Thoracic Aortic Aneurysm

Background

Aneurysmal degeneration can occur anywhere in the human aorta. By definition, an aneurysm is a localized or diffuse dilation of an artery with a diameter at least 50% greater than the normal size of the artery.

A blood vessel has 3 layers: the intima (inner layer made of endothelial cells), media (contains muscular elastic fibers), and adventitia (outer connective tissue). Aneurysms are either true or false. The wall of a true aneurysm involves all 3 layers, and the aneurysm is contained inside the endothelium. The wall of a false or pseudoaneurysm only involves the outer layer and is contained by the adventitia. An aortic dissection is formed by an intimal tear and is contained by the media; hence, it has a true lumen and a false lumen.

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, and 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.

NextHistory of the Procedure

The development of treatment modalities for thoracic aneurysms followed successful treatment of abdominal aortic aneurysms. Estes' 1950 report revealed that the 3-y survival rate for patients with untreated abdominal aortic aneurysms was only 50%, with two thirds of deaths resulting from aneurysmal rupture.[1] Since then, increased attempts were made to devise methods of durable repair.

Most of these initial successful repairs involved the use of preserved aortic allografts, thus triggering the establishment of numerous aortic allograft banks. Simultaneously, Gross and colleagues successfully used allografts to treat complex thoracic aortic coarctations, including those with aneurysmal involvement.[2]

In 1951, Lam and Aram reported the resection of a descending thoracic aneurysm with allograft replacement.[3] Ascending aortic replacement required the development of cardiopulmonary bypass and was first performed in 1956 by Cooley and DeBakey.[4] They successfully replaced the ascending aorta with an aortic allograft. Successful replacement of the aortic arch, with its inherent risk of cerebral ischemia, was understandably more challenging and was not reported until 1957 by DeBakey et al.[5]

Although the use of aortic allografts as aortic replacement was widely accepted in the early 1950s, the search for synthetic substitutes was well underway. Dacron was introduced by DeBakey. By 1955, Deterling and Bhonslay believed that Dacron was the best material for aortic substitution.[6] Numerous types of intricately woven hemostatic grafts have since been developed and are now used much more extensively than their allograft counterparts. Such Dacron grafts are used to replace ascending, arch, thoracic, and thoracoabdominal aortic segments.

However, some patients required replacement of the aortic root, as well. Subsequently, combined operations that replaced the ascending aneurysm in conjunction with replacement of the aortic valve and reimplantation of the coronary arteries were performed by Bentall and De Bono in 1968, using a mechanical valve with a Dacron conduit.[7] Ross, in 1962, and Barratt-Boyes, in 1964, successfully implanted the aortic homograft in the orthotopic position.[8, 9] In 1985, Sievers reported the use of stentless porcine aortic roots.[10]

More recently, less invasive therapy for descending thoracic aortic aneurysm have been developed. Dake et al reported the first endovascular thoracic aortic repair in 1994.[11] In March 2005, the US Food and Drug Administration (FDA) approved the first thoracic aortic stent graft, the GORE TAG graft (W.L. Gore and Associates; Flagstaff, AZ).[12] Since 2005, 2 other devices have gained FDA approval: the Talent Thoracic endograft (Medtronic; Santa Rosa, CA) and the Cook TX2 endograft (Cook; Bloomington, IN). Several successive next-generation reiterations of all of these devices have also gained approval.

Given the relative acceptance of the indications for thoracic endografts as an alternative to open procedures in the treatment of uncomplicated diseases of the descending thoracic aorta, experienced users of the devices now use them "off-label" in increasingly more complex indications, including use via "hybrid-procedures" in the ascending aorta and aortic arch. However, little long-term data are available at this time to support use in this fashion.

PreviousNextProblem

Aneurysms are usually defined as a localized dilation of an arterial segment greater that 50% its normal diameter. Most aortic aneurysms occur in the infrarenal segment (95%). The average size for an infrarenal aorta is 2 cm; therefore, abdominal aortic aneurysms are usually defined by diameters greater than 3 cm.

The normal size for the thoracic and thoracoabdominal aorta is larger than that of the infrarenal aorta, and aneurysmal degeneration in these areas is defined accordingly. The average diameter of the mid-descending thoracic aorta is 26-28 mm, compared with 20-23 mm at the level of the celiac axis.

PreviousNextEpidemiologyFrequency

Although findings from autopsy series vary widely, the prevalence of aortic aneurysms probably exceeds 3-4% in individuals older than 65 years.

Death from aneurysmal rupture is one of the 15 leading causes of death in most series. The estimated incidence of thoracic aortic aneurysms is 6 cases per 100,000 person-years. In addition, the overall prevalence of aortic aneurysms has increased significantly in the last 30 years. This is partly due to an increase in diagnosis based on the widespread use of imaging techniques. However, the prevalence of fatal and nonfatal rupture has also increased, suggesting a true increase in prevalence. Population-based studies suggest an incidence of acute aortic dissection of 3.5 per 100,000 persons; an incidence of thoracic aortic rupture of 3.5 per 100,000 persons; and an incidence of abdominal aortic rupture of 9 per 100,000 persons. An aging population probably plays a significant role.

PreviousNextEtiology

Aneurysmal degeneration occurs more commonly in the aging population. Aging results in changes in collagen and elastin, which lead to weakening of the aortic wall and aneurysmal dilation. According to the law of Laplace, luminal dilation results in increased wall tension and the vicious cycle of progressive dilation and greater wall stress. Pathologic sequelae of the aging aorta include elastic fiber fragmentation and cystic medial necrosis. Arteriosclerotic (degenerative) disease is the most common cause of thoracic aneurysms.

A previous aortic dissection with a persistent false channel may produce aneurysmal dilation; such aneurysms are the second most common type. False aneurysms are more common in the descending aorta and arise from the extravasation of blood into a tenuous pocket contained by the aortic adventitia. Because of increasing wall stress, false aneurysms tend to enlarge over time.

Authorities strongly agree that genetics play a role in the formation of aortic aneurysms. Of first-degree relatives of patients with aortic aneurysms, 15% have an aneurysm. This appears especially true in first-degree relatives of female patients with aortic aneurysms. Thus, inherited disorders of connective tissue appear to contribute to the formation of aortic aneurysms.

Marfan syndrome is a potentially lethal connective-tissue disease characterized by skeletal, heart valve, and ocular abnormalities. Individuals with this disease are at risk for aneurysmal degeneration, especially in the thoracic aorta. Marfan syndrome is an autosomal dominant genetic condition that results in abnormal fibrillin, a structural protein found in the human aorta. Patients with Marfan syndrome may develop annuloaortic ectasia of the sinuses of Valsalva, commonly associated with aortic valvular insufficiency and aneurysmal dilation of the ascending aorta.

Type IV Ehlers-Danlos syndrome results in a deficiency in the production of type III collagen, and individuals with this disease may develop aneurysms in any portion of the aorta. Imbalances in the synthesis and degradation of structural proteins of the aorta have also been discovered, which may be inherited or spontaneous mutations.

Atherosclerosis may play a role. Whether atherosclerosis contributes to the formation of an aneurysm or whether they occur concomitantly is not established. Other causes of aortic aneurysms are infection (ie, bacterial [mycotic or syphilitic]), arteritis (ie, giant cell, Takayasu, Kawasaki, Behçet), and trauma. Aortitis due to granulomatous disease is rare, but it can lead to the formation of aortic and, on occasion, pulmonary artery aneurysms. Aortitis caused by syphilis may cause destruction of the aortic media followed by aneurysmal dilation.

Traumatic dissection is a result of shearing from deceleration injury due to high speed motor vehicle accidents (MVA) or a fall from heights. The dissection occurs at a point of fixation, usually at the aortic isthmus (ie, at the ligamentum arteriosum, distal to the origin of the left subclavian artery), the ascending aorta, the aortic root, and the diaphragmatic hiatus.

The true etiology of aortic aneurysms is probably multifactorial, and the condition occurs in individuals with multiple risk factors. Risk factors include smoking, chronic obstructive pulmonary disease (COPD), hypertension, atherosclerosis, male gender, older age, high BMI, bicuspid or unicuspid aortic valves, genetic disorders, and family history. Aortic aneurysms are more common in men than in women and are more common in persons with COPD than in those without lung disease.

PreviousNextPathophysiology

The occurrence and expansion of an aneurysm in a given segment of the arterial tree probably involves local hemodynamic factors and factors intrinsic to the arterial segment itself.

The medial layer of the aorta is responsible for much of its tensile strength and elasticity. Multiple structural proteins comprise the normal medial layer of the human aorta. Of these, collagen and elastin are probably the most important. The elastin content of the ascending aorta is high and diminishes progressively in the descending thoracic and abdominal aorta. The infrarenal aorta has a relative paucity of elastin fibers in relation to collagen and compared with the thoracic aorta, possibly accounting for the increased frequency of aneurysms in this area. In addition, the activity and amount of specific enzymes is increased, which leads to the degradation of these structural proteins. Elastic fiber fragmentation and loss with degeneration of the media result in weakening of the aortic wall, loss of elasticity, and consequent dilation.

Hemodynamic factors probably play a role in the formation of aortic aneurysms. The human aorta is a relatively low-resistance circuit for circulating blood. The lower extremities have higher arterial resistance, and the repeated trauma of a reflected arterial wave on the distal aorta may injure a weakened aortic wall and contribute to aneurysmal degeneration. Systemic hypertension compounds the injury, accelerates the expansion of known aneurysms, and may contribute to their formation.

Hemodynamically, the coupling of aneurysmal dilation and increased wall stress is defined by the law of Laplace. Specifically, the law of Laplace states that the (arterial) wall tension is proportional to the pressure times the radius of the arterial conduit (T = P x R). As diameter increases, wall tension increases, which contributes to increasing diameter. As tension increases, risk of rupture increases. Increased pressure (systemic hypertension) and increased aneurysm size aggravate wall tension and therefore increase the risk of rupture.

Aneurysm formation is probably the result of multiple factors affecting that arterial segment and its local environment.

PreviousNextPresentation

Most patients with aortic aneurysms are asymptomatic at the time of discovery. Thoracic aneurysms are usually found incidentally after chest radiographs or other imaging studies. Abdominal aortic aneurysms may be discovered incidentally during imaging studies or a routine physical examination as a pulsatile abdominal mass.

The most common complication of abdominal aortic aneurysms is rupture with life-threatening hemorrhage manifesting as pain and hypotension. The triad of abdominal pain, hypotension, and a pulsatile abdominal mass is diagnostic of a ruptured abdominal aortic aneurysm, and emergent operation is warranted without delay for imaging studies.

Patients with a variant of abdominal aortic aneurysm may present with fever and a painful aneurysm with or without an obstructive uropathy. These patients may have an inflammatory aneurysm that can be treated with surgical repair.

Other presentations of abdominal aortic aneurysm include lower extremity ischemia, duodenal obstruction, ureteral obstruction, erosion into adjacent vertebral bodies, aortoenteric fistula (ie, GI bleed), or aortocaval fistula (caused by spontaneous rupture of aneurysm into the adjacent inferior vena cava [IVC]). Patients with aortocaval fistula present with abdominal pain, venous hypertension (ie, leg edema), hematuria, and high output cardiac failure.

Patients with thoracic aneurysms are often asymptomatic. Most patients are hypertensive but remain relatively asymptomatic until the aneurysm expands. Their most common presenting symptom is pain. Pain may be acute, implying impending rupture or dissection, or chronic, from compression or distension. The location of pain may indicate the area of aortic involvement, but this is not always the case. Ascending aortic aneurysms tend to cause anterior chest pain, while arch aneurysms more likely cause pain radiating to the neck. Descending thoracic aneurysms more likely cause back pain localized between the scapulae. When located at the level of the diaphragmatic hiatus, the pain occurs in the mid back and epigastric region.

Large ascending aortic aneurysms may cause superior vena cava obstruction manifesting as distended neck veins. Ascending aortic aneurysms also may develop aortic insufficiency, with widened pulse pressure or a diastolic murmur, and heart failure. Arch aneurysms may cause hoarseness, which results from stretching of the recurrent laryngeal nerves. Descending thoracic aneurysms and thoracoabdominal aneurysms may compress the trachea or bronchus and cause dyspnea, stridor, wheezing, or cough. Compression of the esophagus results in dysphagia. Erosion into surrounding structures may result in hemoptysis, hematemesis, or gastrointestinal bleeding. Erosion into the spine may cause back pain or instability. Spinal cord compression or thrombosis of spinal arteries may result in neurologic symptoms of paraparesis or paraplegia. Descending thoracic aneurysms may thrombose or embolize clot and atheromatous debris distally to visceral, renal, or lower extremities.

Patients who present with ecchymoses and petechiae may be particularly challenging because these signs probably indicate disseminated intravascular coagulation (DIC). The risk of significant perioperative bleeding is extremely high, and large amounts of blood and blood products must be available for resuscitative transfusion.

The most common complications of thoracic aortic aneurysms are acute rupture or dissection. Some patients present with tender or painful nonruptured aneurysms. Although debate continues, these patients are thought to be at increased risk for rupture and should undergo surgical repair on an emergent basis.

PreviousNextIndications

Indications for surgery of thoracic aortic aneurysms are based on size or growth rate and symptoms. Because the risk of rupture is proportional to the diameter of the aneurysm, aneurysmal size is the criterion for elective surgical repair. Elefteriades published the natural history of thoracic aortic aneurysms and recommends elective repair of ascending aneurysms at 5.5 cm and descending aneurysms at 6.5 cm for patients without any familial disorders such as Marfan syndrome.[13, 14] These recommendations are based on the finding that the incidence of complications (rupture and dissection) exponentially increased when the size of the ascending aorta reached 6.0 cm (31% risk of complications) or when the size of the descending aorta reached 7.0 cm (43% risk).[15, 14] Patients with Marfan syndrome or familial aneurysms should undergo earlier repair, when the ascending aorta grows to 5.0 cm or the descending aorta grows to 6.0 cm.

In addition, relative aortic aneurysm size in relation to body surface area may be more important than absolute aortic size in predicting complications.[16] Using the aortic size index (ASI) of aortic diameter (in cm) divided by body surface area (m2), patients are stratified into 3 groups: ASI 2 are at low risk for rupture (4%/y), ASI 2.75-4.25 cm/m2 are at moderate risk (8%/y), and ASI >4.25cm/m2 are at high risk (20-25%/y).[16, 17]

Rapid expansion is also a surgical indication. Growth rates average 0.07 cm/y in the ascending aorta and 0.19 cm/y in the descending aorta.[14] A growth rate of 1 cm/y or faster is an indication for elective surgical repair.

Symptomatic patients should undergo aneurysm resection regardless of size. Acutely symptomatic patients require emergent operation. Emergent operation is indicated in the setting of acute rupture. Rupture of the ascending aorta may occur into the pericardium, resulting in acute tamponade. Rupture of the descending thoracic aorta may cause a left hemothorax.

Patients with acute aortic dissection of the ascending aorta require emergent operation. They may present with rupture, tamponade, acute aortic insufficiency, myocardial infarction, or end-organ ischemia. Acute dissection of the descending aorta does not require surgical intervention, unless complicated by rupture, malperfusion (eg, visceral, renal, neurologic, leg ischemia), progressive dissection, persistent recurrent pain, or failure of medical management.

Patients who undergo surgery for symptomatic aortic insufficiency or stenosis with an associated enlarged aneurysmal aorta should have concomitant aortic replacement if the aorta reaches 5 cm in diameter. Concomitant aortic replacement should be consider for patients with bicuspid aortic valves with an aorta >4.5 cm in diameter.

As one may imagine, the quality of data and level of evidence supporting these recommendations widely vary. Given this discrepancy and important subject matter, in 2010, a joint task force spearheaded by the American College of Cardiology Foundation and the American Heart Association, and composed of members of many professional societies specializing in treatment of diseases of the thoracic aorta, produced an Executive Summary detailing guidelines for diagnosis and management of this disease, which will be annually updated.[18]

Summary of indicationsAortic size Ascending aortic diameter ≥5.5 cm or twice the diameter of the normal contiguous aortaDescending aortic diameter ≥6.5 cmSubtract 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/ySymptomatic aneurysmTraumatic aortic ruptureAcute type B aortic dissection with associated rupture, leak, distal ischemiaPseudoaneurysmLarge saccular aneurysmMycotic aneurysmAortic coarctationBronchial compression by aneurysmAortobronchial or aortoesophageal fistulaPreviousNextRelevant Anatomy

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.

PreviousNextContraindications

Aneurysm surgery has no strict contraindications. The relative contraindications are individualized, based on the patient's ability to undergo extensive surgery (ie, the risk-to-benefit ratio). Patients at higher risk for morbidity and mortality include elderly persons and individuals with end-stage renal disease, respiratory insufficiency, cirrhosis, or other comorbid conditions. For descending thoracic aneurysms, endovascular stent grafting is less invasive and is an ideal alternative (with appropriate anatomic considerations) to open repair for patients at high risk for complications of open repair. Stent grafts are also a reasonable alternative (with the appropriate anatomy) to open repair in patients who are not at high risk for complications. Patients must understand that life-long follow-up is required and that long-term durability is unknown.

PreviousProceed to Workup , Thoracic Aortic Aneurysm

Read More

Thoracic Endovascular Aortic Repair

Overview

In 1994, Dake et al first reported the use of thoracic "stent-grafts" for the treatment of descending thoracic aortic aneurysms in patients who were believed to be at excessive risk for conventional open surgery.[1] These authors showed that thoracic stent grafts, otherwise known as Thoracic EndoVascular Aortic Repair (TEVAR), could be performed from a technical standpoint with relatively low morbidity; however, they noted that long-term follow-up would be required. The initial stent grafts were actually constructed by the implanting physicians themselves and were later restricted to devices under investigational study.

In 2005, The US Food and Drug Administration (FDA) approved the first commercially available thoracic stent graft, the W. L. Gore TAG endograft system (Flagstaff, Ariz), and, in 2008, the US FDA approved the Cook Zenith TX2 (Bloomington, Ind)[2] and the Medtronic Talent (Santa Rosa, Calif) thoracic endograft systems; all 3 were approved for use in the treatment of thoracic aortic aneurysms.

The randomized clinical trial that led to the approval of the TAG device demonstrated that, in patients with appropriate anatomy, TEVAR could be performed with lower operative mortality versus open surgery (2.1% vs 11.7%) and with less spinal cord ischemia (3% vs 14%), respiratory insufficiency (4% vs 20%), and renal failure (1% vs 13 %).[3] However, more vascular access–related complications occurred in the TEVAR group. Importantly, a small percentage of patients who were undergoing TEVAR did not have their aneurysms entirely excluded from the aortic circulation at 1- and 2-year follow-up. Once more, these authors maintained that all patients undergoing TEVAR required close long-term follow-up.

Dake et al and investigators in Europe later showed TEVAR could be performed from a technical standpoint in patients with descending thoracic aortic dissections (patients with tears in the wall of their aortas).[4] Nonetheless, ongoing studies are still trying to identify which patients with thoracic aortic dissection can benefit from TEVAR. Patients with complicated dissections, including cases of malperfusion (where a blood supply is impeded by flaps of aortic tissue caused by the dissection), appear to benefit from TEVAR to seal the site of dissection and reappose aortic wall layers.[4]

Note that historically open surgical approaches in patients with malperfusion have had a high mortality rate.[5] Accordingly, in the United States, a clinical trial is examining TEVAR for patients with complicated dissection (STABLE trial, Cook Inc, Bloomington, Ind). It would seem logical that TEVAR could also be used in patients with uncomplicated dissections. To address this question, a prospective randomized clinical trial has recently been completed in Europe, the INSTEAD trial (INvestigation of STEnt grafts in patients with type B aortic dissection), though the results have not yet been published.[6]

Since the 2005 FDA approval of the TAG device for thoracic aneurysms, the use of endovascular stent grafts for thoracic aortic disease has increased dramatically. In recent years, surgeons have devised novel techniques to facilitate the use of TEVAR in higher-risk patients. Branch vessels that would have been occluded by the stent grafts can often be bypassed, and the diameter of larger areas of aorta can often be reduced to accommodate stent grafts.[5, 7, 8] Indeed in the authors' own experience at the University of Florida, a several-fold increase has been seen in TEVAR over open cases in the past few years, as shown in the graph below.

University of Florida/Shands Hospital in Gainesville, Florida, experience with open repair and Thoracic EndoVascular Aortic Repair (TEVAR) repair of thoracic aortic disease with a shift toward TEVAR. NextIndications

Descending thoracic aortic aneurysm

The official FDA-approved "on-label" indication for the commercially available stent grafts currently available in the United States (W. L. Gore TAG, Cook TX2, Medtronic Talent Thoracic) are for patients with descending thoracic aortic aneurysms that are at least 2 times greater than the adjacent aorta. Furthermore, sufficient aorta of normal dimensions must be present on either side of the aneurysm (so-called landing zones) for the stent graft to adhere to the aortic walls. Of note, several patients were specifically excluded from the randomized trial that led to the TAG approval, including patients with acute or chronic dissections, patients with ruptured or infected (mycotic) aneurysm, and patients with connective tissue disorders such as Marfan disease.[3] Nonetheless, at the discretion of individual surgeons, TEVAR has been performed "off label" in other patient groups, especially at times of emergency. As an example, in cases of aortic rupture secondary to massive blunt traumatic injury (eg, motor vehicle accidents), TEVAR has been used as a less-invasive method to perform aortic repair in patients with multiple, extensive injuries.[9]

Focal penetrating ulcer: Patients with focal penetrating ulcers in their thoracic aorta are another group in which TEVAR may prove beneficial because these patients have defined, limited areas of their thoracic aorta where a loss in the integrity of the endothelium leads to potentially life-threatening rupture. Coverage of the ulcer with a stent graft can be performed with minimal morbidity. However, patients with penetrating ulcers often have extensive peripheral vascular disease, which may limit the use of TEVAR in these patients.[6, 10]

Complicated descending thoracic aortic dissection: Some evidence indicates that TEVAR may be the optimal treatment of patients with complicated descending thoracic aortic dissections compared with open surgery.[4, 5] In the United States, the Zenith TX-D endograft system (Cook, Bloomington, Ind) is currently under investigation for complicated dissection.

PreviousNextContraindications

Patients undergoing TEVAR must have suitable anatomy in order to deploy the endografts. Specifically, patients who have undergone TEVAR must have appropriate landing zones, typically 2 cm of suitable aortic diameter that can accommodate an endograft on either side of the thoracic aortic pathology.

Patients who will have branch vessels occluded by the stent graft (including the celiac and subclavian or carotid arteries) may not be candidates; however, these branch vessels can often be bypassed to create landing zones in so-called hybrid techniques.[11]

Patients with connective tissue disorders in whom a high likelihood exists of further tissue degeneration (eg, Marfan disease) were specifically excluded from the trials that led to the FDA approval of the devices available in the United States (TAG, TX2, Talent).

PreviousNextAnesthesia

Both general anesthesia and continuous spinal anesthesia have been used by these authors. Large-bore intravenous access for volume infusion is mandatory, along with continuous arterial pressure monitoring.

More recently, the authors have used spinal drains routinely in the patients undergoing Thoracic EndoVascular Aortic Repair (TEVAR); they are placed to drain at 10 mm Hg (15 cm H2 O) pressure for 24 hours and are then removed at 48 hours. Other surgical groups reserve spinal drains for patients deemed to be at highest risk for spinal ischemia (patients undergoing extensive coverage of the thoracic aorta and patients with a history of prior abdominal aortic aneurysm repair). Patients require vigilant monitoring in the early postoperative period for the development of neurologic deficits. Delayed neurologic deficits can still be reversed with elevation of systemic arterial pressure and drainage of spinal fluid.[12]

PreviousNextEquipment

The operative suite should have a fixed imaging system, as shown below, to ensure optimal results from TEVAR.

Cannulation of left common femoral artery with a 4F catheter in an endovascular suite with fixed overhead imaging system.

Hybrid operating rooms provide optimal imaging technology for endovascular procedures and also are sufficiently large to accommodate open surgery for cases in which it is required. Ceiling mounted monitors showing the patient’s vital signs and preoperative CT scans are recommended.

The operating table should allow free access to the imaging C-arm below and be long enough to accommodate the long guidewires that are used via the femoral artery access points.

PreviousNextPositioning

The patient remains in the supine position with the arms in "surrender" position to allow lateral angiography.

When brachial artery access is required, the arms are placed at 90-degree angles and prepared and draped in the operating field.

Bilateral femoral artery access points are prepared along with the abdomen to the level of the nipples.

The entire field is covered with iodine-impregnated adhesive wrap as shown below.

Cannulation of left common femoral artery with a 4F catheter in an endovascular suite with fixed overhead imaging system. PreviousNextTechnique

The key to a successful procedure begins with meticulous preoperative planning to determine the precise size of the endograft, its length, and its relation to critical branch vessels, as in the image below. Access sites are chosen based on CT scan reconstruction of the anatomy. The femoral artery must be of sufficient diameter to pass the endograft; otherwise, a conduit (10-mm Dacron tube graft) needs to be attached to the larger iliac artery via a retroperitoneal incision.[13]

Three-dimensional CT reconstruction of thoracic aorta with aneurysm in the arch aorta.

Close cooperation with the anesthesia team is required. Place spinal drainage catheters prospectively in patients, especially in those at highest risk for spinal injury (patients undergoing complete thoracic aortic coverage or with a previous abdominal aneurysm repair).

Position and sterilely prepare the patient as outlined above (see Positioning).

Obtain percutaneous femoral arterial access on the side that will not be used for delivering the endograft, as shown in the image below. Insert a 5F introducer sheath, and pass a pigtail catheter over a 0.035-in guidewire. Confirm catheter position with a brief injection of contrast.

Cannulation of left common femoral artery with a 4F catheter in an endovascular suite with fixed overhead imaging system. Confirmation angiogram showing appropriate cannulation of the left common femoral artery.

After meticulous removal of all air bubbles to avoid air emboli, connect the pigtailed catheter to a mechanical injection system like the one shown below.

Automated contrast injection system attached to the 5F pigtail catheter inserted via the left common femoral artery.

Perform an arch arteriogram, typically at 30 degrees left anterior obliquity to delineate the arch vessels, as depicted in the image below.

Baseline aortogram showing arch anatomy.

Obtain open exposure of the contralateral common femoral artery that will deliver the stent graft, as shown below, and pass a vessel loop for proximal control. Of note, if the common femoral artery is too small to pass the large delivery catheters, then sew a Dacron graft "conduit" to the side of the iliac artery via a retroperitoneal incision and use it to pass the stent graft into position.

Retroperitoneal incision to access the right common iliac artery. Dacron conduit attached to the right common iliac artery brought out below through a separate incision.

Directly cannulate this conduit using an 18-ga needle, and pass a 0.035-in guidewire into the ascending aorta under fluoroscopic guidance. Then exchange this flexible wire for a "superstiff" wire (eg, Lunderquist) that will be used to provide a rail to deliver the stent graft into position.

On the back table, prior to use, meticulously prepare the endograft delivery system (shown below) according to manufacturer instructions to remove air bubbles and to ensure proper delivery of the endograft.

Thoracic endograft being prepared on the back table prior to deployment.

Use the radiographic markers on the endograft to position it exactly where it is to be deployed, and obtain confirmation angiographic images as necessary, as shown below. Sufficient landing zone (2 cm) is required to seat the endograft; occasionally, this requires deploying the endograft across the left subclavian artery. Deploy the thoracic endograft.

Predeployment angiogram showing the endograft in the arch aorta.

Perform balloon dilation of the endograft as appropriate to ensure apposition of the endograft to the wall of the thoracic aorta in order to minimize the potential for endoleaks around the endograft.

Obtain completion angiographic images, as depicted in the images below. If necessary, the left subclavian artery can be bypassed and/or occluded with coil embolization to prevent endoleaks.

Angiogram performed following endograft deployment. Coil embolization of left subclavian artery to prevent endoleak.

Carefully remove delivery catheters and sheaths with the contralateral guidewire remaining in position. The "delivery" femoral or iliac artery is routinely repaired.

Remove the guidewire from the "imaging femoral artery" and seal the femoral artery access point.

Confirm distal pulses prior to leaving the operating suite.

Transfer patients to the cardiac intensive care unit for monitoring of neurologic and hemodynamic function.

PreviousNextPearls

Multidisciplinary collaboration between skilled endovascular therapists and cardiovascular surgeons is critical to safe and successful development of an endovascular aortic treatment program. Although the incidence of intraoperative surgical conversion remains low, late complications and remedial secondary procedures may require complex thoracic aortic reconstructions. Despite the seeming simplicity of these procedures, unforeseen anatomic and device-related complexities can transform these cases into some of the most complicated endovascular procedures that require advanced endovascular skills in order to bring the procedure to a safe and successful conclusion.

Maintaining proper guidewire access throughout the procedure is critical to the safety of the procedure. The guidewire is analogous to "proximal" control of a blood vessel during open vascular surgery. As long as guidewires remain in position, life-saving occlusion balloons can be passed proximal to iliac or femoral artery sites that have been known to tear during sheath retrieval.

Catheter and guidewire "hygiene" is important to avoid air embolism and thromboembolism of clot and fibrin debris that tend to collect around the guidewires. The guidewires should be wiped, and the catheters should be flushed frequently with heparinized saline during the procedure.

Implanting appropriate-sized endografts is critical; if too large a device is deployed, it can collapse or infold and cause aortic occlusion.

PreviousNextComplications

As with any surgical therapy, complications are associated with TEVAR. The most severe complications in the W.L. Gore TAG pivotal clinical trial included stroke (4%), paraplegia/paraparesis (3%), peripheral vascular injury (14%), and death (2%).[3] Stroke can occur because the guidewires that are placed in the aortic arch to direct the endografts into position can dislodge a thrombus or atheromata, which can embolize via the cerebral vasculature to the brain. For that matter, emboli can also lead to limb and mesenteric ischemia. Spinal ischemia occurs when the intercostal blood vessels supplying the spinal cord are covered by the stent grafts. Paraplegia occasionally can be reversed by elevating the blood pressure and draining spinal fluid.[12]

Because of the large size of the stent grafts, they can damage the femoral and iliac arteries as they are passed into position. The most worrisome concern is complete avulsion of the arteries, which can be controlled with balloon occlusion; this is the reason guidewires must be left in position until the very end of the case. Concern for these rare but major vascular catastrophes is one reason TEVAR should be performed only by surgeons experienced with open repair techniques.

Endoleaks occur when the aneurysm is not completely isolated from the bloodstream; this was found in 6% and 9% of patients at 1 and 2 years, respectively, in the TAG trial.[3] Accordingly, emphasizing that patients undergoing TEVAR require lifelong follow-up with annual CT scans is important. The classification system for endoleaks is as follows:

Type I endoleaks occur when the seal on either end of the stent graft is incomplete.Type II endoleaks occur because of back bleeding from smaller vessels (typically intercostals) that are covered with the endograft.Type III endoleaks occur when leak occurs between overlapping stent grafts.Type IV endoleaks were seen with earlier stent grafts when porosity of the graft material led to seepage of blood components through the graft walls, resulting in tension within the excluded aneurysmal segment (rarely seen today). Previous, Thoracic Endovascular Aortic Repair

Read More

Thoracic Aneurysm

Background

Thoracic aortic aneurysm (TAA) is a life-threatening condition that causes significant short- and long-term mortality due to rupture and dissection. Aneurysm is defined as dilatation of the aorta of greater than 150% of its normal diameter for a given segment. For the thoracic aorta, a diameter greater than 3.5 cm is generally considered dilated, whereas greater than 4.5 cm would be considered aneurysmal.

Aneurysms may affect one or more segments of the thoracic aorta, including the ascending aorta, the arch, and the descending thoracic aorta. As many as 25% of patients with TAA also have an abdominal aortic aneurysm. Thoracic aortic aneurysm most commonly results from degeneration of the media of the aortic wall as well as from local hemodynamic forces.

Descending thoracic aortic aneurysm with mural thrombus at the level of the left atrium. NextPathophysiology

Degenerative changes in the wall of the aorta lead to cystic medial necrosis. This causes damage to collagen and elastin, loss of smooth muscle cells, and increased amounts of basophilic ground substance in the medial (elastic) layer of the aorta. The ascending thoracic aorta is generally most affected by cystic medial necrosis, whereas a descending thoracic aneurysm is primarily a consequence of atherosclerosis.

In Marfan syndrome, abnormalities of the gene encoding for the synthesis of fibrillin have been implicated in the predisposition to form aneurysms. Mutations in the gene responsible for this structural lipoprotein found in the aortic wall have been found in patients who do not have Marfan syndrome but have aneurysms.

As many as 75% of patients with a bicuspid aortic valve have shown evidence for cystic medial necrosis, which may be because of inadequate fibrillin production. Other inherited forms of medial degeneration have been associated with defects in the genes for fibrillin and are associated with higher rates of thoracic aortic aneurysm (TAA).

Weakening of the aortic wall is compounded by increased shear stress, especially in the ascending aorta. This segment of the aorta is most exposed to the pressure of each cardiac systole (dP/dt) as well as the dynamic heart motion transmitted from each cardiac cycle. As local wall weakness causes dilatation of the aorta, wall tension increases (described by the Laplace law (T=PR), where wall tension equals the radius of a cylinder multiplied by the pressure within it). Small tears in the intimal (innermost) layer of the aorta can permit blood to penetrate the medial layer, leading to aortic dissection.

PreviousNextEpidemiologyFrequencyUnited States

The incidence of aortic aneurysm is 5.9 cases per 100,000 person-years.[1]

Mortality/Morbidity

The cumulative risk of rupturing a thoracic aortic aneurysm (TAA) is related to aneurysm diameter. In a recent series of 133 patients with TAA, risk of rupture at 5 years was 0% for diameter less than 4 cm, 16% for diameter 4-5.9 cm, and 31% for aneurysms greater than 6 cm in diameter.[2]

Race

Thoracic aortic aneurysm is most common among whites.

Sex

Men are affected 2-4 times more frequently than women.

Age

The mean patient age at diagnosis is 60-65 years.

PreviousProceed to Clinical Presentation , Thoracic Aneurysm

Read More