Open Surgical Treatment of Thoracic Aortic Aneurysms Andreas Greiner, Jochen Grommes and Michael M.J. Jacobs Descending thoracic aortic aneurysms (TAAs) are categorized into three types. In type A the descending TAA starts at the level of the left subclavian artery and ends at the level of T6. Type B starts at T6 and ends at the level of the diaphragm. Type C involves the total descending thoracic aorta. It is not uncommon for descending TAAs to involve the distal aortic arch. In degenerative aneurysms, the more proximal arch is usually not dilated. Indications for Repair Most patients with TAAs are asymptomatic. Elective treatment of degenerative aneurysms is usually advised if the diameter exceeds 6.0 cm. Risk factors for rupture beside diameter and pain include age, presence of chronic obstructive pulmonary disease, renal insufficiency, extent of the aneurysm, and expansion rate of the aneurysm. The average growth rate of descending TAAs (0.42 cm/yr) is greater than that for abdominal aortic aneurysms (AAAs) (0.28 cm/yr). Symptoms like chest or back pain, dyspnea, or dysphagia are also indications for treatment. For patients with aneurysms secondary to inherited connective tissue disorders, the recommended threshold for repair is an aneurysm diameter exceeding 5.0 cm. These patients have a higher incidence of dissection and rupture in descending aortic aneurysms compared with other patients with degenerative aneurysms. Marfan’s syndrome and Ehlers–Danlos syndrome type IV are the most significant disorders causing aneurysmal dilatation of the thoracic aorta. Chronic type B dissections are the second most common cause of descending TAA formation. Up to 39% of patients with descending TAAs exhibit this pathology. Of all patients with aortic dissections, 20% to 40% will require subsequent aortic replacement during the follow-up. The growth rate of thoracic aortic dissections is significantly greater compared with that of AAAs but comparable to those of degenerative descending TAAs. Diameter indication for asymptomatic post-dissection descending TAAs is the same as for degenerative aneurysms (6.0 cm), except for patients with syndromic conditions such as Marfan’s (5.0 cm). False aneurysms in the thoracic aorta can be the result of previous aortic surgery or trauma. Anastomotic aneurysms as well as acute traumatic aneurysms immediately distal to the left subclavian artery can often be treated by endovascular means. Failure of thoracic endovascular aneurysm repair (TEVAR) is a new challenging entity in open aortic surgery. Most complications after endovascular stent graft treatment are repaired by an additional endovascular procedure. However, progression of dilation after endovascular treatment of post-dissection aneurysms is the most common reason for open aneurysm repair. Operative Planning Comorbidity Assessment The most common complications during descending TAA surgery include myocardial infarction, pulmonary insufficiency, kidney failure, and stroke. A careful evaluation of factors contributing to these complications is essential for preoperative risk reduction. Patients with these aneurysms are older and have more cardiovascular risk factors than the younger post-dissection patients. Impaired left ventricular ejection fraction appears to be the strongest predictor of perioperative mortality. Cardiac function can be evaluated by electrocardiogram, echocardiography, and stress testing. The threshold for coronary arteriography and antecedent mechanical intervention for coronary artery disease is lower in preparation for TAA surgery compared with that for other general surgical procedures. Chronic pulmonary disease and a history of smoking are important predictors for postoperative pulmonary complications. Preoperative pulmonary function is impaired in up to 36% of these patients, which can induce oxygenation problems during operation in case of single lung ventilation, and it elevates the risk of prolonged postoperative ventilation and pneumonia. Cessation of cigarette smoking for at least 4 weeks before surgery is mandatory. In patients with marginal pulmonary reserve, a period of pulmonary rehabilitation with appropriate medications is indicated. However, it is important that preoperative therapy does not include the addition of systemic steroids, because steroids might be associated with aneurysm rupture. Preoperative kidney impairment is the single most powerful predictor of postoperative kidney failure and is associated with a high rate of postoperative mortality. Although kidney dysfunction cannot be modified before operation, identification can influence adjunctive measures regarding protection of the kidneys during surgery. In case of anticipated cross clamping in the aortic arch, duplex imaging of the carotid arteries is advised to minimize the risk of stroke. Measures for End-Organ Protection Various combinations of extracorporeal circulation methods and adjunctive measures for end-organ protection are used when treating different extents of TAAs. Extracorporeal Circulation by Atriofemoral Perfusion Distal aortic perfusion by partial left heart bypass is the most commonly performed means of providing distal aortic flow during distal TAA repair. In this method, venous cannulation is performed via the left atrial appendage or more commonly and conveniently through the left inferior pulmonary vein. Through a centrifugal pump, the blood is returned through a left femoral artery cannula. Besides distal aortic perfusion and the possibility of selective side-branch perfusion, this provides decompression of the cardiac and cerebral perfusion during thoracic cross clamping. The bypass flow rate is adjustable in accordance with preservation of an adequate proximal aortic pressure. Distal mean aortic pressure should be approximately 60 mm Hg, but it can be adjusted according to urine-production and spinal cord–function monitoring tests. The bypass circuit is simple in concept and execution, and it can be used with an extrapericardial access to the left atrium. Because it is used with anticoagulant-impregnated tubing, it requires only a modest dose of heparin. An in-line heat exchanger can provide moderate systemic hypothermia and rewarming during the later stages of the reconstruction. Bleeding complications with this technique are greatly reduced when compared with full cardiopulmonary bypass, wherein an oxygenator is required in the circuit with much larger heparin doses. Alternatively, this technique can be changed to venous cannulation of the right atrium by way of the left femoral vein. Hypothermic Arrest Profound hypothermic circulatory arrest with total cardiopulmonary bypass can be installed by arterial and venous femoral cannulation and full heparinization. As noted earlier, the majority of surgeons agree this technique should only be used when there is no other technical option to repair the TAA. After fibrillation and placement of a left ventricular vent, full cardiopulmonary bypass can be achieved. This technique is most useful when proximal control is not feasible because of rupture, the aneurysm’s size, or the location of the dissection tear. Furthermore, an open anastomosis without cross clamping may be necessary in the case of bad aortic tissue quality (such as an acute type B dissection) or during a simultaneous repair of the aortic arch. Only gold members can continue reading. 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Open Surgical Treatment of Thoracic Aortic Aneurysms Andreas Greiner, Jochen Grommes and Michael M.J. Jacobs Descending thoracic aortic aneurysms (TAAs) are categorized into three types. In type A the descending TAA starts at the level of the left subclavian artery and ends at the level of T6. Type B starts at T6 and ends at the level of the diaphragm. Type C involves the total descending thoracic aorta. It is not uncommon for descending TAAs to involve the distal aortic arch. In degenerative aneurysms, the more proximal arch is usually not dilated. Indications for Repair Most patients with TAAs are asymptomatic. Elective treatment of degenerative aneurysms is usually advised if the diameter exceeds 6.0 cm. Risk factors for rupture beside diameter and pain include age, presence of chronic obstructive pulmonary disease, renal insufficiency, extent of the aneurysm, and expansion rate of the aneurysm. The average growth rate of descending TAAs (0.42 cm/yr) is greater than that for abdominal aortic aneurysms (AAAs) (0.28 cm/yr). Symptoms like chest or back pain, dyspnea, or dysphagia are also indications for treatment. For patients with aneurysms secondary to inherited connective tissue disorders, the recommended threshold for repair is an aneurysm diameter exceeding 5.0 cm. These patients have a higher incidence of dissection and rupture in descending aortic aneurysms compared with other patients with degenerative aneurysms. Marfan’s syndrome and Ehlers–Danlos syndrome type IV are the most significant disorders causing aneurysmal dilatation of the thoracic aorta. Chronic type B dissections are the second most common cause of descending TAA formation. Up to 39% of patients with descending TAAs exhibit this pathology. Of all patients with aortic dissections, 20% to 40% will require subsequent aortic replacement during the follow-up. The growth rate of thoracic aortic dissections is significantly greater compared with that of AAAs but comparable to those of degenerative descending TAAs. Diameter indication for asymptomatic post-dissection descending TAAs is the same as for degenerative aneurysms (6.0 cm), except for patients with syndromic conditions such as Marfan’s (5.0 cm). False aneurysms in the thoracic aorta can be the result of previous aortic surgery or trauma. Anastomotic aneurysms as well as acute traumatic aneurysms immediately distal to the left subclavian artery can often be treated by endovascular means. Failure of thoracic endovascular aneurysm repair (TEVAR) is a new challenging entity in open aortic surgery. Most complications after endovascular stent graft treatment are repaired by an additional endovascular procedure. However, progression of dilation after endovascular treatment of post-dissection aneurysms is the most common reason for open aneurysm repair. Operative Planning Comorbidity Assessment The most common complications during descending TAA surgery include myocardial infarction, pulmonary insufficiency, kidney failure, and stroke. A careful evaluation of factors contributing to these complications is essential for preoperative risk reduction. Patients with these aneurysms are older and have more cardiovascular risk factors than the younger post-dissection patients. Impaired left ventricular ejection fraction appears to be the strongest predictor of perioperative mortality. Cardiac function can be evaluated by electrocardiogram, echocardiography, and stress testing. The threshold for coronary arteriography and antecedent mechanical intervention for coronary artery disease is lower in preparation for TAA surgery compared with that for other general surgical procedures. Chronic pulmonary disease and a history of smoking are important predictors for postoperative pulmonary complications. Preoperative pulmonary function is impaired in up to 36% of these patients, which can induce oxygenation problems during operation in case of single lung ventilation, and it elevates the risk of prolonged postoperative ventilation and pneumonia. Cessation of cigarette smoking for at least 4 weeks before surgery is mandatory. In patients with marginal pulmonary reserve, a period of pulmonary rehabilitation with appropriate medications is indicated. However, it is important that preoperative therapy does not include the addition of systemic steroids, because steroids might be associated with aneurysm rupture. Preoperative kidney impairment is the single most powerful predictor of postoperative kidney failure and is associated with a high rate of postoperative mortality. Although kidney dysfunction cannot be modified before operation, identification can influence adjunctive measures regarding protection of the kidneys during surgery. In case of anticipated cross clamping in the aortic arch, duplex imaging of the carotid arteries is advised to minimize the risk of stroke. Measures for End-Organ Protection Various combinations of extracorporeal circulation methods and adjunctive measures for end-organ protection are used when treating different extents of TAAs. Extracorporeal Circulation by Atriofemoral Perfusion Distal aortic perfusion by partial left heart bypass is the most commonly performed means of providing distal aortic flow during distal TAA repair. In this method, venous cannulation is performed via the left atrial appendage or more commonly and conveniently through the left inferior pulmonary vein. Through a centrifugal pump, the blood is returned through a left femoral artery cannula. Besides distal aortic perfusion and the possibility of selective side-branch perfusion, this provides decompression of the cardiac and cerebral perfusion during thoracic cross clamping. The bypass flow rate is adjustable in accordance with preservation of an adequate proximal aortic pressure. Distal mean aortic pressure should be approximately 60 mm Hg, but it can be adjusted according to urine-production and spinal cord–function monitoring tests. The bypass circuit is simple in concept and execution, and it can be used with an extrapericardial access to the left atrium. Because it is used with anticoagulant-impregnated tubing, it requires only a modest dose of heparin. An in-line heat exchanger can provide moderate systemic hypothermia and rewarming during the later stages of the reconstruction. Bleeding complications with this technique are greatly reduced when compared with full cardiopulmonary bypass, wherein an oxygenator is required in the circuit with much larger heparin doses. Alternatively, this technique can be changed to venous cannulation of the right atrium by way of the left femoral vein. Hypothermic Arrest Profound hypothermic circulatory arrest with total cardiopulmonary bypass can be installed by arterial and venous femoral cannulation and full heparinization. As noted earlier, the majority of surgeons agree this technique should only be used when there is no other technical option to repair the TAA. After fibrillation and placement of a left ventricular vent, full cardiopulmonary bypass can be achieved. This technique is most useful when proximal control is not feasible because of rupture, the aneurysm’s size, or the location of the dissection tear. Furthermore, an open anastomosis without cross clamping may be necessary in the case of bad aortic tissue quality (such as an acute type B dissection) or during a simultaneous repair of the aortic arch. 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 Open Surgical Treatment of Thoracic Aortic Aneurysms Full access? Get Clinical Tree
