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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. 8.26 Stepwise technique for the replacement of the descending aorta. A: The distal suture line. B:
Wrapping the graft.
FIG. 8.27 Stepwise technique for the replacement of the descending aorta: Reimplantation of the intercostal
arteries into the tube graft.
Perfusion of Upper Body
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Rarely, one may encounter a situation while on left heart bypass in which the descending aortic aneurysm has
been opened, only to note that the appropriate proximal margin of resection is indeed beyond the proximal clamp
within the arch of the aorta. This necessitates total circulatory arrest. As retrograde perfusion through the femoral
artery cannot perfuse the head and the upper part of the body with the thoracic aorta cross-clamped, the
ascending aorta needs to
be cannulated separately. This can be performed quite easily through the standard left thoracotomy, especially
when the heart is decompressed on left heart bypass. Otherwise, the thoracotomy incision is extended medially
to provide adequate exposure. It is important for the surgeon and the perfusionist to communicate and
choreograph the conduct of the procedure to ensure adequate perfusion of both the lower and upper parts of the
body. When the continuity of the aorta has been reestablished, further perfusion and rewarming can be achieved
through the femoral or preferably the aortic cannula.
FIG. 8.28 Completing the descending aortic replacement after an elephant-trunk procedure.
Circulatory Arrest and Antegrade Cerebral Protection
During cooling for circulatory arrest, the left subclavian artery is isolated. A small side-biting vascular clamp is
applied and a 1 cm longitudinal arteriotomy is made. An 8-mm Hemashield Dacron tube graft is sutured to the left
subclavian artery in an end-to-side manner using 5-0 Prolene suture. When circulatory arrest commences, the
left subclavian artery is clamped proximally and perfused distally at a pressure of 50 to 60 mm Hg. Antegrade
cerebral perfusion through the left vertebral artery and the Circle of Willis is confirmed by the backflow coming
out of the left carotid and innominate arteries.
Connection of the True with the False Distal Lumen
It is of utmost importance to maintain a connection between the true and false lumens when the chronic
dissection extends distally. This entails removing a short segment of the intima flap wall just distal to the distal
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anastomosis. In this manner, all the aortic branches arising from the false as well as true lumen are perfused.
Esophageal Injury
Deep suturing may inadvertently include the esophagus. Transection and dissection of the posterior aspect of
the aorta allow precise placement of the sutures, thereby preventing possible esophageal injury.
Hypertension from Cross-Clamping
Aortic cross-clamping often produces proximal hypertension, which must be controlled with the use of
antihypertensive agents.
Spinal Cord Ischemia
A significant decrease in distal perfusion pressure can occasionally result in paraplegia. This is a grave
complication that should be prevented using all available means. Many techniques, including partial bypass from
the left atrium or pulmonary artery to the femoral artery, or the femoral vein to the femoral artery have been
employed with some success. Heparin-bonded tubes for left-sided heart bypass have also been used. However,
it appears that keeping the time of aortic cross-clamping short provides the best protection against the
development of paralysis.
Drainage of Cerebrospinal Fluid
Clamping of the descending aorta causes a significant decrease in distal perfusion pressure, including that to the
spinal arteries. Conversely, there is resultant hypertension proximal to the clamp. This produces engorgement of
the intracranial structures and increases in cerebrospinal fluid pressure, which may contribute to spinal cord
ischemia. Although there are no definite data to support the beneficial effect of reducing cerebrospinal fluid
pressure, it has been our practice to drain the cerebrospinal fluid in the operating room and continue drainage for
the first 1 or 2 days postoperatively, maintaining a pressure of approximately 10 mm Hg.
Spinal Cord Protection Techniques
Spinal cord function can be monitored during the time when the aorta is clamped. Monitoring somatosensory
evoked potentials entails stimulating the posterior tibial nerve and recording its response in the cerebral cortex.
Although many centers use this monitoring technique, its clinical pertinence has not been fully established.
ENDOVASCULAR REPAIR OF DESCENDING THORACIC AORTIC ANEURYSMS
Open surgical repair of descending thoracic aortic aneurysms can be performed safely in great majority of
patients. Distal perfusion using extracorporeal circulation, multiple spinal cord protection techniques, and
reimplantation of the selected intercostals arteries have resulted in improved outcomes. However, a left
thoracotomy incision and cross-clamping of the thoracic aorta constitute a highly invasive approach. The
reported cumulative morbidity associated with open surgical repair exceeds 50%. Most patients may need a
recovery time of 4 to 6 months to return to full functionality. Furthermore, a significant number of patients with
comorbid conditions are deemed to be at a prohibitive risk for open repair and are denied surgery. Therefore,
endovascular repair of descending thoracic aortic aneurysms is an attractive approach.
Candidates for endovascular repair should have an inner aortic diameter of 23 to 37 mm adjacent to the
aneurysm without significant thrombus or calcification in these so-called landing zones. They should have at
least 2 cm of normal aorta both proximal and distal to the aneurysm to ensure adequate fixation of the device
(Fig. 8.29). A number of endografts are now commercially available and able to accommodate various neck
geometries and angulation.
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FIG. 8.29 Endograft with adequate distal and proximal fixation.
Type I Endoleak
With poor fixation, a type I endoleak of the aneurysm may be encountered. An aneurysm with the type I endoleak
is considered untreated. Type I endoleaks may occasionally be treated with balloon dilation of the fixation
segments. But more frequently, deployment of proximal or distal extension cuffs is required to exclude the
aneurysm completely.
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FIG. 8.30 Required preoperative measurements of the diameters, lengths, and angulation of the descending
thoracic aorta. (From the GORE TAG training manual.)
Correct Sizing of the Endograft
Endografting of the descending thoracic aorta requires preoperative measurements of the diameter of the
proximal and distal necks of the aneurysm, treatment length, and proximal and distal angulation. This information
can be obtained from computed tomographic angiography using three-dimensional reconstruction (Fig. 8.30).
Center-line distances should be used to estimate the length of prosthesis that is required. Undersizing of the
endograft will result in poor fixation, endoleak, or migration of the device. Excessive oversizing of the graft may
cause crimping and occlusion of the graft or aortic injury and rupture.
Technique
The procedure is performed in a surgical or angiography suite equipped with a fluoroscopy machine. Most
patients are placed under general endotracheal anesthesia. Most endovascular devices can be inserted through
a 20, 22, or 24 French sheath. The size of the sheath is determined on the basis of the device size. The
preoperative computed tomography images with contrast should include the abdomen and pelvis to assess the
femoral and iliac arteries for size, tortuosity, and calcification. A 24 French sheath has an outer diameter of
approximately 9 mm. If the femoral arteries cannot accommodate the intended sheath, a Dacron
conduit should be anastomosed to the iliac artery for the insertion of sheath. This anastomosis can be performed
through a small flank incision (Fig. 8.31).
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FIG. 8.31 Surgical exposure of the terminal aorta, common, internal, and external iliac arteries through a flank
incision.
Iliac Artery Injury
If a sheath larger than the external iliac artery diameter is inserted, iliac artery injury can occur. This injury is
usually manifested upon withdrawal of the sheath after deployment of the device. The iliac artery injury and
massive retroperitoneal bleeding will present as severe hypotension. If guidewire access is maintained, a balloon
occlusion catheter (CODA balloon, Cook, Bloomington, IN) can be quickly passed into the terminal aorta to
temporarily stop the bleeding. An ipsilateral retroperitoneal approach to the iliac artery is needed to repair the
injured artery with an interposition graft (Fig. 8.31).
In general, before insertion of the device or anastomosis of an iliac conduit, systemic heparin is administered. A
contralateral femoral artery access is obtained using a 5 French sheath. This access is used for the insertion of
a pigtail arteriography catheter over a guidewire. Arteriography of the aortic arch, descending and proximal
abdominal aorta is performed to mark and roadmap the location of the arch and mesenteric vessels. Adequate
imaging and arteriography of the aorta require rapid injection of contrast using a power injector. The access to
the aorta for the insertion of the device is obtained using an exchange length guidewire under fluoroscopic
control. A utility catheter (Glide catheter) is inserted over the guidewire to maintain access. The large sheath with
the tapered dilator is inserted over a stiff guidewire (Lunderquist or Amplatz super stiff guidewire).
All guidewire, catheter, and sheath insertions must be performed under fluoroscopic control to avoid false
passages and intimal injury. Under fluoroscopic control, the device is inserted over the stiff guidewire and
deployed. Usually, additional devices are needed to achieve the desired treatment length.
Endografts of the same diameter or one to two sizes larger can be deployed overlapping a previously
inserted graft.
Sizing of Additional Endografts
Inadvertent insertion of a smaller endograft inside a larger graft will result in lack of fixation and migration of the
smaller graft. Excessive oversizing of an endograft inside a smaller graft may result in crimping and occlusion of
the larger graft.
Inadequate Proximal Neck
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If a normal segment of the aorta 23 to 37 mm in diameter of at least 2 cm in length is not present distal to the left
subclavian artery, then deployment in the arch between the left common carotid and left subclavian arteries may
be considered.
Occlusion of Subclavian Artery
In general, occlusion of the left subclavian artery with the endovascular graft may be well tolerated without
adjunctive procedures. However, there are patients who are dependent on antegrade subclavian blood flow.
These include patients with a diminutive right vertebral artery and a dominant left vertebral artery who would be
at risk for a posterior cerebral vascular accident. Patients who have previously undergone coronary artery
bypass grafting of the left anterior descending coronary artery using the left internal thoracic artery also require a
patent left subclavian artery. In these patients, a left carotid-subclavian bypass must be performed before
endografting of the descending thoracic aorta to avoid cerebral or cardiac complications. The left carotid-
subclavian bypass may be performed through a small supraclavicular exposure of the left carotid and subclavian
arteries (Fig. 8.32).
Inadequate Distal Cuff
In some patients, the distal aneurysm extension is close to the celiac artery such that a 2 cm length of the aorta
proximal to the celiac axis in not present. These patients are traditionally considered for a thoracoabdominal
repair. The thoracoabdominal repair should be considered for most patients with low risk for open surgery. In
higher risk patients, de-branching of the abdominal aorta may provide adequate length for endovascular repair.
In this combined open-endovascular approach, the celiac and superior mesenteric arteries may be bypassed
using grafts from the terminal aorta or the iliac arteries. These patients still require a transperitoneal abdominal
or retroperitoneal approach to the abdominal aorta. After rerouting of the mesenteric vessels, the thoracic portion
of the aorta can be repaired using an endograft. This approach obviates the
need for a combined thoracic and abdominal incision and cross-clamping of the aorta.
FIG. 8.32 Supraclavicular exposure and completion of a left carotid-subclavian artery bypass.
Patients at High Risk for Spinal Ischemia
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Some patients may have previously undergone repair of abdominal aortic aneurysms or may have occlusion of
the internal iliac arteries. Other patients may have extensive aneurysms from the proximal arch to the level of the
diaphragm requiring multiple overlapping endografts. These patients have been found to be at increased risk for
spinal cord ischemia after endovascular repair of thoracic aortic aneurysms. Occlusion of the left subclavian
artery with the endovascular graft may exacerbate this risk due to compromise of the vertebral artery as a
collateral to the anterior spinal artery. In these patients, insertion of a lumbar drain preoperatively may reduce the
risk. In addition to the lumbar drain, avoiding intraoperative and postoperative hypotension is an important
consideration to maintain spinal perfusion.
Endoleaks
Some aneurysms maintain continuity with the circulation after placement of endovascular grafts. These
endoleaks may be recognized at the time of treatment on the completion angiogram of the aorta. Frequently, the
endoleaks are recognized on follow-up imaging such as computed tomography with contrast. Depending on the
type and location of the endoleaks, various therapeutic options may be available.
Type I leak is the most commonly encountered type, and involves a leak from the proximal or distal fixation site.
Treatment is usually successful with the placement of a graft extension cuff.
Type II leaks occur from side-branch vessels such as intercostal or lumbar arteries that continue to remain
patent in the aneurysm sac. They are generally treated with catheter-based coil embolization.
Type III leaks result from a tear in the graft, attachment of the modular grafts, graft disconnection, or graft
disintegration. These should be treated routinely, usually with additional endografts within the old graft.
Type IV occurs when blood leaks through the suture holes between the graft material and the metal stent. If
persistent, treatment involves the insertion of a covered stent-graft (endograft) inside the original graft.
Type V or endotension refers to the expansion of the aneurysm despite treatment without any documented
leak into the aneurysm sac, potentially through the graft fabric. If the aneurysm continues to expand, redo
endografting may be performed.
The patients who have undergone endovascular repair of thoracic aortic aneurysms are followed up closely with
serial computed tomography of the chest, abdomen, and pelvis. Routinely, after an uneventful repair, the first
postoperative scan is obtained 2 to 4 weeks after surgery and annually thereafter. The follow-up computed
tomographic scans with contrast are carefully examined. All postoperative type I and type III endoleaks should be
treated. Type II endoleaks (patent intercostal arteries) in general may be observed if there is no expansion of the
aneurysm. Persistent type II endoleaks may be treated with embolization of the culprit patent intercostal artery.
FIG. 8.33 Debranching of the aortic arch. A: The distal ends of graft limbs are anastomosed to the left
subclavian, the common carotid, and the innominate arteries. B: The stent-graft is deployed.
ENDOVASCULAR REPAIR OF AORTIC ARCH ANEURYSM
In patients who are at high operative risk with open surgical repair of aortic arch and circulatory arrest, an
endovascular approach (debranching procedure) may be considered. In this combined open-endovascular
procedure, the innominate, left carotid and left subclavian arteries are bypassed using a graft(s) from the
ascending aorta. The aneurysmal aortic arch is then stented with occlusion of the origin of the head vessels.
Technique
A number of debranching techniques and modifications are now available depending on the aortic pathology. All
include diversion of blood flow to the head vessels followed by endovascular coverage of the diseased aorta and
coverage of the origin of the head vessels. The operation can be performed without the use of cardiopulmonary
bypass through a median sternotomy. In cases when the ascending aorta is not diseased, a side-biting clamp is
placed on the mid-ascending aorta. An anastomosis is performed to the main body of a bifurcated or trifurcated
graft. The distal anastomoses are performed to the left subclavian, the common carotid and the innominate
arteries individually (Fig. 8.33A). These can be performed in an end-to-end or end-to-side fashion. Finally, a
stent-graft is deployed either antegrade through the branched graft or retrograde through the femoral vessels as
described previously (Fig. 8.33B).
Inaccessible Left Subclavian Artery
In cases when the left subclavian artery is difficult to mobilize, a left carotid-subclavian bypass is performed
through a separate supraclavicular approach (Fig. 8.32).
Inadequate Length of Ascending Aorta
If a limited amount of aorta is available between the sinotubular junction and the take-off of head vessels,
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cardiopulmonary bypass with aortic cross clamping should be utilized.
If the ascending aorta is diseased and needs to be replaced (porcelain arota or severe atherosclerotic disease),
a hybrid approach to the aorta may reduce the period of circulatory arrest and the complexity of the operation. In
these operations, cardiopulmonary bypass is initiated in a standard manner using axillary or distal arch aortic
cannulation. After cooling and application of the cross clamp, the ascending aorta is reconstructed using a 4-
branched graft (Fig. 8.34A). After adequate cooling, a period of circulatory arrest is initiated, usually with the use
of antegrade or retrograde cerebral perfusion. The head vessels are dissected and the distal end of the dacron
graft is attached to
the aortic arch (Fig. 8.34B). Now circulation is established through the 4th limb of the graft and the individual
head vessels are attached to the graft branches (Fig. 8.34C). Each branch is de-aired and unclamped before the
next head vessel anastomosis. The origins of the head vessels can now be stapled. This is then followed by
warming, separation from bypass, and finally stent-graft deployment through the 4th limb of the graft (Fig. 8.34D).
FIG. 8.34 Replacement of ascending aorta and debranching of aortic arch. A: Proximal anastomosis of the aortic
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