11.1: Septal Defects

Atrial septal defect

Case Report

Introduction

Atrial septal defect (ASD) is common, accounting for approximately 7 percent of congenital heart disease. The ASD’s can occur in several different anatomic portions of the atrial septum, and the location of the defect generally reflects the abnormality of embryogenesis that led to the anomaly. The functional consequences of an ASD are determined by its diameter, the anatomic location and the presence or absence of other cardiac anomalies.

Figure 11.1.1: Heart from the right side view, showing different locations of atrial septal defects.

Figure 11.1.2: Schematic drawing showing the location of different types of ASD, the view is into an opened right atrium. VCS, superior caval vein. VCI, inferior caval vein. HV, right ventricle. 1, upper sinus venosus defect. 2, lower sinus venosus defect. 3, secundum defect. 4, defect involving coronary sinus. 5, primum defect.

Classification

The various forms of ASD’s are differentiated from each other by the structures of the heart involved and the formation during embryological development.

The ostium secundum defect is the most frequent form of ASD (70%), localized at the fossa ovalis with a diameter of about 1 – 2 cm. It commonly arises from an enlarged foramen ovale, inadequate growth of the septum secundum or excessive absorption of the septum primum.

The sinus venosus defect (15% of all ASD’s) is localized high in the atrial septum, at the inflow of the superior caval vein. Note that in 80-90% of patients this defect is accompanied by an anomalous pulmonary venous drainage of the right pulmonary vein into the right atrium. Inferior sinus venosus defects do exist, but are very exceptional.

The ostium primum defect is localized low in the atrial septum at the atrioventricular junction. It forms the atrial component of the category of congenital heart disease referred to as atrioventricular defects, with a common atrioventricular junction and an abnormal atrioventricular valve.

The coronary sinus defect, localized at the atrial ostium of the coronary sinus, is rare and usually accompanied by other cardial defects like anomalous drainage of the superior vena cava.

Pathophysiology

The presence of an ASD will in all cases gradually lead to a left to right shunt across the defect. At birth the volume of blood shunting from systemic to pulmonary circulation is small, because the right ventricle is still relatively thick-walled and noncompliant. In response to a decrease in pulmonary vascular resistance after birth, the right ventricle remodels and its compliance increases. This leads to a decrease in right atrial pressure and an increase in shunt volume across the defect during the first years of life.

The blood shunts during the late systole and early diastole, leading to a diastolic volume overload of the right atrium and right ventricle, but also the pulmonary veins and arteries. This volume overload of the pulmonary circulation will consequently lead to right-sided dilatation. The end diastolic increase in pressure of pulmonary circulation can result in systemic venous stuwing. This stuwing is augmented by another mechanism caused by the right ventricular volume overload; deviation of the ventricular septum to the left and the decrease in left ventricle preload because of the left to right shunt, lead to a decrease in stroke volume of the left ventricle. The renine-angiotensin system is activated, leading to an increase in intravascular volume and signs of venous stuwing. The right-sided volume overload is usually well tolerated for years, but in adulthood hemodynamic factors can influence the shunt size in both directions. If the right ventricle will start failing due to chronic volume overlad, the left to right shunt can decrease. If the left ventricle function will decline due to hypertension or coronary artery disease, the lef to right shunt can increase. In 10-20% of adult patients with an isolated ASD pulmonary hypertension will develop, leading to a decrease in left to right shunt and eventually right to left shunt with cyanosis (Eisenmenger syndrome).

Evaluation and therapy

Most ASDs less than 8mm in diameter close spontaneously in infants, however above the age of 4 years spontaneous closure is unusual. During childhood and early adulthood most patients with moderate to large uncorrected ASDs are asymptomatic. Most of them will become symptomatic during adulthood (usually from the age of 40) and require closure of the defect. Indications for closure of an ASD in adulthood are development of symptoms and a high rate of shunt flow. Decreased exercise tolerance, fatigue, dyspnoe, syncope and paradoxal embolization are manifestions of such symptomatic ASDs that warrant closure of the defect. Atrial arrhythmias are usually one of the first presenting symptoms, however these symptoms alone are not an indication for closure, since the incidence after the procedure is not likely to be reduced.

Figure 11.1.3: Chest radiograph, left lateral view, of a 34-year old female who recently underwent percutaneous closure of her ASD with an Amplatzer device.

When closure of the ASD is indicated, this can be performed with surgery or percutaneous intervention. Surgical closure is usually performed using a patch of pericardium or Dacron. Prior to surgery, a comprehensive noninvasive evaluation is essential to exclude pulmonary hypertension and associated anatomic defects such as anomalous pulmonary and systemic venous connections. In nearly all cases, echocardiography can resolve these questions, obviating the need for cardiac catheterization.Transcatheter closure avoids cardiopulmonary bypass, thoracotomy, and atriotomy, and is associated with excellent outcomes. As a result, this approach has largely replaced surgery in many centers for patients with a defect that is less than 20 mm in diameter.

Outcome

The short- and long-term outcomes are generally excellent after either surgical or transcatheter closure of an isolated ASD in children. Several investigations showed that there is almost no increase in long-term mortality or serious morbidity compared to controls, following surgical repair of an ASD under 25 years of age. The perioperative mortality is low (< 1%) and there are few perioperative complications (about 10%). However late in adulthood about 50% of all patients develop sinusknoopdysfunctie and symptomatic supraventricular tachyarrhythmias.

When the ASD is closed percutaneously the short-term outcomes (less than one year) are excellent, with reported procedure success rates of 88 to 98%.

Ventricular septal defect

Case report

Introduction

The ventricular septal defect is the most common congenital heart defect in childhood (30%). Most patients have an isolated VSD, however a VSD also occurs in combination with other defects like Tetralogy of Fallot, which will be discussed elsewhere. About five percent of all patients with a VSD have a chromosomal abnormality, including trisomy 13, 18 and 21. Due to a high rate of spontaneous closure (50%) VSD is less seen in adulthood.

There are three main anatomic components of the interventricular septum (Figure 11.1.4); the septum of the atrioventricular canal (1), the muscular septum (2), the parietal band or distal conal septum (3). VSDs may occur at various locations in any of the three components. The location of the defect is not of particular interest when taking the characteristics of the intracardiac shunt in account. However it is important in terms of the frequency of involvement of the atrioventricular valves and the rate of spontaneous closure and additionally the relation to the AV pathway when considering surgical correction.

Figure 11.1.4: Schematic drawing showing three main anatomic components of the interventricular septum: the septum of the atrioventricular canal (1), the muscular septum (2), the parietal band or distal conal septum (3).

Classification

Figure 11.1.5: Heart from the right side view, showing different locations of ventricular septal defects.

The VSD can be classified into four types, related to the anatomic components involved;

• Type 1 is the infundibular VSD, which results from a defect in the septum below the aortic and pulmonary valves. The loss of support to the adjacent septal leaflets of these valves causes cusp prolapse into the VSD leading to progressive aortic regurgitation, which is the hallmark of this defect.
• Type 2, the membranous VSD, is the most common type of VSD (around 80%) and results from a deficiency of the membranous septum. This defect borders the septal leaflet of the tricuspid valve and might also extend into the muscular septum when it is referred to as a perimembranous VSD.
• Type 3 are inlet VSDs, located beneath both mitral and tricuspid valves. Despite proximity to those valves, this type of defect is not associated with mitral or tricuspid regurgitation unless associated with atrioventricular canal defect. This typically large defect is often associated with Down syndrome.
• Muscular defects (type 4) are located within the trabecular septum and accounts for 5 – 20% of all VSDs. It is bordered only by muscle, away from the cardiac valves. Muscular defects can be small or large in size and consist of a single or multiple defects.

Pathophysiology

The severity of the shunt across the VSD is determined by its size and the ratio of pulmonary to systemic vascular resistance. In small or restrictive VSDs the diameter of the defect is ≤25% of the aortic annulus diameter. These small defects cause small left to right shunts with no left ventricular overload or pulmonary hypertension.

Moderate sized VSDs, measuring 25 – 75% of the aortic annulus diameter, result into mild volume overload of the pulmonary arteries, left atrium and left ventricle with no or only mild pulmonary hypertension.

In large defects, defined as those with diameters equal or greater than 75% of the aortic annulus, there is no restriction of blood flow across the septum, leading to equal pressures in both right and left ventricle. The large left to right shunt initially only leads to excessive volume overload in the pulmonary arteries, left atrium and left ventricle. The chronic pressure and volume overload combined with the increase flow leads to irreversible changes of the pulmonary vasculature, which results in an increase in pulmonary vascular resistance. This increase in resistance leads to a reversal of the shunt through the VSD causing right to left shunt with cyanosis (Eisenmenger syndrome).

Evaluation

Small defects are usually asymptomatic, however are fairly easy to detect during physical examination. There can be a palpable thrill accompanied by a holosystolic murmur grade 4-6. In some muscular defects the murmur is non holosystolic, due to the contraction and therby closure of the defect during systole. In moderate sized defects, with a large systemic to pulmonary flow of at least 1:2, a middiastolic rumble is audible due to the increased flow across the mitral valve. The pulmonary component of the second heart tone is loud. Only in a large VSD accompanied by the Eisenmenger syndrome and central cyanosis there is barely any shunt murmur audible. However there are murmurs audible caused by the pulmonary hypertension; an earlydiastolic murmur due to the pulmonary valve regurgitation and a holosystolic murmur due to the tricuspid valve regurgitation. Defects with large shunts that cause symptoms like decreased exercise tolerance and dyspnoe are usually detected and closed early in childhood.

The ECG and chest X-ray of a patient with a small VSD are usually normal, but can show signs of left atrial and left ventricle overload in moderate sized defects.

With echocardiography the localisation, size and hemodynamic influence of the VSD can be investigated. Dilatation of the left atrium and left ventricle might be present and the pressures in the pulmonary artery can be estimated by means of the tricuspid regurgitation. Invasive measurement by means of catheterization is only indicated when there is doubt about the shunt size and the pulmonary vascular resistance.

Treatment

Treatment and prognosis of a VSD depends on the size en localisation of the defect, the pulmonary vascular resistance and possible concomitant defects. Spontaneous closure occurs mainly in small defects, of which 75 percent closes before age 10. In patients with a small defect no pulmonary hypertension develops, however there is an increased risk of endocarditis.

In patients with significant shunts studies have shown that surgical closure reduces pulmonary artery pressure and improves long-term survival. Therefore, repair of VSD should be considered in all adult patients who are symptomatic or have signs of left ventricular volume overload.

Medical treatment is reserved for (1) asymptomatic patients without evidence of left ventricular volume overload and (2) patients with symptoms and/or left ventricular volume overload who are not candidates for repair such as those with large defects and Eisenmenger syndrome.

Repair of VSD has been historically performed surgically. However, percutaneous VSD repair has been growing given the desire of young adults to avoid surgery. Surgical and percutaneous VSD closure should be performed by surgeons and cardiologists with appropriate training and expertise.

Indications for closure of a VSD in an adult are included in the 2008 American College of Cardiology/American Heart Association (ACC/AHA) adult congenital heart disease guidelines as follows. Similar recommendations are included in the European Society of Cardiology and the Canadian Society of Cardiology guidelines.

• Closure of a VSD is indicated when there is a Qp/Qs ≥2 and clinical evidence of LV volume overload.
• Closure of a VSD is indicated when the patient has a history of infective endocarditis.
• Closure of a VSD is reasonable when there is net left to right shunting with a Qp/Qs ≥1.5 with pulmonary artery pressure less than two thirds of systemic pressure and PVR is less than two thirds of systemic vascular resistance.
• Closure of a VSD is reasonable when there is net left to right shunting with a Qp/Qs ≥1.5 in the presence of LV systolic or diastolic dysfunction or failure.

Indications for surgical closure of VSD in infants and young children may include:

• Infants <6 months (<3 months for those with trisomy 21) who have uncontrolled heart failure despite maximal medical and dietary interventions or who have pulmonary hypertension.
• Children with a persistent significant shunt (Qp:Qs >2:1), should undergo surgical repair even in the absence of elevated PA pressures.
• Subpulmonic and membranous defects, regardless of size, with aortic regurgitation should be surgically corrected before the aortic valve is permanently damaged. The decision to close small defects with aortic valve prolapse without aortic regurgitation is controversial.

Closure of a VSD is not recommended in patients with severe irreversible pulmonary artery hypertension.

Transcatheter device VSD closure is a treatment option for isolated uncomplicated muscular VSDs, and for certain membranous VSDs, in selected patients with suitable anatomy. Appropriate anatomy for transcatheter closure includes a VSD location remote from the tricuspid and aortic valves with an adequate rim. Successful transcatheter closure has been accomplished in the presence of multiple muscular or membranous fenestrations.

The technical success rate of transcatheter closure of selected muscular and membranous VSDs is high (93-100%) and the mortality rate is low (0 – 2.7%).

Outcome

The long-term outcome for children who undergo surgical closure of VSD in childhood is generally excellent. Early surgical repair results in near normal long-term growth in the vast majority of patients. Most survivors are asymptomatic and lead normal lives.

Adults with repaired VSD without residua have excellent outcomes and normal survival, with a 25year survival of 83%. However, long-term survival is less favorable when repair is done at older age or in presence of pulmonary hypertension. Although the prognosis after surgical repair of uncomplicated VSD is excellent in the majority of patients, long-term residua and sequelae are not uncommon including conduction disease, cardiac arrhythmias, residual VSD, endocarditis, tricuspid regurgitation, ventricular dysfunction, pulmonary hypertension, and aortic regurgitation.

Development of complete atrioventricular block is the most significant of the transcatheter procedural complications. Approximately 6% of patients who underwent transcatheter closure of membranous defects, developed complete heart block necessitating pacemaker implantation. Real-time three-dimensional transesophageal echocardiography has been increasingly used to guide such procedures. Given the lack of data on long-term outcomes following catheter closure of VSD in adults, patients should be followed every one to two years at an adult congenital heart disease center.

Atrioventricular septal defect

Case report

Introduction

The atrioventricular septal defect (AVSD) consist of several different lesions with a common atrioventricular (AV) junction and abnormal AV valves, consisting of five leaflets (Figure 11.1.6). The AVSD makes 3 procent of all congenital heart defects in children.

When the AVSD is complete it consists of a defect on the atrial and on the ventricular side of the common AV-valve ring. (Figure 11.1.6, middle). The complete AVSD is usually associated with Down Syndrome, but also with other cardiac defects like ASD type 2, persisting left inferior caval vein and tetralogy of Fallot.

Figure 11.1.6: Left: schematic drawing of a normal heart with a normal mitral (M) and tricuspid (T) valve. Middle: a complete AVSD where the mitral and tricuspid valve is replaced by a common valve with a right anterosuperior leaflet (1), a right inferior leaflet (2), a superior bridging leaflet (3), an inferior bridging leaflet (4), and a left mural leaflet (5). Right: showing the anatomic arrangement in an incomplete AVSD. a=aorta, p= pulmonary artery.

In an incomplete AVSD the superior and inferior bridging leaflets are connected with each other and with the interventricular septum in the centre. (Figure 11.1.6, right) Due to this connection there are two divided AV inlets, leaving no open communication between the ventricles, thus no VSD exists. However there is a rather large defect in the interatrial septum. The incomplete AVSD is often referred to as ostium primum defect or ASD type 1. The left AV-valve consist of three leaflets (there is a cleft in the mitral valve) and is usually incompetent. Due to one common AV junction in both types of AVSD, the aortic valve is not in the usual wedged position between the two separate AV inlets, but located more anterior. Therefore the outflow tract of the left ventricle is elongated and slightly constricted. In angiography this abnormally shaped outflow tract is known as a gooseneck.

Pathophysiology

The exact pathophysiology depends on the location and severity of the defect. In a complete AVSD there is combined right and left ventricular overload due to the left-to-right shunt at atrial and ventricular level combined with the regurgitation of the right and left AV valve. As a result the elevated pulmonary pressures due to the extremely high flow will rapidly convert to pulmonary hypertension. This will lead to bidirectional shunting across the defect with a preferably right-to-left shunt and cyanosis (Eisenmenger syndrome).

In an incomplete AVSD the hemodynamic consequences are comparable to an ASD type 2. However the serious left AV-valve regurgitation can cause an increase in the atrial left-to right shunt.

Evaluation

The complete AVSD leads to symptoms of heart failure early in childhood and most patients will have been surgically corrected in adulthood. During physical examination signs of a residual shunt or regurgitation of the AV-valves might be present. This defect is rarely diagnosed in adulthood and usually there is Eisenmenger syndrome present, with clinical signs previously described in isolated ASD or VSD. The clinical symptoms of an incomplete AVSD are comparable with those of an ASD type 2. During physical examination a murmur of the regurgitant AV-valve might be audible.

The ECG shows a deviation of the heart axis to the left, in contrast to the right axis deviation in atrial septal defects. This is due to the abnormal position of the His bundle which causes a delay in conduction through the left anterior fascicular branch.

Treatment and outcome

The survival for patients with a complete AVSD without corrective surgery is very limited, most patients will not reach adulthood. Therefore surgical correction at an early age (usually in the first year of life) is advised. Patients with a corrected complete AVSD need lifelong cardiologic follow up, due to frequent residual defects like residual VSD, progressive regurgitation of the left AV-valve, pulmonary hypertension and often rhythm- or conduction disorders. Patients with Down Syndrome and complete AVSD are more likely to develop progressive pulmonary hypertension, even after corrective surgery.

The aberrant anatomy of the AV-valves, even after corrective surgery, is important when reviewing echocardiographic images. They can, for example, be easily mistaken for vegetations in endocarditis.

The survival for patients with an incomplete AVSD is higher compared to the complete AVSD, but generally worse compared to other ASD types. This is due to the concomitant disorders of the left AV-valve and the conduction system. Left AV-valve regurgitation will lead to an increase in left-to-right shunt and earlier development of pulmonary hypertension compared to ASD type 2. In childhood there is usually already an indication for correction of the defect in which the anatomically abnormal AV-valve can be repaired. However a slight amount of regurgitation will remain present. In some cases the progressive failure of the AV-valve will require a second repair or replacement, but in most patients the insufficiency will remain mild.

Besides the AV-valve problems there are frequent rhythm and conduction disorders; atrial fibrillation, supraventricular tachycardia, complete heartblock or sinus dysfunction. Depending on the kind of disorder patients can require medical treatment or a pacemaker.