Descending Aortic Repair
Approaches to the Thoracic Aortic Aneurysm.
A YouTube PowerPoint Video / Discussion:
Part I
[youtube=https://www.youtube.com/watch?v=2ljGBvUhX14]
Endovascular Stent Grafting for ascending and aortic arch repair
by John Ikonomidis MD
Part II
https://www.youtube.com/watch?v=5__ctxT-C90
Endovascular Stent Grafting for ascending and aortic arch repair
by John Ikonomidis MD
Anatomy
Discussion Below Cited from: Medscape
https://emedicine.medscape.com/article/424904-overview
Most aortic aneurysms (AA) occur in the abdominal aorta; these are termed abdominal aortic aneurysms (AAA). Although most abdominal aortic aneurysms are asymptomatic at the time of diagnosis, the most common complication remains life-threatening rupture with hemorrhage.
Aneurysmal degeneration that occurs in the thoracic aorta is termed a thoracic aneurysm (TA). Aneurysms that coexist in both segments of the aorta (thoracic and abdominal) are termed thoracoabdominal aneurysms (TAA). Thoracic aneurysms and thoracoabdominal aneurysms are also at risk for rupture. A recent population-based study suggests an increasing prevalence of thoracic aortic aneurysms.
Thoracic aortic aneurysms are subdivided into 3 groups depending on location:
- ascending aortic
- aortic arch
- descending thoracic aneurysms or thoracoabdominal aneurysms
Aneurysms that involve the ascending aorta may extend as proximally as the aortic annulus and as distally as the innominate artery, whereas descending thoracic aneurysms begin beyond the left subclavian artery.
Arch aneurysms are as the name implies.
Dissection is another condition that may affect the thoracic aorta. An intimal tear causes separation of the walls of the aorta. A false passage for blood develops between the layers of the aorta. This false lumen may extend into branches of the aorta in the chest or abdomen, causing malperfusion, ischemia, or occlusion with resultant complications. The dissection can also progress proximally, to involve the aortic sinus, aortic valve, and coronary arteries.
Dissection can lead to aneurysmal change and early or late rupture. A chronic dissection is one that is diagnosed more than 2 weeks after the onset of symptoms. Dissection should not be termed dissecting aneurysm because it can occur with or without aneurysmal enlargement of the aorta.
The shape of an aortic aneurysm is either saccular or fusiform. A fusiform (or true) aneurysm has a uniform shape with a symmetrical dilatation that involves the entire circumference of the aortic wall. A saccular aneurysm is a localized outpouching of the aortic wall, and it is the shape of a pseudoaneurysm.
Treatment of abdominal aortic aneurysms, thoracoabdominal aneurysms, and thoracic aneurysms involves surgical repair in good-risk patients with aneurysms that have reached a size sufficient to warrant repair.
Surgical repair may involve endovascular stent grafting (in suitable candidates) or traditional open surgical repair.
Ascending Aortic Aneurysms
Occur as proximally as the aortic annulus and as distally as the innominate artery. They may compress or erode into the sternum and ribs, causing pain or fistula. They also may compress the superior vena cava or airway. When symptomatic by rupture or dissection, they may involve the pericardium, aortic valve, or coronary arteries. They may rupture into the pericardium, causing tamponade. They may dissect into the aortic valve, causing aortic insufficiency, or into the coronary arteries, causing myocardial infarction.
Aortic arch aneurysms
Involve the aorta where the innominate artery, left carotid, and left subclavian originate. They may compress the innominate vein or airway. They may stretch the left recurrent laryngeal nerve, causing hoarseness.
Descending thoracic aneurysms
Originate beyond the left subclavian artery and may extend into the abdomen.
Thoracoabdominal aneurysms are stratified based on the Crawford classification.
- Type I involves the descending thoracic aorta from the left subclavian artery down to the abdominal aorta above the renal arteries.
- Type II extends from the left subclavian artery to the renal arteries and may continue distally to the aortic bifurcation.
- Type III begins at the mid-to-distal descending thoracic aorta and involves most of the abdominal aorta as far distal as the aortic bifurcation. Type IV extends from the upper abdominal aorta and all or none of the infrarenal aorta.
Descending thoracic aneurysms and thoracoabdominal aneurysms may compress or erode into surrounding structures, including the trachea, bronchus, esophagus, vertebral body, and spinal column.
Summary of Indications:
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Aortic size
- Ascending aortic diameter ≥5.5 cm or twice the diameter of the normal contiguous aorta
- Descending aortic diameter ≥6.5 cm
- Subtract 0.5 cm from the cutoff measurement in the presence of Marfan syndrome, family history of aneurysm or connective tissue disorder, bicuspid aortic valve, aortic stenosis, dissection, patient undergoing another cardiac operation
- Growth rate ≥1 cm/y
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Symptomatic aneurysm
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Traumatic aortic rupture
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Acute type B aortic dissection with associated rupture, leak, distal ischemia
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Pseudoaneurysm
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Large saccular aneurysm
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Mycotic aneurysm
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Aortic coarctation
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Bronchial compression by aneurysm
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Aortobronchial or aortoesophageal fistula
Repair
Descending thoracic aneurysms may be repaired with open surgery or, if appropriate, with endovascular stent grafting techniques.
Stent graft repair of descending thoracic aortic aneurysms should be performed if the predicted operative risk is lower than that of an open repair. Patient age, comorbidities, symptoms, life expectancy, aortic diameter, characteristics and extent of the aneurysm, and landing zones, should also be taken into consideration.
Surgically, descending thoracic aneurysms may be repaired with or without the use of a bypass circuit from the left atrium to the femoral artery or femoral vein–femoral artery cardiopulmonary bypass, depending on the length of the anticipated ischemic cross-clamping and the experience of the surgeon.
Discrete aneurysms with an anticipated clamp time of less than 30 minutes may be repaired without left heart or cardiopulmonary bypass (ie, “clamp and go” technique). More complex or larger aneurysms are probably safer to repair with the aid of either left heart, partial, or full cardiopulmonary bypass with hypothermic circulatory arrest. The use of left heart or cardiopulmonary bypass is favored to reduce hemodynamic instability and the risk of spinal cord paraplegia.
Descending thoracic aneurysms with the appropriate anatomy may now be repaired by endovascular stent grafts.
The GORE TAG is an FDA-approved nitinol-based stent graft designed for descending thoracic aneurysm repair. An appropriate proximal neck of 2 cm prior to the aneurysm is required.
Ideally, the proximal landing zone is beyond the left subclavian artery, though, in some circumstances, the stent may be placed proximal to the left subclavian artery.
Distally, a sufficient landing zone of 2 cm prior to the celiac artery is required. The aortic inner neck diameters in the proximal and distal landing zones must fall within 23-37 mm. In addition, appropriately sized femoral and iliac arteries (typically >8 mm in diameter) that lack tortuosity and calcium are required for implantation.
