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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. 5.59 A: The aortic bileaflet prosthesis in the tilted position with proper orientation of the leaflets. B: Position
with possible interference of the leaflet function.
Inappropriate Size of the Prosthesis
It is pointless to attempt to insert a prosthesis whose internal orifice is larger than the orifice of the left ventricular
outflow tract or aortic annulus. If the left ventricular outflow tract is too narrow, the tilting technique of valve
replacement obviously will not be very rewarding (Fig. 5.60).
FIG. 5.60 A: Obstruction of the flow due to a left ventricular outflow tract that is larger than the internal orifice of
the prosthesis. B: Maximal possible flow when left ventricular outflow tract is same size as the internal orifice of
the prosthesis. C: No increase of flow with a left ventricular outflow tract that is smaller than the internal orifice of
the prosthesis.
Septal Myectomy
Septal hypertrophy may be significant in patients with severe aortic stenosis. At times, the left ventricular outflow
tract may become narrower than the aortic root. The hypertrophied septal mass may interfere with the normal
function of mechanical prosthetic valves. A limited myectomy or shaving off excess septal muscle bulging into the
left ventricular outflow tract may allow for a wider lumen and ensure the normal function of the valvular prosthesis
(Fig. 5.24).
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Patch Enlargement Technique
It is always preferable to use the largest possible prosthesis whenever valve replacement is contemplated. A
prosthesis larger than the aortic annulus, however, does not abolish the obstructive gradient across the left
ventricle and the aorta (Fig. 5.60). Therefore, if the aortic annulus is a dominant obstructive factor, it must be
enlarged to accept a larger prosthesis. Often the subaortic curtain is long enough to allow satisfactory
enlargement of the aortic root. The oblique aortotomy is extended downward through the commissure between
the noncoronary and the left coronary aortic annuli onto the subaortic fibrous curtain up to, but not including, the
mitral annulus (Fig. 5.61A). A patch of glutaraldehyde-treated autologous pericardium or bovine pericardium is
cut in the appropriate shape and size and sewn into place with a continuous 3-0 Prolene suture (Fig. 5.61B).
When further enlargement is warranted, the incision is extended across the subaortic curtain, through
the mitral annulus, and for a variable distance onto the anterior leaflet of the mitral valve. This necessarily entails
incision of the left atrial wall to a similar extent from the mitral annulus (Fig. 5.62A). A patch of glutaraldehyde-
treated autologous pericardium or bovine pericardium of appropriate size and shape is then sewn into place with
3-0 continuous Prolene suture, incorporating the left atrial wall and the anterior mitral leaflet (Fig. 5.62B). Rarely,
this approach may distort the mitral valve, particularly in patients with a small left atrium. The atrial opening may
be enlarged by incorporating a second patch of pericardium (Fig. 5.62C). These techniques of aortic root
enlargement have the added advantage that the left ventricular outflow tract, as well as the aortic annulus, can
be enlarged considerably. The aortic prosthesis of choice is then inserted using the technique described
previously (Fig. 5.63).
Tilting the Prosthesis
The prosthesis should be sewn in with a slight tilt, as described earlier, so that the anchoring sutures that cross
the patch can be tied on the outside wall of the patch 4 or 5 mm above the annulus. This patch is then used to
augment the aortotomy closure with a continuous 4-0 Prolene suture. If the autologous pericardium appears to
be thin and insecure, it can be reinforced by a patch of Gore-Tex.
Hemolysis
If a Gore-Tex patch or Dacron graft is used, it may be lined with autologous pericardium to prevent possible
hemolysis in the postoperative period.
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FIG. 5.61 A: Aortotomy is extended onto the subaortic curtain. B: Enlargement of the aortic root with a patch of
pericardium.
Narrow Left Ventricular Outflow Tract
The previously discussed techniques enlarge the aortic annulus quite effectively. If the left ventricular outflow
tract is too narrow, however, it remains a limiting factor. Placement of a larger prosthesis or enlargement of the
aortic annulus will not relieve the basic hemodynamic problem.
Use of Aortic Homograft or Stentless Valves
The excellent hemodynamics of aortic homografts and stentless bioprotheses in smaller valve sizes may provide
satisfactory results without the need for a root enlargement procedure.
The obstruction associated with a small aortic root can be satisfactorily relieved in most patients using one of
these techniques. The Rastan-Konno aortoventricular septoplasty is rarely indicated in adult patients (see
Chapter 24).
Endocarditis
Infective endocarditis is a debilitating disease and is associated with a very high mortality. The native aortic valve
leaflets become infected, and the infection may extend into the annulus and the surrounding tissues, resulting in
paravalvular and root abscesses. In patients with prosthetic aortic valves, the infection affects the leaflets and
the sewing ring of the pericardial and porcine valves. The mechanical valve sewing ring is always involved.
Homografts and pulmonary autografts follow the same pattern of infection as the native aortic valve. Often,
vegetations form on the valve leaflets and cause systemic embolization with serious consequences.
It is important to bear in mind that anticoagulation does not prevent the embolization of vegetations.
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FIG. 5.62 A: Aortotomy is extended onto the mitral annulus and anterior leaflet of the mitral valve. Note entry into
the left atrium (see text). B: Enlargement of the aortic root with a patch of pericardium. Note the incorporation of
the left atrial wall and mitral leaflet (see text). C: Separate patch closure of left atrial opening.
Accurate diagnosis and prompt aggressive medical management are essential. Immediately after obtaining blood
for culture, the patient is started on the appropriate antibiotics, which are continued for 6 weeks. Early surgical
intervention is indicated for patients who continue to show signs of sepsis after 3 to 4 days on appropriate
antibiotics. The presence of refractory congestive heart failure, recurrent systemic embolization, acute aortic
valve leaflet tear, and evidence of a paravalvular aortic root abscess demand immediate surgery.
Staphylococcus aureus endocarditis is very virulent and causes aggressive tissue destruction. Therefore,
early surgical intervention is indicated when this organism is involved.
Size of Vegetations
Some organisms form bulky vegetations that are more likely to embolize. Surgery is generally indicated if a
vegetation on the aortic valve is 1 cm or greater in diameter.
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Patients with infective endocarditis of the aortic valve who become surgical candidates often have multiorgan
system deficiencies. They are frequently in heart failure, have ongoing sepsis, renal insufficiency, and many
have evidence of a recent stroke due to septic emboli. Optimum myocardial protection is crucial in these
compromised patients to allow for adequate time to completely remove all infected material, reconstruct the aortic
root, and achieve a competent aortic valve.
FIG. 5.63 Insertion of the prosthesis into the enlarged aortic root.
Dislodgement of Vegetations
The antegrade infusion of cardioplegia into the aortic root under high pressure may dislodge and break up large
vegetations that can embolize into the coronary arteries. In these cases, retrograde cardioplegia is infused until
cardiac contraction ceases. The aorta is opened and cardioplegic solution is administered into the coronary
arteries under direct vision.
Cross Contamination
To reduce the possibility of recurrence of endocarditis, every effort should be made to prevent cross
contamination. This entails changing gloves, local drapes, and surgical instruments used to remove the infected
material from the operative field.
Complete Debridement
The most crucial aspect of the procedure is the complete debridement of all the infected tissues, even if that
entails the resection of the entire aortic root and adjacent tissues.
In areas where the aortic annulus is destroyed, the left ventricular outflow tract and the aorta are reapproximated
with a patch of glutaraldehyde-treated autologous pericardium or bovine pericardium. At times, it may be
necessary to create a new annulus by sandwiching the aorta and left ventricular outflow tract with two strips of
pericardium. The aortic valve is replaced using the standard techniques described in the preceding text.
Subannular Necrotic Cavities
Removal of necrotic tissue from the subannular area can create small cavities. The surrounding friable tissue will
not hold sutures well. Deep bites with pericardial pledgeted sutures are taken to occlude these cavities. When
tied, the sutures may later be used to anchor the new prosthesis into position.
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Extensive infection and abscess formation involving the aortic annulus is a serious condition. Following radical
debridement, it may be difficult to reestablish continuity between the aorta and left ventricular outflow tract. An
effective technique is to replace the aortic root with either an aortic homograft or a stentless bioprosthesis as
described in the preceding text.
Use of Pulmonary Autograft
Although many surgeons are reluctant to perform a Ross procedure in the face of aortic endocarditis for fear of
introducing infection into the right ventricular outflow tract, the pulmonary autograft is another replacement option
in younger patients with endocarditis.
PARAVALVULAR LEAKS
In most patients, paravalvular dehiscence resulting in leaks around the aortic prosthesis is secondary to
imperfect surgical technique. Some of the predisposing factors, such as a calcified or infected annulus (which
allows the sutures to cut through the tissues), have been discussed previously. Paravalvular leaks tend to occur
more commonly along the noncoronary annulus and the adjacent half of the left coronary annulus. Massive
calcification affecting the aortomitral leaflet continuity may obscure the annulus and interfere with correct
placement of anchoring stitches. In addition, the exposure of the noncoronary annulus is sometimes difficult from
the surgeon's side (patient's right side). Often, the annular sutures are inadvertently placed in the less ideal
aortic wall above the annulus. In time, these sutures may cut through the aortic wall and produce a paravalvular
leak. Attention to these details when performing aortic valve replacement helps prevent late paravalvular leaks.
Technique for Repair
The paravalvular defect is identified under direct vision. The tissue margin of the defect commonly becomes
fibrous after 2 to 3 months. Pledgeted sutures are passed deeply through the tissue margin of the defect and
then through the sewing ring of the prosthesis before tying (Fig. 5.64).
When the integrity of the tissue margin of the defect is not satisfactory, sutures are passed through the sewing
ring of the prosthesis before taking a deep bite near the annulus through the full thickness of the aortic wall to
the outside of the aorta. The sutures are then tied over Teflon felt pledgets (Fig. 5.64).
When there are multiple paravalvular leaks or the site of the leak is not obvious, it is necessary to explant the
prosthesis and implant a new one, ensuring that all the valve sutures bites incorporate healthy tissues.
FIG. 5.64 Technique for repair of a paravalvular leak (see text).
Interventional Closure of Periprosthetic Leaks
Recently, some institutions have closed paravalvular defects with an atrial septal defect or ductal occluder
device in the catheterization laboratory. This procedure may be useful in elderly or critically ill patients to avoid a
reoperation.
TRANSCATHETER AORTIC VALVE REPLACEMENT
Despite ever-improving results of surgical aortic valve replacement in the setting of symptomatic aortic stenosis,
some elderly frail patients are at high risk of mortality and morbidities after surgical aortic valve replacement.
Transcatheter Aortic Valve Replacement (TAVR) technologies have evolved to meet the needs of these high-risk
patients. Currently, TAVR technology is approved in the United States for patients with a calculated mortality risk
of 7.5% (Society of Thoracic Surgeons Risk Calculator), or for those who have other major confounding
conditions such as frailty, liver disease, and calcified ascending aortas, among others.
Patient Selection
Much like traditional cardiac surgery, many patient factors and data must be evaluated to deem a patient
appropriate for TAVR. Patients must have severe calcific aortic stenosis (regardless of pressure gradients), have
a life expectancy of at least one year, and be high risk for surgical valve replacement.
Multimodality imaging of the aortic root is required to evaluate annular size, coronary height, and calcification.
Echocardiography and multi-slice CT scans with 3D reconstruction are used in a complementary fashion to
evaluate the patient for TAVR. Annular sizing is typically obtained from CT scan and confirmed using
echocardiography, while coronary height is obtained using center-line distances on CT. Other issues such as
presence of left ventricular thrombus, bicuspid aortic valve, ventricular aneurysm, subaortic stenosis, and
endocarditis are also assessed. In general, aortic annulus sizes less than 19 mm or greater than 31 mm are
regarded as relative contraindications for the use of currently available commercial devices.
Imaging of the entire aorta, iliacs, and femoral vessels is required to evaluate the vascular access required for
delivery sheath insertion. While first-generation devices were 24 French and required large caliber, newer
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expandable sheaths (14 French) now accommodate vessels as small as 6 mm depending on the extent of
calcification. A detailed assessment of the patient's vasculature is essential to choosing the appropriate access
site with the least risk of complications. Given the size of the delivery systems for the current commercially
available TAVR prostheses, groin vascular complications remain a major risk occurring in 12% to 19% of
patients. These involve dissection of the iliac and femoral arteries and less commonly, avulsion and massive
hemorrhage. While the recommended minimal luminal diameter for the femoral vessels is 7-8 mm depending on
valve size, the extent of vascular calcification and tortuosity impact the incidence of these complications.
Operative Technique
TAVR is best performed in a hybrid suite capable of both surgical and interventional procedures. A temporary
ventricular pacemaker is advanced into the right ventricle under fluoroscopy and tested. Femoral arterial access
is obtained in both groins and the larger artery is used to insert the delivery sheath (18 to 24 French), while the
other is accessed with a 5 French sheath for delivery of the pigtail catheter. These vessels can be accessed with
a surgical cut-down or percutaneously in most cases. Usually, two preclosure devices are deployed before the
introduction of the large sheath. After the introduction of a long sheath into the descending aorta, a stiff wire with
a floppy tip is used to enter the ascending aorta and the root. Now the valve is crossed and the stiff wire is
inserted into the left ventricle through the long sheath. The patient should be heparinized. Now a contralateral
pigtail is also advanced and left in one of the aortic sinuses. A balloon valvuloplasty is performed under rapid
ventricular pacing. At this point, an appropriately sized valve is mounted on the delivery system and advanced
over the stiff wire with the end in the left ventricle. Appropriate images of the aortic root are critical with the nadir
of all sinuses being visible during a root injection through the pigtail (Fig. 5.65). These measurements along with
valve dimensions are reviewed to ensure
that the valve will not obstruct the coronary ostia. Now the valve is carefully positioned and inflated under rapid
ventricular pacing (Fig. 5.66). An aortogram combined with echocardiography and hemodynamic measurements
should be used to assess the function of the valve with particular attention to paravalvular leaks. Once
satisfactory function of the valve is confirmed, wires are withdrawn and the femoral vessels closed as
appropriate.
FIG. 5.65 Optimal alignment of the fluoroscopic imaging plane to align the nadir of all three aortic cusps.
FIG. 5.66 Alignment of the valve to avoid occlusion of the coronary ostia after inflation.
Sheath Removal
Removal of the large sheath should be done over a wire that is retained and in the presence of contralateral
access in case of a vascular injury.
For the transapical technique, it is important to identify a safe area of cannulation lateral to the true apex of the
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heart. This avoids disruption of the LAD while providing a more secure area for cannulation. Generally, a limited
anterior left thoracotomy is used to access the pericardium. Finger pressure and echocardiography are used to
identify a suitable are that is in line with the aortic valve for deployment. Two concentric purse-strings with large
felt pledgets are used to secure the myocardium around a 26 French sheath that is introduced after serial
dilations. The remainder of the procedure is performed as above. Sheath removal should be performed under
hemodynamic control and rapid ventricular pacing.
Weak Myocardial tissue
In cases of a fragile myocardium or redo operations, the ventricular purse-strings should incorporate the
native pericardium to provide more structural support.
Cardioplumonary support
In patients with significant pulmonary hypertension, poor ventricular function or those with untreated significant
coronary arterial lesions, rapid access to cardiopulmonary bypass and circulatory support through the femoral
vessels should be available.
The stiff and yet fragile nature of the aortic annulus in TAVR candidates can predispose these patients to
annular rupture upon aggressive balloon valvuloplasty or valve expansion. This complication often presents with
cardiac tamponade.
Pericardial tamponade may occur in a minority of patients and may be due to wire perforation of either the atria
or the ventricles, bleeding from the transapical access site, annular rupture, or aortic dissection. These
complications may be managed by percutaneous drains and reversal of coagulopathy but may eventually require
open surgical repair. Annular rupture and dissection requiring surgery carry a dismal prognosis.
Valve embolization or poor deployment occurs in about 1% of patients undergoing TAVR. The strategy to rectify
a malpositioned valve depends on the site, hemodynamic stability of the patient, and overall risk. Often the
valves can be pulled back into the aorta using intravascular snares. Once in the descending aorta, another
TAVR valve can be placed within the original and reestablish antegrade flow. Ventricular embolization of the
valve often requires open cardiac surgery.
Coronary obstruction can occur in the presence of bulky calcium on the native leaflets, a distance of <10 mm
from the coronary ostia to the annulus and shallow aortic sinuses. Fortunately, many are treated with emergency
coronary interventions and stenting. However, emergent hemodynamic support via cardiopulmonary bypass and
even surgical revascularization may be required as deemed necessary by the team.
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