart cavities and then to the pulmonary circulation, but also blood shunted into the pulmonary circulation through the PDA, which has bypassed the systemic circulation. Therefore, the LV needs to pump more blood (both the amount of blood that will pass into the systemic circulation plus the shunt that bypasses the systemic circulation through the PDA.
LV volume overload, when large, may cause left heart failure. Increased blood flow through the pulmonary circulation, when there is a large shunt, can cause gradual changes in the pulmonary arterioles resulting in an elevated pulmonary vascular resistance and the occurrence of pulmonary arterial hypertension after some years.
If pulmonary arterial pressure increases to levels equal to or greater than the systemic blood pressure, then the shunt will reverse. That is, the shunt will have an opposite direction, from the pulmonary artery to the aorta (Eisenmenger syndrome). In case of a PDA, if Eisenmenger syndrome occurs, the murmur is only systolic or inaudible (the amount and velocity of the shunting blood is reduced due to a smaller pressure difference between the two communicating arteries). Moreover, the leakage of non-oxygenated blood from the pulmonary artery through the PDA to the descending aorta causes differential hypoxemia and differential cyanosis. This means that a low hemoglobin oxygen saturation and cyanosis are present in the lower extremities, but not in the face, nor in the upper extremities. The reason is that non-oxygenated blood enters the pulmonary artery into the aorta at the site of the PDA, i.e. distal to the origins of the arteries of the head and the upper limbs.
Clinical manifestations of a patent ductus arteriosus (PDA)Patients with a small PDA with an audible continuous murmur, do not have any clinical manifestations except from rare cases of infectious endarteritis (infective endocarditis at the site of the abnormal arterial communication). In a moderate or large-sized PDA, patients may have dyspnea (due to left ventricular volume overload and failure or due to pulmonary hypertension) or palpitations, resulting from atrial fibrillation or flutter (the left atrial dilation resulting from the increased pulmonary venous return is a predisposing factor for these arrhythmias).
Physical examinationCardiac auscultation reveals a continuous murmur best heard on the first or second intercostal space at the left sternal border, with its maximum intensity at end-systole.
In cases of a PDA of a large or moderate size:
- There are bounding peripheral arterial pulses and a wide pulse pressure (an elevated difference between the systolic and the diastolic pressure), due to runoff of blood into the pulmonary artery during diastole.
- The apical impulse of the left ventricle (LV) can be prominent and laterally displaced (due to LV enlargement/ LV volume overload).
The ECG in PDA if the L-R shunt is small is normal. If the ductus is large, the ECG shows left ventricular or biventricular hypertrophy .
The chest X-ray in a large PDA shows a prominent
pulmonary artery with increased pulmonary vascular markings. When the shunt is large the chest X-ray usually shows enlargement of the left atrium and left ventricle.
Εchocardiography in PDA will show in the basal parasternal short axis view, a jet of systolic and diastolic (usually both) retrograde turbulent flow in the pulmonary artery. Left atrial and left ventricular
enlargement will be present only if the shunt is large.
A video ( ECG and echocardiography of a woman with a patent ductus arteriosus)
A 30-year-old woman, who presented for cardiac evaluation, because of a continuous cardiac murmur (grade 3/6, best heard at the second left intercostal space). She was asymptomatic. Physical examination also revealed a wide pulse pressure. Echo showed patent ductus arteriosus of small to moderate size, and normal estimated pulmonary arterial pressure. The PDA was closed with a transcatheter closure device in a specialized center.
Treatment of a PDADuct closure is usually recommended, irrespective of the patient's age, if a duct is clinically detectable, i.e. there is a continuous murmur in the left subclavicular area. The reason is to avoid long-term complications, such as endarteritis (which is also possible with a small ductus), or if the
ductus is of a moderate to large size, arrhythmias, left ventricular failure or pulmonary hypertension. Transcatheter device closure is usually preferred and feasible for ducts with a diameter up to 14 mm. If transcatheter closure is not feasible, then surgical closure is undertaken. Before repair of large ducts, the presence of severe pulmonary vascular disease should be excluded. Pulmonary hypertension is not a contraindication to surgical or transcatheter PDA closure at any age if cardiac catheterization demonstrates that shunt flow is still predominantly left to right and that severe pulmonary vascular disease is not present.
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Bibliography and links
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