Surgery of Thoracic Aorta

Overview

A thoracic aortic aneurysm, which is an abnormal bulge in the weakening wall of the aorta in the chest, can produce a number of symptoms and, in some cases, life-threatening problems. Because of the considerable hazards it poses, a thoracic aneurysm must be diagnosed and treated as soon as possible.

Each year, around 15,000 persons in the United States are affected with thoracic aortic aneurysms, which are the 13th largest cause of mortality. According to research, people with untreated big thoracic aortic aneurysms are more likely to die from problems linked with their aneurysms than from any other cause.

The best way to treat an aortic thoracic aneurysm depends on its size and pace of development, location, and general health. When an aneurysm is more than double the typical diameter of a healthy aortic blood artery, the risk of rupture increases.

What is Thoracic Aortic Aneurysm?

The aorta is the body's major blood artery. It is responsible for transporting oxygenated blood from the heart to the rest of the body. An aortic aneurysm is a bulging, weakening region of the aortic wall. The blood artery expands with time and is at danger of bursting (rupture) or separating (dissection). This can result in life-threatening bleeding and, in extreme cases, death.

Once established, an aneurysm will gradually grow in size and become weaker. A thoracic aneurysm can be repaired or removed surgically, or a metal mesh coil (stent) can be inserted to support the blood artery and prevent rupture.

The term "thoracic" refers to the aorta section that goes through the chest (thoracic aortic aneurysm). Aneurysms are more common in the aorta that flows through the belly (abdominal aortic aneurysm).

Location

Thoracic Aortic Aneurysm (TAA) occurs in the thoracic aorta, or the upper part of the aorta, and is also subject to rupture.

TAAs are further subdivided into the following three groups:

• Ascending aortic aneurysms.
• Aortic arch aneurysms (arteries that branch off the top of the aorta and form an arch).
• Descending thoracic aneurysms, also called thoracoabdominal aneurysms 
• Thoracoabdominal aneurysms (TAAAs) - Aneurysms that coexist in both segments of the aorta (thoracic and abdominal) are termed thoracoabdominal aneurysms (TAAAs).

Causes & Risk Factors

There are several causes for this. Aneurysms in people under the age of 40 typically affect the ascending aorta due to aortic wall weakness caused by connective tissue diseases such as the Marfan and Ehler-Danlos syndromes or congenital bicuspid aortic valve. After an aortic dissection, younger people may develop thoracoabdominal aortic aneurysms.  A blunt injury might also cause it. Atherosclerosis is the most common cause of descending aortic aneurysms, whereas aortic arch aneurysms can be caused by dissection, atherosclerosis, or inflammation.

The most important risk factors are hypertension and smoking, while the role of hereditary variables is becoming increasingly acknowledged. Around 10% of patients have other family members who have aortic aneurysms. It is also worth noting that people who have had aneurysms in other sections of their bodies are more likely to acquire a thoracic aortic aneurysm.

How Common Is TAA?

Each year, around 45,000 individuals in the United States die from disorders of the aorta and its branches. Aorta dissection, a potentially fatal occurrence caused by a tear in the aortic wall, affects 5 to 10 people per million each year, mostly males between the ages of 50 and 70; approximately half of those in women under the age of 40 occur during pregnancy. The majority of these deaths are caused by thoracic aneurysmal disease complications.

Signs & Symptoms

Thoracic aortic aneurysms may not be accompanied by symptoms. When symptoms do emerge, they may be related to the location, size, and rate of growth of the aneurysm.

Sudden, acute pain caused by a thoracic aneurysm might indicate a life-threatening medical emergency.

Symptoms of a thoracic aneurysm may include:

• Pain in the jaw, neck, or upper back.
• Pain in the chest or back.
• Wheezing, coughing, or shortness of breath as a result of pressure on the trachea (windpipe).
• Hoarseness as a result of pressure on the vocal cords.
• Trouble swallowing due to pressure on the esophagus.

The symptoms of a thoracic aortic aneurysm may look like other conditions. See your doctor for a diagnosis.

How is a thoracic aortic aneurysm diagnosed?

Your doctor will do a complete medical history and physical exam. Other possible tests include:

1. CT scan (computed tomography). This test use X-rays and computer technologies to create horizontal or axial pictures (also known as slices) of the body. A CT scan provides comprehensive pictures of any region of the body, such as the bones, muscles, fat, and organs. CT scans provide more information than ordinary X-rays.
2. Magnetic resonance imaging (MRI). This test produces comprehensive pictures of organs and structures within the body by combining huge magnets, radiofrequencies, and a computer.
3. The echocardiogram (also called echo). This test assesses the anatomy and function of the heart by utilizing sound waves captured on an electronic sensor to create a moving image of the heart and heart valves, as well as structures within the chest such as the lungs and the space around the lungs and the chest organs.
4. Echocardiogram transesophageal (TEE). This test employs echocardiography to detect aneurysms, the status of heart valves, and the existence of an aortic lining tear. TEE is performed by inserting a probe with a transducer down the throat.
5. X-ray of the chest. This test employs invisible electromagnetic radiation beams to create pictures on film of interior tissues, bones, and organs.
6. Angiogram (angiogram). This is an X-ray picture of the blood vessels that is used to diagnose diseases such as aneurysms, blood vessel narrowing, or blockages. A dye (contrast) will be injected into an artery using a thin, flexible catheter. On an X-ray, the dye makes the blood vessels visible.

Can Aortic Dissection Complicate TAA?

Yes, An aortic dissection begins with a tear in the inner layer of the thoracic aorta's aortic wall. The aorta wall is composed of three layers of tissue. When the innermost layer of the aortic wall tears, blood is directed into the aortic wall, separating the layers of tissues. This causes a weakening of the aortic wall, with the possibility of rupture. Aortic dissection is a potentially fatal condition. Severe, persistent chest or upper back pain, frequently characterized as "tearing" is the most commonly reported symptom of an acute aortic dissection. The discomfort may shift from one location to another.

When an aortic dissection diagnosis is established, urgent surgery or stenting is generally performed.

Indications

Indications for surgical treatment may be summarized as follows:

1. 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 if you have Marfan syndrome, a family history of aneurysm, or connective tissue disorder, bicuspid aortic valve, aortic stenosis, dissection, or are having another cardiac operation; growth rate 1 cm/
2. Symptomatic aneurysm; Symptomatic patients, regardless of aneurysm size, should have an aneurysm excision. Patients with severe symptoms necessitate an emergency procedure.
3. Traumatic aortic rupture: An emergency procedure is recommended in the case of an acute rupture. An ascending aortic rupture into the pericardium might result in acute tamponade. A left hemothorax can result from a rupture of the descending thoracic aorta.
4. Acute ascending aortic dissection: Patients with acute ascending aortic dissection require immediate surgery. They can cause rupture, tamponade, acute aortic insufficiency, myocardial infarction, or end-organ ischemia. Acute descending aortic dissection does not require surgical intervention unless it is exacerbated by rupture, malperfusion (eg, visceral, renal, neurologic, or limb ischemia), progressive dissection, chronic recurring pain, or failure of medicinal therapy.
5. Pseudoaneurysm: A pseudoaneurysm, also known as a vessel pseudoaneurysm, arises when a blood vessel wall is ruptured and leaky blood gathers in the surrounding tissue. It is also known as a fake aneurysm. The artery or vessel weakens and bulges in a true aneurysm, occasionally generating a blood-filled sac.
6. Large saccular aneurysm.
7. Mycotic aneurysm.
8. Aortic coarctation.
9. Bronchial compression by aneurysm.
10. Aortobronchial or aortoesophageal fistula.

Thoracic Aortic Aneurysm Surgery

Ascending aortic surgery:

• Valve-sparing aortic-root replacement:

The valve is examined for proper anatomy after the aorta is transected at the sinotubular junction. If saving is possible, the proper size tube graft is chosen to allow aortic valve leaflet coaptation without aortic insufficiency. The tube graft is designed to produce aortic sinuses during the remodeling procedure. The original aorta's sinuses of Valsalva are excised, and the coronary ostia are mobilized. The tube graft neosinuses are sutured to the scalloped aortic valve with flowing 4-0 polypropylene and a felt strip.

Tycron sutures are put along the subannular horizontal plane and threaded through the tube graft in the reimplantation procedure. The scalloped aortic valve is inserted into the tube graft, and the proximal suture line is closed. To establish valve competence, the scalloped aortic valve is positioned in the graft, and the subcoronary suture line along the scalloped valve is accomplished using flowing 4-0 polypropylene. The competence of the valve within the graft is evaluated. In the graft, the coronary ostia are reimplanted. The graft is sutured to the distal aorta after being measured distally.

• Aortic-root replacement:

The aorta is cut and the aortic valve removed. The annulus is sized, and the proper valved conduit, stentless root, mechanical composite, or homograft is sent to the field. The coronary ostia have been activated. Annular sutures are threaded through the valve conduit. Thus, the proximal suture is secured. Reimplantation of the coronary ostia The distal suture line is accomplished for the mechanical valve composite, however, depending on the length of the stentless roots or homografts, an extra Dacron graft extension may be necessary.

The right and left coronary arteries are dissected as a button and reimplanted into the Dacron composite graft as an aortic button in the modified Bentall procedure ("buttons").

Although it is infrequently utilized, the Cabrol technique may be employed when an aortic rip or dissection reaches into the coronary ostia. It may also be employed when appropriate mobilization of the coronary ostia is not feasible (for example, as a result of scarring after a reoperation) or when the coronary ostia are too low. The coronary buttons are dissected and connected to a separate 6- or 8-mm Dacron interposition graft, which is subsequently connected to the Dacron composite graft.

This approach leads in a tension-free anastomosis of the coronary buttons as well as improved hemostasis access. It is, however, prone to twisting and kinking, resulting in myocardial ischemia, and so is not as repeatable as the modified Bentall.

• Open distal anastomosis:

Deep hypothermic circulatory arrest is employed, either with or without antegrade or retrograde brain perfusion. When the temperature reaches 18°C (64.4°F), the pump is shut off and the arterial line is pinched. The aortic cross-clamp is removed and the patient is put in the Trendelenburg position. The distal anastomosis is done open using flowing 4-0 polypropylene and a felt strip. The distal anastomosis might occur at the level of the innominate artery or, in the event of hemiarch replacement, down the arch's undersurface to the level of the left subclavian artery.

After the anastomosis is finished, the pump is restarted with blood flow antegrade into the new graft and open proximal tube graft to flush out air and debris. The graft is subsequently clamped, and the proximal aortic repair is done while the patient is rewarming.

Hypothermia reduces oxygen use. The oxygen consumption of the tissues is lowered by 10% for every 1o C reduction in temperature.

In blood, air (i.e., nitrogen) is weakly soluble. By saturating the surgical field with carbon dioxide, the danger of air embolism is lowered. Carbon dioxide has a higher density than air and hence displaces it. It dissolves quickly in the blood and reduces the danger of embolization. Any carbon dioxide absorbed in the circulation is eliminated by raising the cardiopulmonary bypass sweep speed.

Aortic arch aneurysm repairs:

Cannulation for arch repairs differs across groups. The femoral artery, right axillary artery and ascending aorta are among them. Arch repairs necessitate hypothermic circulatory arrest; the safe period of arrest to minimize neurologic harm is 30-45 minutes at 18°C (64.4°F), although some recommend a shorter period of 25 minutes. Antegrade cerebral perfusion is thus recommended to reduce neurologic damage. Others recommend cooling to 11-14°C.

The circuit is shut off once the patient has been cooled to the appropriate temperature. Flow via the superior vena cava is established for retrograde cerebral perfusion during arch reconstruction. Flow is continued through the axillary artery with the innominate artery clamped for antegrade cerebral perfusion, or separate perfusion catheters are inserted into the innominate, left carotid, and left subclavian arteries.

Descending thoracic aneurysm repairs

CSF drainage, reimplantation of intercostal arteries, partial bypass, and moderate hypothermia are all measures to decrease spinal cord damage. A thoracoabdominal incision or a left thoracotomy is performed. For Crawford types I and II, the aorta is cross-clamped immediately beyond the left subclavian or between the left carotid and left subclavian. Crawford types III and IV have a more distal cross-clamp.

Atrial femoral bypass is established via a Bio-Medicus circuit, and the patient is chilled to 32-34°C (89.6-93.2°F). T4-T7 distal cross-clamping is used to maintain spinal cord, visceral, and renal perfusion. Running 4-0 polypropylene and a felt strip are used to achieve the proximal anastomosis. When the procedure is finished, the proximal clamp is withdrawn and reapplied further distally on the tube graft. If possible, the distal cross-clamp is pushed down successively to facilitate visceral and renal perfusion. The intercostal arteries may be reimplanted if desired or oversewn.

Direct catheters may be inserted in the visceral and renal arteries to provide continuous perfusion if sequential cross-clamping is not possible.

If the distal aneurysm extends to the rentals, the distal anastomosis may be beveled to include the visceral, renal, and distal aorta vessels. The visceral and renal arteries are reattached to the tube graft if the distal aneurysm extends to the bifurcation. Although the left renal artery normally requires a separate anastomosis, the celiac, superior mesenteric, and right renal arteries are frequently combined as a single island. As the tube graft perfuses the intercostals and abdominal vessels, the patient is rewarmed and the partial bypass is terminated. An open distal method is used to perform the distal anastomosis at the bifurcation.

Endovascular stent grafting is a viable option for suitable descending TAAs. Femoral or iliac artery exposure is conducted under general or local anesthetic and sedation, depending on the size of the patient's femoral or iliac arteries and the amount of the stent-graft required. A sheath is implanted, and a wire is directed into the arch using fluoroscopy. When the floppy wire is in the right location, it is replaced with a soft catheter and rewired to a firmer wire for device insertion. The sheath is swapped out with the correct device sheath. Angiocatheter placement is done in the contralateral groin.

Following angiography and stent placement, the device is loaded and positioned, and deployed under fluoroscopic supervision. For stability, more than one stent may be utilized, with as much overlap as possible. To seal the endograft to the aorta, the proximal and distal landing zones are inflated. The overlaying stent-graft portions are inflated as well. Endoleaks are detected via angiography. Endoleaks may need the use of additional stents.

TAAAs can affect the arteries that supply the abdominal viscera. In this example, aortic stent grafts with fenestrations or branches orientated towards the target covered arteries have been designed for a totally endovascular repair. These grafts are often personalized to the patient's anatomy, but new research suggests that noncustomized branch grafts may function for the majority of patients.

The aortic stent graft is then carefully placed, with the fenestrations or branches precisely aligned to the abdominal viscera. The abdominal visceral arteries are then cannulated with separate guide wires in a retrograde way for cranially oriented arteries or in an antegrade fashion for caudally oriented arteries through the brachial artery. After that, a bridging-covered stent is used to form a visceral seal zone.

The arch reconstructions are also varied. They basically involve performing the distal anastomosis to the aorta beyond the left subclavian artery as an open distal procedure with or without an elephant trunk. The three head vessels may be reanastomosed individually or as an island. They may be reimplanted directly to the graft or anastomosed to a separate graft, which is then attached to the arch graft.

Complications

Early morbidity and death are associated with bleeding, brain damage (e.g., stroke), heart failure, and pulmonary failure (eg, acute respiratory distress syndrome [ARDS]). Emergency surgery, older age, dissection, congestive heart failure (CHF), longer CPB time, arch replacement, prior cardiac surgery, a necessity for simultaneous coronary revascularization, and reoperation for bleeding are all risk factors. Late mortality is mainly caused by cardiac or distal aortic diseases.

Stroke is a leading cause of morbidity and death, and it is usually caused by embolization of atherosclerotic material or a clot. TEE and epiaortic US may be useful in determining where to clamp. Patients having arch repairs are at the highest risk of both permanent and temporary brain damage. Retrograde cerebral perfusion is useful for clearing away embolic debris, but it can be harmful, resulting in increased intracranial pressure and cerebral edema. Antegrade cerebral perfusion reduces neuronal damage during a hypothermic circulatory stoppage. The risk of stroke is the same for open surgical surgery versus endovascular treatment of descending TAAs.

Myocardial infarction can develop as a result of technical difficulties with coronary ostia implantation during root replacement for ascending aortic aneurysms, necessitating reoperation. Other potentially fatal consequences include pulmonary dysfunction and renal failure.

The most catastrophic consequences of descending TAA and TAAA repairs are paraparesis and paraplegia, either immediate or delayed. Despite CSF draining, intercostal artery reimplantation, evoked potential monitoring, moderate hypothermia, and atrial femoral bypass, spinal cord damage occurs. Endovascular stent grafting has not abolished spinal cord paraplegia; the prevalence varies greatly, with a 2.7 percent overall incidence.

Endoleaks, stent fractures, stent-graft migration or thrombosis, iliac artery rupture, retrograde dissection, microembolization, and aortoesophageal fistula are among endovascular stenting complications.

Conclusion

Thoracic aortic aneurysm is a gradual deterioration of an enlargement or ballooning of a portion of the aorta within your chest (thorax). The aorta, the body's major blood vessel, begins in the heart and travels to the pelvis, where it branches toward the legs. The greater the aneurysm, the more likely it may burst, causing aortic wall damage and perhaps fatal hemorrhage.

Thoracic aortic aneurysms are commonly discovered by chance when you are checked for another cause.

A thoracic aortic aneurysm can be spotted on a routine X-ray in some cases. More information is provided by advanced imaging tests such as computed tomography (CT) scans or magnetic resonance imaging (MRI).

When the risk of rupture outweighs the risk of the procedure, surgery is recommended. TAA is an abbreviation for open thoracic aortic aneurysm repair.

A thoracic aortic dissection is another name for a separate mechanism that generates a tear in the aortic wall. This can be caused by an aneurysm or develop spontaneously into an aneurysm.

Endovascular therapy is occasionally utilized and is a less intrusive procedure. Thoracic aortic endograft repair (TEVAR) addresses aneurysms using a tiny device inserted into the aorta by a minor incision or groin puncture.