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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3683_Библиотеки_им_академика_М_И_Перельмана
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an appropriate pericardial or homograft patch.
Flooding of the Pulmonary Circulation
The site of the shunt must be occluded with the initiation of cardiopulmonary bypass, or flooding of the lungs will
occur. If this cannot be achieved with a vascular forceps or clamp, the right and left pulmonary arteries should be
encircled before beginning cardiopulmonary bypass, and snared or clamped.
Technique: Potts Shunt
Closure of Potts shunt is performed on cardiopulmonary bypass with moderate hypothermia. The patient is
placed in the Trendelenburg position, and with the heart decompressed, the perfusion pressure is temporarily
reduced. A longitudinal incision is made on the main pulmonary artery
and extended onto the left pulmonary artery. The site of a shunt orifice in the left pulmonary artery is identified
and closed with a purse-string suture or patch.
Flooding of the Pulmonary Circulation
Before instituting cardiopulmonary bypass, the site should be identified by palpating for a thrill along the left
pulmonary artery. The shunt flow can be interrupted or markedly reduced by digital pressure on this site.
Air Embolism through Aortic Opening
When the left pulmonary artery is opened, some flow must be maintained through the aortic cannula to prevent
air embolism.
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19
Atrial Septal Defect
Defects in the atrial septum are relatively common. They appear at various sites in the septum and can be
associated with other congenital abnormalities. In addition, there is a real or potential slit-like opening, the
foramen ovale, where the fossa ovalis flap disappears behind the superior septal limbus. Generally, the higher
pressure in the left atrium keeps the fossa ovalis flap in apposition to the superior septal limbus, and therefore
the opening remains closed. In 20% of the population, however, the foramen ovale is patent and has the
potential to allow shunting under certain circumstances. When pressure in the right atrium increases, as in right-
sided heart failure, the septum becomes stretched and allows the foramen ovale to enlarge with significant
shunting at the atrial level.
The sinus venosus atrial septal defect occurs high in the atrial septum and extends into the orifice of the superior
vena cava, which becomes malpositioned slightly toward the left. There is usually anomalous drainage from the
right superior pulmonary vein associated with these defects (Fig. 19.1).
The fossa ovalis type, also known as the ostium secundum defect, is the most common variety. This defect
occurs in the midseptum in the vicinity of the fossa ovalis and may be small or very large. Infrequently, the defect
may occur low in the septum and extend into the orifice of the inferior vena cava, which also becomes
malpositioned toward the left. This type of defect is sometimes referred to as a sinus venosus defect of the
inferior vena caval type and may be associated with anomalous pulmonary venous drainage. Rarely, the whole
septum may be absent, giving rise to a single common atrium.
A defect low in the interatrial septum that extends down to the level of the atrioventricular valve orifices is part of
the atrioventricular septal defect complex (see Chapter 22).
SURGICAL ANATOMY OF THE RIGHT ATRIUM
Although the right atrium is morphologically molded into a single chamber, it is formed by two components: the
sinus venarum and the right atrial appendage (sometimes referred to as the body of the atrium). Systemic
venous return flows in from opposing directions through the superior and inferior venae cavae into the sinus
venarum. This smooth-walled area is the most posterior portion of the right atrium and stretches between the
orifices of the caval veins. From the viewpoint of the surgeon looking down into the right atrium, the sinus
venarum is more or less horizontal with the superior vena cava entering from the left and the inferior vena cava
(bounded by the eustachian valve) entering from the right (Fig. 19.2).
Just below and medial to the orifice of the superior vena cava arises a muscle bundle, the crista terminalis, which
springs into prominence as it circles the orifice of the superior vena cava to the right lateral wall of the atrium and
continues inferiorly toward the inferior vena cava, thereby forming the boundary between the sinus venarum and
the atrial appendage. This muscle bundle is evidenced on the outside of the atrium by a groove, the sulcus
terminalis. Lying subepicardially in the sulcus terminalis, just below the entrance of the superior vena cava, is the
sinoatrial node, which may be vulnerable to injury from the various surgical incisions and cannulations commonly
performed on the right atrium. The remainder of the right atrium is made up of atrial appendage, which begins at
the crista terminalis and extends forward (upward from the surgeon's perspective) to surround the tricuspid valve
and form an expanded chamber.
In contrast with the smooth-walled sinus venarum, the lateral wall of the atrial appendage is ridged with multiple
narrow bands of muscle, the musculi pectinati. These bands arise from the crista terminalis and pass upward to
the most anterior part of the atrium. Functionally, they supply the right atrium with enough pumping capacity to
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propel the venous inflow through the tricuspid valve into the right ventricle.
Just above the sinus venarum in the center of the medial wall is the fossa ovalis, a horseshoe- or elliptically
shaped depression. The true interatrial septum consists of the fossa ovalis with variable contributions from the
superior, anterior, and inferior limbic muscle bundles that surround it. The aortic root is hidden behind the
anteromedial atrial wall between the fossa ovalis and the termination of the heavily trabeculated right atrial
appendage. Segments of
the noncoronary and right sinuses of Valsalva are in close apposition to the atrial wall in this area. Their location
may be manifested by the aortic mound, which is a bulge above and slightly to the left of the fossa ovalis. The
aortic valve here can be more clearly visualized if its continuity, through the central fibrous body, with the
adjacent tricuspid valve annulus is taken into consideration.
FIG. 19.1 Types of atrial septal defects.Ostium secundum atrial septal defectOstium primum atrial septal
defectInferior sinus venousus defectSinus venosus atrial septal defectRight superior pulmonary veins
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FIG. 19.2 Surgical anatomy of the right atrium. SVC, superior vena cava; SA, sinoatrial; IVC, inferior vena cava;
AV, atrioventricular.
Also, often invisible to the surgeon is the artery to the sinoatrial node, which can run through this same area.
Although its origin and exact course are unpredictable, it takes a variable course toward the superior cavoatrial
angle and the sinus node.
The tricuspid valve is located anteroinferiorly in the right atrium, where it opens widely into the right ventricle.
The annulus of the tricuspid valve crosses over the membranous septum, dividing it into atrioventricular and
interventricular segments. The membranous, or fibrous, septum is a continuation of the central fibrous body,
through which the tricuspid, mitral, and aortic valves are connected. Immediately below the upper or
atrioventricular section of the membranous septum lies the hidden atrioventricular node. It is situated at the apex
of the triangle of Koch, the boundaries of which are the annulus of the septal leaflet of the tricuspid valve, the
tendon of Todaro (running intramyocardially from the central fibrous body to the eustachian valve of the inferior
vena cava), and its base, the coronary sinus. Anderson describes the tendon of Todaro as a fibrous extension of
the commissure between the eustachian valve (of the inferior vena cava) and the thebesian valve (of the
coronary sinus). Conduction tissue passes from the atrioventricular node as the bundle of His, below the
membranous septum, and down into the muscular interventricular septum. The coronary sinus, draining the
cardiac veins, is situated alongside the tendon of Todaro, between it and the tricuspid valve.
Incision
All forms of atrial septal defect can be approached through a median sternotomy. Many surgeons now use a
lower ministernotomy approach or submammary right thoracotomy for simple secundum atrial septal defects.
Others prefer the Brom modification of the median sternotomy incision to allow full exposure of the pericardial
space with acceptable cosmetic results in female patients (see Chapter 1).
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Cannulation
The ascending aorta is cannulated in the usual manner (see Chapter 2). The superior vena cava is usually
cannulated directly, although it may be cannulated through the right atrial appendage. The inferior vena cava is
cannulated through the atrial wall, just above the origin of the inferior vena cava. Tapes are then passed around
both cavae. For those defects thought to be low in the atrial septum or for inferior sinus venosus defects, it is
imperative to cannulate low on the inferior vena cava itself.
Aortic Cannulation with Minimally Invasive Approaches
The more distal ascending aorta is not easily accessible through a lower ministernotomy or submammary right
thoracotomy. The aorta should be cannulated in its midportion where control of bleeding is relatively easy.
Enough room should be left below the cannula to allow for deairing procedures.
Exposure of the Superior Vena Cava
A tie is placed on the right atrial appendage. Inferior traction on the appendage allows adequate visualization of
the right superior vena cava for direct cannulation in most instances. If direct cannulation is not feasible, a
straight venous cannula can be passed into the superior vena cava through a purse-string suture on the right
atrial appendage.
Left Superior Vena Cava
The left superior vena cava cannot be cannulated through minimally invasive incisions. Preoperative
echocardiography must determine the presence or absence of a left superior vena cava.
Myocardial Preservation
Cold cardioplegic arrest of the myocardium is achieved by infusion of cold-blood cardioplegia into the aortic root
(see Chapter 3).
Alternatively, closure of a simple septum secundum-type defect can be accomplished safely without clamping the
aorta by inducing ventricular fibrillation (see subsequent text). This approach is used with minimally invasive
incisions because aortic cross-clamping in these cases may be difficult.
SINUS VENOSUS ATRIAL SEPTAL DEFECT
Sinus venosus atrial septal defects usually occur high on the septum close to the orifice of the superior vena
cava and are associated with anomalous drainage of right upper lobe pulmonary veins into the superior vena
cava and right atrium (Fig. 19.3). Approximately 10% of patients with this type of atrial septal defect also have a
persistent left superior vena cava, which may be suspected from a large coronary sinus on the preoperative
echocardiogram.
Technique
The superior vena cava is cannulated directly high above the entry site of the highest anomalous pulmonary vein
or preferably at the innominate/caval junction.
The aorta is cross-clamped, and cardioplegic solution is administered into the aortic root (see Chapter 3). The
vena caval snares are then snugged down. A longitudinal atriotomy is made starting at a point 0.5 to 1 cm
posterior
and parallel to the sulcus terminalis. The edges of the incision are then retracted to provide good exposure of the
septal defect (Fig. 19.3). If additional exposure is required, the atriotomy is extended superiorly and
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posterolaterally across the superior vena caval-right atrial junction and onto the vena cava as far as necessary.
FIG. 19.3 Sinus venosus atrial septal defect and the superior extension of the atriotomy posterior to the sinoatrial
node.
Drainage of Venous Return from a Left Superior Vena Cava
Although the venous return from a persistent left superior vena cava can be removed by pump suction, direct
cannulation with a third venous cannula is the preferred approach. If an innominate vein is present and of
adequate size, the left superior vena cava may be temporarily occluded with a snare.
Injury to the Sinoatrial Node
The superior extent of the atriotomy may have to be extended across the atriocaval junction onto the superior
vena cava to provide adequate exposure. The sinoatrial node can be injured unless the atriotomy is extended
well posterior to it.
Persistent Left-to-Right Shunt
It is important to ascertain that the tape around the superior vena cava is well above the level of the drainage of
all the anomalous veins. Leaving a pulmonary vein draining into the superior vena cava results in a residual left-
to-right shunt.
Difficult Exposure
The azygos vein, as it joins the superior vena cava, may at times obscure the surrounding structures. In this
case, it may be ligated and divided to free up the superior vena cava and to provide better exposure of the
anomalous pulmonary veins.
A patch of glutaraldehyde-treated autologous pericardium or Gore-Tex is cut to an appropriate size and shape
after examining the extent of the defect. With a continuous suture of 5-0 or 6-0 Prolene, the patch is sewn around
the orifices of the anomalous veins and across to the anteromedial margin of the atrial septal defect (Fig. 19.4).
Preventing Ostial Stenosis of Anomalous Veins
Sometimes it is necessary to place several sutures through the patch and the right atrial or superior vena caval
wall around the openings of the anomalous veins before lowering the patch into position. Accurately placed
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sutures, well away from the anomalous vein orifices, will prevent subsequent stenosis.
Obstruction of the Pulmonary Venous Return
If the atrial septal defect is relatively small, it should be enlarged to prevent obstruction of the pulmonary venous
return. In addition, the patch should be generous, creating a hood when the heart fills with blood and allowing
unobstructed flow under the patch into the left atrium.
Injury to the Aortic Root/Valve
Care must be taken when enlarging the atrial septal opening, especially if the aortic root is enlarged or
pressurized. The extension from the sinus venosus defect to the fossa ovalis should be kept posterior, and if
possible a clamp should be placed through the sinus venosus defect or patent foramen ovale and used to lift the
atrial septum away from the aortic root while incising the septum. Enlarging the atrial septal opening in this way
also avoids injury to the sinus node artery.
The atriotomy is then closed. Occasionally, this can be done primarily with a continuous suture of 5-0 Prolene.
Most often, a second patch of pericardium is required to prevent narrowing of the superior vena caval-right atrial
junction (Fig. 19.4, inset).
FIG. 19.4 First patch baffling anomalous pulmonary veins and closing the sinus venosus atrial septal defect.
Inset: Second patch enlarging the superior vena caval-right atrial junction.
Air Removal
By having the anesthesiologist inflate the lungs before securing the septal patch, the left side of the heart is
flooded with blood to displace any loculated air bubbles from within the pulmonary veins and left atrium. The
patch is kept partially open with the tip of a forceps, while a sustained ventilation fills the left atrium with blood
and the suture line is snugged down before the lungs are deflated.
Preventing Obstruction of the Superior Vena Cava
Often the atriotomy has been extended onto the superior vena cava for some distance for precise exposure of
the anomalous pulmonary veins. Direct closure may cause narrowing of the superior vena cava and give rise to
subsequent obstruction. Unless the superior vena cava is unusually large, it should be enlarged with a patch of
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pericardium (Fig. 19.4, inset). Alternatively, a V-Y atrioplasty can be performed if the right atrium is very large.
Sinoatrial Node Injury
As mentioned previously, the atrial and superior vena caval closure line is in close proximity to the sinoatrial
node. The edges of the atriotomy should be handled with care to prevent conduction abnormalities from
sinoatrial node injury.
The caval snares are removed following right atrial closure, the heart is filled, and the aortic clamp is removed.
Standard deairing is performed, and the patient is weaned from cardiopulmonary bypass.
Cyanosis Following Cardiopulmonary Bypass
If decreased systemic oxygen saturations are noted after separation from cardiopulmonary bypass, consideration
should be given to the existence of a right-to-left shunt. This may occur if a large azygos vein is included in the
baffle of pulmonary veins to the sinus venosus atrial septal defect. Ligating the azygos vein will rectify this
situation.
Caval Division Technique (“Warden”)
Some surgeons use the technique of superior vena caval division and anastomosis of the proximal superior vena
caval opening to the right atrial appendage for sinus venosus atrial septal defects; this technique is particularly
effective if the entrance of several of the right pulmonary veins are high on the superior vena cava, making baffle
placement without caval obstruction difficult. The superior vena cava is divided just above the highest anomalous
pulmonary vein, and the distal opening of the superior vena cava is closed, taking care not to compromise the
opening of the anomalous vein(s) (Fig. 19.5). The tip of the right atrial appendage is amputated, and it is
additionally important that all of the pectinate muscles in the amputated right atrial appendage are excised (Fig.
19.5). Through a right atrial incision, a
patch of pericardium or Gore-Tex is used to baffle the orifice of the superior vena cava to the sinus venosus
defect (Fig. 19.6). This technique avoids a long incision and patch on the superior vena cava, especially when
the anomalous veins enter high above the cavoatrial junction. The superior vena cava is then anastomosed to a
mobilized portion of the right atrial appendage with care taken not to “purestring” the connection (Fig. 19.6).
Often an additional patch augmentation of the caval-atrial anastomosis is required to reduce tension on the
connection as well.
FIG. 19.5 The tip of the atrial appendage is amputated and the SVC is divided above the level of entry of the
anomalous right pulmonary veins. It is important to resect all of the trabecular tissue within the atrial appendage
so as to mitigate future systemic venous obstruction.
OSTIUM SECUNDUM ATRIAL SEPTAL DEFECT
Ostium secundum defects are the most common form of atrial septal defect. They are usually large and include
the entire fossa ovalis (Fig. 19.7A).
Technique
The aorta is cross-clamped, and cardioplegic solution is administered into the aortic root (see Chapter 3).
Alternatively, if a minimally invasive approach has been used, two pacing wires are secured on the anterior right
ventricle and connected to a fibrillator to induce ventricular fibrillation. The vena caval snares are then snugged
down. An oblique atriotomy is made and is extended toward the orifice of the inferior vena cava. The edges of
the incision are retracted to provide good exposure of the septal defect.
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FIG. 19.6 Completed Warden procedure. Note the patch on the superior vena cava, which can be necessary at
times so as not to have pulmonary venous obstruction that can occur with direct suture closure (if the entrance of
the veins is close to the innominate-SVC junction). Arrows indicate the direction of flow of both the pulmonary
and systemic venous return.
Some smaller secundum defects can be closed directly. Sutures are placed at the superior and inferior ends of
the defect and continued toward each other, incorporating the margins of the defect (Fig. 19.7B).
Depth of Sutures
The sutures must incorporate the thickened endocardium on both sides of the interatrial septum. The tissue of
the fossa ovalis is usually too weak and friable to provide secure closure. Deep sutures should be avoided along
the superior aspect of the defect because this area overlies the aortic root, as well as laterally to avoid narrowing
the orifice of the right pulmonary veins (Fig. 19.2).
Using the Fossa Ovalis Flap to Close a Defect
Occasionally, the fossa ovalis flap is of sufficient size and quality to allow a tension-free primary suture closure,
approximating the superior edge of the flap to the superior limbus (Fig. 19.7C). This is often the case in infants
with a stretched patent foramen ovale. One must always check for fenestrations in the inferior aspect of the flap
that could result in residual atrial septal defects. If fenestrations are present or the flap is thin and friable, patch
closure should be undertaken.
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