Atrial septal defects are the most common intracardiac defects encountered in surgical practice. They may occur in isolation or in association with other more complex cardiac anomalies. These defects were not clinically recognized until the 1940s and have been successfully closed since late in that decade. A variety of closed techniques used in the pre-bypass era have now been superseded by open operations on cardiopulmonary bypass. Surgical closure using hypothermia with inflow occlusion is still practised in developing countries with comparable results. The limitation of non-bypass techniques lies in the difficulties in adapting to unforeseen lesions such as partial anomalous pulmonary venous drainage or very large atrial septal defects. The three main types are secundum atrial septal defects (defects of the fossa ovalis), sinus venosus defects, and coronary sinus defects.

Twenty-five per cent of the population have a persistent foramen ovale. These are usually asymptomatic unless the interatrial communication is large. The clinical picture reflects the left to right shunt leading to increased pulmonary blood flow. The increased volume over load increases the right ventricular end-diastolic volume, the long-term consequence being right heart failure. The increased pulmonary blood flow eventually leads to pulmonary hypertension with shunt reversal: right to left shunting leads to cyanosis and overt cardiac failure. In children with significant interatrial communication, recurrent respiratory infections and dyspnoea on exertion may be presenting features. Right-sided cardiac failure is more likely to be seen in older patients, some of whom are in the seventh decade of life. Such symptoms are accompanied by signs of right ventricular enlargement and a pulmonary systolic murmur due to the increased blood flow. A systolic murmur in the tricuspid area is suggestive of gross right ventricular enlargement and dilatation of the right atrioventricular valve ring. The first heart sound has a widely split loud second component. Mild cyanosis in patients with an isolated atrial septal defect is suggestive of a very high or low defect or a coronary sinus type interatrial septal defect, the right to left shunting in this setting being due to ‘streaming’ of the blood flow.

Radiology confirms an enlarged right atrium and ventricle. The main pulmonary artery is also enlarged with evidence of increased blood flow to both lung fields. Right bundle branch block is an invariable finding on electrocardiography. Echocardiography allows direct visualization of the defect. Increased right ventricular volume with parodoxical septal movement reflects the left to right shunt. In patients with uncomplicated defects this is the investigation of choice and obviates the need for cardiac catheterization. Cardiac catheterization continues to be of value in infants who may have additional abnormalities, as well as in older patients in whom assessment of pulmonary vascular resistance is important in planning management. A step-up in oxygen saturation at the mid-atrial level is diagnostic of a secundum atrial septal defect. Such step-ups at the level of the vena caval orifices indicate high or low defects. Selective injection into the pulmonary veins will define the drainage pattern.

This is the most common form of atrial septal defect and represents a true deficiency of the floor of the fossa ovalis (Fig. 1) 1690. The defect is bounded by the superior, anterior, posterior, and inferior limbus. The limbus itself may be deficient to a variable extent. Absence of the inferior part of the limbus gives rise to a low atrial septal defect, bounded inferiorly by the opening of the inferior vena cava and the eustachian valve. Deficiency of the posterior limbus results in a posterior atrial septal defect.

This defect is unrelated to the fossa ovalis and superior to the limbus. It lies at the mouth of the superior vena cava and is almost always associated with abnormal drainage of the right pulmonary veins (commonly the right upper and middle veins).

These defects are associated with an unroofed coronary sinus into which a left-sided superior vena cava commonly drains.

A significant proportion of secundum defects close during the first year of life. Haemodynamically important defects that persist beyond this period are closed electively at a socially convenient time. A persistent, significant left to right shunt would eventually produce the consequences described above. A pulmonary to systemic (Qp : Qs) flow ratio greater than 1.5 is an indication for elective surgery. On this basis, following diagnosis in infancy, planned surgery is normally undertaken between 1 and 2 years of age.

Closure of the defect is performed on cardiopulmonary bypass established with an aortic cannula and two vena caval cannulae. Under moderate hypothermia (32–34°C) the heart is arrested with cold cardioplegic solution following aortic cross-clamping. Arrest of the heart allows careful inspection of the right atrium and its morphology. The defect itself may be repaired by primary direct suture, or using a pericardial or Dacron patch. The former technique is satisfactory in patients with adequate fossa ovalis tissue. Larger defects are closed with a patch, avoiding distortion of the atrial chambers. Autologous pericardial patches are used in preference in view of their reduced thrombogenicity. In older patients, associated regurgitation of the tricuspid and mitral valves can be repaired concurrently.

Contemporary techniques have reduced the early mortality after surgical repair to zero. Following repair there is complete relief of symptoms. Arrhythmias associated with the volume overload to the right atrium also improve.

The first reported repair of a ventricular septal defect was in 1954, using the technique of cross-circulation. Their closure today is performed on cardiopulmonary bypass with or without deep hypothermia and circulatory arrest. Ventricular septal defects occur in isolation or associated with other more complex anomalies, including tetralogy of Fallot, transposition of the great arteries, tricuspid atresia, and truncus arteriosus. The most common associated lesion remains a persistent arterial duct (6 per cent).

Symptomatic presentation reflects the size of the ventricular septal defect and the resulting shunt. Infants may present with a precordial pansystolic murmur only; a large defect may cause gross cardiac failure, with tachypnoea, hepatomegaly, and failure to thrive. A high pulmonary blood flow gives rise to a mitral diastolic flow murmur and a loud pulmonary component of the second heart sound. While 80 per cent of ventricular septal defects presenting at birth may close in infancy only 25 per cent of those persisting at 1 year do so. The long-term outcome in a persisting, haemodynamically significant ventricular septal defect is pulmonary hypertension. The rise in pulmonary vascular resistance eventually leads to shunt reversal and cyanosis.

Radiography shows cardiomegaly with pulmonary plethora, reflecting the increased pulmonary blood flow and biventricular hypertrophy in patients with a significant shunt. The development of irreversible pulmonary hypertension gives rise to large proximal pulmonary arteries with decreased peripheral lung markings. Associated compression of the bronchioles gives rise to alveolar hyperinflation. Two-dimensional Doppler echocardiography demonstrates clearly the position of the defect and the gradient across it. In addition, the size of the ventricles and any associated abnormalities may be visualized. Angiocardiography demonstrates all four chambers and enables the size of shunt and pulmonary vascular resistance to be calculated. Most importantly, a left ventricular injection reveals the profile of the interventricular septum and demonstrates the presence of additional ventricular septal defects.

Ventricular septal defects have been classified in a variety of ways. More recent analysis of the morphology of the ventricular septum allows the defects to be divided into two types: perimembranous defects and muscular defects (Fig. 2) 1691. In addition, the muscular septum is divided into three components: inlet septum, trabecula septum, and outlet septum. The vast majority of defects (80 per cent) are perimembranous in type, abutting on to the membranous part of the ventricular septum. The relationship of these defects to the adjacent muscular septum allows them to be described as being inlet, trabecular, or outlet perimembranous defects.

The conduction axis (bundle of His) passes along the left ventricular aspect of the posteroinferior rim of perimembranous defects. The septal leaflet of the tricuspid valve overlies inlet type defects with varying chordal attachments to the rim. Outlet perimembranous defects are bounded superiorly by a varying amount of the outlet septum. Almost total absence of the outlet septum produces a subarterial defect, with only a fibrous rim separating the aortic and pulmonary valves. Excessive over-ride of one or other of the great vessels leads to a double outlet left or right ventricle. Such a defect may also be associated with aortic regurgitation secondary to prolapse of the right (most commonly) coronary cusp. In patients with long-standing defects the sinus itself prolapses giving rise to an aneurysm of the sinus of Valsalva.

Muscular defects vary in size and are usually located centrally or anteriorly; they may be single or multiple. Anteriorly and centrally placed multiple ventricular septal defects give rise to a ‘Swiss cheese’ appearance that is difficult to manage surgically (Fig. 2) 1691.

Primary closure of the defect at presentation is the general rule in symptomatic patients. In neonates and in patients with the Swiss cheese defect, banding of the pulmonary artery will reduce pulmonary blood flow and allow growth. Repair is undertaken at about 5 years of age in the latter group. Closure of a single ventricular septal defect is undertaken within 6 months of banding. Persistent defects in asymptomatic patients more than 12 months of age are electively closed within 2 years to prevent the development of pulmonary hypertension in the long term. Successful closure at this age may be considered curative. Closure is no longer an option once significant pulmonary hypertension develops with or without shunt reversal: such patients require heart–lung transplantation, though closure with a bilateral lung transplant may become possible.

Closure of the defects is undertaken on cardiopulmonary bypass, with or without deep hypothermia and circulatory arrest. The heart is arrested by instilling cardioplegic solution into the aortic root following aortic cross-clamping. The two most common approaches to the defects are through the right atrium and via the tricuspid valve or through a transverse or longitudinal right ventriculotomy. The latter approach is particularly useful in outlet type defects. A left ventricular or transpulmonary approach is used less often. The former provides access to anteriorly placed muscular ventricular septal defects while the latter provides good exposure for sub-arterial defects.

Perimembranous defects are all closed using a Dacron patch, placed in position using either interrupted or continuous sutures. Posteroinferiorly the placement of sutures through the base of the septal leaflet of the tricuspid valve avoids damage to the underlying bundle of His. Circular muscular defects also require patch closure, while oval shaped or slit-like defects may be closed directly by interrupted sutures reinforced with Teflon or pericardial pledgets. Multiple defects are closed separately or with a large patch, as with the Swiss cheese defects.

Early mortality for repair of isolated uncomplicated ventricular septal defects approaches zero in centres familiar with the operative and perioperative care required by patients with such defects. Incremental risk factors include young age (<3 months), multiple defects, particularly the Swiss cheese defects, and established pulmonary hypertension. Immediate postoperative complications are related to transient atrioventricular dissociation, complete heart block, low output cardiac failure, or residual shunts. A degree of shunting across Dacron patches is to be expected for up to 48 h. Significant shunts are investigated early and may require reoperation.

Long-term outcome is excellent in patients who undergo repair prior to any irreversible pulmonary vascular changes. Complete heart block is a rare occurrence; however, right bundle branch block occurs in 30 to 40 per cent of patients, irrespective of the approach used for the repair.

Atrioventricular septal defects have in the past been called partial or complete atrioventricular canal defect, endocardial cushion defect, or ostium primum defects. The realization that there is no deficiency of the interatrial septum has now led to the universal acceptance of the term ‘atrioventricular septal defect’. The other terms are more easily understood if described as atrioventricular septal defects with separate or common atrioventricular orifice.

The first successful repair of the separate orifice defect was reported in 1955. Early repairs carried out on cardiopulmonary bypass were associated with considerable morbidity and mortality. More recently, the improved understanding of the morphology and function of the atrioventricular valve and the disposition of the conduction tissue has decreased the risk incurred during surgery.

Clinical presentation reflects the spectrum of the defect. In the presence of an atrial communication only with a competent left atrioventricular valve the signs and symptoms mimic those of a secundum atrial septal defect, and patients present in the first decade of life or even later. At the other end of the spectrum; patients with a common atrioventricular valve orifice and shunting at the atrial and ventricular levels develop signs and symptoms soon after birth, when there is gross cardiac failure associated with tachypnoea, hepatomegaly, poor peripheral perfusion, and failure to thrive. These children develop significant pulmonary hypertension within 24 months and rarely survive beyond this age. The cardiac impulse is prominent and an apical systolic murmur signifies regurgitation of the left atrioventricular valve. Left to right shunting and atrial overload produces a mid-diastolic flow murmur. The second heart sound is loud and widely split with an accentuated pulmonary component. Mild cyanosis may be present when a ‘primum’ type defect is associated with a large secundum defect, giving rise to a common atrium. More significant cyanosis, present in 20 per cent of patients, is indicative of more complex associated abnormalities such as tetralogy of Fallot, double outlet right ventricle, transposition of the great arteries, or a completely unroofed coronary sinus. A persistent arterial duct is an associated anomaly in about 10 per cent of patients with atrioventricular septal defects.

Chest radiographs invariably demonstrate cardiomegaly with pulmonary plethora. Due to the gross left to right shunting the main pulmonary artery and the vessels at the hila are prominent. Loss of peripheral lung markings indicate established pulmonary vascular disease and hypertension. The electrocardiogram shows left axis deviation and biventricular hypertrophy. Atrial fibrillation occurs late and may point to poor long-term prognosis. Two-dimensional and Doppler echocardiography adequately define the anatomy associated with these defects. When a clear diagnosis of a defect associated with a double orifice and no interventricular communication is established, repair is undertaken on this evidence. However, in the presence of a common atriventricular valve with an interventricular communication and atrioventricular valve regurgitation, cardiac catheterization is performed. Angiocardiography demonstrates the extent of the shunts and allows calculation of pulmonary vascular resistance. Other abnormalities may also be excluded. Typically, a left ventricular injection of contrast shows regurgitation of the left atrioventricular valve directly into the right atrium: this is significant in 40 to 60 per cent of patients. Anterior displacement of the aorta and left ventricular outflow tract together with the discrepancy in length between the inlet and outlet portions of the ventricular septum gives rise to a ‘goose-neck’ deformity on ventriculography.

Atrioventricular septal defects are characterized by absence of the membranous and muscular part of the atrioventricular septum (Fig. 3) 1692. The defect is associated with a resultant anomaly of the atrioventricular valve, together with displacement of the aorta and the course of the conduction axis.

The aortic root normally lies wedged between the mitral and tricuspid valves. In patients with atrioventricular septal defect the aorta is displaced anteriorly, producing an elongated and narrowed left ventricular outflow tract. The atrioventricular valve is a five leaflet structure. The crest of the interventricular septum is straddled by an anterior and posterior bridging leaflet: the so-called cleft in the left atrioventricular valve is merely the space between the left components of the anterior and posterior bridging leaflets. In defects associated with separate orifices, the bridging leaflets are joined by a connecting tongue of tissue giving rise to two orifices. Further attachments by valve tissue to the crest of the interventricular septum prevents any interventricular communication, producing the ‘primum’ defect. The extent of bridging of the anterior leaflet is variable, and formed the basis of the previously reported Rastelli classification of the common orifice defect, Type A defects being those with minimum bridging and Type C, those where extensive bridging to the anterior leaflet occurs extending across into the right side and being attached to the medial papillary muscle together with the anterosuperior leaflet of the right atrioventricular valve.

Competence of the atrioventricular valve is maintained in many patients. The acceptance of the left atrioventricular valve as a tri-leaflet structure has modified the surgical approach to repair of the defect.

The atrioventricular node normally lies in the triangle of Koch. The latter is bounded by the tendon of Todaro, the coronary sinus, and the tricuspid valve. In patients with atrioventricular septal defect, this node is displaced posteriorly and inferiorly. It lies in a new nodal triangle, bounded by the annulus of the right component of the bridging leaflet, the coronary sinus, and the lower edge of the interatrial septum. The common trunk passes deep to the posterior bridging leaflet and along the crest of the interventricular septum on the left side (Fig. 3) 1692. The interventricular septum, though complete, has a ‘scooped’ out appearance (Fig. 4) 1693. In addition there is significant discrepancy between the inlet and outlet portions, the former being shorter than the latter. This discrepancy on the surface results in a shorter diaphragmatic surface compared to the left cardiac silhouette. The interventricular septum may be deviated into one or other ventricle, thereby reducing ventricular volume, and this has a significant impact on surgical outcome.

Patients with an interatrial communication only and a competent left atrioventricular valve may present in the first decade of life or later. Closure is undertaken electively to avoid the long-term complications of increased pulmonary blood flow and right-sided overload. Patients with a common atrioventricular valve (single orifice) present soon after birth or within 12 months. In very small neonates palliative procedures such as pulmonary artery banding may be undertaken to reduce pulmonary blood flow and allow growth. With modern techniques, total repair is undertaken at presentation in more patients. This approach avoids the not insignificant morbidity and mortality associated with pulmonary artery banding.

Repair is undertaken on cardiopulmonary bypass with moderate hypothermia or with deep hypothermia and circulatory arrest. The heart is arrested with cold cardioplegia instilled into the aortic root following cross clamping. In both types of atrioventricular septal defect the repair of the interatrial and ventricular communication, the preservation or restoration of atrioventricular valve function, and the avoidance of damage to the conduction tissue are the crux to successful repair.

Early repair of the single orifice (common atrioventricular valve) was previously undertaken using two separate patches to close the ventricular and atrial defects. While early results showed significant mortality, repair using a one-patch technique improved early outcome, although the latter technique requires careful resuspension of the left atrioventricular valve to avoid stenosis. With the two-patch technique the interventricular communication is closed with a Dacron patch and the atrial defect with a pericardial patch. A single Dacron patch is used for the single-patch method. It is tempting to close the ‘cleft’ in the atrioventricular valve completely in an attempt to create a normal appearance of the mitral valve, but the morphology of the left atrioventricular valve is such that this will cause narrowing of the orifice and postoperative regurgitation due to distortion of the geometry of the valve apparatus. In a large proportion of patients the valve is competent and therefore no attempt should be made to ‘reconstruct’ it. Competence is assessed by filling the left ventricular cavity with cold saline and studying the ‘lie’ of the leaflets, as in diastole. This may localize small areas of regurgitation that require repair. In a significant number of patients there is no regurgitation and nothing further need be done.

An understanding of the disposition of the atrioventricular conduction axis is crucial in determining the site of attachment of the inferior edge of the interatrial patch. The safest technique is to suture the lower edge of the baffle along the right component of the inferior bridging leaflet, thereby keeping to the right of the non-branching bundle. Subsequently, the suture line passes lateral to the coronary sinus before running along the lower edge of the atrial septum. This leaves the coronary sinus in the left atrium but the resulting shunt is of no haemodynamic significance unless there is a left superior vena cava draining into the coronary sinus. However, the associated orifice of the sinus is much larger and sutures may be safely placed within it. A third option is to place the inferior suture line into the left ventricular component of the bridging leaflet along the septal crest. Care is taken to place sutures through leaflet tissue only. It is possible to place all sutures to the left and avoid injury to the conduction axis (Fig. 3) 1692.

Any associated anomalies are corrected at the same time. The improved understanding of anatomy has all but eliminated the incidence of complete heart block. Measurement of left atrial pressure with the heart beating allows assessment of the repair and function of the left atrioventricular valve.

Reports on the early mortality in recent years vary from 0 to 30 per cent. Absence of an interventricular communication greatly improves outcome with the patients tending to present later. Risk factors include small age and size, anatomy of the left atrioventricular valve and extent of regurgitation, presence of other associated anomalies, and the preoperative symptomatic status.

Following successful repair, the procedure may be regarded as ‘curative’. A small number of patients may require left atrioventricular valve replacement. Residual ventricular septal defects present early and invariably require reoperation and closure.

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