Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3683_Библиотеки_им_академика_М_И_Перельмана
.pdf
P.49
of the aorta or with aortic dissection, the arterial cannulation may need to be altered, and the conduct of the
procedure modified (see Management of Unclampable Aorta).
Myocardial Preservation
Detailed techniques for preservation of the myocardium have already been discussed in Chapter 3. A modified
synchronized technique for myocardial protection has been used in our practice for valvular surgery, particularly
for aortic valve disease.
Technique
With a retrograde cardioplegic cannula in place in the coronary sinus and an antegrade cannula in the aortic
root, cardiopulmonary bypass is initiated and hypothermia (32°C) is achieved. 500 mL of cold blood cardioplegic
solution (4°C to 8°C) is administered into the aortic root, followed by an additional 500 mL via coronary sinus.
Myocardial activity ceases, and electrocardiographic monitoring reveals a flat line.
Left Ventricular Distention
Antegrade administration of blood cardioplegic solution into the aortic root can be satisfactorily accomplished
only if the aortic valve is relatively competent (see Chapter 3). Presence of significant aortic valve insufficiency
results in backflow of the cardioplegic solution into the noncontracting left ventricular cavity. This causes left
ventricular distention and possible myocardial injury. Therefore, when the aortic valve is incompetent, the blood
cardioplegic solution should be administered using a retrograde technique to achieve complete cardiac standstill.
In addition, a left ventricular vent should be placed through the right superior pulmonary vein. Myocardial
protection can be augmented by administering cardioplegic solution into the coronary ostia after the aorta has
been opened.
Difficulty in Cannulation of Coronary Sinus
Rarely, the retrograde cannula cannot be introduced safely into the coronary sinus. Bicaval cannulation is
performed, and the retrograde cannula in placed in the coronary sinus under direct vision (see Chapter 3).
Cardioplegic Arrest with Retrograde Cardioplegia
Cardioplegic arrest of the heart using a retrograde technique alone may at times be slow, particularly when the
heart is enlarged. In these cases, aortotomy should be performed and cardioplegic solution administered directly
into the coronary arteries.
Calcium Deposits
The aortic leaflets may become so deformed because of calcific deposits that they physically obstruct
cannulation of the coronary arteries and prevent satisfactory administration of blood cardioplegic solution. In this
case, the left coronary cusp should be quickly excised to facilitate direct cannulation and infusion of blood
cardioplegic solution into the left coronary ostium. Infusion into the right coronary artery can be performed when
the heart has been arrested and the diseased aortic valve has been excised.
Cold blood cardioplegia is administered (usually every 10 minutes) in a retrograde manner to ensure the
complete cessation of electrical activity of the myocardium. Between cardioplegia doses, cold oxygenated blood
is continuously infused through the retrograde cannula whenever clear visualization of the aortic root is not
required (such as placement of valve sutures in the sewing ring of the prosthetic valve). For optimal protection of
the right ventricle, direct infusion of blood cardioplegic solution into the right coronary artery is carried out every
20 minutes, and ice wrapped with gauze is placed topically on the heart to minimize surface rewarming.
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
P.50
When the aortic valve has been seated and the valve sutures are being tied, the patient is rewarmed.
Retrograde infusion of cold blood or cold blood cardioplegic solution through the coronary sinus is continued to
ensure a complete cessation of myocardial activity. When the aortotomy closure is started, warm blood is infused
retrogradely through the coronary sinus. Often concurrent with closure of the aortotomy, normal cardiac activity
is observed. If the patient has undergone concomitant coronary artery bypass grafting, blood cardioplegia or cold
blood can be infused simultaneously antegradely through the vein grafts and retrogradely through the coronary
sinus.
Right Coronary Artery Air Embolism
Infusion of warm blood using the retrograde technique is continued for several minutes after the cross-clamp is
removed to minimize the risk of air bubbles trapped in the aortic root entering the right coronary artery.
Exposure of the Aortic Valve by Transverse Aortotomy
A low transverse incision is perhaps most commonly used and is preferred by many surgeons (Fig. 5.2). The
epicardial fat and adventitial tissue from the right ventricular outflow tract and pulmonary artery may overlie the
desired line of aortic incision. These can be dissected free and retracted with a few pledgeted sutures (Fig.
5.2A). Fine Prolene sutures are inserted in the adventitia of the aortic wall on each side of the proposed incision
line, which should be 10 to 15 mm above the origin of the right coronary artery. When the ascending aorta has
been cross-clamped, the aortic wall is incised for a short distance between these sutures. A small leaflet retractor
is introduced into the lumen of the aorta to expose the aortic valve.
Retractor Injury
Often the aortic wall is dilated and thinned out, particularly in elderly patients with poststenotic dilation.
Aggressive traction may result in a transverse tear of the wall of the aortic root (Fig. 5.3). This may necessitate
replacement of the ascending aorta or patch repair of the aortic wall.
Under direct vision, the opening is then extended on both sides; care must be taken to stay approximately 10 mm
above the aortic commissures (Fig. 5.2B). Alternatively, the incision can be extended obliquely upward and/or
downward, converting it to an oblique incision or tailoring it to provide optimal exposure (Fig. 5.2C, dashed line).
FIG. 5.2 A: A low transverse incision to expose the aortic valve. B: Extension of transverse incision. C: Initial
small transverse aortotomy may be extended transversely or obliquely.
Aortotomy too Close to the Right Coronary Ostium
Poststenotic dilation, which is commonly seen in patients with aortic stenosis and congenital bicuspid aortic
valve, may distort the aortic root and cause upward displacement of the ostium of the right coronary artery. The
usual transverse aortotomy may then be too low and impinge on the right coronary ostium. Care must be
exercised in these patients to identify the origin of the right coronary artery before opening the aorta.
Exposure of the Aortic Valve by Oblique Aortotomy
An oblique or hockey-stick incision is started high on the medial aspect of the aorta and is then continued
diagonally downward into the noncoronary sinus stopping 10 mm above the aortic annulus. The aortic walls are
then retracted on each side (Fig. 5.4). This incision is particularly useful in patients with small aortic roots.
Excessive Inferior Extension of the Aortotomy
The lower limit of the incision should be well above the aortic annulus to avoid difficulty in placing sutures in the
annulus for insertion of the prosthesis. This will also facilitate the aortic closure.
Right Ventricular Hematoma
Epicardial fat overlying the right ventricle is very friable and if traumatized can develop into a large hematoma in
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
P.51
P.52
heparinized patients. The epicardial fat can be gently retracted away from the operative field with pledgeted
traction sutures (Fig. 5.2A).
FIG. 5.3 A: Surgical view of a diseased aortic valve. Note that the aortotomy is approximately 10 mm above the
commissures. B: Retractor injury to the aortic wall.
AORTIC VALVE REPLACEMENT
Valve replacement is required in nearly all patients with aortic stenosis and many patients with aortic
insufficiency. The choice of replacement valve depends on the patient's age, concomitant disease, lifestyle, and
anatomic factors. Contemporary mechanical valves include bileaflet and, which normally do not require
rereplacement, but do require anticoagulation and have a higher risk of thromboembolic events. Stented
bioprostheses include bovine
pericardial and porcine valves that perform well without the need for anticoagulation for a number of years, but
do experience structural deterioration and require reoperation. Stentless bioprosthetic valves offer better
hemodynamics, especially in smaller valve sizes, but are technically more demanding to implant and undergo
degenerative changes leading to valve rereplacement surgery. Aortic homografts have advantages similar to
stentless valves and are usually more durable, but availability is a problem. The pulmonary autograft is the best
replacement option for infants and children, offering growth potential and long-term freedom from reoperation on
the aortic valve. However, it is a two-valve procedure with a need for reintervention on the pulmonary
replacement valve.
FIG. 5.4 Oblique incision to expose the aortic valve.
Excision of the Aortic Valve
The diseased valve leaflets are excised with scissors, leaving a 1- to 2-mm margin at the annulus (Fig. 5.5). The
calcified segments of the annulus are crushed between pituitary rongeurs, and the calcium fragments are gently
milked away or excised (Fig. 5.6).
Limits of Excision
Excision of the aortic valve too close to the annulus may disrupt the annulus and leave little tissue to hold the
sutures securely. Therefore, a margin of valve leaflet should be left behind and may be trimmed away
subsequently if it is deemed necessary.
Detachment of Calcium Particles
Care must be taken to not allow fragments of calcium to fall into the left ventricular cavity because they can result
in systemic embolization. The sucker tip is detached, and the assistant must suction all debris as the valve
leaflets are being excised. A folded segment of sponge or tampon may be placed in the left ventricle after valve
excision before attempting further removal of calcium from the aortic annulus (Fig. 5.7). The gauze sponge or
tampon guards the left ventricular outflow tract. Calcium particles or debris fall onto the tampon or sponge
instead of being lost in the left ventricular cavity. The left ventricular cavity is flushed and irrigated with cold
saline solution. The tampon or sponge is then removed.
Some institutions may require the tampon or the sponge to incorporate radiopaque markers.
Protecting the Coronary Ostia
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
P.53
P.54
To prevent coronary embolization during calcium removal or extraction of the sponge, the coronary ostia can be
temporarily occluded with a cotton swab, a handheld cardioplegic cannula, or the tip of the suction head. These
precautions are especially useful for protection of the left coronary ostium; the right ostium is less likely to be
exposed to calcium particles because of its anterior position and the fact that it is often covered by the blade of a
retractor.
Anterior Mitral Leaflet Detachment
Because of the continuity of portions of the aortic and mitral valves, the anterior mitral leaflet can become
detached from its annulus during excision of the aortic valve leaflets. The surgeon should also be aware of this
possibility during the removal of calcium and the trimming of the aortic annulus near the left and noncoronary
cusps (Fig. 5.8). The
anterior mitral leaflet is especially likely to become detached with the removal of noncoronary cusp; this results in
a defect in the aortic root, which opens directly into the left atrium. This misadventure is most likely to occur
when there is massive calcification of the aortic valve extending, as it often does, onto the mitral valve. The
anterior leaflet of the mitral valve must then be reattached to its annulus by means of interrupted pledgeted
suture(s) incorporating the torn peripheral edge of the mitral valve and the annulus (Fig. 5.9).
FIG. 5.5 Excising the diseased aortic valve. A: Right coronary leaflet. B: Noncoronary leaflet.
FIG. 5.6 Crushing and removing calcium fragments from a diseased annulus.
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
FIG. 5.7 Use of a sponge to prevent calcium particles from falling into the left ventricular cavity.
FIG. 5.8 Injudicious pulling on the calcium embedded in the aortic annulus, creating a defect through the aortic
root to other chambers of the heart or the pericardium (see Fig. 5.4).
P.55
P.56
FIG. 5.9 A: Partial detachment of the anterior mitral leaflet, creating a defect in the left atrium. B: The defect is
closed with pledgeted sutures, which can also be used to anchor the prosthesis.
Annular Weakness
Aggressive pulling on the calcium while attempting to remove it from the aortic annulus may occasionally weaken
an area, which can result in perforation either outside the heart or into the other chambers of the heart. The
weakened area must be recognized and approximated with pledgeted sutures (Fig. 5.9).
Sizing the Aortic Prosthesis
The prosthesis chosen for replacement of the aortic valve must fit snugly in the annulus. Three simple sutures
are inserted, one in each commissure (Fig. 5.10A) or in the annulus near each commissure (Fig. 5.10B). The
aortic
orifice can be opened by applying traction to these three sutures. At times, sutures placed in the nadir of the
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
annulus between the commissures will open the left ventricular outflow tract more optimally, making sizing easier
(Fig. 5.10C). Differently sized obturators are then serially introduced into the annulus, starting with the smallest
one. The correctly sized prosthesis is therefore selected.
FIG. 5.10 A: Three simple sutures being inserted in the aortic valve annulus, one in each commissure. B:
Sutures can be alternatively placed through the annulus near each commissure. C: Sutures placed in the nadir
of the annulus for optimal sizing.
Loose Prosthetic Fit
A very loose fit indicates that the patient will not benefit from the largest possible prosthesis, which will have the
optimal hemodynamics.
Tight Prosthetic Fit
A tight fit may make satisfactory seating of the prosthesis difficult. Oversizing the prosthesis may cause
disruption of the aortic annulus and/or make closure of the aortotomy difficult.
Соседние файлы в папке Библиотека им академика М.И. Перельмана