There are several classification schemes for VSDs. Since VSDs are generally approached from the right side of the heart, these schemes are focused on the right ventricular aspect of the VSD.

VSD Nomenclature and Classification of Stella and Richard Van Praagh

Richard Van Praagh defined the four main anatomic components of the interventricular septum as [2],[3]

1. the septum of the atrioventricular canal,
2. the muscular septum,
3. the proximal conal septum (septal band or trabecula septomarginalis) and
4. the distal conal septum (infundibular septum or parietal band).

VSDs were then defined as occurring within and between these four geographical septal components, and also fell into four categories Figure 1):

1. AV canal type VSDs,
2. Muscular VSDs,
3. Conoventricular VSDs, and
4. Conal septal defects

AV canal type VSDs lie in the inlet septum, beneath and adjacent to the tricuspid valve. This type of VSD is present in a complete AV canal defect, but can also occur in hearts without a complete canal defect, for example with a straddling tricuspid valve. Muscular VSDs occur in the muscular septum, so that their rim is entirely made up of muscle. Their location may vary in the muscular septum, being midmuscular, anterior, posterior, or apical. Conoventricular defects lie between the distal conal septum and either the muscular septum or the proximal conal septum. These defects are often paramembranous, or lying beside the membranous interventricular septum. In this case, they abut the commissure of the tricuspid valve. In some, the conal septum may be malaligned, resulting in accompanying outflow tract obstruction. Anterior malalignment, as seen in tetralogy of Fallot, is accompanied by right ventricular outflow tract obstruction, while posterior malalignment accompanies interrupted aortic arch with left ventricular outflow tract obstruction. Conal septal defects result from defects in the distal conal septum. They may also be referred to as subpulmonary, supracristal, or outlet VSDs. They typically adjoin the pulmonary valve superiorly.[2],[3]

Figure 1

VSD Nomenclature and Classification of Robert Anderson

Robert Anderson advocates a classification which is centered on the margins of the VSD, and its opening into the right ventricle.[4],[5] This classification places VSDs into one of three groups (Figure 2):

1. Perimembranous,
2. Muscular, and
3. Doubly committed subarterial

A muscular defect has completely muscular borders and may open into the inlet, trabecular or outlet components of the right ventricle. A perimembranous defect has as a part of its border the fibrous tissue comprising the junction between cardiac valves and the central fibrous body of the heart. Depending on the defect, this border may include areas of fibrous continuity between the tricuspid, mitral, and aortic valves. A perimembranous defect may open, or extend, into the inlet, trabecular or outlet part of the septum. Defects which extend into the outlet septum may be accompanied by malalignment between the outlet septum and the trabecular septum, with resulting outflow tract obstruction, as described above. Doubly committed subarterial defects are bordered superiorly by an area of fibrous continuity between the pulmonary and aortic valves. In these defects, the outlet (or infundibular) septum, which normally lies between the pulmonary and aortic valves, is absent. In a normal heart, the pulmonary valve is bordered by muscle around 360 degrees. This subpulmonary infundibulum allows removal of the pulmonary autograft from the right ventricular outflow tract in a Ross operation. In the presence of a doubly committed subarterial defect, the subpulmonary infundibulum is incomplete, due to absence of its septal component. The postero-inferior margin of these defects may be either muscular, or extend to the central fibrous body. In the latter case, the defect is both doubly committed and perimembranous, which has important implications for its relationship to the conduction tissue. In Anderson’s classification, the VSD component of a complete atrioventricular septal defect (AV canal) is considered separately from the classification for isolated VSD’s.[4],[5]

Figure 2

VSD Nomenclature and Classification of The Society of Thoracic Surgeons Congenital Heart Surgery Database

The International Congenital Heart Surgery Nomenclature and Database project assimilated previous classifications into the system used in the STS Congenital Heart Surgery Database.[6] This anatomic nomenclature recognizes 4 types of VSD (Figure 3)[6]

1. Type 1 is the supracristal, infundibular, juxtaarterial, or conal defect. This defect lies beneath the semilunar valves in the conal or outlet septum.
2. Type 2 is perimembranous, paramembranous or conoventricular. This defect is confluent with the membranous septum.
3. Type 3 defects are inlet or atrioventricular canal VSDs. These are defects in the inlet portion of the right ventricular septum immediately inferior to the atrioventricular valves.
4. Type 4 defects are muscular, completely surrounded by muscle. This nomenclature currently serves as the basis for data entry and outcome tracking in the STS Congenital Heart Surgery.

Figure 3

In the STS Congenital Heart Surgery Database, Type 2 VSDs (perimembranous) comprise 80%, Type 1 (doubly committed subarterial) 8%, Type 4 (muscular) 4%, and Type 3 (inlet) 3% of the defects reported.[7] Doubly committed subarterial defects are known to be more common in the Asian population.

VSD Nomenclature and Classification of The International Paediatric and Congenital Cardiac Code (IPCCC)

As described in Chapter 2 of this Pediatric and Congenital Cardiac Section of this STS E-Book (Chapter 2: Nomenclature for Pediatric and Congenital Cardiac Care), both The International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11) provide the following hierarchy for VSD [8]:

As described in Chapter 2 of this Pediatric and Congenital Cardiac Section of this STS E-Book (Chapter 2: Nomenclature for Pediatric and Congenital Cardiac Care), both The International Paediatric and Congenital Cardiac Code (IPCCC) and the Eleventh Iteration of the International Classification of Diseases (ICD-11) provide definitions for all of the above terms in the hierarchy for VSD [8]. All of these definitions are provided in Table 2 of Chapter 2 of this Pediatric and Congenital Cardiac Section of this STS E-Book (Chapter 2: Nomenclature for Pediatric and Congenital Cardiac Care). Listed below are the definitons for the top two levels of the above hierarchy for VSD [8]:

• Ventricular septal defect (VSD) is defined as “a congenital cardiac malformation in which there is a hole or pathway between the ventricular chambers”.
• Perimembranous central ventricular septal defect is defined as “a congenital cardiovascular malformation in which there is a ventricular septal defect that 1) occupies the space that is usually closed by the interventricular part of the membranous septum, 2) is adjacent to the area of fibrous continuity between the leaflets of an atrioventricular valve and an arterial valve, 3) is adjacent to an area of mitral-tricuspid fibrous continuity, and 4) is located at the center of the base of the ventricular mass”.
• Inlet ventricular septal defect without a common atrioventricular junction is defined as “a congenital cardiac malformation in which there is a ventricular septal defect that opens predominantly into the inlet component of the right ventricle in the absence of a common atrioventricular junction”.
• Trabecular muscular ventricular septal defect is defined as “a congenital cardiac malformation in which there is a ventricular septal defect within the trabeculated component of the ventricular septum”.
• Outlet ventricular septal defect is defined as “a congenital cardiac malformation in which there is a ventricular septal defect that opens to the outlet of the right ventricle between or above the limbs of the septal band”.
• Ventricular septal defect hemodynamically insignificant is defined as “a congenital cardiac malformation in which there is one or more small, clinically insignificant ventricular septal defect(s) in the absence of flow-related cardiac chamber dilation or abnormal elevation of pulmonary arterial pressure”.
• Multiple ventricular septal defects is defined as “a congenital cardiac malformation in which there are multiple ventricular septal defects, which could be of any type”.

Anatomy

The anatomy of a VSD has important implications for the surgical technique of closure. This applies particularly to the relationship of the conduction system and the cardiac valves to the borders of the VSD. The location of the conduction system is consistent for perimembranous VSD’s (Figure 4). In hearts with normal ventricular looping and atrioventricular concordance, the atrioventricular node is situated at the apex of the triangle of Koch. From here the conduction bundle penetrates the central fibrous body and passes to the left side of the septum along the postero-inferior rim of the VSD. A muscular VSD in the inlet septum lies under the septal leaflet of the tricuspid valve and must be distinguished from the more common perimembranous VSD. This is done at the time of surgery by noting that the margin of the muscular VSD consists entirely of ventricular septal muscle, with a muscular bar separating the VSD from the tricuspid annulus, as well as the tricuspid valve from the mitral valve. In contrast, the margin of the perimembranous defect includes a fibrous portion along the tricuspid valve, where the tricuspid, mitral and aortic valves meet. The conduction system passes antero-superior to the inlet muscular VSD, but postero-inferior to the perimembranous defect (Figure 5).[9] In the rare situation in which a perimembranous and a separate inlet muscular defect occur together, the conduction system passes in the muscular bridge between the two defects. Muscular defects in the trabecular or outlet septum are remote from the proximal conduction system. Doubly committed subarterial defects with a muscular inferior rim are also remote from the conduction system. In a VSD which is both doubly committed subarterial and perimembranous, the conduction system runs along its postero-inferior border, as for any perimembranous defect. It should be noted a VSD which occurs in the setting of atrioventricular discordance (including congenitally corrected transposition) has a different relationship to the conduction system. This relationship and its implications for suture placement during VSD closure are covered in the chapter on congenitally corrected transposition.

Figure 4

Figure 5

Associated Defects

As noted above, VSDs often occur as components of more complex defects, which are not covered in this chapter. “Isolated” VSDs are frequently accompanied by a defect in the atrial septum, either a patent foramen ovale, or secundum ASD. There may also be associated patent ductus arteriosus, or coarctation of the aorta. Over time, the presence of a VSD can lead to associated acquired defects. These include double chambered right ventricle (DCRV), aortic valve prolapse with aortic insufficiency, and subaortic stenosis. DCRV occurs due to muscular hypertrophy and obstruction in the mid-portion of the right ventricle and the proximal right ventricular outflow tract. The obstruction therefore lies between the VSD and the pulmonary valve. Associated aortic insufficiency occurs due to proximity of the VSD to the aortic valve, with prolapse of one of the aortic valve leaflets into the VSD. A pressure-restrictive VSD results in a high velocity jet with an accompanying low pressure zone (the Venturi effect). The low pressure is believed to pull the aortic leaflet into the VSD with resulting prolapse and insufficiency.[10] Aortic insufficiency can be seen with either a doubly committed subarterial VSD, or a perimembranous VSD with outlet extension. The prolapsing aortic valve leaflet is most commonly the right, and less commonly the noncoronary leaflet. The leaflet may effectively produce partial or near-complete closure of the VSD. Subaortic stenosis may be seen as a thin, discrete ridge of fibrous tissue on the left ventricular aspect of the inferior edge of the VSD. DCRV, aortic insufficiency and subaortic stenosis are rare in infancy and generally require several years to develop. As a consequence, these accompanying lesions are important to identify in older children with small VSDs which have not previously been repaired.

VSD may be accompanied by either overriding or straddling of an atrioventricular valve. Overriding is defined as positioning of the atrioventricular valve orifice over the crest of the septum, so that the valve orifice is partially aligned with the opposite ventricle. However, the chordal support of an overriding valve is still located within the appropriate ventricle (right ventricle for the tricuspid valve and left ventricle for the mitral valve). Straddling occurs when a portion of the atrioventricular valve chordal support originates in the opposite ventricle. Straddling chords therefore extend from the valve, across the VSD, to their origin. Straddling may occur with either the tricuspid or mitral chordal support, and is more commonly seen with VSDs located in the inlet portion of the septum.

Surgical History

The first surgical treatment for VSD was banding of the main pulmonary artery. Carried out by by Muller and Damann at UCLA in 1951, pulmonary artery banding decreases distal pulmonary artery pressure, pulmonary blood flow, Qp:Qs, and left-to-right shunt at the VSD.[28]

VSD closure was first carried out by C. Walton Lillehei at the University of Minnesota in March 1954.[29] Lillehei used the technique of cross-circulation, in which an adult served as the biological pump oxygenator for the patient. His initial 12 operations for VSD included 5 infants; 8 of the 12 patients survived.[30] Lillehei approached the VSD through a right ventriculotomy and closed the defect primarily, without a patch. The operations were carried out without the use of either an aortic cross-clamp or cardiotomy suckers.

John Kirklin at the Mayo Clinic described the first VSD closures using a mechanical pump oxygenator and cardiopulmonary bypass in 1955.[31] The right atrial approach to VSD closure was introduced by Lillehei in 1957.[32] In the 1950s, symptomatic infants with VSD were treated by pulmonary artery banding followed by band removal and VSD closure at an older age. This was due to the prohibitive risk of open heart surgery in infants at the time. Successful single stage repair in infants with VSD was introduced in the late 1950s by Kirklin, and by Herbert Sloan at the University of Michigan.[33],[34] However, the morbidity and mortality associated with cardiopulmonary bypass in young infants remained quite high. Single stage repair gained in popularity with the introduction of hypothermic circulatory arrest by Barratt-Boyes at Green Lane Hospital in Auckland, New Zealand in 1969.[35],[36] Device closure for VSD was introduced by Lock at Boston Childrens Hospital in 1987 in 6 patients, 4 with postinfarction VSD, and 2 with congenital VSD.[37]

Indications for Surgery

In current practice, the primary indications for surgical closure of a VSD include symptoms, evidence of pulmonary hypertension, accompanying defects such as infundibular right ventricular obstruction (DCRV), aortic valve prolapse with aortic insufficiency, and subaortic stenosis, and anatomic considerations. Less common indications are the avoidance of endocarditis, and the psycho-social aspects of eliminating a known cardiac defect. As discussed below, the surgical risk of VSD closure is low enough, even in small infants, that the threshold for surgery has also become quite low.

Symptoms of congestive heart failure and failure to thrive in an infant, which are believed to be due to a VSD, are a common indication for surgery. The VSD in such cases is usually moderate to large in size. In most practices, the need for high doses of diuretics, and/or tube feeding to achieve growth, are indications for proceeding with VSD closure. In some cases, it may not be completely clear that the patient’s symptoms are due to the VSD. In such cases the VSD may be small to moderate in size, and there may be other clinical factors which could contribute to growth failure, such as extracardiac defects and genetic abnormalities. Echocardiographic evidence of a large shunt, such as left atrial and left ventricular enlargement, can be helpful to guide decision-making in these cases. However, given the low risk of surgery, it is often appropriate to proceed with VSD closure to take the VSD out of the clinical picture and allow the family and providers to concentrate on the other clinical issues. Cardiac catheterization is rarely either helpful or utilized in the decision for surgery in young infants. Surgical timing is guided by the clinical picture. Once surgery is indicated, it can be carried out at any age, including early infancy (4-6 weeks of age). Patients with symptoms that respond to medical treatment, but whose VSD remains large, should undergo closure at around 6 months of age, when potential problems related to cardiopulmonary bypass in early infancy may be avoided.

In the absence of symptoms, evidence of elevated pulmonary artery pressure or resistance is an indication for surgery. Elevation of pulmonary resistance should be strongly suspected in the patient with a large VSD and lack of symptoms. Such infants can have normal or near-normal growth. Echocardiography can be helpful if elevated pulmonary artery pressure is suggested by the velocity of either a tricuspid insufficiency, or pulmonary insufficiency jet. As noted above, it is important in such cases that practitioners not be “fooled” into nonsurgical management by the lack of symptoms: these patients are at risk for developing fixed elevation of pulmonary resistance over time. Cardiac catheterization may be useful to verify the pulmonary artery pressure. Surgical timing is elective and generally at around 6 months of age, when surgical morbidity is low and the risk of having developed pulmonary vascular obstructive disease is also low. Surgery should not be delayed beyond one year of age.

Patients without symptoms, and in whom there is strong evidence that the pulmonary artery pressure is low, may be followed over longer periods of time without surgery. These are often patients with small to moderate size VSDs, which can close spontaneously. Strong evidence of low pulmonary artery pressure usually includes a high velocity VSD jet, which indicates low right ventricular pressure. If there is a question about the pulmonary artery pressure based on echocardiogram alone, such patients can benefit from a cardiac catheterization to measure Qp:Qs, pulmonary artery pressure, and pulmonary vascular resistance.

Patients being followed with an open VSD can develop muscular right ventricular outflow tract obstruction (DCRV). The natural history of such obstruction is to worsen over time. If this obstruction is severe, it can result in elevated pressure in the proximal right ventricle, with flow reversal at the VSD and resulting cyanosis. DCRV with a peak echo gradient above 30-40 mmHg, and certainly accompanying cyanosis, is an indication for surgical VSD closure along with right ventricular outflow tract muscle bundle division and resection.

Prolapse of an aortic valve leaflet into the VSD with or without accompanying aortic insufficiency may also develop over time. Improvements in the quality of echocardiographic imaging have made the diagnosis of aortic leaflet prolapse very accurate in current practice, even in the absence of aortic insufficiency. The natural history of prolapse with insufficiency is to worsen over time, so the detection of prolapse with even trivial valve insufficiency is a generally accepted indication for surgery. In many practices, leaflet prolapse, even in the absence of aortic insufficiency, is an indication for VSD closure, in order to avoid the development of aortic insufficiency. The development of a subaortic ridge of tissue, particularly if it worsens over time, can also be an indication for VSD closure.

Anatomic factors particular to the VSD may provide an indication for surgical closure. Spontaneous closure should not be expected in either a doubly committed, subarterial VSD (other than by prolapse of the aortic valve, which is undesirable) or a VSD with malalignment of the ventricular septum. A doubly committed, subarterial VSD also has a high incidence of aortic valve prolapse over time. Thus the presence of either of these types of VSD can be taken as an indication for surgical closure.

For patients with a small VSD and no other indication for surgery, there remains debate. There is a low incidence of bacterial endocarditis (1.8%),[38] which incidence probably exceeds the surgical risk in current practice. While a successfully closed VSD is no longer an indication for antibiotic endocarditis prophylaxis,[39] concern remains that patients may remain at a low risk for endocarditis even following VSD closure. Consideration can also be given to the psychosocial aspects of continued follow-up for a patent VSD, and the anxiety that may be generated by the presence of a known, uncorrected cardiac defect. Finally, the presence of a murmur may prevent the patient from participating in desired activities, such as competitive sports, or military service. A history of documented, successfully treated endocarditis in the presence of a small VSD is generally considered an indication for VSD closure.

Contraindications for surgical VSD closure are relatively rare. An occasional young, small infant with a large VSD will develop severe pulmonary infection with ventilator-dependent respiratory failure. This situation is generally due to viral infection, most commonly respiratory syncytial virus (RSV). Such a patient may tolerate cardiopulmonary bypass poorly, and be considered for a temporary pulmonary artery band, with VSD closure following respiratory improvement. Other extracardiac conditions, such as intracerebral bleed, may also be reasons to consider a pulmonary artery band rather than open VSD closure.

Significant, fixed elevation of pulmonary vascular resistance is a contraindication to VSD closure. This is most often seen in an older child who for some reason has not undergone closure of a large VSD. Cardiac catheterization is appropriate in such cases. If the pulmonary vascular resistance is greater than 6-8 wood units, testing with pulmonary vasodilators, to include 100% oxygen and nitric oxide, should be carried out. If the pulmonary resistance is responsive and falls to a value below about 6 wood units, VSD closure can be undertaken. If the pulmonary resistance is fixed above 6-8 wood units, VSD closure can be expected to result in a poor outcome, with RV failure early or late after surgery.[40] In such cases, consideration can be given to long-term treatment with pulmonary vasodilator medications, or placement of a pulmonary artery band to allow distal pulmonary vascular remodeling over time. Patients with fixed pulmonary vascular obstructive disease and Eisenmenger’s syndrome may be candidates for lung transplantation with concomitant VSD closure.[41]

Surgical Techniques

The typical approach for surgical closure of a VSD is via a median sternotomy incision. The skin incision can be kept low, starting at the sternomanubrial junction. Subsequent retraction of the superior end of the skin incision cephalad with a tacking stitch is effective in providing adequate exposure, particularly in infants, whose chest wall tissues are quite mobile. Other incisions utilized for VSD closure have included partial sternotomy, subxyphoid, right thoracotomy, and transaxillary approaches. Compared to a median sternotomy, these may offer some cosmetic advantages, but make exposure more challenging, and have not been widely adopted. Following sternotomy, the thymus is subtotally resected; preservation of the left thymic lobe does not compromise exposure for an isolated VSD, and may offer some longterm advantages for T cell function.[42] The edges of the pericardial incision are suspended to the skin; suspension on the left is limited to a single superior suture, to allow the ventricular mass to rotate leftwards in the mediastinum, which aids in exposure of the right atrium and VSD.

VSD closure utilizes cardiopulmonary bypass with cardioplegic myocardial arrest. Ascending aortic and bicaval cannulation is routine. The IVC is cannulated with a right angle, metal tip cannula. The SVC may be similarly cannulated directly, or with a straight cannula via the right atrial appendage. The latter approach is preferable if there is hemodynamic instability prior to bypass, and in small infants, to avoid placing a pursestring suture in a small SVC. However, the positioning of an atrial appendage cannula may impinge on exposure of the superior aspect of VSDs with significant outlet extension. If there is a patent ductus arteriosus, this is exposed and ligated as soon as bypass is initiated. Cardiopulmonary bypass is maintained at “full flow” throughout the operation (150 – 200ml/kg/min) with systemic cooling to 28-32 degrees Celsius. A left atrial vent is placed just anterior to the right superior pulmonary vein. The ascending aorta is cross-clamped and the heart arrested with antegrade cardioplegia. Our practice uses del Nido cardioplegia dosed at 30 ml/kg.[43] A single dose of cardioplegia is sufficient for closure of an isolated VSD. For longer repairs, additional doses of 15-20 ml/kg are given every 60 minutes.

Perimembranous VSD Closure Via Right Atrial Approach

Isolated perimembranous VSDs are closed via a right atrial approach. A standard oblique right atriotomy to the right of, and parallel to the atrioventricular groove is made. The left side of the atriotomy is tacked to the skin. On the right side, a single tacking suture from the crista terminalis to the pericardium everts the atrium and pulls the tricuspid valve into view. The right atrium is examined for the presence of an atrial septal defect or PFO. The locations of the coronary sinus and the atrioventricular node at the apex of the triangle of Koch are noted. 3-4 Prolene stay sutures are placed in the septal and anterior leaflets of the tricuspid valve. These sutures are pulled to the patient’s right, which everts the tricuspid valve and pulls the VSD into the surgeon’s view. Exposure can be aided by a small finger retractor placed under the anterior tricuspid leaflet and pulled superiorly by the assistant. No retractors are placed inferiorly, in the vicinity of the AV node; retraction trauma to the node has been implicated in postoperative junctional ectopic tachycardia (JET).

An occasional patient may have significant collateral return which enters the right ventricle from the main pulmonary artery during the repair and obscures exposure. This is unusual in an isolated VSD, and more common in patients with some degree of cyanosis, such as tetralogy of Fallot. Such return can be managed by placing a flexible pump sucker across the pulmonary valve once the heart is open, or by snaring the main pulmonary artery during the repair.

The VSD is identified and its anatomy carefully examined. This includes a full assessment of all of its margins, and the relationship to the right ventricular outflow tract. The presence of tricuspid chords passing to the margins of the VSD, or in the case of straddling, across the VSD, is noted. Particular note should be taken of the superior and inferior aspects of the VSD. At the superior aspect, the aortic valve is identified as well as its area of fibrous continuity with the tricuspid valve. Accurate identification of the aortic valve is important to avoid inadvertent placement of suture bites into the valve leaflets, particularly in cases with prolapse of an aortic leaflet into the VSD. Delineation of the aortic valve can be aided by a brief infusion of cardioplegia into the aortic root while observing the valve through the VSD. At the inferior intersection of the VSD margin with the tricuspid valve annulus, the remnant of the membranous interventricular septum can usually be identified. This serves as a good landmark for the inferior margin of the defect, and the location of the conduction system. A mental plan for suture placement in this location to avoid the conduction system is made.

Once the anatomy has been clearly defined, a patch is cut slightly larger than the defect. Our preference for patch material is bovine pericardium. A variety of materials may be used, including autologous pericardium, Gore-Tex and dacron. It is important to err on cutting the patch too large at this point, as its size can be reduced during suturing, while a patch cut too small for the defect will result in unnecessary tension on the closure. Our preference is to use a running suture of 6-0 or 5-0 Prolene on a BV-1 or TF needle (Figure 7A, B). The curve of the TF needle is useful in taking the superior bites in defects with marked outlet extension. An interrupted suture technique with pledgetted sutures may also be used.[3],[27] Use of a continuous suture minimizes or eliminates knot-tying on the fragile ventricular myocardium, results in a less cluttered field, and may take somewhat less time. However, each bite of the continuous suture must be secure, as one bite which tears through may result in loosening of the entire suture line. In the end, the decision between continuous and interrupted suture technique is made by the preference and training of the surgeon.

Figure 7

When utilizing a running suture technique, tension on each throw of the suture pulls the next bite into view. Visualization of the superior edge of the VSD may be aided by external compression of the right ventricle at the base of the aortic root with the surgeon’s left hand. At the inferior intersection of the muscular VSD rim with the tricuspid valve, the conduction system penetrates to run on the left ventricular side of the septum. Injury to the conduction system is avoided by placing suture bites on the right ventricular side of the septum, slightly off of the edge of the VSD, without passing full thickness into the left ventricle. If prominent, the remnant of membranous septum can be used as a location for suture placement, although it is important that bites in this location not pass more deeply into the muscular portion of the septum. In most cases it is safer to place the suture bites in this location off of the border of the VSD, leaving the membranous remnant on the left ventricular side of the VSD patch. A thin strip (3-4mm) of pericardium may be placed on the right atrial side of the septal leaflet of the tricuspid valve (Figure 7B). Suturing along the septal leaflet then uses a horizontal mattress technique from right atrium to right ventricle and back, sandwiching the septal leaflet between the VSD patch on the right ventricular side and the pericardial strip on the right atrial side (Figure 7B). The pericardial strip provides reinforcement of the closure along the tricuspid valve and avoids small patch leaks from the left ventricle to the right atrium

Tricuspid valve chords which insert on the edge of the VSD can generally be negotiated by weaving the VSD suture line around the sites of chordal insertion. In some cases, tricuspid chordal apparatus and accessory tissue may obscure visualization of portions of the VSD. In this situation, several approaches may be taken. The septal and/or anterior leaflet(s) of the tricuspid valve may be taken down from the annulus 2-3 mm from their insertions and reapproximated once the VSD patch is in place (Figure 8). When making the incision in the tricuspid leaflets, care must be taken to avoid injury to the aortic valve. Alternatively, a radial incision may be made in the tricuspid valve for exposure, and subsequently closed. A final alternative is to divide tricuspid supporting chords/tissue at their insertion on the septum, and resuspend the divided support to the septum or the patch once the VSD is closed. Each of these approaches may be useful depending on the exact anatomy. The Children’s Hospital of Philadelphia reported use of tricuspid valve detachment in 21% of patients undergoing transatrial VSD closure.[44] At a mean follow-up of 17 months, no patient had greater than mild tricuspid insufficiency, and none required reoperation for tricuspid insufficiency.

Figure 8

Once the VSD suture line is completed, the circumference of the patch is inspected for residual defects, and reinforced as needed. The tricuspid valve is assessed by filling the right ventricle with saline. Competence is often improved by 1-2 sutures at the anteroseptal commissure. The left side of the heart is deaired by turning the vent off while any atrial septal defect, as well as the aortic cardioplegia site, are open. Saline can be infused across the ASD to fill the left atrium. Once no further air is coming across the atrial septum, any ASD or PFO is closed. The ventricles are manually massaged to encourage air to make its way up to the opening in the ascending aorta. Deairing can be augmented by infusing warm blood via a retrograde cardioplegia catheter to deair the coronaries. Once blood with no further air is coming out of the ascending aortic site, the cross clamp is removed. The aortic site is left open to bleed freely as myocardial activity returns. The right atrium is closed, allowing it to fill with blood prior to tying down the suture line. The vent is removed “underwater” and ventilation recommenced. Rewarming is started during the latter half of the VSD closure and is carried out to a rectal temperature of 35 degrees Celsius. Filling pressure is monitored in the right atrium via either an internal jugular line or a transthoracic line in the right atrial appendage. We do not use internal jugular central lines in patients weighing < 8-10 kg in order to avoid the risk of SVC thrombosis. Left atrial pressure can be measured via a line placed in the vent site, but is not usually monitored unless there is difficulty weaning from bypass. The use of a pulmonary artery line is rare and limited to patients with significantly elevated pulmonary resistance. The line is placed across the right atrial free wall and passed via the tricuspid and pulmonary valves into the main PA. This approach avoids the risk of bleeding from a site in the right ventricle or pulmonary artery during line removal in the ICU. Temporary epicardial atrial and ventricular pacing wires may be placed. Transesophageal echocardiography is used to look for residual air in the left side of the heart. Once none is seen, the aortic site is closed and the patient weaned from bypass. Arteriovenous modified ultrafiltration (MUF) may be used.

The VSD repair can be assessed in several ways. Transesophageal echo is carried out during the period of MUF. A careful search is made for a residual VSD; ventricular function as well as aortic and tricuspid competence are examined. The remainder of the interventricular septum is imaged for a second VSD, which might not have been seen on the preoperative studies. A residual VSD which measures more than 3-4 mm by TEE can be considered significant.[45] Residual defects less than 2 mm in size will close spontaneously in the majority of cases within one year.[46] Direct measurement of right ventricular pressure with a needle verifies that PA pressure is low and that there is not a large residual VSD. If there is any question of a residual on the TEE, the Qp:Qs is determined by drawing oxygen saturations as follows. Oxygen saturation is measured (by co-oximetry) in samples drawn from the pulmonary artery and either the SVC or right atrium. It is important to draw these samples once MUF is complete, since the MUF return can affect the right atrial saturation. It is also important to lower the ventilator FiO2 to 40-50% in order to minimize the contribution of dissolved oxygen to the calculation. Under these conditions, Qp:Qs can be calculated by the ratio of saturations:

(Aorta – SVC (or RA)) / (Pulmonary vein –Pulmonary artery)

A residual VSD with a Qp:Qs > about 1.5:1, or a saturation stepup greater than 5-10% from right atrium to pulmonary artery, should prompt consideration of return to bypass for closure. In a study of patients following repair of teralogy of Fallot, a pulmonary artery saturation greater than 80% in the intensive care unit was found to correlate with a Qp:Qs greater than 1.5 at one year postoperative catheterization.[47] Once the assessment of the repair is complete, protamine is administered, the pericardium loosely pulled together, and the incision closed.

Doubly committed, subarterial VSD Closure via Pulmonary Artery Approach

Doubly committed, subarterial VSDs are closed via the main pulmonary artery. The general setup and approach to cardiopulmonary bypass and myocardial protection are as above. Once the heart is arrested, a transverse incision is made in the main pulmonary artery just distal to the sinotubular junction (Figure 9). The VSD lies immediately beneath the leaflets of the pulmonary valve. Exposure is aided by inferior and rightward retraction of the inferior edge of the pulmonary arteriotomy. Careful note is made of the area of fibrous continuity between the aortic and pulmonary valves, which constitutes the superior margin of the VSD. There may be a fibrous ridge between the two valves. The continuous VSD suture line is started inferiorly, in the middle of the muscular margin of the VSD, and run rightwards, towards the surgeon. The superior bites may be taken through the fibrous ridge between the pulmonary and aortic valves, if one is present. Otherwise the suture is run back and forth, horizontal mattress style, through the exact base (annulus) of the pulmonary valve. Particularly if the pulmonary leaflet tissue is thin, this suturing may be reinforced on the pulmonary artery side of the valve with a thin strip of pericardium. Care is taken to minimize distortion of the pulmonary valve, as some of these patients may later be candidates for a Ross procedure.

Figure 9

A doubly committed, subarterial VSD which has a muscular inferior rim is remote from the conduction system. In cases where the VSD extends to the area of the membranous septum, the defect is both doubly committed subarterial, and perimembranous. In such cases, the conduction system lies along the left ventricular side of the inferior edge of the VSD, as with any perimembranous defect. Suturing in this area follows the same precautions as for a perimembranous defect (above). Adequate exposure of this type of VSD may require a combined approach, via the right atrium for the inferior portion, near the tricuspid valve, and via the pulmonary artery for the superior portion, near the semilunar valves.

Muscular VSD Closure Via Right Atrial Approach

The approach for closure of a muscular VSD depends on its location in the septum.[48] Outlet muscular defects can be approached via either the right atrium, or the pulmonary artery, depending on their proximity to the pulmonary valve. Mid-muscular and inlet muscular defects are approached via the right atrium and tricuspid valve. Apical muscular defects are covered separately (below).

For the right atrial approach to a muscular VSD, the general setup and approach to cardiopulmonary bypass and myocardial protection are as they are for a perimembranous VSD (above). On inspection through the tricuspid valve, the location of the defect is often apparent. If not, identification can be aided by passing a blunt right angle clamp via the atrial septum and mitral valve into the left ventricle and probing the left side of the septum while observing the right side through the tricuspid valve. Accurate identification of the borders of a muscular VSD can be challenging. A single defect in the trabecular portion of the septum is often clearly delineated when viewed from the left ventricle, but can appear to be multiple defects when viewed from the right ventricle, due to the overlying trabeculations.

Midmuscular defects often lie adjacent to, or under, the moderator band. Exposure can be aided by passing a vessiloop around the moderator band for retraction. The edges of the defect are carefully assessed. This may require division of right ventricular trabeculations which obscure the margins of the defect. In occasional cases, the moderator band is divided, although this is generally avoided due to its potential negative effects on right ventricular conduction and function. If it is divided, the moderator band can be reapproximated after the VSD is closed. A useful technique to identify the borders of the defect is to look through the VSD into the left ventricle, and then trace the left ventricular aspect of the defect around 360 degrees. The left ventricular aspect is usually more clearly defined than the right ventricular aspect. The VSD is then closed with a patch and running Prolene suture. The conduction system is remote, and relatively deep bites can be taken in the septal muscle, particularly in areas where the margin is obscured by trabeculations. Smaller defects can often be directly closed with interrupted, pledgetted, horizontal mattress sutures.

Anterior muscular VSDs can lie immediately under the course of the left anterior descending coronary artery (LAD), where the ventricular free wall constitutes the anterior border of the defect. Exposure can be quite difficult, but is usually adequate via the right atrium, aided by external pressure on the anterior ventricles. When suturing the anterior border, the surgeon should be cognizant of the course of the LAD, and check the repair from outside the heart for excessive dimpling or kinking of the artery. Alternatively, a “sandwich technique” can be used, in which mattress sutures are placed from the edge of the septal muscle, through the anterior wall of the right ventricle, taking care to avoid the LAD (Figure 10).[49]

Figure 10

Inlet muscular VSDs lie immediately under the septal leaflet of the tricuspid valve, towards the diaphragmatic surface of the heart. Unlike a perimembranous defect, the inlet muscular defect is separated from the tricuspid valve by a rim of muscle. The conduction system runs along the superior border of the defect, in contrast to the situation with a perimembranous defect. Suturing is into muscle around the circumference of the defect, keeping the bites along the superior margin on the right ventricular aspect of the septum to avoid the conduction system. If the muscular rim along the tricuspid valve is thin, suturing in this area can pass through the tricuspid valve instead, as described for a perimembranous defect. On occasion, an inlet muscular defect coexists with a separate, perimembranous defect. In this case, the conduction system runs in the muscular bridge between the two defects. Division of this bridge, to join the 2 defects, will result in heart block. The safest approach to this situation is to use a single patch to cover both defects, completely avoiding suturing along the muscular bridge (Figure 11).

Figure 11

Apical Muscular VSD Closure

Apical muscular VSDs lie between the apices of the two ventricles. The apex of the right ventricle can be divided into two components, the apex of the right ventricular inflow, which lies posterior and rightwards, and the apex of the right ventricular infundibulum, which lies anterior and leftwards (Figure 12).[50],[51],[52]

Figure 12

Closure of an apical muscular VSD has been approached via the right atrium,[53] via the left ventricle,[49],[54] and via the right ventricle.[51],[52],[55],[56] The right atrial approach can require fairly extensive division of right ventricular trabeculations, as well as vigorous retraction. Alternatively, exposure can be achieved via an apical left ventriculotomy, just to the left of the LAD (Figure 13). The left ventricular aspect of an apical VSD is often a clearly defined, single opening in the septum, making closure via this approach straightforward. However, there are concerns about the deleterious effects of the ventriculotomy on long-term left ventricular function.[57],[58],[59] Our preferred approach to an apical muscular VSD is via an apical right ventriculotomy (Figure 14). The apex of the heart is elevated by epicardial stay sutures and the course of both the LAD and the posterior descending coronary arteries identified. An incision is made in the right ventricle, to the right of the distal LAD, and extending inferiorly just to or around the acute margin of the heart. Complete exposure of the VSD requires division of apical trabeculations on the right ventricular side of the defect. The patch is brought up to the ventriculotomy anteriorly. The ventriculotomy is closed with running suture in 2 layers, taking care not to compromise the LAD. The conduction system is remote from apical muscular defects.

Figure 13

Figure 14

Multiple Muscular VSDs

Multiple VSDs may occur concomitantly in any portion of the septum. As discussed above, the VSDs will appear more numerous when viewed from the right ventricle than from the left. The term “Swiss Cheese septum” is not precisely defined, but is generally accepted to mean a situation in which a significant portion of the muscular septum consists of defects, at least 4 in number.[57] Often the Swiss Cheese septum extends to, or includes, defects in the apical portion of the septum.

While the general approach to multiple muscular defects is similar to the approach to isolated muscular VSDs, multiple defects present particular challenges to identification and closure. As a consequence, a wide range of approaches has been described. These have included direct closure with a patch or mattress sutures.[53],[57] A large patch can be placed through the defect into the left ventricle, and secured to the septum with several interrupted sutures (Figure 15).[49] This approach relies on left ventricular pressure to keep the patch applied to the septum until healing further seals its edges. Separate patches can be placed on the right and left ventricular sides of the septum to sandwich the defects between the two patches.[60],[61] A re-endocardialization strategy relies on double-layer suturing of septal trabeculations with multiple superficial, running sutures.[62] Guidance of patch placement has been described by prebypass epicardial echocardiography with perventricular wire placement,[61] or by cardioscopy.[63] Device closure of multiple muscular VSDs can be carried out via a percutaneous, perventricular, or intraoperative approach.

Figure 15

The number and variety of these innovative approaches is a testament to the difficulty which can be encountered in attempting to close multiple muscular VSDs. All of these approaches can be effective, and their use will depend on the preferences and capabilities of the surgical team. Some of these alternatives may be particularly applicable for closure of multiple muscular VSDs in the apical septum.

The young infant who is symptomatic due to multiple muscular VSDs, particularly if there is a Swiss cheese septum, is one of the rare instances in which it may be appropriate to place a pulmonary artery band to allow for growth before attempting VSD closure, either surgical or interventional. Ventricular hypertrophy induced by the band may result in closure of some smaller defects, but also may make intraoperative visualization of the remaining defects more difficult. Thus this decision must be made on a case-by-case basis, taking into account the anatomy, as well as the capabilities of the surgical and interventional teams.

Evaluation of the Repair

Surgical closure of muscular VSDs, especially if they are apical or multiple, carries an increased risk of leaving a residual defect. Evaluation of the repair in the operating room therefore assumes particular importance. Evaluation should include TEE and an oxygen saturation run, following the guidelines outlined above. If the TEE shows a significant residual VSD or VSDs, and the saturation run indicates a Qp:Qs above about 1.5:1, a decision must be made whether to resume cardiopulmonary bypass, rearrest the heart, and attempt closure of the residual defects. This decision should take into account the location and number of the residual VSDs, the difficulty of the exposure at the first attempt, and the general condition of the patient, including the length of the operation. An alternative is device closure of the residual defects, either via a perventricular approach, or in the cardiac catheterization lab at a later time. Depending on the capabilities of the surgical and interventional team, another alternative is to place a pulmonary artery band. The patient can then be reevaluated by a cardiac catheterization at a later date and a plan made for band removal +/- closure of the residual defects. Design of the band to allow dilation (removal) in the cardiac catheterization lab may offer the possibility of avoiding another operation if the residual defects largely close over time.

Acquired Associated Defects

Acquired associated defects are repaired concomitantly with the VSD. Infundibular ventricular outflow tract obstruction is visualized via the tricuspid valve. Repair is accomplished by encircling obstructing muscle bundles with a clamp and dividing or resecting them. Care must be taken not to divide structures involved in tricuspid valve support.

Aortic valve prolapse accompanying a VSD is approached by VSD closure. If the aortic insufficiency is trivial or mild, VSD closure alone will generally stabilize the aortic valve, preventing further prolapse and insufficiency.[64] Aortic insufficiency which is more than mild indicates aortic valve repair via the aortic root. Our preferred repair is plication of the prolapsing leaflet by central plication (Figure 16).[65] This has proven more reliable than commissural plication (Trusler’s repair) (Figure 17).[66]

Figure 16

Figure 17

Accompanying subaortic stenosis lies along the left ventricular side of the inferior, or proximal aspect of a perimembranous VSD. If the subaortic ridge is limited and thin, it can often be visualized and sharply resected from the septum by looking through the VSD from the right side. Care is taken to avoid inferior traction on the inferior edge of the VSD with mechanical retractors, as the conduction system lies in this location. More advanced subaortic stenosis requires exposure via the aortic root. VSD closure alone often results in a right bundle branch block, being seen in as many as 40-60% of patients (62%; page 199)[3] (44%).[67] In this setting, subaortic stenosis resection is therefore limited to resection of the fibrous ridge without an accompanying left ventricular myectomy, in order to avoid additional left bundle branch block and potential complete heart block.

Other Approaches

A small VSD can be closed with interrupted, horizontal mattress sutures rather than a patch. Closure without a patch is most commonly used for small muscular VSDs. Direct closure can also be used for a doubly committed, subarterial VSD, although the potential for distortion of either the pulmonary or aortic valve should be considered. Direct closure of a perimembranous defect is most commonly applicable when the indication for surgery is an accompanying defect, such as DCRV, rather than the VSD itself. Small perimembranous VSDs can be rimmed and partially closed by fibrous and accessory tricuspid valve tissue. Since the conduction tissue runs in muscle, this fibrous tissue is a safe site for suture placement. However, the surgeon must ensure that the accessory fibrous tissue is not obscuring the true edges of the VSD, in which case simply approximating the fibrous tissue will leave a residual defect.

Approach to an isolated VSD via the aortic valve is rarely used in current practice. However it may be a useful approach to a residual VSD at the anterior-superior margin of a previously placed VSD patch. Such a defect may be quite difficult to expose via the right atrium.

VSD closure via an incision in the body of the right ventricle is also unusual for an isolated defect. However, this is a common approach to VSD closure during repair of more complex defects, such as DORV, and operations involving an RV to PA conduit, such as truncus arteriosus and tetralogy of Fallot with pulmonary atresia.