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_3608_Библиотеки_им_академика_М_И_Перельмана
.pdf
434
Proximal Dissection
Distal Dissection Proximal and Distal
CH
35
DeBakey Type II
Stanford Type A
Dissection
DeBakey
IIIa
DeBakey
IIIb
DeBakey Type III
Stanford Type B
FIGURE 351 This simplified, descriptive classification scheme categorizes aortic dissection based on involvement of proximal aorta, distal aorta, or both
segments. Corresponding traditional classifications are included for comparison. The primary limitation of the Stanford classification is that it is based solely on presence (type A) or
absence (type B) of ascending aortic involvement; it does not provide information about distal aortic involvement, a factor that has important management and prognostic implications.
AB
D
A
C
B
C
E
E
F
DeBakey Type I
Stanford Type A
D
F
FIGURE 352 Common life-threatening sequelae of aortic dissection. Weakened aortic wall can rupture at any location and often results in fatal exsanguination.
Rupture of ascending aorta into pericardial space (A) causes cardiac tamponade. Aortic dissection can lead to acute cardiac failure via (B) extension into coronary
ostia, causing myocardial ischemia, and (C) disruption of aortic valve commissures, causing valvular insufficiency. Complications of branch vessel malperfusion include
(D) stroke or upper-extremity ischemia when brachiocephalic branches are involved, paraplegia when segmental intercostal and lumbar arteries are compromised,
(E) renal failure or mesenteric ischemia when visceral vessels are disrupted, and (F) lower-limb ischemia when iliac arteries are occluded.
Box 35-1 Definitions of Severe Malperfusion
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
Severe Myocardial Malperfusion
Acute infarction diagnosed by electrocardiographic changes or elevated
myocardial-specific enzyme levels associated with new-onset ventricular
dysfunction
Severe Cerebral Malperfusion
Generalized nonresponsiveness or severe localized neurological deficit
lasting >48 hours
Severe Visceral Malperfusion
Abdominal pain, physical findings consistent with an acute abdomen, and
associated abnormal laboratory findings
Severe Extremity Malperfusion
New-onset absence of pulse for more than 4 hours associated with pain,
neurological symptoms, and physical findings consistent with threatened
limb function
Adapted from Deeb GM, Williams DM, Bolling SF, et al: Surgical delay for acute type A
dissection with malperfusion. Ann Thorac Surg 64:1669–1675, 1997.
grafts, and adhesions due to scarring and fibrosis around the aortic
wall are considered protective. They can potentially prevent rupture, protect from valvular dehiscence, and prevent coronary malperfusion, the lethal complications of proximal aortic dissection. In
one study by the International Registry of Acute Aortic Dissection
(IRAD) investigators, patients with acute proximal dissection and
a history of previous cardiac operations were less likely to present with chest pain and cardiac tamponade than those without
a history of previous cardiac operations.
the strategy of initial medical management in ten patients with
ascending aortic dissection in the setting of prior cardiac surgery.
Duration from prior cardiac surgery to dissection ranged from
2 months to 20 years. Medical therapy was successful in eight
patients (80%), and all patients were discharged after the initial
hospitalization. The two deaths in the series occurred at 4 months
and 2 years after the dissection.
15
It must be emphasized that the reduced risk of rupture does
not apply to dissections that occur during the initial 3 weeks after
cardiac surgery.16 In fact, acute dissection during the early postoperative period carries a high risk of rupture and tamponade; these
patients should undergo early operation.
higher operative mortality (31% vs. 14%) and higher stroke rates
(10% vs. 3%) in patients undergoing early operative repair for acute
proximal dissection with prior cardiac surgery than in patients
without prior cardiac surgery.
18
In their series, patients with prior
cardiac surgery presented with similar incidences of tamponade
and malperfusion symptoms as patients without prior cardiac surgery, although the series included patients with acute dissections
occurring as early as 3 days after cardiac surgery.
TRANSPORT TO SPECIALIZED CENTERS
Patients with proximal aortic dissections frequently require transport to centers where cardiac surgery can be performed. Even in
centers where cardiac surgery is available, transfer to high-volume
centers can be justified in hemodynamically stable patients, and
there is evidence of improved outcomes in patients transferred
to specialized centers.
19–21
Before proceeding with transport, the
patient's condition must be optimized. Aggressive pharmacological management should be initiated and metabolic disturbances
corrected. Reliable delivery and titration of vasoactive medications
during transport can be facilitated by central venous and arterial
catheters, respectively. Inotropes and diuretics can be administered
to patients with low cardiac output and acute ventricular distention
due to aortic valvular insufficiency and volume overload. If
patients with pericardial tamponade must be transferred, a pericardial drain should be placed to allow intermittent drainage during transport.
22
Whenever possible, patients with limb- threatening
14
Hassan et al. explored
17
Estrera et al. noted
ischemia should undergo revascularization— usually via femoralto-femoral artery bypass—before transport to minimize the severe
metabolic derangements that result from prolonged limb ischemia
and improve chances of survival after aortic repair.
12
Standardized treatment protocols have been developed to
optimize the hemodynamic management of patients with AAD
during transport. Implementation of the protocol developed by the
Stanford Health Care Life Flight program decreased the number of
patients who arrived at the receiving center with inadequate blood
pressure control.
23
Results from a German study show that transporting patients with proximal aortic dissections by helicopter is
no better than emergency ground transport with regard to survival
benefit. Air transport did allow coverage of areas more than twice
the distance, but at eight times the cost.
24
Surgical Repair
PREOPERATIVE CONSIDERATIONS
With the noted considerations just discussed, most institutions
repair proximal aortic dissections on an urgent or emergent basis.
Important considerations that may change operative planning
include the presence of connective tissue disorder and preexisting aneurysms in the aortic root or aortic arch. Dissections originating from preexisting aneurysms will likely require replacement of
that segment. Preoperative computed tomography (CT) scans can
provide valuable information about true lumen compression and
existing malperfusion. Knowledge of which leg will access the true
lumen may have implications in hemodynamic monitoring, cannulation for CPB, or subsequent requirement for adjunctive procedures
such as femoral-femoral bypass. Degree of aortic valve regurgitation
on preoperative echocardiography and any existing contraindications to anticoagulation will also have implications with regard to
the need for aortic valve replacement and valve choice.
CARDIOPULMONARY BYPASS
Anterior exposure by median sternotomy provides standard access
to the heart and proximal aorta. Most surgeons perform proximal
aortic dissection repairs during a period of hypothermic circulatory arrest.
sis” with direct inspection of the entire arch and avoids creating
additional tears that can result from placing a clamp across the
fragile aorta. Peripheral options in cannulation for arterial inflow
during mechanical circulation include the femoral artery and
axillary artery. Many groups currently advocate axillary access by
either direct cannulation or graft conduit. The axillary site usually
allows perfusion of true lumen and simplifies antegrade cerebral
perfusion.
mon site of arterial inflow in acute dissections. One advantage is
rapid access in emergent situations, although malperfusion and
retrograde atheroembolization can occur. Central aortic perfusion,
either by direct ascending aortic cannulation
the cannula into the ascending aorta via the LV apex, is a feasible
alternative. Venous drainage is typically achieved with the use of a
dual-staged cannula placed in the inferior vena cava (IVC) via the
right atrium.
Two methods of cerebral protection are hypothermia and cerebral perfusion. Hypothermia alone decreases metabolic activity to
allow circulatory arrest, but surgeons must be aware of time limitations to ensure good neurological outcomes.
retrograde cerebral perfusion has declined over the past decade,
the technique is still used in some centers. Retrograde cerebral
perfusion delivers cold oxygenated blood from the pump into
a cannula placed in the superior vena cava.
was that the retrograde delivery of blood would provide oxygen to
the brain. Unfortunately, accumulating evidence suggests that this
technique does not provide cerebral oxygenation.
of this technique include maintenance of cerebral hypothermia
and retrograde flushing of air and debris.
3,11,25–27
This strategy allows an “open distal anastomo-
28
Previously, femoral cannulation was the most com-
29
or advancement of
30,31
Although use of
26,32
The initial hope
33–35
The benefits
435
CH
35
SURGICAL THERAPY FOR AORTIC DISSECTION
436
We and others currently use selective antegrade cerebral perfusion
as a standard adjunct in proximal dissection repairs.
lation of the innominate and left carotid arteries can be performed
using flexible balloon catheters. However, right axillary cannulation
for CPB can provide direct flow into the right carotid
Traditionally, circulatory arrest was initiated with deep hypothermia
CH
at 18°C, but this level of hypothermia has negative implications in CPB
35
duration and degree of coagulopathy. Recent experience supports
the safe use of moderate hypothermia during circulatory arrest.
current target temperature on CPB is 24°C. Once the target temperature is reached, CPB flows are decreased to 1 to 1.5 L/min. A snare
is used to occlude the innominate artery, thereby initiating circulatory arrest to the body and antegrade right cerebral perfusion. With
the aorta open, we selectively use left carotid perfusion by a separate
balloon catheter on the basis of the anticipated length of circulatory
arrest and near-infrared spectroscopy (NIRS) cerebral monitoring.
Electroencephalography (EEG) is useful during deep hypothermia
when cerebral electrical silence is desired. However, with moderate
hypothermia, EEG silence is usually not achieved.
DISTAL AORTIC CONSIDERATIONS
With the ascending aorta opened, the transverse aortic arch
can be carefully inspected, and a decision can be made regarding the extent of aortic arch resection (
36,37
Direct cannu-
28,38,39
Box 35-2). At the least,
(Fig. 35-3) .
40
Our
most patients require graft replacement of the segment of the
ascending aorta between the sinotubular junction and the origin of the innominate artery. In the setting of emergent operation for acute dissection, increasingly aggressive repairs of the
aortic arch are associated with increasing early morbidity and
mortality.
41
Therefore, the repair is generally only extended
into the arch if the arch is aneurysmal or if the primary tear is
located within the arch. When only the proximal portion of the
arch is involved in the disease process, a beveled graft replacement of the lesser curvature is performed (see
Fig. 35-3). This
open distal hemi-arch replacement remains the most common
scenario. Total arch replacement (Fig. 35-4) is performed only if
the primary tear is located in the arch or if the entire arch is
aneurysmal. If malperfusion was an issue preoperatively owing
to true lumen compression in the descending thoracic aorta,
patency of the true lumen can be assisted by open placement
of an endovascular stent-graft in the descending thoracic aorta.
ASCENDING AND HEMI-ARCH REPLACEMENT
The dissecting membrane that separates the true and false
lumens is excised to the distal aortic cuff (see
Fig. 35-3B). The
distal aortic cuff is prepared by tacking the inner and outer
walls together and using surgical adhesive to obliterate the false
lumen and strengthen the tissue
11,25
(see Fig. 35-3C). A Foley
A
B
FIGURE 353 Graft repair of
ascending aorta and proximal
tran sverse aortic hemi-arch with
concomitant aortic valve resuspension. A, Operation is performed via
median sternotomy. Cardiopulmonary
bypass inflow is established via the right
axillary artery. B, After initiating circulatory
arrest and antegrade cerebral perfusion,
ascending aorta is opened, and dissecting
membrane is excised. C, Distal aortic
cuff is prepared using surgical adhesive;
balloon catheter in descending aorta
prevents distal migration of adhesive. D,
Open distal anastomosis between graft
C
D
and aorta is completed and reinforced
with additional adhesive.
Continued
437
EF
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
CH
35
SURGICAL THERAPY FOR AORTIC DISSECTION
FIGURE 353Cont'd E, After
resum ing full cardiopulmonary
bypass, aortic valve is resuspended.
F, Proximal aortic cuff is repaired with
adhesive. G, Proximal anastomosis is
performed.
Box 35-2 Options for Managing Aortic Arch
Ascending replacement only
Beveled hemi-arch replacement
Total arch replacement with island reattachment of brachiocephalic
branches
Total arch replacement with bypass grafts to brachiocephalic branches
Elephant trunk technique
During Proximal Aortic Dissection Repair
G
of the innominate snare. Rewarming is initiated, and the proximal portion of the repair is started (see
TOTAL AORTIC ARCH REPLACEMENT
Extensive aneurysms involving the entire arch usually require total
arch replacement. Primary tears affecting the greater curvature
or any of the brachiocephalic branch vessels should be resected.
Distal anastomosis is created beyond the primary tear at the transverse arch or at the proximal descending thoracic aorta, using
a tube graft. Our preference currently is for reattachment of the
catheter balloon carefully inflated at the distal aortic arch can
be helpful in preventing surgical adhesive from migrating distally in the false lumen. A polyester tube graft is sutured to the
distal aortic cuff (see
Fig. 35-3D). With the false lumen obliter-
ated at the distal aortic cuff, the anastomosis between the graft
and the aorta is constructed to a single true lumen; this often
alleviates mild distal malperfusion problems that were present
preoperatively. We routinely reinforce the distal anastomosis
with a second suture line or interrupted pledgets. The graft is
de-aired and clamped, and full CPB is resumed with the release
brachiocephalic vessels individually, using a trifurcated or bifurcated graft
phalic branches is anastomosed to the ascending aortic graft. In
the most extreme cases, the aneurysm extends past the arch and
into the descending thoracic aorta. This can be managed using
Borst's elephant trunk technique for total arch replacement.
The distal anastomosis is constructed so that a portion of the graft
is left suspended within the true lumen of the proximal descending thoracic aorta. In addition to directing flow into the true lumen,
this “trunk” can be used to assist repair of the descending thoracic
aorta during a subsequent operation.
42
(see Fig. 35-4). The single outflow to the brachioce-
Fig. 35-3E).
43,44
438
CH
35
FIGURE 354 Graft replacement
of entire transverse aortic arch
involves a distal anastomosis to
descending thoracic aorta and
separate reattachment of brachiocephalic branches. This approach is
generally reserved for patients with
primary tears within the arch or large
A
B
aortic arch aneurysms. (Used with
permission of Baylor College of Medicine.)
ANTEGRADE DESCENDING THORACIC STENT-GRAFTS
Even with aggressive resection of the primary intimal tear and
elimination of the false lumen at the distal aortic anatomosis,
the false lumen often persists at the level of the descending
thoracic aorta and beyond. The distal false lumen presents two
considerations. First, presence of a false lumen after proximal
aortic dissection continues to be a significant risk factor for
late aneurysm formation, need for reoperation, and death.
45–47
Second, and more important in the acute setting, true lumen
compression in the descending thoracic aorta can cause malperfusion in the mesenteric vessels, renal vessels, and lower
extremities. Concurrent endovascular stent-graft deployment in
the descending thoracic aorta with either standard ascending
or hemi-arch reconstruction or in an extended total arch reconstruction in a “frozen elephant trunk” are options other investigators are exploring.
48–50
We use an endovascular stent-graft in the descending thoracic
aorta if clinically significant malperfusion (e.g., ischemia in the lower
extremities, paraplegia, renal compromise) existed preoperatively
with evidence of true lumen compression on imaging. The stentgraft is sized to the true lumen with care not to oversize within the
friable dissected aorta. A guidewire is advanced into the true lumen
of the open descending aorta under direct vision during circulatory
arrest. The stent-graft is deployed in an antegrade fashion, with the
proximal landing zone just distal to the left subclavian artery. One
or two tacking sutures can be placed to fix the stent-graft to the distal arch to prevent migration. We do not dilate the stent-graft under
hypothermic conditions. The goal of the distal stent-graft is to direct
flow into the true lumen, eliminate malperfusion, and potentially
help in remodeling the descending thoracic aorta by thrombosis of
the false lumen. Addition of a descending stent-graft is well tolerated, although long-term outcomes remain unknown.
PROXIMAL AORTIC CONSIDERATIONS
Presence of preexisting annuloaortic ectasia/aortic root aneurysm
or connective tissue disorder, the degree to which the dissection
flap extends into the root, and the degree of aortic valve distortion are some of the factors for consideration when evaluating a
proximal dissection for repair. Potential repairs addressing the aortic valve are listed in
Box 35-3.
Box 35-3 Options for Managing Aortic Valve
During Proximal Aortic Dissection Repair
Aortic valve repair:
Commissural resuspension
Commissural plication annuloplasty
Resuspension and annuloplasty
Aortic valve replacement with mechanical or biological prosthesis
Aortic root replacement:
Composite valve graft
Aortic homograft
Stentless porcine root
Valve-sparing techniques (controversial)
SUPRACOMMISSURAL ANASTOMOSIS WITH
AORTIC VALVE REPAIR
In the absence of intrinsic aortic root pathology and significant
aortic valve distortion, the root can be repaired. The majority of
these patients have separation of one or more commissures from
the outer aortic wall; the resulting valve regurgitation can be
corrected by resuspending the commissures into their normal
position51 (Fig. 35-5). Many surgeons use surgical adhesive within
the false channel to strengthen this aortic root reconstruction.
The proximal aortic cuff is prepared with tacking sutures and surgical adhesive (see
anastomosis (see
Fig. 35-3F) before performing the proximal aortic
Fig. 35-3G). If there is mild to moderate annular
dilation, a commissural plication annuloplasty helps restore and
maintain effective leaflet coaptation. Once the root and valve
repairs are complete, the proximal aortic anastomosis is completed at the supracommissural position.
By preserving the aortic valve, long-term anticoagulation is often
avoided; this is believed to favor thrombosis of the false lumen
and thereby prevent subsequent dilation of the thoracoabdominal
aorta. Another advantage of these valve-sparing techniques is that
they only require a few stitches (usually between one and six) and
can be performed quickly. Limiting the extent of repair reduces
cardiac ischemia, CPB, and overall operative times and translates
into lower postoperative morbidity and mortality. Therefore, although
more extensive procedures can reduce risk of reoperation, limited
repairs are performed whenever possible to increase the chance of
12,25,52
FIGURE 355 Cross-sectional drawing of aortic root illustrates
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
dehiscence of two aortic valve commissures, which causes acute
valvular regurgitation. Resuspending commissures onto outer aortic wall
restores valve competency.
survival after the initial operation.53 In a recent report of 200 patients
who were discharged from the hospital after aortic valve repair for
type A dissection, freedom from reoperation for aortic valve insufficiency was 97%, 92%, and 84% at 5, 10, and 15 years, respectively.
54
AORTIC VALVE REPLACEMENT
Many patients undergoing proximal aortic dissection repair require
concomitant correction of aortic valve pathology. Occasionally the
valvular damage caused by the dissection is too severe to repair. In
this case, separate replacement of the valve and graft replacement
of the tubular segment of the ascending aorta are performed. This
is also an option for patients who have significant preexisting aortic
valvular disease (unrelated to the dissection). Separate aortic valve
replacement with supracommissural graft anastomosis is generally
not an option for patients with annuloaortic ectasia or Marfan's syndrome (MFS) because progressive dilation of the remaining sinus
segment eventually leads to complications requiring reoperation.
AORTIC ROOT REPLACEMENT
Full aortic root replacement employs a mechanical or biological graft that has both valve and aortic conduit components. Three
commercially available graft options are (1) composite valve grafts,
which comprise a mechanical valve attached to a polyester tube
graft, (2) aortic root homografts, which are harvested from cadavers and cryopreserved, and (3) stentless porcine aortic root grafts.
Valve-sparing aortic root reimplantation is an alternative to full root
replacement and involves excision of the aortic sinuses, attachment of a prosthetic graft to the native annulus, and resuspension
of the native aortic valve inside the graft. Superior hemodynamics of the native valve and avoidance of anticoagulation are major
advantages to this approach. Experienced centers have performed
valve- sparing root replacements in patients with acute dissection and
have obtained mixed results.
55–58
Because of the substantial technical demands and lack of long-term outcome data, the role of valvesparing root replacement in patients with AAD remains controversial,
especially in patients with MFS.
59
OUTCOMES
For operations performed from 1994 to 2007 in series including more than 100 patients with proximal aortic dissection, the
reported early mortality has ranged from 14% to 24% (Table 35-1).
As operative techniques and critical care have improved, so has
mortality at most centers. At one center, mortality improved in a
stepwise fashion from 21% during their first quartile (1979-1980) to
just 4% during their last quartile (2000-2003).
60
Reported risk factors for operative mortality include increasing patient age, cardiac
tamponade, preoperative shock, preoperative neurological deficits, delay in diagnosis, repair of the aortic arch, coronary artery
disease (CAD), acute myocardial infarction (AMI), concomitant
coronary artery bypass, and malperfusion. Despite the substantial
risks involved with surgical treatment, contemporary results are
excellent compared with the lethality of unrepaired acute proximal aortic dissection.
61
In the ongoing experience of IRAD, 155
patients (17%) were managed nonoperatively, resulting in an inhospital mortality of 59% compared with 24% in those treated sur-
62
gically.
dissection ranges from 60% to 97%; survival drops to 37% to 71%
at 10 years.
the majority of deaths reported being due to nonaortic etiologies
such as stroke, heart failure, and malignancy.
One-year survival after surgical repair of proximal aortic
27,41,45,47,60,63,64
Late deaths have been multifactorial, with
47,65
The most common
aorta-related late deaths resulted from rupture of the distal aortic segment. In recent studies focusing on long-term survival after
proximal aortic dissection repair, persistent false lumen patency
has been noted as a risk factor for late aorta-related mortality and
need for intervention.
46,65
The incidence of patent false lumen varies significantly in the literature, from 20% to 90%. Instances of
partial thrombosis have been noted, with, it appears, a higher incidence of persistent false lumen patency in the abdomen. Longterm implications of persistent false lumen patency have been the
impetus for concurrent intervention at the distal segment of the
initial proximal repair; however, outcomes for this strategy remain
to be seen. What is certain is that patients with residual dissection
in the distal aortic segments will require aggressive management
and surveillance for long-term complications, including aneurysm
formation.
Chronic Proximal Dissection
Occasionally, patients with proximal aortic dissection present for
repair in the chronic phase. With rare exceptions, the mere presence of proximal aortic dissection continues to warrant surgical
repair to prevent aortic rupture. In most regards, the operation is
conducted in a manner similar to that of acute dissection repair,
but the improved tissue strength in the chronic setting makes it
easier to obtain secure hemostatic suture lines. Additionally,
instead of obliterating the false lumen at the distal anastomosis,
the dissecting membrane is fenestrated or resected into the arch
to assure blood flow in both lumens and to prevent postoperative
439
CH
35
SURGICAL THERAPY FOR AORTIC DISSECTION
TABLE 35-1 In-Hospital or 30-Day Mortality for Patients with Type A Dissection
STUDY YEAR PUBLISHED NO. OF PATIENTS SERIES RANGE YRS MORTALITY
Girdauskas
Fattouch
Trimarchi (IRAD)
Goda
Song
99
45
100
47
62
2009 276 1994-2008 18.8%
2009 189 1996-2006 15.1%
2010 750 1996-2004 23.8%
2010 301 1997-2007 13.6%
2010 118 1997-2007 17.8%
440
peripheral ischemia. The absence of both acute inflammation and
malperfusion simplifies perioperative management considerably.
These factors partially account for substantial differences in outcomes between patients who undergo surgery in the acute setting
and those who undergo repair in the chronic phase. Compared
with patients who undergo repairs in the acute phase, those who
CH
undergo repair of chronic dissection have lower incidences of
35
death and stroke. Contemporary series report both early mortality
and stroke rates below 8%.
37,66,67
Acute Distal Dissection
In most centers, nonoperative management of acute distal aortic
dissection results in significantly lower morbidity and mortality
than open surgical treatment.
therapy includes pharmacological treatment for blood pressure
and heart rate control (“anti-impulse therapy”) and close monitoring for complications of an AAD (see Chapter 34). Monitoring
entails frequent clinical assessments in an intensive care unit (ICU)
setting, continuous arterial line blood pressure measurement, and
repeated imaging to assess for acute changes in the dissected aorta.
Operative therapy is reserved for aneurysmal changes, impending
rupture, or malperfusion in the acute period.
Indications for Operation
Aortic rupture and end-organ ischemia are the most common
causes of death during the acute phase, so operative indications
are aimed at these complications. Specific indications for operative treatment include aortic rupture, rapid aortic expansion, uncontrolled hypertension, malperfusion, and persistent pain despite
aggressive pharmacological therapy. Acute dissection superimposed
on a preexisting aneurysm is considered a life-threatening condition and is also an indication for operation. Most patients with acute
distal dissections have a serosanguineous left pleural effusion; this
does not indicate impending rupture and is not a sole indication
for surgery. However, increasing periaortic or pleural fluid associated
with other worrisome findings, such as aortic expansion, warrants
consideration of aortic repair. Finally, surgical treatment should be
considered in patients who are noncompliant with medical therapy,
provided they are otherwise satisfactory operative candidates.
Surgical Repair
OPERATIVE TECHNIQUES
A wide range of surgical techniques are potentially applicable for
treating complications of acute distal aortic dissection. Therapy
should be tailored to the goals of treatment, condition of the
patient, anatomical considerations, and capabilities of the institution. Malperfusion of the extremities can be managed by peripheral
extra-anatomical bypass. A femoral-femoral bypass or carotidsubclavian bypass may restore blood flow to an ischemic extremity
and allow continued nonoperative management of the dissected aorta.
Endovascular surgical options, discussed separately in Chapter 36,
have recently expanded surgical alternatives. Visceral and renal malperfusion can ideally be addressed by endovascular techniques.
Endovascular fenestration of the dissecting membrane or placement of stents into obstructed branch vessels can restore organ perfusion. In compromised patients with mesenteric ischemia or renal
failure, endovascular reperfusion may allow clinical stabilization for
other subsequent therapies or decision making. Aortic endovascular stent-grafting has also been used recently, with the goals of treating distal aortic malperfusion, excluding the dilated thoracic aorta,
or promoting long-term remodeling to prevent the late sequella of
aneurysm formation.
treat acute dilations of limited thoracic dissections. Results from the
IRAD investigators show a mortality of 11% for endovascular operations, compared with 34% after open operations for acute type B
dissections.68 Long-term data are currently lacking regarding the fate
74
Aortic stent- grafting may perhaps be ideal to
68,69
The initial strategy for medical
70,71
25,71–73
of the false lumen and the implications of late aneurysm formation
after endovascular treatment of long thoracoabdominal dissections
and uncomplicated dissections. Results from the only randomized
prospective trial of uncomplicated chronic type B dissections for
which aortic stent-grafting was performed between 2 and 52 weeks
after dissection show no significant differences in mortality or
adverse event rates at 2 years.
75
When the endovascular approach is unavailable or unsuccessful
in treating complications of the acute distal dissection, open surgical options—including graft replacement of the aorta, open aortic
fenestration, and branch artery bypass—should be considered.
In the acute setting, the primary goals of surgery are to prevent fatal
rupture and restore branch artery blood flow. A limited graft repair
of the life-threatening segment can achieve these objectives while
minimizing risks.
63
Because the most common site of rupture is in
the upper third of the descending thoracic aorta, replacement usually extends from the level of the left subclavian artery to the middescending level. The distal portion of the descending thoracic
aorta is also replaced if it is aneurysmal. Graft replacement of the
entire thoracoabdominal aorta is only considered if there is a large
coexisting aneurysm. Similarly, the repair is not extended proximally into the arch, even if the primary tear is located there, unless
the arch is substantially enlarged.
Because surgery for acute distal aortic dissection carries an
increased risk of postoperative paraplegia, adjuncts that provide
spinal cord protection (discussed later in detail) are used liberally.
Cerebrospinal fluid drainage and left heart bypass are often used,
even when the planned repair is limited to the upper descending
thoracic aorta. Proximal control is usually obtained by placing
a clamp between the left common carotid and left subclavian
arteries. Manipulation of mediastinal hematoma around the proximal descending thoracic aorta is avoided until proximal control
is established. The aorta is opened, and the dissecting membrane
is removed from the segment being replaced. The proximal and
distal anastomoses incorporate all layers of the aortic wall, thereby
obliterating the false lumen with the suture lines and directing
all blood flow into the true lumen. Although there are usually
multiple patent intercostal arteries, the extreme tissue fragility
often precludes their reattachment.
OUTCOMES
Aggressive pharmacological management has led to a substantial
decrease in mortality for patients with acute distal aortic dissection. Still, some 10% to 20% of medically treated patients die
during the initial treatment phase.
69,71,77
Primary causes of death
during nonoperative management include rupture, malperfusion,
and cardiac failure. Risk factors associated with medical treatment failure—defined as death or need for surgery—include an
enlarged aorta, persistent hypertension despite maximal treatment,
oliguria, and peripheral ischemia.
Patients undergoing surgery for acute distal aortic dissection are
a high-risk group that includes patients with rupture, neurological
dysfunction, renal failure, and peripheral ischemia. Therefore, it is
not surprising that results after surgery for AADs are often worse
than those of medical therapy. Contemporary reports on acute distal dissection repairs document mortality and paraplegia rates of
up to 34%.
67,69,71,74,77–81
Despite the early survival advantage with nonoperative management compared to surgical treatment, long-term results are similar in patients in both groups. The reported actuarial survival rates
with nonoperative management are 58% to 76% at 5 years and 25%
to 56% at 10 years.
range from 63% to 80% and 39% to 55%, respectively.
61,70,71
Five- and 10-year survival rates after repair
71,80
Chronic Distal Dissection
Chronic aortic dissection is a progressive disease that requires lifelong management. The rationale for careful surveillance lies in the
clinical history of the disease. Surgical intervention is eventually
70,76
required in 25% to 35% of patients. Rupture and ischemic events
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
related to the dissection are responsible for 15% to 30% of late
71,82
deaths.
441
surgical candidates, elective repairs replace the entire descending
thoracic aorta and often extend to include the thoracoabdominal
aorta (Figs. 35-6 and 35-7).
Indications for Operation
Operative repair for a chronic distal aortic dissection is required
in the setting of a type III dissection for which successful medical management initially was achieved or in the setting of residual
distal disease after a previous successful proximal repair of a type
I dissection. Although subsequent dissection, malperfusion, and
ischemic events can occur in a chronically dissected aorta, the
majority of patients will require operative intervention for the aneurysmal sequella of chronic dissections. Interval surveillance is critical in monitoring the growth of the aneurysm. Although the entire
thoracoabdominal aorta may be dissected, dissection in and of itself
is not an indication for graft replacement. In asymptomatic patients,
an elective operation is considered when the aneurysmal segment
has reached 5 to 6 cm or when it has enlarged more than 1 cm
during a 1-year period. A lower threshold is often used for patients
with connective tissue disorders, including Marfan, Loeys-Dietz,
and other familial aortic syndromes.
Urgent operation is considered if the aneurysm becomes symptomatic. Patients with symptomatic aneurysms are at increased risk
of rupture and deserve expeditious evaluation and treatment. The
onset of new pain in a patient with a known aneurysm is particularly concerning and may herald significant expansion, leakage, or
impending rupture. Emergent surgery is reserved for patients with
clinical signs or imaging findings of rupture. Operative strategies
are considerably different in emergent versus elective procedures.
Patients with chronic dissection who require emergency repair
because of acute pain or rupture undergo limited graft replacement of the symptomatic segment. Although the entire thoracoabdominal aorta may be dissected and aneurysmal, typically a
relatively localized segment is the cause of the symptoms. Limited
repair minimizes early postoperative morbidity. In appropriate
Preoperative Assessment
Given the influence of preexisting comorbidity on surgical outcomes, a careful preoperative assessment of physiological reserve
is critical. Most patients undergo a thorough evaluation before
undergoing elective operation. Preoperative assessment focuses
on cardiovascular, pulmonary, and renal status.
CARDIOVASCULAR STATUS
Coronary artery occlusive disease is common in patients with
thoracic aortic aneurysms (TAA) and contributes to a substantial
proportion of early and late postoperative deaths. Additionally,
valvular pathology and myocardial dysfunction have important
implications when planning anesthetic management and strategies for aortic repair. Transthoracic echocardiography (TEE)
is routinely obtained to evaluate both valvular and ventricular
functions. Nuclear stress tests or comparable imaging studies
are used selectively to identify reversible myocardial ischemia.
Cardiac catheterization with coronary arteriography should be
considered in patients who have evidence of coronary disease
(on the basis of history or noninvasive studies) or an ejection
fraction of 30% or less. Patients who have asymptomatic distal
aortic aneurysms and severe coronary artery occlusive disease
may undergo percutaneous angioplasty or surgical revascularization before aneurysm repair.
The hemodynamic changes that occur during thoracic aortic
repair can precipitate stroke in patients with significant cerebrovascular disease. Therefore, carotid duplex ultrasound studies
are also routinely obtained to detect occult carotid artery stenosis. It is recommended that significant carotid artery stenosis be
corrected with an endarterectomy before proceeding with the
aortic operation.
CH
35
SURGICAL THERAPY FOR AORTIC DISSECTION
FIGURE 356 Crawford's classification categorizes thoracoabdominal aortic aneurysms
(TAAA) based on extent of aortic
repair. Extent I repairs begin in upper
descending thoracic aorta, often near
left subclavian artery, and extend to
region of visceral and renal arteries.
Extent II repairs also involve upper
descending thoracic aorta but extend
distally beyond renal arteries, often
to aortic bifurcation. Extent III repairs
begin in lower descending thoracic
aorta (below sixth rib) and extend
into abdominal segment. Extent IV
repairs begin at diaphragmatic crura
and extend distally, often involving
entire abdominal aorta. (Reproduced
with permission of Coselli JS, Bozinovski J,
LeMaire SA: Open surgical repair of 2286
thoracoabdominal aortic aneurysms.
Ann Thorac Surg 83:S862–S864, 2007
[Fig. 1, p. S863].)
IIIIII IV
442
AB
CH
35
FIGURE 357 These drawings and
aortograms illustrate presentation
(A) and repair (B) of an extent II
thoracoabdominal aortic aneurysm
(TAAA) aneurysm that developed
secondary to chronic distal aortic
dissection. Patient had previously
undergone repair of a proximal aortic
dissection.
PULMONARY STATUS
The most common complication after descending thoracic and
thoracoabdominal aortic repairs is pulmonary dysfunction.
83
Therefore, pulmonary function testing, including arterial blood
gases and spirometry, is also routinely obtained before surgery
to assess risk and allow optimization of the patient's pulmonary
status. Patients with an forced expiratory volume in the first second of expiration (FEV
of carbon dioxide (P
able candidates for elective surgery. In selected patients, border-
) exceeding 1 liter and a partial pressure
1
co
) below 45 mmHg are considered reason-
2
line pulmonary function can be improved with a 1- to 3-month
regimen that includes smoking cessation, exercise, weight loss,
and treatment of bronchitis. In most cases, operation is not withheld in patients with symptomatic aneurysms and poor pulmonary reserve. Surgical techniques, however, can be modified to
improve the chance of recovery in these high-risk patients. For
example, precautions can be taken to ensure preservation of the
left recurrent laryngeal and phrenic nerves. Diaphragm-sparing
techniques may also be helpful in such patients.
84
RENAL STATUS
Preoperative renal status is evaluated on the basis of serum electrolytes, blood urea nitrogen (BUN), and creatinine (Cr) measurements.
The computed tomography (CT) or magnetic resonance imaging
(MRI) studies obtained to evaluate the aorta also provide information
regarding kidney size and perfusion. Accurate information regarding
baseline renal function has important prognostic and therapeutic
implications. For example, patients with severely impaired renal function frequently require at least temporary hemodialysis after operation; these patients are also at increased risk of death.
85
Additionally,
perfusion strategies and perioperative medications are adjusted on
the basis of renal function. Finally, patients with poor renal function
due to renal malperfusion from a dissection flap or from occlusive
disease can undergo renal endarterectomy, stenting, or bypass grafting during thoracoabdominal aortic aneurysm (TAAA) repair.
Surgical Repair
OPERATIVE TECHNIQUES
Surgical strategies are determined on the basis of the extent of the
aneurysm being repaired.
the chest and are therefore repaired through a left thoracotomy.
In patients with TAAAs, this incision is extended across the costal
margin and into the abdomen (
dominal replacement is defined by the Crawford classification
of TAAAs (see
Fig. 35-6). A double-lumen endobronchial tube is
used to allow selective right lung ventilation and left lung deflation. Transperitoneal exposure of the thoracoabdominal aorta is
achieved by dividing the diaphragm and performing medial visceral rotation.
Aortic repair usually is performed during a period of aortic
clamping. The clamp is ideally applied distal to the left subclavian artery but is often required between the left common carotid
artery (CCA) and left subclavian artery because of the anatomy of
the aneurysm. In patients who have undergone previous coronary
artery bypass surgery using the left internal thoracic artery, clamping proximal to the left subclavian artery can precipitate severe
myocardial ischemia and cardiac arrest. When clamping at this
location is anticipated in these patients, a left common carotid–
to-subclavian bypass is performed to avoid cardiac complications.
In certain situations, hypothermic circulatory arrest is required;
the primary indication for this approach is the inability to clamp
the aorta because of rupture, an extremely large aneurysm, or
extension of the aneurysm into the distal transverse aortic arch.
Regardless of the technique, once proximal control is established,
the aneurysmal segment of aorta is replaced with a polyester tube
graft (
Fig. 35-8B-J).
Because of the periaortic inflammation caused by the dissection, the vagus and left recurrent laryngeal nerves are often adherent to the aortic wall and susceptible to injury during repair of the
proximal descending segment. Careful separation of the proximal
descending thoracic aorta from the underlying esophagus before
86,87
Descending TAAs are confined to
Fig. 35-8A). Extent of the thoracoab-
79
performing the proximal anastomosis minimizes the risk of a
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
secondary aortoesophageal fistula. Important branch vessels—
including the intercostal, celiac, superior mesenteric, renal, and
lumbar arteries—are reattached to openings made in the graft.
When the dissection extends into the visceral or renal arteries, the membrane can be fenestrated or the false lumen can be
obliterated using sutures or intraluminal stents.
88
Asymmetrical
expansion of the false lumen often displaces the left renal artery
laterally enough to require separate reattachment or use of a side
branch graft. If the dissection stops at the level of the visceral vessels, the distal anastomosis can be beveled to include the abdominal branches. Although it is tempting to resect as much of the
dissected aorta as possible, risks of the operation are incrementally
increased with the greater extent of aortic replacement. Adjacent
dissected aorta that is not aneurysmal is fenestrated by resecting
wedges of the dissecting membrane proximally and distally from
within the aortic cuffs, allowing blood to flow through both true
and false channels after the reconstruction is completed. The distal
anastomosis is accomplished in an open fashion with rapid direct
reinfusion of the filtered whole blood via a cell saver system.
ORGAN PROTECTION
Clamping the descending thoracic aorta creates ischemia of the
spinal cord and abdominal viscera. Clinically significant postoperative manifestations of hepatic, pancreatic, and bowel ischemia are
relatively uncommon. Acute renal failure and spinal cord injury,
however, are the main causes of morbidity and mortality after these
operations. Therefore, several aspects of the operation are devoted
to minimizing spinal and renal ischemia
86
(Box 35-4). A multimodality approach to spinal cord protection includes cerebrospinal
fluid drainage, mild permissive hypothermia (32°C-34°C, nasopharyngeal), moderate systemic heparinization to prevent small-vessel
thrombosis, distal aortic perfusion with left heart bypass during
proximal anastomosis, sequential clamping of the lower aortic
segments to reestablish flow to proximal organs as the proximal
anastomoses are completed, and reattachment of the segmental
intercostal and lumbar arteries. Cerebrospinal fluid drainage is
used in extensive thoracoabdominal repairs (i.e., extents I and II)
and in selected redo surgeries or other complicated situations.
Benefits of cerebrospinal fluid drainage, which improves spinal
perfusion by reducing cerebrospinal fluid pressure, have been confirmed by a randomized clinical trial.
89
Left heart bypass, which
provides perfusion of the distal aorta and its branches during the
proximal clamp period, is also used during extensive thoracoabdominal aortic repairs.
90
Because it unloads the heart, left heart
bypass is also useful in patients with poor cardiac reserve. The
visceral and distal aortic anastomoses are completed in an open
fashion with the distal clamp off. During this time, balloon perfusion cannulas connected to the left heart bypass circuit can be
used to deliver blood directly to the celiac axis and superior mesenteric artery (SMA) during their reattachment. Potential benefits
of reducing hepatic and bowel ischemia include reduced risks of
postoperative coagulopathy and bacterial translocation, respectively. Whenever possible, renal protection is enhanced by perfusing the kidneys with cold (4°C) crystalloid.
91,92
443
CH
35
SURGICAL THERAPY FOR AORTIC DISSECTION
FIGURE 358 Surgical techniques
involved in repairing an extent II
thoracoabdominal aortic aneurysm
(TAAA) related to chronic aortic
dissection. A, Repair is performed
through left thoracoabdominal incision.
B, Aortic clamps are applied after
establishing distal aortic perfusion via a
left heart bypass circuit. C, The segment
of aorta isolated between clamps is
opened. D, Dissecting membrane is
excised, and intercostal arteries are
ligated.
Left Heart
Bypass
Circuit
Cold Renal
A
Perfusion
System
B
False
lumen
C
D
Continued
Соседние файлы в папке Библиотека им академика М.И. Перельмана