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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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FIG. 23.13 Resection and reapproximation of anterior wall of the right ventricle, and placement of prosthetic
valve in outflow tract.
Larger-Sized Prosthesis
Securing the prosthesis below the pulmonary annulus to the infundibular muscle posteriorly allows placement of
a larger prosthesis.
Tricuspid Valve
Many patients with chronic pulmonary regurgitation and right ventricular dysfunction have at least moderate
tricuspid insufficiency and should undergo a concomitant tricuspid annuloplasty (see Chapter 7).
Percutaneous Pulmonary Valve Implantation
Percutaneous implantation of pulmonary valves is an evolving field, and may allow some patients with right
ventricular outflow tract dysfunction to avoid surgery. However, patients with large transannular patches are
currently not candidates for this technology, and this approach does not allow for surgical right ventricular
remodeling.
APPENDIX
Sizing the Pulmonary Outflow Tract
The internal diameter of the narrowest part of the pulmonary outflow tract is determined by passing calibrated
Hegar dilators of increasing size through the pulmonary valve and into the pulmonary artery. Referring to the
data from Rowlatt et al. (Rowlatt UF, Rimoldi HJA, Lev M. The quantitative anatomy of the normal child's heart.
Pediatr Clin North Am. 1963;10:499-588.) allows the surgeon to determine if the annulus and/or right ventricular
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outflow tract is adequate for a given patient. With the diameters shown, only a 15% probability exists that the
right ventricular-left ventricular pressure ratio will be more than 0.65.
Body Surface Area (m2) Diameter (mm)
0.15 5.9
0.20 7.3
0.25 8.4
0.30 9.3
0.35 10.1
0.40 10.7
0.45 11.3
0.50 11.9
0.55 12.3
0.60 12.8
0.65 13.2
0.70 13.5
0.75 13.9
0.80 14.2
0.90 14.8
1.0 15.3
1.2 16.2
1.4 17.0
1.6 17.6
1.8 18.2
2.0 18.7
24
Left Ventricular Outflow Tract Obstruction
CONGENITAL AORTIC STENOSIS
Pathologic findings in congenital aortic stenosis can vary. The valve may be bicuspid, tricuspid, or unicuspid,
and the commissures may be fused together in any combination. The functional orifice of the aortic valve,
however, is usually between the left and noncoronary cusps, whereas the other cusp and commissures are
fused and deformed to various degrees.
Infants or neonates with critical aortic stenosis may require urgent intervention. Neonates may present in
extremis with marked metabolic acidosis. Infusion of prostaglandin E1 may improve the circulation in these
neonates by reopening the ductus arteriosus. It is critical in these cases to differentiate isolated, critical aortic
stenosis from a form of hypoplastic left heart syndrome that requires a modified Norwood procedure (see
Chapter 30). Although percutaneous balloon valvuloplasty for critical aortic stenosis in the neonate and infant is
being performed with satisfactory results, surgery is still indicated for some patients.
Valvotomy Technique
A median sternotomy approach is used. Surgical valvotomy is performed on cardiopulmonary bypass.
Cannulation is carried out with a standard aortic cannula and a single venous cannula in the right atrial
appendage and a vent in the right superior pulmonary vein. Cardiopulmonary bypass is begun, and the ductus
arteriosus is closed with a heavy tie or metal clip. The aorta is cross-clamped, and cardioplegic solution is
administered (see Chapter 3). The aorta is incised transversely, the aortic valve is exposed, and its anatomy is
studied closely. A no. 15 blade is used to incise the fused commissures to within 2 mm of the aortic annulus (Fig.
24.1).
Aortic Insufficiency
The purpose of the surgery is to relieve obstruction to the left ventricular outflow tract in these very sick infants
as effectively as possible, without producing aortic insufficiency. Therefore, overzealous incision of the
commissures or division of a rudimentary raphe only results in gross aortic insufficiency and may necessitate
aortic valve replacement (Fig. 24.2).
Inadequate Relief of Obstruction
Conversely, inadequate relief of the obstruction may not help the child very much. Experience provides the good
judgment required to incise to just the right extent at the precise area of a grossly deformed aortic valve.
Exposing the Aortic Valve
When the aorta is small, an oblique rather than transverse aortotomy provides better exposure of the aortic
valve.
Awareness of Subvalvular Obstruction
It is of paramount importance to inspect the aortic subvalvular area and rule out the presence of a fibrous
diaphragm or other forms of left ventricular outflow tract obstruction. A Hegar dilator of appropriate size can be
used for precise evaluation of the valvular orifice and the left ventricular outflow tract.
Severely Deformed or Maldeveloped Aortic Leaflets
A satisfactory commissurotomy with long-lasting good results depends on how well the valve was formed initially.
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When there is severe deformity and maldevelopment of the aortic valve, surgical relief of left ventricular outflow
tract obstruction is only temporary and palliative. These subgroups of patients should be followed closely so that
a more definitive form of treatment can be performed before permanent left ventricular dysfunction ensues.
FIG. 24.1 Technique for aortic commissurotomy.
FIG. 24.2 Overzealous incision of the commissures, causing aortic insufficiency.
RESECTION OF THE SUBVALVULAR DIAPHRAGM
A fibrous, muscular, or membranous rim of tissue arising from the anterior two-thirds of the left ventricular outflow
tract may be present within 1 cm below the aortic annulus. The aortic valve leaflets are retracted gently with
narrow ribbon retractors. Often, exposure is greatly aided by placing three suspension sutures at each of the
commissures, and three additional fine prolene sutures just below the nadir of each cusp on the left ventricular
side, thereby producing a hexagonal opening that is unobstructed and requires no additional retraction from the
surgical assistant (Fig. 24.3). The fibromuscular diaphragm is then excised with a no. 15 blade (Fig. 24.4A, B).
This shelf of abnormal tissue can also be mobilized and enucleated in its whole circumference with an
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endarterectomy spatula.
FIG. 24.3 Technique for exposure of the subaortic obstruction. Stay sutures are placed at the top of each
commissure, as well as at the nadir of each aortic cusp. When retracted radially, these provide a view of the
subaortic region, often obviating the need for additional retraction from an assistant.
Myotomy or Myectomy
A myotomy or a limited myectomy involving the bulging septum is recommended to prevent the possible
persistence of a significant residual obstruction (Fig. 24.4C). This may also help to prevent recurrence of the
membrane, the incidence of which is higher the younger the patient is when the initial surgery is performed.
Ventricular Septal Defect
A substantial segment of the abnormal fibromuscular tissue can be excised and removed from the septal area
without producing a defect in the interventricular septum. If such a complication does occur, the defect must be
identified and closed. Pledgeted sutures are essential to protect the friable muscular tissue.
Injury to Conduction Tissue
Only the white fibrous tissue should be mobilized and removed from the area immediately below the
rightward half of the right cusp and the commissure between the right and noncoronary cusps. Otherwise,
the conduction tissue may be injured resulting in heart block (Fig. 24.4B).
Valvular Insufficiency
Occasionally, the membranous tissue is adherent to the underside of the right coronary leaflet of the aortic valve.
It must then be meticulously dissected free without damaging the aortic valve to avoid producing valvular
insufficiency.
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FIG. 24.4 Resection of a subvalvular diaphragm. A: Dashed line depicts the extent of resection. B: Only the
white fibrous tissue is resected near the penetrating bundle. C: As an extra precaution against inadequate relief
of an obstruction, a limited myectomy is also carried out.
Injury to the Mitral Valve
Occasionally, the lesion may extend and become adherent to the anterior leaflet of the mitral valve; in this case,
it should be dissected free with the utmost care. Injury to the mitral valve near its annulus may result in an
opening into the left atrium.
HYPERTROPHIC OBSTRUCTIVE CARDIOMYOPATHY
Hypertrophic obstructive cardiomyopathy is usually not a surgical lesion. Many patients respond to β-blockers or
calcium channel blockers. Dual-chamber cardiac pacemakers may be useful in some patients. For severely
symptomatic patients, ventricular septal myectomy is an established treatment. A relatively thick segment (1-cm
deep by 1.5-cm wide) of septal wall extending downward to the base of the papillary muscles is excised and
removed (Fig. 24.5).
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Exposure of Hypertrophied Septum
Most surgeons use a transaortic approach. Exposure is facilitated by extending the aortotomy obliquely down to
the noncoronary annulus and placing plegeted sutures just above the valve commissures. By placing traction on
these sutures, the hypertrophied septum can be visualized. After the initial wedge resection, a small rake
retractor can be placed into the septum and pulled upward toward the aortic annulus to allow visualization and
resection of the apical portion of the septum.
FIG. 24.5 Myectomy for idiopathic hypertrophic subaortic stenosis. Two longitudinal incisions, one below the
commissure between the left and right leaflets and the other below the nadir of the right cusp are made. These
are connected with an incision 1 cm below the valve, and a wedge of septal muscle is excised.
Surgery on the Mitral Valve
When systolic anterior motion of the anterior leaflet of the mitral valve is a significant component of the left
ventricular outflow tract obstruction, an adequate septal myectomy usually resolves the abnormal motion of the
anterior leaflet and any mitral regurgitation. However, some patients have associated abnormalities of the mitral
subvalvular apparatus, which must be recognized and treated at the time of surgery. These include anomalous
papillary muscle insertion directly into the anterior leaflet of the mitral valve and abnormal chordae tendineae
attaching to the ventricular septum. If present, the abnormal chords are resected, and any areas of fusion of the
papillary muscle(s) to the septum or free wall are divided. Occasionally, a valvuloplasty procedure to shift the
coaptation level of the valve posteriorly may be required. This may involve anterior and/or posterior leaflet
plication usually combined with an annuloplasty. A simple technique that may be effective is an Alfieri stitch
placed 1 cm away from the free edges connecting the central portion of the anterior and posterior leaflets (see
Chapter 6). Rarely, the mitral valve must be replaced with a low-profile prosthesis, resecting the entire anterior
subvalvular apparatus. When combined with a myectomy, these techniques result in relief of the obstruction.
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Flail Leaflet
All anomalous chords attached to the free edge of the anterior leaflet must be preserved to prevent a flail leaflet.
Embolism from Muscle Fragments Falling into the Ventricular Cavity
During the process of excising the hypertrophied muscle, fragments may fall into the left ventricular cavity,
resulting in a subsequent embolism. This can be prevented to some degree by pulling on the desired segment to
be excised with a 4-0 or 5-0 Prolene stitch (Fig. 24.5). A biopsy forceps may be used to resect muscle from the
more apical portions of the septum. Care should be taken to remove all debris from within the left ventricular
cavity.
Inadequate Exposure
Exposure may be inadequate through the retracted aortic leaflets. The obstructing muscle may then be removed
through a left atriotomy working through the mitral valve.
Extent of resection
The myectomy can be considered complete when the mitral chordae and papillary support apparatus is clearly
visualized through the left ventricular outflow tract.
LEFT VENTRICULAR TUNNEL OBSTRUCTION
When the left ventricular outflow tract is diffusely obstructed by a congenitally narrow tunnel, none of the
aforementioned techniques are helpful to any significant degree. A left ventricular apical conduit to the ascending
or descending aorta is an alternative, but not a favored one. The Rastan-Konno aortoventricular septoplasty,
although a somewhat radical procedure, provides satisfactory results. In infants and children, a Ross-Konno
procedure (replacing the aortic root with the pulmonary autograft, completing the ventriculoseptoplasty, and
reconstructing the right ventricular outflow tract with a pulmonary homograft) is the operation of choice for this
diagnosis.
Rastan-Konno Aortoventricular Septoplasty
Bicaval and aortic cannulations are made in the usual manner. On cardiopulmonary bypass with moderate
cooling, the aorta is cross-clamped and cardioplegic arrest of the heart is achieved by the usual techniques (see
Chapter 3). The aorta is incised anteriorly in a longitudinal direction. The incision is then extended downward
under direct vision into the root of the aorta.
Direction of the Aortotomy
The direction of the aortotomy should be as far as possible to the left of the right coronary artery ostium, but not
reaching the commissure between the right and left sinuses. This prevents injury to the ostium of the right
coronary artery.
FIG. 24.6 Oblique incision on the aortic root and incision on right ventricle to expose the interventricular septum
in the Rastan-Konno aortoventricular septoplasty.
The anterior surface of the right ventricular outflow tract is then incised obliquely downward from the aortic root
for a distance sufficient to provide good exposure of the interventricular septum (Fig. 24.6). Alternatively, the right
ventriculotomy is made first and then extended upward into the aortic root.
Injury to the Pulmonic Valve
The right ventricular outflow tract should be opened before cutting across the aortic annulus to ensure that the
native pulmonic valve is not injured. Late pulmonary insufficiency is seen not infrequently following this
procedure.
FIG. 24.7 Continuation of the oblique aortotomy on the interventricular septum.
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Abnormal Distribution of Right Coronary Artery Branches
The possibility of abnormal distribution of right coronary artery branches crossing the right ventricular outflow
tract to supply the left ventricular mass must be borne in mind when incising the infundibulum to prevent ischemic
injury to the heart.
The aortotomy is then continued obliquely downward across the aortic annulus onto the massively thickened
interventricular septum (Fig. 24.7). The distorted aortic leaflets are then removed.
Septal Infarction
Division of an aberrant septal artery may result in a septal infarction.
An appropriately sized, oval Hemashield patch of generous width is sewn on the right ventricular side of the
interventricular septum, up to the level of the annulus of the resected aortic valve (Fig. 24.8).
Reinforcing the Sutures on the Interventricular Septum
The interventricular septum is thick and friable; a continuous Prolene suture may tear through it, causing suture
leaks and a resulting shunt across the septum. The suture line can be reinforced by buttressing the sutures over
a strip of Teflon felt or pledgets on the left or right ventricular side (or both) of the septum (Fig. 24.8). Using
interrupted sutures buttressed with pledgets results in surface-to-surface coaptation of the patch to the septum,
thereby reducing the possibility of leaks (Fig. 24.8B).
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