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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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the Gore-Tex, resulting in shortening of its length. The correct length of the artificial chords allows both the
papillary muscle and the Gore-Tex suture to be barely taut, not tight, and certainly not too loose. There should
be no “bowing” of the Gore-Tex chord. Often, it is possible to retain the native posterior chordal attachments and
replace only the anterior chords with Gore-Tex suture (Fig. 6.32C).
Sizing the Mitral Orifice
The largest possible prosthesis should be chosen for mitral valve replacement. Sizers are introduced
sequentially into the annulus until the correct size can be selected. The sizer should fit loosely.
Injury from the Sizer
It is important not to push the sizer forcefully into the annulus.
FIG. 6.33 Sutures to anchor the mitral prosthesis. A: Simple sutures. B: Figure-of-eight sutures. C: Everting
pledgeted mattress sutures. D: Ventricular pledgeted mattress sutures.
Combined Mitral and Aortic Valve Replacement
When a double valve replacement is performed, both prostheses should be undersized to ensure proper seating
of both valves.
Valve Choices
Although many prostheses have been successfully used in the past, we believe that technical complications are
markedly reduced when a bileaflet mechanical or a low-profile tissue valve is implanted in the mitral position,
especially when the subvalvular apparatus is retained.
Technique for Suture Insertion
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Simple, figure-of-eight, everting pledgeted mattress, and ventricular pledgeted mattress sutures are commonly
used in anchoring the mitral prosthesis. If the annulus is well defined and strong, simple or figure-of-eight sutures
of 2-0 Tevdek will be adequate. Conversely, if the annulus is degenerative, pledgeted and horizontal mattress
sutures provide added security (Fig. 6.33). Occasionally, a continuous 2-0 Prolene suture may be preferred. The
use of everting, pledgeted mattress sutures (Fig. 6.33C) is favored by most surgeons and is the preferred
technique in our unit.
Simple sutures can be inserted in the sewing ring of the prosthesis, either singly or in vertical mattress manner.
FIG. 6.34 Placement of sutures into the sewing ring of the bileaflet prosthesis (St. Jude Medical, Minneapolis,
MN).
Figure-of-eight sutures and mattress sutures are placed into the sewing ring in a horizontal mattress manner
(Fig. 6.34). When all the sutures have been passed through both the annulus and the valve sewing ring, the
prosthesis is gently lowered into position and the sutures are tied snugly. Any retained redundant subvalvular
apparatus must be pulled above the mitral annular plane when the sutures are tied to prevent interference with
the mechanism of the mechanical prostheses or left ventricular outflow tract obstruction (Fig. 6.35). If extensive
retained leaflet tissue is present in the left atrium, it may be secured away from the prosthetic sewing ring with a
4-0 Prolene suture attaching the leaflet tissue to the left atrial wall.
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FIG. 6.35 Pulling retained chordal button tissue above the mitral annular plane as valve sutures are tied.
Sites of Suture Injury
There are important anatomic structures in the immediate vicinity of the mitral annulus (Fig. 6.36). The left
circumflex coronary artery courses through the atrioventricular groove just outside the posterior mitral annulus.
The coronary sinus also traverses around the annulus and is likely to be encountered in the region of the
posteromedial commissure. Failure to respect this relationship may result in a valve suture incorporating the
retrograde cardioplegia cannula. The artery to the atrioventricular node sometimes runs parallel to the annulus
just above the posteromedial commissure. The aortic leaflets, being continuous with the anterior leaflet of the
mitral valve, can also be occasionally incorporated in a stitch.
Degenerative or Delicate Annular Tissue
Degenerative or otherwise delicate annular tissue will not hold sutures securely enough to support a valve
prosthesis. Pledgets should always cushion the sutures so that they will not cut through the friable annulus
and allow paravalvular leaks. Sutures that are not adequately tightened will also result in leaks.
Handling of Tissue Valves
Tissue valves must be kept moist by intermittently rinsing them with room temperature physiologic saline
solution. If this vital precaution is not taken, the heat of the operating room lights will soon dry and permanently
damage the valve tissue.
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FIG. 6.36 Possible sites of suture injuries.
Antibiotics and Tissue Prosthesis
Tissue prostheses should never be exposed to antibiotic solutions because of possible tissue-chemical
interaction, which may result in premature fibrosis and calcification.
Interference with the Occluding Mechanism of Mechanical Prostheses
Pledgets on the ventricular aspect may occasionally interfere with the normal function of disc prostheses.
Excess Suture Material
The sutures, when tied, should be cut short. Excessive suture material may interfere with the normal occluding
mechanism of some prostheses.
Excess Retained Chordal Button Tissue
Excess retained chordal and leaflet tissue above the mitral annular plane should be sutured to the atrial wall
away from the sewing ring to prevent interference with the prosthetic mechanism.
Detached Chords
Unattached chords hanging loose can be drawn into the prosthesis and prevent its normal closure, resulting in
incompetence of the prosthesis (Fig. 6.37).
Obstructive Calcium Deposits
Calcium in the ventricular wall that protrudes into the ventricular cavity near the annulus can seriously impair
normal excursion of the mechanical leaflet mechanism.
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FIG. 6.37 Calcium or loose chords impairing the movement of prosthetic disc mechanisms.
Strut Projection
The struts of the prosthesis must project freely into the left ventricular cavity. Every precaution must be taken to
prevent these struts from coming into contact with or becoming embedded in the left ventricular wall. This can
result in intractable dysrhythmia and can also interfere with normal prosthetic function (Fig. 6.38).
Prosthetic Obstruction of the Left Ventricular Outflow Tract
A bioprosthesis must be placed in such a way that the struts do not obstruct the adjacent left ventricular outflow
tract
(Fig. 6.39). The pericardial bioprosthesis is the commonly used tissue prosthesis for the mitral position. There
are markings on the sewing cuff of the bioprosthesis to ensure the optimal alignment of the struts in the left
ventricular outflow tract.
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FIG. 6.38 Strut embedded in the posterior left ventricular wall.
FIG. 6.39 Prosthetic obstruction of the left ventricular outflow tract.
FIG. 6.40 Deeply placed sutures cutting through the left ventricular wall.
Strut Entanglement
The struts of the prosthesis can become encircled by the sutures or the subvalvular apparatus, which causes
distortion of the leaflets and interferes with valve function. It is therefore important to “tighten” the struts of the
bioprosthesis, prior to lowering the valve into the left ventricular cavity, to minimize the chance of catching any
sutures or part of subvalvular apparatus.
Suture Placement
Sutures must always incorporate annular and leaflet tissues. Inadvertent placement of sutures into left ventricular
musculature will cut through the left ventricular wall (Fig. 6.40). This can cause a hematoma of the left ventricle,
which may enlarge and rupture outside the heart after ventricular contraction resumes.
Paravalvular Leak
Weakness or tearing of the posterior annulus may result in disruption of the prosthetic attachment during the
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surgery as well as postoperatively; consequent paravalvular leak may ensue. Such a complication must be noted
and corrected by reinserting the sutures, now reinforced with pledgets, into a stronger part of the posterior
annulus. This should allow the prosthesis to be securely reseated.
Exclusion of the Left Atrial Appendage
The left atrial appendage can be closed to prevent blood stasis and subsequent possible thromboembolism. This
is especially important when the patient is in atrial fibrillation. Exclusion is accomplished by tying off the auricle or
stapling it closed from the outside, or by occluding its orifice from the inside of the left atrium with a purse-string
suture (Fig. 6.41).
FIG. 6.41 Exclusion of the left atrial appendage.
Mitral Valve Replacement in Children
Selection of an appropriately sized mitral prosthesis in the very young can be challenging. We have found aortic
bileaflet mechanical prostheses satisfactory when implanted upside down in the mitral position. In this manner,
the leaflets and occluding mechanism will be well above the mitral annulus, sitting entirely in the left atrium,
thereby allowing a larger prosthesis to be implanted safely.
This concept can also be used in reoperation for mitral prosthetic malfunction when there has been prosthetic
patient mismatch and the mitral annulus is fibrotic or too small for the patient's body surface area.
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Supraannular Bileaflet Aortic Prosthesis
This modification of the bileaflet aortic prosthesis must never be used in an upside-down manner in the mitral
position because this would result in the entire valve housing and leaflets residing in the left ventricle itself.
Regurgitant Fraction of the Bileaflet Valve
There is an 8% to 10% regurgitant flow across the bileaflet prosthesis. In young hearts with a small left ventricle,
the regurgitant fraction may be significant compared with the stroke volume, and the prosthesis may not
therefore provide optimal hemodynamics.
An alternative technique is to implant a tissue prosthesis. The struts are first introduced through the mitral
annulus. The sewing ring is then sewn to the atrial wall. Of course, this is a temporary measure because the
prosthesis calcifies in children rather rapidly.
Obstruction to Pulmonary Veins
The sewing ring must be sewn to the atrial wall well away from the orifices of the pulmonary veins to prevent
pulmonary venous obstruction.
LATE ANNULAR COMPLICATIONS
Posterior Subannular Aneurysm
Inadvertent injury to the subvalvular membrane of the posterior mitral annulus (see Surgical Anatomy of the
Mitral Valve section) during mitral valve replacement predisposes to the development of a subannular
aneurysm. This kind of injury commonly occurs during leaflet excision or an aggressive removal of annular
calcific deposits. Patients with this condition require reoperation. The prosthesis is removed so that the
edges of the aneurysm can be identified and closed either with horizontal pledgeted mattress sutures or
with a Dacron patch (Fig. 6.42). The valve can then be reimplanted placing the posterior annular sutures
through the reinforced aneurysm suture closure or the upper edge of the Dacron patch.
Paravalvular Leaks
In most patients, paravalvular dehiscence resulting in leaks around the mitral prosthesis is due to imperfect
surgical technique. Some of the predisposing factors, such as calcified or degenerative annulus (which
allows the sutures to cut through the tissues), have been referred to previously. Paravalvular leaks tend to
occur commonly along the posterior annulus. Massive calcification affecting the aortomitral leaflet continuity
may obscure the annulus and interfere with correct placement of anchoring stitches. In addition, exposure of
the annulus in the vicinity of the aortic valve may not be ideal. The annulus stitches may be inadvertently
placed in the atrial wall or fleshy muscular ventricular wall instead of the annulus. In time, these sutures may
cut through the muscular walls and produce paravalvular leaks. It is therefore important for surgeons to be
aware of these fine details so that necessary precautions can be taken.
The paravalvular defect is identified under direct vision. The tissue margin of the defect has commonly
become fibrous since the time of surgery. Pledgeted sutures are passed deeply through the tissue margin of
the defect and then through the sewing ring of the prosthesis before tying.
FIG. 6.42 A and B: Primary suture closure of a mitral subannular aneurysm. C: Closure of a mitral
subannular aneurysm with a Dacron patch.
When the tissue margin of the defect is not satisfactory, sutures are first passed through the sewing ring of
the prosthesis before taking a deep bite in the vicinity of the annulus through the full thickness of the atrial
wall. The sutures are then tied over a strip of Teflon felt. If dehiscence of the annular suture line is
extensive, the prosthesis may need to be removed. Taking all the aforementioned precautions into
consideration, the surgeon must implant a new prosthesis.
Injury to the Circumflex Artery
Deep sutures may cause injury to the circumflex artery. This will result in myocardial injury, bleeding, and
inability to wean the patient from bypass.
ATRIAL CLOSURE
Interatrial Groove Approach
A double-armed suture of 4-0 Prolene with large half-circle needles is used, starting at each end of the left
atriotomy. For a secure closure, the interatrial groove tissue should be included for its buttressing effect (Fig.
6.43). To ensure adequate hemostasis, a bite of tissue beyond the ends of the incision should be taken before
continuing the closure (Fig. 6.43, inset). Suturing is continued in both directions. The suture line on each side is
then oversewn with the other arm of the suture. Whenever the left atriotomy is extended inferiorly behind the
heart, the closure is facilitated if the sewing is begun from the inside of the atrium under direct vision (Fig. 6.43).
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Atriotomy Closure
Although a single-layer closure is adequate, a second over-and-over suture provides a more secure atriotomy
closure.
Transatrial Oblique Approach
The divided interatrial septum is approximated with a continuous suture of 4-0 Prolene, starting at the far
(anterior) end of the incision and progressing toward the right superior pulmonary vein. Another suture is used to
close the right atriotomy. The edges of the right superior pulmonary vein are then approximated with a third
suture (Fig. 6.44).
Injury to the Right Phrenic Nerve
Caution must be exercised in closing the right superior pulmonary vein to avoid incorporating the phrenic nerve
in the suture line.
FIG. 6.43 Closure of posterior interatrial groove incision. Inset: Inclusion of tissue beyond the ends of the
incision.
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