VSDs located near the ventricular apex can be very difficult to expose, and an apical ventriculotomy

may be necessary. Once the defect is exposed, it is closed using a polytetrafluoroethylene patch and a

running polypropylene suture, although other centers may prefer other patch material or interrupted

suture technique. It is important to understand the anatomy of the conduction tissue when closing VSDs.

The AV node is an atrial structure that lies at the apex of an anatomic triangle (known as the triangle of

Koch) formed by the coronary sinus, the tendon of Todaro (a prominent band leading from the inferior

vena cava and inserting in the atrial septum), and the septal attachment of the tricuspid valve. The node

then gives rise to the bundle of His, which penetrates the AV junction beneath the membranous septum.

The bundle of His then bifurcates into right and left bundle branches, which pass along either side of the

muscular ventricular septum. In the presence of a perimembranous VSD, the bundle of His passes along

the posterior and inferior rim of the defect, generally on the left ventricular side. In this critical area,

sutures must be placed superficially on the right ventricular side a few millimeters from the edge of the

defect. The bundle of His also tends to run along the posterior and inferior margin of inlet VSDs. The

conduction tissue is usually remote from outlet and trabecular VSDs.

PA banding is a palliative maneuver that is used to protect the pulmonary circulation from excessive

blood flow. PA banding is currently performed only in patients who are felt to be poor candidates for

VSD closure, either due to associated illness or due to anatomic complexity, such as multiple trabecular

VSDs (“Swiss cheese” septum). Banding is performed without the need for cardiopulmonary bypass. A

band is placed around the main PA and tightened to achieve a distal PA pressure of about one-half

systemic. The band is secured to the adventitia of the PA to prevent its migration. Distal migration may

result in narrowing and poor growth of one or both branch pulmonary arteries, whereas proximal

migration can cause deformity of the pulmonary valve. Later, when the patient is a candidate for VSD

closure, the band must be removed. Repair of the main PA at the band site is also usually necessary and

can typically be accomplished by scar resection and primary closure or patch repair.

Surgical closure of a VSD is associated with a mortality less than 1%.23 Potential complications

include injury to the conduction tissue and injury to the tricuspid or aortic valves. Transient heart block

may result from tissue swelling or injury from retraction, but permanent heart block occurs in less than

1% of cases. When heart block develops after surgery, patients are usually observed for a period of 7 to

10 days prior to permanent pacemaker implantation. Closure of perimembranous and inlet VSDs may

result in distortion of the tricuspid valve, which may cause significant regurgitation. Aortic valve injury

may occur as a result of inaccurate suturing, especially in perimembranous and outlet defects. A residual

VSD is seen in about 5% of cases, and reoperation is indicated when significant shunting persists (Qp/Qs

ratio >1.5). The Qp/Qs ratio can be calculated by measuring oxygen saturations and using the following

formula derived from the Fick equation:

Qp/Qs = (Ao - SVC)/(PV - PA)

where Ao is the aortic (or systemic) saturation, SVC is the saturation in the superior vena cava, PV is

the saturation in the pulmonary veins (which is usually estimated to be 95% to 100%), and PA is the

saturation in the pulmonary arteries. Intraoperative echocardiography is used routinely to identify

residual defects, which can then be repaired before the patient leaves the operating room.

Recently, transcatheter devices have been developed to allow closure of some VSDs in the cardiac

catheterization laboratory or by periventricular deployment without the use of cardiopulmonary

bypass.24,25 Device closure is optimal for large muscular defects with sufficient rims for securing the

device. These defects are often difficult to visualize and close surgically. Periventricular closure allows

the use of VSD device closure in smaller infants with symptomatic muscular VSDs with excellent results

without the challenges of transvenous access in this population.25 The use of devices for

perimembranous VSDs remains limited by the risk of damage to the conduction system or impingement

on the function of the tricuspid or aortic valves. A recent series demonstrated a 22% rate of complete

heart block, which is prohibitively high in comparison to the surgical rate of complete heart block of

less than 1%.26

ATRIOVENTRICULAR SEPTAL DEFECT

4 Defects in the embryologic development of the endocardial cushions may result in a variety of

morphologic abnormalities in the AV valves and the atrial and ventricular septa. These anomalies range

from ostium primum ASD to complete AVSD (or AV canal defect), with a spectrum of intermediate

forms. PDA and TOF are occasionally seen in association with these defects. A high percentage of

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patients with abnormalities of the AV structures have trisomy 21 (Down syndrome). All infants with

trisomy 21 should have an echocardiogram to rule out congenital heart disease given a prevalence of

50%.

Complete AVSD is an anomaly characterized by a common AV orifice, rather than separate mitral and

tricuspid orifices, and a deficiency of endocardial cushion tissue, which results in a primum ASD and an

inlet type of VSD. Complete AVSDs were subclassified by Rastelli et al.27 into three types according to

the morphology of the anterior leaflet of the common AV valve (Table 81-1). Incomplete AVSDs are

variants in which there is partial fusion of the AV valves, resulting in separate right and left AV valve

orifices. The ostium primum ASD is a type of incomplete AVSD in which the VSD component is absent.

Table 81-1 Rastelli Classification of Atrioseptal Ventricular Defects

When both left and right AV valves equally share the common AV valve orifice, the AVSD is termed

balanced. Occasionally, the orifice may favor the right AV valve (right dominance) or the left AV valve

(left dominance). In marked right dominance, the left AV valve and LV are hypoplastic, and frequently

coexist with other left-sided abnormalities, including aortic stenosis (AS), hypoplasia of the aorta, and

coarctation. Conversely, marked left dominance results in a deficient right AV valve with associated

hypoplasia of the right ventricle, PS or atresia, and TOF. Patients with severe imbalance require staged

single-ventricle reconstruction.

The conduction tissue is displaced in an ASVD and is at risk during surgical repair. The AV node is

located posteriorly and inferiorly of its normal position toward the coronary sinus in what has been

termed the nodal triangle. This triangle is bounded by the coronary sinus, the posterior attachment of the

inferior bridging leaflet, and the rim of the ASD. The bundle of His courses anteriorly and superiorly to

run along the leftward aspect of the crest of the VSD, giving off the left bundle branch and continuing as

the right bundle branch.

A number of other cardiac anomalies are associated with AVSDs including a PDA (10%) and TOF

(10%).28 Important abnormalities of the left AV valve include single papillary muscle (parachute mitral

valve) (2% to 6%) and double orifice mitral valve (8% to 14%).29 A persistent left superior vena cava

with or without an unroofed coronary sinus is encountered in 3% of patients with an AVSD. Doubleoutlet right ventricle (DORV) (2%) significantly complicates or may even preclude complete surgical

correction.28 Left ventricular outflow tract obstruction from subaortic stenosis or redundant AV valve

tissue occurs in 4% to 7%.30,31

Patients with an incomplete AVSD generally present in a similar fashion as a patient with a large

secundum ASD. Patients with a complete AVSD with both atrial and ventricular level shunting generally

present early in infancy with signs and symptoms of CHF. In addition, moderate or severe left AV valve

regurgitation occurs in approximately 10% of patients with an AVSD, worsening the clinical picture. On

physical examination, the precordium is hyperactive, often with a prominent thrill. Auscultatory

findings include a systolic murmur along the left sternal border, a high-pitched murmur at the apex

from left AV valve regurgitation, and a middiastolic flow murmur across the common AV valve. In the

presence of elevated PVR, there may be a split first heart sound. Significant cardiomegaly and

pulmonary overcirculation are found on the chest radiograph. ECG reveals biventricular hypertrophy,

atrial enlargement, prolonged PR interval, leftward axis, and counterclockwise frontal plane loop.

Doppler/echocardiography is diagnostic, defining the atrial and ventricular level shunting, valvular

anatomy, and any associated anomalies. Cardiac catheterization should be performed for patients older

than 1 year of age, for patients with signs or symptoms of increased PVR, or in some cases to further

evaluate other associated major cardiac anomalies. If the PVR is high, it is important to remeasure it

while the child is breathing 100% oxygen with and without nitric oxide. If the pulmonary resistance

falls, it implies that much of the elevated resistance is dynamic and can be managed in the perioperative

period by ventilatory manipulation, supplemental oxygen, and nitric oxide. More recently, sildenafil has

been shown to decrease elevation in PVR in children with CHF.32 Markedly elevated pulmonary

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resistance (>10 Woods units/m2) that does not respond to oxygen administration is generally

considered a contraindication to repair.

Operative treatment is almost always necessary as soon as symptoms are observed to prevent further

clinical deterioration. Even in the absence of symptoms, operation is best performed before 6 months of

age. PA banding, which permits delaying the repair until the child is larger, is no longer used today

except in select complex or single-ventricle cases, extremely low birth weight or prematurity, and very

poor clinical condition. This approach exposes the child to the risks of two operations, and the overall

mortality exceeds that of primary repair in infancy.

Correcting AVSDs requires patch closure of both septal defects, with any necessary valve

reconstruction. Separate atrial and ventricular patches or a single patch for both chambers can be

used.33 During closure of the ventricular defect, the surgeon must carefully avoid injury to the

conduction system, which passes along the posterior and inferior rim of the ventricular septum.

The short- and long-term success of the operation is highly dependent on the status of the PVR and

the surgeon’s ability to maintain competence of the mitral valve. Although earlier reports recommend

that the cleft in the left AV valve should not be closed and the valve treated as a trileaflet structure,

most surgeons now believe that closure of the cleft is an important mechanism in preventing

postoperative left AV valve regurgitation. Significant AV valve regurgitation at the conclusion of

surgery, severe dysplasia of the left AV valve, and failure to close the cleft of the left AV valve have

been identified as important risk factors for reoperation.34 Significant postoperative left AV valve

regurgitation is also a risk factor for operative and long-term mortality.30,34 The cleft should not be

completely closed in the presence of a single papillary muscle to avoid causing left AV valve stenosis. In

the case of a double-orifice valve, the bridging tissue should not be divided to create a single opening in

the valve.

Operative mortality is related largely to associated cardiac anomalies and left AV valve regurgitation.

Mortality for repair of uncomplicated incomplete AVSDs ranges from 0% to 0.6%, and the addition of

left AV valve regurgitation increases mortality to 4% to 6%.30,35 For complete AVSDs, the mortality

without left AV valve regurgitation is approximately 5%, compared with 13% when significant degrees

of regurgitation are present.30

The majority of reoperations after repair of AVSD are due to left AV valve regurgitation or subaortic

stenosis with reoperation rates at 5 years of 11% and 10%, respectively.36 Significant postoperative AV

valve regurgitation occurs in 10% to 15% of patients, necessitating reoperation for valve repair or

replacement in 7% to 12%.34,37,38 Long-term survival is excellent with rates at 1, 3, and 5 years of 98%,

95%, and 95%, respectively.36

TETRALOGY OF FALLOT

5 TOF is the most common cyanotic congenital heart defect. It occurs in 0.6 per 1,000 live births and

has a prevalence of about 5% among all patients with congenital heart disease.7 The pathologic anatomy

is frequently described as having four components: VSD, overriding aorta, PS, and right ventricular

hypertrophy (Fig. 81-3). Embryologically, the anatomy of TOF is thought to result from a single defect:

anterior malalignment of the infundibular septum.39 The infundibular septum normally separates the

primitive outflow tracts and fuses with the ventricular septum. Anterior malalignment of the

infundibular septum creates a VSD due to failure of fusion with the ventricular septum and also

displaces the aorta over the VSD and right ventricle. Infundibular malalignment also crowds the right

ventricular outflow tract, causing PS and, secondarily, right ventricular hypertrophy. Prominent muscle

bands also extend from the septal insertion of the infundibular septum to the right ventricular free wall

and contribute to the obstruction of the right ventricular outflow tract. The pulmonary valve is usually

stenotic and is bicuspid in 58% of cases.40 Pulmonary atresia occurs in about 7% of cases of TOF. The

branch pulmonary arteries in TOF may exhibit mild diffuse hypoplasia or discrete stenosis (most

frequently of the left PA at the site of ductal insertion). Coronary artery anomalies are frequently

present. The origin of the left anterior descending from the right coronary artery, which occurs in 5% of

cases, is clinically important because the vessel crosses the right ventricular infundibulum and is

vulnerable to injury at the time of surgery. A right aortic arch is present in 25% of patients with TOF.

Associated defects include ASD, complete AVSD, PDA, or multiple VSDs.

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Figure 81-3. The four anatomic features of tetralogy of Fallot. The primary morphologic abnormality, anterior and superior

displacement of the infundibular septum, results in a malalignment ventricular septal defect, overriding of the aortic valve, and

obstruction of the right ventricular outflow. Right ventricular hypertrophy is a secondary occurrence.

Patients with TOF develop cyanosis due to right-to-left shunting across the VSD. The degree of

cyanosis depends on the severity of obstruction of the right ventricular outflow tract. Frequently,

cyanosis is mild at birth and may remain undetected for weeks or months. Neonates with severe

infundibular obstruction or pulmonary atresia will develop symptoms shortly after birth and will

require a prostaglandin infusion to maintain ductal patency to ensure adequate PBF. In other patients,

the right ventricular outflow tract obstruction is minor, and the predominant physiology is that of a

large VSD with left-to-right shunting and CHF.

The occurrence of intermittent cyanotic spells is a well-known feature of TOF. The etiology of

spelling is still controversial but is clearly related to a transient imbalance between pulmonary and

systemic blood flow. A spell may be triggered by hypovolemia or peripheral vasodilation (e.g., after a

bath or vigorous physical exertion). Spells may occur in neonates, but are most frequently reported in

infants between the ages of 3 and 18 months. Most spells resolve spontaneously within a few minutes,

but some spells may be fatal. Older children have been observed to spontaneously squat to terminate

spells. The squatting position is thought to increase systemic vascular resistance, which thereby favors

PBF.

Cyanosis is the most frequent physical finding in tetralogy. Auscultation reveals a normal first heart

sound and a single second heart sound. A systolic ejection murmur is present at the left upper sternal

border. Older children may develop clubbing of the fingers and toes. Chest radiography typically

demonstrates a boot-shaped heart due to elevation of the cardiac apex from right ventricular

hypertrophy. Pulmonary vascular markings are usually reduced. A right aortic arch may be present. An

ECG shows right ventricular hypertrophy. Echocardiography is definitive, and catheterization is not

necessary in most cases.

The medical management of TOF is directed toward the treatment and prevention of cyanotic spells.

The immediate treatment of the spelling patient includes administration of oxygen, narcotics for

sedation, and correction of acidosis. Transfusion is indicated for anemic infants. a-Agonists are useful for

increasing systemic vascular resistance (which favors PBF). Some centers have used beta blockers as a

form of long-term therapy to suppress the incidence of spells.

All patients with TOF should undergo surgical repair. Asymptomatic patients should be repaired

electively between 4 and 6 months of age. Early repair is indicated for neonates with severe cyanosis

and for infants who have had a documented spell or worsening cyanosis.

Classically, the repair of TOF was accomplished in two stages. During the first stage, PBF was

augmented by creating a connection (or shunt) between a systemic artery and the PA. At the second

stage, the shunt was taken down, and a complete repair was performed. The first shunt procedure was

the Blalock–Taussig shunt, in which the subclavian artery was mobilized and divided distally, and an

end-to-side anastomosis was created between the inferiorly deflected subclavian and the ipsilateral PA.

Other shunt operations were subsequently developed and involved connections between the ascending

aorta and right PA (Waterston shunt) or between the descending aorta and left PA (Potts shunt). The

modified Blalock–Taussig shunt is the most common type of shunt used today and consists of an

interposition graft (polytetrafluoroethylene) between the innominate or subclavian artery and the

ipsilateral PA. Creation of a shunt may be accomplished with or without the use of cardiopulmonary

bypass.

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