Endovascular Treatment of Thoracic Aortic Aneurysms Jan S. Brunkwall The first description of a remote placement of a stent graft was by Volodos in 1986, although it was undertaken in treating a stenosis and dissection. Because it was published in Russian, there was little notice in the English-speaking countries. After the 1991 publications by Volodos and Parodi of the treatment of abdominal aortic aneurysms, the technique of endovascular aneurysm repair (EVAR) gained popularity. The first publication by Dake in 1994 describing using stent grafts for treatment of thoracic aortic aneurysms (TAAs) was a breakthrough for thoracic endovascular aneurysm repair (TEVAR). Later the placement of stent grafts for TAAs rapidly increased in number. Stent Grafts There are several stent grafts commercially available and most of them are based on the same principle, with a polyester Dacron or polytetrafluoroethylene (PTFE) graft combined with a Gianturco or Gianturco-like stent of stainless steel or nitinol. The stents are either sutured to the graft or melded into the wall. The ring stents used in the abdominal aorta (Anaconda, Aorfix) are not in clinical use for the thoracic aorta except in one trial. Compared to abdominal aortic stent grafts, the ones used for the descending TAAs are simpler in that they are constructed as straight tubes without the need for complicated branches. Only the Zenith stent graft uses hooks to facilitate the anchoring, whereas the others rely on the radial force. Most stent grafts have several available sizes with respect to diameter as well as the length. Although it is currently possible to custom make a stent graft, using several commercial stent grafts in a trombone technique for the desired length is faster, and with overlapping (>5cm), these devices are durable. Thoracic stent grafts have evolved since the turn of the century, but dramatic changes have been relatively scarce. There are currently eight CE-marked stent grafts available for treatment of thoracic aortic aneurysms in Europe: Gore TAG, Gore CTAG, Cook Zenith TX2, Medtronic Valiant Captivia, Bolton Relay, Jotec E-vita, and Lemaitre Endofit. In the United States there are fewer FDA-approved devices: Gore TAG, Zenith TX2, Talent, and Medtronic Valiant Captivia. Most design changes have been to make the delivery system smaller, with more flexibility and hydrophilic sheaths. Indications Even though the trauma to the patient is much less than with the open surgery, there is at the moment no indication for broadening of the indication for TEVAR than for the open surgery. A diameter of 6 cm of the descending thoracic aorta is generally accepted as the minimum size for intervention to prevent rupture. However, the lesser immediate risks with TEVAR mean that patients denied open surgery owing to their poor general condition may be accepted for treatment with stent grafts. Thus there are fewer, but other (see later), contraindications for stent grafts than for the open repair. Requirements for safe anchoring of the stent graft include a good landing zone of at least 2 cm length from the left subclavian artery, or if this artery is to be overstented, 2 cm from the left common carotid artery, as well as good radial force or a stent with hooks and barbs. The length of 2 cm is not well established but is patterned after experience with EVAR for abdominal aortic aneurysms (AAAs). When the anchoring zone is shorter than 2 cm the likelihood for type 1 endoleak and migration is higher, and when the anchoring zone is shorter than 1 cm, the risk may be eightfold greater for this complication. Available stent grafts in the United States are in the range of 21 to 46 mm, thus allowing treatment of aortic necks that are 16 to 42 mm in diameter. The risk for failure over time is higher when the diameter is larger, suggesting that the more diseased neck carries a greater risk to enlarge over time. Technique Successful TEVAR procedures require careful planning. Thus the procedure starts at the computer with thin-slice computed tomography (CT) scans that may be reconstructed to display the three-dimensional route of the aorta. One of the difficulties might be small iliac vessels, especially if they are calcified, and thus it is wise to run the CT to include the upper thoracic aperture and the groins. If a good work station is available, no angiography is necessary unless specific questions arise from the CT scan. Thoracic stent grafts are available with delivery systems sized from 18 Fr to 25 Fr (outer diameter). Depending on whether they are premounted or if they require an introducer sheath, the size to be used may vary accordingly. The primary route for a stent graft is with an introduction through the femoral artery, traversing the iliac artery and abdominal aorta to the target thoracic aorta. The route through the ascending aorta is hardly ever used for sole treatment of the descending thoracic aorta. Theoretically, an ascending aortic route could be used for placing stent grafts into the descending aorta, and in fact such has been described in case reports involving ascending aortic aneurysms and dissections of the descending aorta. Most vascular surgeons would prefer a surgical cut down with respect to the large sheaths that need to be inserted into the femoral artery. Closing devices have been used after placing thoracic stent grafts, as well as the fascia-closure technique, in which the fascia is sutured ventral to the femoral artery in such a way as to prevent bleeding. Compared to complications attending an open thoracotomy, a groin incision has to be regarded as having minor complications with lymphatic fistula or infection. After puncture of the common femoral artery and through the bloodless change over wire to an introducer, the ascending aorta is catheterized under fluoroscopic visualization with a Terumo Glidewire followed by placement of a stiff wire. If the stent graft is not preloaded in an introducer, a separate large—up to 26 Fr—sheath might be needed in order to have a guided route at least to the abdominal aorta. Among the sheaths on the market, the one that has in our hands proved to seal without any blood loss is the Dryseal. Other sheaths are not as effective at lessening blood loss. Once the stent graft is in the abdominal aorta, the lumen is so large that the stent graft is readily passed to the thoracic aorta. In some patients, the iliac vessels are heavily calcified, and especially in women this can preclude the use of the external iliac artery as route. It is safer in such a setting to make an extraperitoneal incision and implant a 10-mm Dacron graft as conduit from the common iliac artery to the groin and, if necessary, use it as an iliofemoral bypass to the common femoral artery once the procedure is done. For sealing purposes, the puncture of the graft can be made as if it is the common femoral artery. As the stent graft is positioned at the desired level, its precise position needs to be defined angiographically. The contralateral groin is usually used for introduction of the angiography catheter, but one may use the left brachial artery. An advantage of the left brachial artery is that the catheter may be used as marker for the left subclavian artery and its orifice. Another advantage would be to have a rescue way for revascularizing the left subclavian artery. In a similar manner, the celiac trunk may be catheterized and the catheter left in place to mark it. The stent graft may then be deployed according to the recommendations of the manufacturer. If it is deployed in the straight portion of the descending aorta, no other precaution, other than a normal to low intraoperative blood pressure, is necessary. Should the anchorage zone to the left subclavian artery not suffice, it may become necessary to overstent and cover it. This may usually be done without hesitation, in that most patients will not develop any effort fatigue of the extremity. The vertebral artery is of importance, especially in elderly patients. A carotid–subclavian bypass or subclavian transposition to the left common carotid artery may be needed to prevent the risk of cerebellar stroke in select cases. A thin-slice CT scan with the neck vessels depicted may be sufficient to answer who is at risk. Conventional arteriography may be necessary to better define these cases. Coverage of the left subclavian artery without revascularization appears associated with a higher risk for paraplegia. An additional, but unique, risk of coverage of the left subclavian artery is in patients with a coronary bypass using the left internal mammary artery, which if covered could lead to a myocardial infarction or angina pectoris. Should the left common carotid artery also be involved in the procedure, a bypass from the right common carotid artery or a chimney technique can extend the landing zone. For the distal landing zone, one normally can go down to the celiac trunk, although with a slightly higher risk for paraplegia when the whole thoracic aorta is to be covered. If one needs to cover the celiac trunk in order to have a sufficient length of landing zone, this may be done safely if the collateralization from the superior mesenteric artery (SMA) through the pancreaticoduodenal arcade has been demonstrated by the balloon blocking test. In these cases, selective arteriography of the SMA reveals filling of the hepatic artery. Current limitations for endovascular exclusion of thoracic aortic aneurysms are short neck lengths and the size of the landing zones. Basically, 2 cm of neck length is needed both for the proximal and the distal fixation. If the aorta is elongated and tortuous, even longer necks may be needed in order to have a good anchoring zone. In the arch where the blood flow along the outer wall of the stent graft is likely to advance it forward, it may be necessary to have longer necks and also a shoulder for the stent graft to lean on. The reason for the size limitation is first, that it might not be possible to pack larger stent grafts into a sheath unless the sheath is made even larger, which can make it hard to introduce the sheath through the iliac artery. Second, the very dilated anchoring zone might not remain stable in size over time. Although there are no data in the literature regarding this issue, in the abdominal aorta where a dilatation of the neck exists, loss of anchorage and migration is encountered in some cases. One of the most feared complications when dealing with thoracic aortic surgery is paraplegia. Briefly, the risk in high-volume centers might be as low as 3% to 5%, but in most registry data the risk exceeds 10%. Because there is no prospective randomized trial comparing TEVAR with open surgery for descending thoracic aortic aneurysm, we are forced to use large nonrandomized descriptive or comparative trial data for comparisons. The risk for paraplegia depends on the length of the thoracic aorta and how many intercostal arteries are covered. The risk is higher when the subclavian artery needs to be covered by the prosthetic material and no revascularization is performed. Therefore, most centers perform a carotid–subclavian bypass or transposition of the subclavian artery to the left common carotid artery before overstenting the left subclavian artery. It seems important to have a high perfusion pressure of the spinal cord, and it might be useful to use spinal fluid drainage combined with an elevated arterial blood pressure when the risk for spinal damage exists. The risk for retrograde dissection, a known contributor to paraplegia, is low when treating a TAA by TEVAR. In case of a tortuous aorta, it may be difficult to advance the stiff wire or the stent graft to the desired position. In such a case, the body-floss technique may be very valuable. In principle, a guidewire introduced from the groin and advanced into the ascending aorta is caught with a snare from the right subclavian artery. Using a Seldinger technique, the guidewire is changed to a stiff wire that may then be pulled to straighten out excess tortuosity. During deployment of the proximal stent graft, the forces from the blood flow displace the stent graft distally. The effect is different for the various stent grafts, but when placing them in the arch displacement is almost always observed. To increase the exactness of the position—to prevent the distal displacement–some measures to reduce the blood flow are available. Reducing the blood pressure is helpful, but it is relatively less effective as rapid pacing with adenosine or using a caval occluding balloon. Rapid pacing is done with transvenous electrodes. The frequency is increased to 160 to 180 beats/min, resulting in blood pressure lowered to 40 to 60 mm Hg. After the stent graft is deployed, the pacing is normalized and the blood pressure increases immediately. The method is safe and fast, and within less than 1 minute it is possible to have completed the graft deployment and to have normalized the blood pressure. Use of adenosine is also a safe and relatively fast method wherein its delivery stops the heart beats for 30 to 60 seconds, during which time it may be possible to deploy the stent graft safely. A caval balloon has been used and relies on the same principle to reduce blood flow, but it is not being used by many centers at present. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease Management of Acute Limb Ischemia Complicating Aortic Reconstruction Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join Tags: Current Therapy in Vascular and Endovascular Surgery Aug 25, 2016 | Posted by admin in CARDIOLOGY | Comments Off on Endovascular Treatment of Thoracic Aortic Aneurysms Full access? Get Clinical Tree
Endovascular Treatment of Thoracic Aortic Aneurysms Jan S. Brunkwall The first description of a remote placement of a stent graft was by Volodos in 1986, although it was undertaken in treating a stenosis and dissection. Because it was published in Russian, there was little notice in the English-speaking countries. After the 1991 publications by Volodos and Parodi of the treatment of abdominal aortic aneurysms, the technique of endovascular aneurysm repair (EVAR) gained popularity. The first publication by Dake in 1994 describing using stent grafts for treatment of thoracic aortic aneurysms (TAAs) was a breakthrough for thoracic endovascular aneurysm repair (TEVAR). Later the placement of stent grafts for TAAs rapidly increased in number. Stent Grafts There are several stent grafts commercially available and most of them are based on the same principle, with a polyester Dacron or polytetrafluoroethylene (PTFE) graft combined with a Gianturco or Gianturco-like stent of stainless steel or nitinol. The stents are either sutured to the graft or melded into the wall. The ring stents used in the abdominal aorta (Anaconda, Aorfix) are not in clinical use for the thoracic aorta except in one trial. Compared to abdominal aortic stent grafts, the ones used for the descending TAAs are simpler in that they are constructed as straight tubes without the need for complicated branches. Only the Zenith stent graft uses hooks to facilitate the anchoring, whereas the others rely on the radial force. Most stent grafts have several available sizes with respect to diameter as well as the length. Although it is currently possible to custom make a stent graft, using several commercial stent grafts in a trombone technique for the desired length is faster, and with overlapping (>5cm), these devices are durable. Thoracic stent grafts have evolved since the turn of the century, but dramatic changes have been relatively scarce. There are currently eight CE-marked stent grafts available for treatment of thoracic aortic aneurysms in Europe: Gore TAG, Gore CTAG, Cook Zenith TX2, Medtronic Valiant Captivia, Bolton Relay, Jotec E-vita, and Lemaitre Endofit. In the United States there are fewer FDA-approved devices: Gore TAG, Zenith TX2, Talent, and Medtronic Valiant Captivia. Most design changes have been to make the delivery system smaller, with more flexibility and hydrophilic sheaths. Indications Even though the trauma to the patient is much less than with the open surgery, there is at the moment no indication for broadening of the indication for TEVAR than for the open surgery. A diameter of 6 cm of the descending thoracic aorta is generally accepted as the minimum size for intervention to prevent rupture. However, the lesser immediate risks with TEVAR mean that patients denied open surgery owing to their poor general condition may be accepted for treatment with stent grafts. Thus there are fewer, but other (see later), contraindications for stent grafts than for the open repair. Requirements for safe anchoring of the stent graft include a good landing zone of at least 2 cm length from the left subclavian artery, or if this artery is to be overstented, 2 cm from the left common carotid artery, as well as good radial force or a stent with hooks and barbs. The length of 2 cm is not well established but is patterned after experience with EVAR for abdominal aortic aneurysms (AAAs). When the anchoring zone is shorter than 2 cm the likelihood for type 1 endoleak and migration is higher, and when the anchoring zone is shorter than 1 cm, the risk may be eightfold greater for this complication. Available stent grafts in the United States are in the range of 21 to 46 mm, thus allowing treatment of aortic necks that are 16 to 42 mm in diameter. The risk for failure over time is higher when the diameter is larger, suggesting that the more diseased neck carries a greater risk to enlarge over time. Technique Successful TEVAR procedures require careful planning. Thus the procedure starts at the computer with thin-slice computed tomography (CT) scans that may be reconstructed to display the three-dimensional route of the aorta. One of the difficulties might be small iliac vessels, especially if they are calcified, and thus it is wise to run the CT to include the upper thoracic aperture and the groins. If a good work station is available, no angiography is necessary unless specific questions arise from the CT scan. Thoracic stent grafts are available with delivery systems sized from 18 Fr to 25 Fr (outer diameter). Depending on whether they are premounted or if they require an introducer sheath, the size to be used may vary accordingly. The primary route for a stent graft is with an introduction through the femoral artery, traversing the iliac artery and abdominal aorta to the target thoracic aorta. The route through the ascending aorta is hardly ever used for sole treatment of the descending thoracic aorta. Theoretically, an ascending aortic route could be used for placing stent grafts into the descending aorta, and in fact such has been described in case reports involving ascending aortic aneurysms and dissections of the descending aorta. Most vascular surgeons would prefer a surgical cut down with respect to the large sheaths that need to be inserted into the femoral artery. Closing devices have been used after placing thoracic stent grafts, as well as the fascia-closure technique, in which the fascia is sutured ventral to the femoral artery in such a way as to prevent bleeding. Compared to complications attending an open thoracotomy, a groin incision has to be regarded as having minor complications with lymphatic fistula or infection. After puncture of the common femoral artery and through the bloodless change over wire to an introducer, the ascending aorta is catheterized under fluoroscopic visualization with a Terumo Glidewire followed by placement of a stiff wire. If the stent graft is not preloaded in an introducer, a separate large—up to 26 Fr—sheath might be needed in order to have a guided route at least to the abdominal aorta. Among the sheaths on the market, the one that has in our hands proved to seal without any blood loss is the Dryseal. Other sheaths are not as effective at lessening blood loss. Once the stent graft is in the abdominal aorta, the lumen is so large that the stent graft is readily passed to the thoracic aorta. In some patients, the iliac vessels are heavily calcified, and especially in women this can preclude the use of the external iliac artery as route. It is safer in such a setting to make an extraperitoneal incision and implant a 10-mm Dacron graft as conduit from the common iliac artery to the groin and, if necessary, use it as an iliofemoral bypass to the common femoral artery once the procedure is done. For sealing purposes, the puncture of the graft can be made as if it is the common femoral artery. As the stent graft is positioned at the desired level, its precise position needs to be defined angiographically. The contralateral groin is usually used for introduction of the angiography catheter, but one may use the left brachial artery. An advantage of the left brachial artery is that the catheter may be used as marker for the left subclavian artery and its orifice. Another advantage would be to have a rescue way for revascularizing the left subclavian artery. In a similar manner, the celiac trunk may be catheterized and the catheter left in place to mark it. The stent graft may then be deployed according to the recommendations of the manufacturer. If it is deployed in the straight portion of the descending aorta, no other precaution, other than a normal to low intraoperative blood pressure, is necessary. Should the anchorage zone to the left subclavian artery not suffice, it may become necessary to overstent and cover it. This may usually be done without hesitation, in that most patients will not develop any effort fatigue of the extremity. The vertebral artery is of importance, especially in elderly patients. A carotid–subclavian bypass or subclavian transposition to the left common carotid artery may be needed to prevent the risk of cerebellar stroke in select cases. A thin-slice CT scan with the neck vessels depicted may be sufficient to answer who is at risk. Conventional arteriography may be necessary to better define these cases. Coverage of the left subclavian artery without revascularization appears associated with a higher risk for paraplegia. An additional, but unique, risk of coverage of the left subclavian artery is in patients with a coronary bypass using the left internal mammary artery, which if covered could lead to a myocardial infarction or angina pectoris. Should the left common carotid artery also be involved in the procedure, a bypass from the right common carotid artery or a chimney technique can extend the landing zone. For the distal landing zone, one normally can go down to the celiac trunk, although with a slightly higher risk for paraplegia when the whole thoracic aorta is to be covered. If one needs to cover the celiac trunk in order to have a sufficient length of landing zone, this may be done safely if the collateralization from the superior mesenteric artery (SMA) through the pancreaticoduodenal arcade has been demonstrated by the balloon blocking test. In these cases, selective arteriography of the SMA reveals filling of the hepatic artery. Current limitations for endovascular exclusion of thoracic aortic aneurysms are short neck lengths and the size of the landing zones. Basically, 2 cm of neck length is needed both for the proximal and the distal fixation. If the aorta is elongated and tortuous, even longer necks may be needed in order to have a good anchoring zone. In the arch where the blood flow along the outer wall of the stent graft is likely to advance it forward, it may be necessary to have longer necks and also a shoulder for the stent graft to lean on. The reason for the size limitation is first, that it might not be possible to pack larger stent grafts into a sheath unless the sheath is made even larger, which can make it hard to introduce the sheath through the iliac artery. Second, the very dilated anchoring zone might not remain stable in size over time. Although there are no data in the literature regarding this issue, in the abdominal aorta where a dilatation of the neck exists, loss of anchorage and migration is encountered in some cases. One of the most feared complications when dealing with thoracic aortic surgery is paraplegia. Briefly, the risk in high-volume centers might be as low as 3% to 5%, but in most registry data the risk exceeds 10%. Because there is no prospective randomized trial comparing TEVAR with open surgery for descending thoracic aortic aneurysm, we are forced to use large nonrandomized descriptive or comparative trial data for comparisons. The risk for paraplegia depends on the length of the thoracic aorta and how many intercostal arteries are covered. The risk is higher when the subclavian artery needs to be covered by the prosthetic material and no revascularization is performed. Therefore, most centers perform a carotid–subclavian bypass or transposition of the subclavian artery to the left common carotid artery before overstenting the left subclavian artery. It seems important to have a high perfusion pressure of the spinal cord, and it might be useful to use spinal fluid drainage combined with an elevated arterial blood pressure when the risk for spinal damage exists. The risk for retrograde dissection, a known contributor to paraplegia, is low when treating a TAA by TEVAR. In case of a tortuous aorta, it may be difficult to advance the stiff wire or the stent graft to the desired position. In such a case, the body-floss technique may be very valuable. In principle, a guidewire introduced from the groin and advanced into the ascending aorta is caught with a snare from the right subclavian artery. Using a Seldinger technique, the guidewire is changed to a stiff wire that may then be pulled to straighten out excess tortuosity. During deployment of the proximal stent graft, the forces from the blood flow displace the stent graft distally. The effect is different for the various stent grafts, but when placing them in the arch displacement is almost always observed. To increase the exactness of the position—to prevent the distal displacement–some measures to reduce the blood flow are available. Reducing the blood pressure is helpful, but it is relatively less effective as rapid pacing with adenosine or using a caval occluding balloon. Rapid pacing is done with transvenous electrodes. The frequency is increased to 160 to 180 beats/min, resulting in blood pressure lowered to 40 to 60 mm Hg. After the stent graft is deployed, the pacing is normalized and the blood pressure increases immediately. The method is safe and fast, and within less than 1 minute it is possible to have completed the graft deployment and to have normalized the blood pressure. Use of adenosine is also a safe and relatively fast method wherein its delivery stops the heart beats for 30 to 60 seconds, during which time it may be possible to deploy the stent graft safely. A caval balloon has been used and relies on the same principle to reduce blood flow, but it is not being used by many centers at present. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease Management of Acute Limb Ischemia Complicating Aortic Reconstruction Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join
