Gian M. Novaro
Diseases of the aorta account for significant cardio-vascular morbidity and mortality. The incidence of these diseases is expected to rise with the increasing age of the population. Diagnostic evaluation of aortic disorders has vastly improved over the last two decades, allowing for earlier diagnosis and therapeutic intervention. This chapter summarizes the major disease entities affecting the aorta.
ANATOMY OF THE AORTA
The aorta is the main conduit and reservoir of blood in the body. It is an elastic artery composed of three layers:
1. The intima, which includes the single-layered endothelium
2. The media, which is the thickest layer of the aortic wall. It is composed of sheets of elastic tissue and collagen, which provide the aorta its tensile strength and distensibility. Smooth muscle cells and ground substance are also present. The components of the media are organized into functional units known as lamellae.
3. The adventitia, which is composed of loose connective tissue and contains nerves and the vasa vasorum, which provides the main blood supply to the aortic wall. Elastin, collagen, and fibroblasts are also present.
Anatomically, the aorta is divided into two main subcomponents:
1. The thoracic aorta consists of the aortic root (from the aortic annulus, including the sinuses of Valsalva, up to the level just above the sinotubular junction), the ascending aorta (average diameter 3 cm), the arch, and the descending thoracic aorta (average diameter 2.5 cm—begins after the origin of the left subclavian artery).
2. The abdominal aorta, which is the part of the descending aorta after it passes through the diaphragm. The abdominal aorta (average diameter 2.0 cm) is further classified as either suprarenal or infrarenal.
PATHOLOGIC PROCESSES
Cystic Medial Degeneration
Cystic medial degeneration is an important predisposing factor to diseases of the aorta, particularly the ascending aorta. It is characterized by smooth muscle cell loss and apoptosis plus fragmentation of elastic fibers within the media of the aortic wall. Basophilic ground substance occupies these areas of structural defects, which are incorrectly termed cysts. This degenerative process also extends to the elastic components of the adventitial layer. The weakened aortic wall is prone to aneurysm formation and dissection. This degenerative process, which may be determined genetically, is seen classically in connective tissue diseases such as Marfan, Loeys-Dietz, and Ehlers–Danlos syndrome. However, various degrees of degeneration can be seen in patients without these disorders, occurring as an idiopathic variant, in familial syndromes, or as an acquired form. Hypertension and advancing age are associated with the latter. Varying degrees of cystic medial degeneration can also be seen in genetically predisposed aortas in association with congenital abnormalities including bicuspid or unicuspid aortic valve, aortic coarctation, Turner syndrome, and Noonan syndrome.
Atherosclerosis
Atherosclerosis appears to play a significant role in diseases of the aortic arch, descending thoracic and abdominal aorta. Atherosclerosis can result in weakening of the aortic wall, making it prone to aneurysm formation or dissection.
The development of aortic atherosclerosis is associated with the traditional cardiac risk factors of smoking, hypertension, hyperglycemia, and atherogenic lipoproteins. Atherosclerosis can also result in formation of complex atheromatous plaques, which are prone to embolization, resulting in cerebral and peripheral arterial events.
Inflammatory Disorders
Inflammatory disorders represent a third broad category in the etiology of aortic diseases. These can occur in isolation or in the context of systemic disorders.
Trauma
Aortic injury from trauma usually occurs as a result of deceleration injuries. It frequently occurs at the level of the left subclavian artery near the aortic isthmus or near the diaphragm, both points of attachment. If the patient survives, injury can progress to form a chronic pseudoaneurysm.
AORTIC DISSECTION
Aortic dissection comprises one of the more ominous acute aortic syndromes (also known as acute thoracic pain syndromes), which include the dissection variants of penetrating aortic ulcers, intramural hematomas, and symptomatic aneurysms. It involves cleaving of the aortic wall, resulting in the formation of an aortic false lumen, which courses along with a true lumen.
The hallmark of aortic dissection is an intimal tear that permits access of pulsatile high-pressure blood into the aortic media, separating it from the basal layers (Fig. 48.1). Typically, the so-called intimal flap is usually an intimal–medial flap.
FIGURE 48.1 TEE in a long-axis view that shows a large dissection flap in the ascending aorta extending from the level of the aortic sinuses.
The initiating event of dissection may be a tear in the intima. Alternatively, primary rupture of the vasa vasorum may result in an intramural hematoma that leads secondarily to an intimal tear as blood vents from the intramural space (Fig. 48.2). Regardless of the initiating event, the force of blood flow propagates the dissection antegrade (and less commonly retrograde), a variable extent along the vessel, cleaving the aortic wall usually along the outer one-third of the medial layer.
FIGURE 48.2 Schematic representing the initiating event of aortic dissection. Panel (A) shows a tear in the intima. Panel (B) shows primary rupture of the vasa vasorum, secondarily leading to an intimal tear as blood vents from the intramural space.
Classification
Dissections are classified by their location of origin and how far along they extend in the aorta. There are two important classification systems: the DeBakey system and the Stanford system (Table 48.1; Fig. 48.3). Dissections are also classified by their duration. Acute dissections are those of <2 weeks’ duration after symptom onset; chronic are those that have been present for more than 2 weeks.
TABLE
48.1 Classification of Aortic Dissections
FIGURE 48.3 Diagram showing the types of aortic dissection by the DeBakey classification. Shown are types I, II, and IIIa, from left to right.
Clinical Presentation
Dissections typically present between the fifth and seventh decades of life, with a male preponderance. Patients typically present with the acute onset of pain, present in up to 95% of cases. Pain is often most severe at its onset and described as a “ tearing,” “ ripping,” or “ stabbing” sensation. Often the pain is migratory, a crucial component of the history, reflecting propagation of the dissection. Involvement of the ascending aorta results in anterior chest or neck pain, with intra-/subscapular pain with involvement of the descending thoracic aorta, and lower back and left flank pain with the thoracoabdominal aorta.
Hypertension upon presentation is common, more so in distal dissection, although hypotension can be seen if complications have developed, particularly in proximal dissections. The dissection may compromise flow to the great vessels, and pulse deficits (these can be transient, as the dissection flap can oscillate) may be present. Actual blood pressure may not be appreciated if the arm utilized has compromise of the brachial vasculature (pseudohypotension).
If the dissection involves the aortic root, commissural involvement of the aortic valve can lead to aortic insufficiency. Dilatation of the root and aortic annulus, without leaflet involvement, can also lead to aortic valve insufficiency. A diastolic murmur will be evident in these cases.
Dissections can involve the ostia of the coronary arteries, resulting in acute myocardial ischemia and infarction (present in 2% to 3% of cases). The right coronary artery ostium is more commonly affected than the left main. The dissection can extend proximally into the pericardial space, resulting in pericardial effusion and tamponade, a common mechanism of syncope and hypotension in dissection. A pericardial friction rub can be a clue to the presence of hemopericardium. Rupture into the pericardial space represents the most common mode of death in patients with aortic dissection. Acute lower-extremity, renal, or mesenteric ischemia can be seen in descending aortic dissections. Focal neurologic deficits can occur with involvement of the great vessels. Compromise of spinal artery perfusion may result in paraparesis.
Although chest pain and pulse deficits are classically described, it is important to recognize that <20% of patients present with these findings. Therefore, a high clinical suspicion for dissection is paramount.
Diagnostic Testing
The chest x-ray can be normal in cases of dissection. A well-recognized finding is mediastinal widening, present in about 60% of cases. Rupture into the pleural or pericardial space manifests as pleural effusions or an enlarged cardiac silhouette (the latter may also be present, as a result of chronic aortic insufficiency). The electrocardiogram may be normal, but it often shows nonspecific ST–T-wave changes. Involvement of the coronary artery ostia may result in ST-segment elevation, representing an acute myocardial injury pattern. Transthoracic echocardiography can on occasion identify a proximal or even distal dissection flap. Even if a flap is not seen, the presence of aortic dilatation, aortic insufficiency, and/or an unexplained pericardial effusion can be important clues in the diagnostic consideration of a patient with chest pain.
More definitive diagnostic modalities include transesophageal echocardiography (TEE), computed tomography (CT), and magnetic resonance angiography (MRA). Each has relative advantages and disadvantages, but all have excellent sensitivity and specificity (Table 48.2).
TABLE
48.2 Comparison of Imaging Modalities for Aortic Dissection
TEE, transesophageal echocardiography; CT, computed tomography; MRA, magnetic resonance angiography.
Angiography is less commonly utilized for the primary diagnosis of aortic dissection. The test of choice is often dependent on expedited availability and expertise at the center where the patient is evaluated. An important caveat is that in most patients, more than one test may be required. If the clinical suspicion is high enough and the initial test is negative or equivocal, then consideration should be given to performing another confirmatory test.
Management
Anti-impulse medical therapy should be initiated as soon as the diagnosis of dissection is considered, even while waiting confirmatory diagnostic testing. In patients who are hypertensive, intravenous beta-blockade followed by sodium nitroprusside is the treatment of choice. Beta-blockade should be initiated prior to sodium nitroprusside to avoid a rise in cardiac contractility and dp/dt associated with the isolated use of vasodilators. In the absence of hypertension, beta-blockers can be used alone. For patients with ascending aortic dissections, these are temporizing agents while preparing for definitive surgical therapy. For patients with descending dissections, these agents are first-line therapy, before longer-acting oral agents are initiated. Intravenous nondihydropyridine calcium antagonists such as verapamil and diltiazem are alternatives for those who cannot tolerate beta-blockers.
Dissections that involve the ascending aorta (proximal, type A) require urgent surgical therapy, as there is a very high early mortality rate (approaching 1% to 2% per hour for the first 24 to 48 hours). Even with timely surgical intervention, the mortality rate of proximal aortic dissection approaches 25%.
An important management point arises with patients who have pericardial effusion or tamponade in association with a proximal dissection. These patients should not undergo percutaneous pericardiocentesis, unless they are in absolute extremis. The evacuation of pericardial blood by such a route has been associated with aortic rupture and increased mortality, perhaps secondary to dissection extension and/or aortic rupture as blood pressure and dp/dt increase after tamponade resolution. Pericardial access should be obtained in the operating room, with the institution of cardiopulmonary bypass.
Dissections that involve the descending aorta (distal, type B) should be initially treated medically. Data suggest that medical therapy is the preferred initial treatment, with surgery guided by a complication-specific approach. This is because acute aortic surgery is associated with a high mortality and paraplegia rate (inadequate protection of the spinal arteries). Surgery should be considered for the following indications: evidence of malperfusion syndromes (organ ischemia secondary to compromise of the branch vessels); persistent pain; aneurysm formation, particularly if saccular; and retrograde dissection to a proximal extent. Alternatively, aortic fenestration, surgical or percutaneous, can also be considered for organ or limb malperfusion in carefully selected patients.
Distal (type B) dissections in Marfan syndrome patients carry a poor prognosis and have thus led to recommendations of early aortic surgery.
Aortic Dissection in the Young
Dissections occurring in younger patients (<40 years old) typically occur in the context of connective tissue disorders such as Loeys-Dietz, Marfan, or Ehlers–Danlos syndrome. Other conditions involving younger patients and dissection include congenital bicuspid aortic valve, patients with prior aortic surgery, or women in the peripartum period. During late pregnancy, it is thought that hormonal changes and a loosening in the ground substance of connective tissue can predispose to a heightened risk of dissection.
Chronic Aortic Dissection
Chronic dissection patients (present for >2 weeks) have survived the period of increased mortality. They can often be managed medically, even in the presence of a proximal dissection. However, their aortas often dilate and are at higher risk for aneurysm formation because of the thinned aortic wall as a result of dissection.
A complication-specific approach can be used for chronic dissection patients to guide elective surgical therapy: recurrent pain; aneurysm formation, particularly if saccular; and retrograde dissection extension to a proximal extent. Serial follow-up imaging (usually with CT or MRA), initially at shorter intervals, is vital in these patients because of their weakened aortic walls.
Iatrogenic Aortic Dissection
Special mention should be afforded to iatrogenic dissections. Angiographic catheters and guidewires can disrupt the intima and result in dissections anywhere along the aorta’s course. These typically result in retrograde dissections, and the false lumens may thrombose spontaneously if dissections are limited. Catheter-related dissections are most often distal, Type B injuries and can often be managed medically unless the dissection is extensive (Fig. 48.4).
FIGURE 48.4 TEE in a long-axis view demonstrating a case of iatrogenic dissection. A bare metal stent is entrapped in the left main trunk and has caused a retrograde dissection to the aortic sinuses with antegrade propagation distally to the descending thoracic aorta (not shown).
Dissections can also occur during aortic cross clamping, cannulation, or manipulation during cardiac surgery. Such dissections are often proximal, Type A dissections, and are diagnosed and treated urgently and successfully at the time of surgery.
INTRAMURAL HEMATOMA AND PENETRATING AORTIC ULCER
Intramural hematoma and penetrating aortic ulcer are two aortic dissection variants that vary from classic dissection by the absence of a classic intimal flap. Recent advances in diagnostic imaging modalities have led to an increased awareness and better understanding of these entities.
Intramural Hematoma
Intramural hematoma consists of a noncommunicating blood collection in the aortic wall. Unlike a true dissection, there is no loss of intimal continuity, no entry tear, and thus no intimal flap. The pathophysiology may be related to rupture of the aortic vasa vasorum.
By TEE, intramural hematoma is characterized by absence of a dissection flap, a regional crescent-shaped thickening of the aortic wall usually >0.7 cm, and central displacement of intimal calcium (Fig. 48.5). At times, intramural echolucencies representing noncommunicating pockets of fresh blood can be seen. Distinguishing intramural hematoma from severe atheroma, a thrombosed false lumen, or aneurysm with mural thrombus can be difficult. Angiography is of limited diagnostic accuracy in the evaluation of hematomas, as it fails to image the aortic wall. If the clinical history is concerning, a negative TEE should not represent the final diagnostic evaluation. CT and MRA represent highly accurate imaging modalities that are frequently used as an initial or complementary study in the evaluation of hematomas.
FIGURE 48.5 TEE in both long- and short-axis views showing an intramural hematoma, characterized by no dissection flap, a crescent-shaped thickening of the aortic wall, central displacement of intimal calcium, and echolucent intramural pockets representing intramural blood.
Intramural hematomas can communicate with the adventitial space, lead to rupture, or progress to overt dissection with an intimal tear. However, they may also have a more benign course and gradually resolve with medical therapy and blood pressure control.
Penetrating Aortic Ulcer
Penetrating aortic ulcer exists when an atheromatous plaque erodes inward into the aortic media. The advanced atherosclerotic disease burden prevents the erosion from extending longitudinally along the vessel as in classic dissection. The ulcer is apparent on imaging modalities as an ulcer crater or contrast-filled outpouching. Depending on how far into the aortic wall the plaque erosion occurs, there may be formation of an intramural hematoma, saccular aneurysm, pseudoaneurysm, or even complete aortic rupture (Fig. 48.6).
FIGURE 48.6 Schematic of a penetrating aortic ulcer and the progression to the various aortic wall complications.
Clinical Presentation
Patients with these acute aortic syndromes often present with the same chest and/or back pain as do patients with classic dissection. They may be associated with a higher incidence of rupture than seen for classic dissections. Compared to intramural hematomas, patients with penetrating ulcers are usually older and tend to have more atherosclerotic burden. Isolated intramural hematomas can occur in both the ascending and descending aorta, whereas intramural hematomas associated with penetrating aortic ulcers are more commonly located in the descending aorta, where the atherosclerotic process is more common.
Management
As in aortic dissection, anti-impulse medical therapy should be initiated as soon as the diagnosis of a dissection variant is considered. Intravenous beta-blockade initially and, if needed for blood pressure control, sodium nitroprusside are the treatment agents of choice.
For the dissection variants involving the ascending aorta, prompt surgical intervention is considered the treatment of choice. However, some data suggest that select patients with intramural hematomas in the ascending aorta, particularly if small (<11 mm) and with nondilated aortas, can be managed medically. Recent data suggest that penetrating ulcer-like findings in an area of intramural hematoma can identify high-risk individuals. Symptoms of sustained or recurrent pain or findings of an increasing pleural effusion are suggestive of disease progression and favor surgical intervention. Guidelines and management strategies for this patient population are still evolving.
For the dissection variants that involve the descending aorta, especially intramural hematoma without penetrating ulcers, medical therapy is the preferred initial treatment. However, some have argued that there should be a lower threshold for surgical intervention than for classic distal dissection, particularly when clinical signs of instability are present. The presence of a severely bulging hematoma or a deeply penetrating ulcer may warrant surgical repair. The development of a saccular aneurysm or pseudoaneurysm should merit consideration for surgical repair. For those treated medically, serial imaging studies are warranted to assess for progression or increase in aortic diameter, in which case surgical repair or stent-graft placement may be considered.
AORTIC ANEURYSM
An aortic aneurysm is present when there is dilatation of the aorta, typically at least 1.5 times its normal reference dimension for an adjacent segment. This dilatation may involve the entire circumference of the aortic wall (fusiform) or a localized protrusion of one of the walls (saccular). Ectasia is characterized by dilatation <1.5 times the normal reference dimension.
Thoracic Aortic Aneurysm
The incidence of thoracic aortic aneurysm (TAA) is estimated at 5.9 cases per 100,000 patient years. Leading etiologies include congenital bicuspid aortic valve, Marfan syndrome (Fig. 48.7), idiopathic annuloaortic ectasia, familial TAA syndrome, inflammatory aortitis, acquired due to increased age and hypertension, syphilis, and trauma.
FIGURE 48.7 TEE in a long-axis view illustrating an ascending TAA, with predominant dilatation at the level of the sinuses, in a patient with Marfan syndrome.
Descending TAA may extend distally and involve the abdominal aorta creating a thoracoabdominal aneurysm. Patients are often asymptomatic at the time of presentation, and the TAA may be diagnosed by an imaging modality ordered for other clinical indications. Physical findings may likewise be absent. When signs and symptoms do manifest, they are often the result of mass effect. The enlarging aorta may compress nearby structures such as the superior vena cava, the trachea, esophagus, and recurrent laryngeal nerve. This may result in superior vena cava syndrome, stridor, dysphagia, and hoarseness, respectively.
Progressive dilatation of the aortic root can lead to aortic insufficiency, which can produce symptoms of congestive heart failure. Enlargement of the aortic sinuses can lead to narrowing of the coronary artery ostia, which can lead to myocardial ischemia and even infarction.
Blood flow can be static in large aneurysms, predisposing to thrombus formation and distal embolization, a process which can be seen in descending thoracic and thoracoabdominal aneurysms.
Noninvasive Imaging
TAA are often noted incidentally on chest x-ray as mediastinal widening or a prominent aortic knob.
Transthoracic echocardiography is the most common modality to initially diagnose and monitor dilatation of the aortic root.
CT scanning and MRA are the preferred techniques to accurately define the entire thoracic aorta and its branch vessels and precisely measure TAA.
Because the thoracic aorta may be tortuous, care must be given to not measure off-axis axial cuts, as these can
overestimate the true cross section as compared to the actual orthogonal diameter. As suggested in the guidelines, measurements of aortic diameter should be made using the internal diameter when taken by echocardiography and the external diameter when taken by CT imaging or MRA.
Medical Treatment
There are data that beta-adrenergic blockade can slow the rate of thoracic aneurysm expansion in patients with Marfan syndrome, resulting in improved survival. Although the data are extrapolated to those without Marfan syndrome, it seems reasonable to recommend such therapy while TAA patients are being followed medically. More recent studies have suggested that angiotensin II receptor blockers may slow the rate of aortic dilation in Marfan patients; prospective investigation using these agents is underway.
Recognizing that patients treated with beta-adrenergic blockade can still manifest aortic dilatation is important, as serial evaluation and imaging is required.
Marfan Syndrome, Thoracic Aortic Aneurysms, and Pregnancy
Women with Marfan syndrome have an increased risk of aortic dissection during pregnancy, particularly during the third trimester.
The risk of dissection greatly increases if the aortic root diameter is >4.0 cm or if there is evidence of rapid aortic root dilatation during pregnancy.
If elective surgical repair is not performed prepartum, betaadrenergic blockade should be used during pregnancy, particularly during the third trimester and peripartum.
Close echocardiographic follow-up and cesarean delivery should be considered if the aortic root size exceeds 4.0 cm or rapid aortic dilatation is evident.
Indications for Surgical Treatment
Dissection and rupture are the feared complications of TAA, and prevention of these conditions is the purpose for elective surgical aortic repair. Size is a clear risk factor and principal harbinger for dissection and rupture. In one series, the annual rate of dissection or rupture was 2% for TAAs < 5 cm, 3% for TAAs between 5.0 and 5.9 cm, and 7% for TAAs > 6 cm. Therefore, prophylactic surgical intervention should be considered before a TAA reaches a size that predisposes to aortic instability.
Although the optimal timing of prophylactic surgery remains uncertain, recommendations for surgical repair are >5.0 to 5.5 cm for an ascending TAA and >6.0 to 6.5 cm for a descending TAA. Patients with Marfan syndrome, Loeys-Dietz syndrome, bicuspid aortic valve, or family history of premature aortic instability should be considered for earlier repair (perhaps at 4.5 to 5.0 cm and 5.5 to 6.0 cm for ascending and descending TAAs, respectively). For patients undergoing aortic valve surgery, concomitant ascending aortic repair should be considered for a TAA > 4.5 cm.
Rapid enlargement of the aorta (>0.5 to 0.75 cm/year) or symptom development has also been advocated as indications for surgery. The decision for operative repair must of course take into account the patient’s medical comorbidities, and a risk/benefit ratio must be individualized for each patient. Patients who are otherwise low medical risk may be considered for intervention at smaller aortic sizes.
Abdominal Aortic Aneurysm
The incidence of abdominal aortic aneurysm (AAA) is estimated at 36.5 per 100,000 person years.
AAA represents the most common form of arterial aneurysm.
The majority of AAAs are infrarenal in location (75%).
Atherosclerosis is the dominant risk factor in the development of an AAA. Additional risk factors associated with AAAs are male gender (AAA is four to five times more common in men), increasing age, smoking, and hypertension.
There is a clear familial predisposition to AAA, with relatives of affected patients having up to 25% increased risk for the development of an AAA.
Asymptomatic AAA is often diagnosed on physical examination by abdominal palpation. The most common symptom is pain, and is usually steady. The pain may be localized abdominal pain, or may radiate to the back, flank, or groin. Sudden onset of severe abdominal and back pain suggests rupture, representing a surgical emergency. Up to only a third of patients with rupture will present with the classic triad of pain, pulsatile abdominal mass, and hypotension. Atheroemboli may be the first manifestation of an AAA.
Noninvasive Imaging
Ultrasonography, CT scanning, aortography, and MRA have all been used in the initial diagnosis, sizing, and monitoring of AAA. Ultrasonography represents the most practical method of screening and serial monitoring, while CT scanning and MRA remain superior in accurately detailing the morphology and extent of the AAA.
At initial diagnosis, the rate of dilatation cannot be determined and thus the next serial study should be performed in 6 months. In general, for AAAs <4.0 cm, yearly surveillance imaging is recommended; for AAAs 4.0 to 5.0 cm, imaging every 6 to 12 months; and for AAAs >5.0 cm, imaging every 3 to 6 months.
Baseline AAA size is the best predictor of rate of dilatation. Larger aneurysms expand at higher rates than smaller ones.
Medical Treatment
Beta-adrenergic blockade with careful control of hypertension appears to have impact on delaying the rate of AAA expansion.
Smoking should be discontinued, as rupture risk is greater among active smokers.
Indications for Surgical Treatment
Mortality from an AAA is primarily related to rupture. As with thoracic aneurysms, increasing size is the harbinger of rupture risk. Aneurysms <4 cm in size have a 0% to 2% risk of rupture over 2 years, whereas those that are >5 cm in size have a 22% risk of rupture over 2 years, with those >6 cm showing the sharpest rise in risk. As such, an aortic diameter of 5.0 to 5.5 cm is recommended as an indication for prophylactic surgery in asymptomatic AAA patients. Although AAAs are less common in women, when they are present they are at greater risk of rupture and at smaller aortic diameters than in men. Thus, it is recommended that women undergo prophylactic AAA repair at 4.5 to 5.0 cm.
Aneurysms that expand rapidly (>0.5 to 1.0 cm/year) are also associated with an increased risk of rupture, and are thus considered for elective surgical repair.
Inflammatory AAA is present in up to 10% of cases. There appears to be a familial tendency for these, and they often occur in the context of smoking. Patients will present with constitutional symptoms and have an elevated sedimentation rate in addition to the classic symptoms of pain. CT scanning or MRA can identify the inflammatory component. Treatment is aortic surgery.
Endovascular Stent-Graft Repair
A relatively recent therapeutic option for AAA repair is the percutaneous placement of an endovascular stent graft. The endovascular stent graft is placed within the aneurysmal segment of the aorta, bridging the normal segments and excluding the aneurysm. However, just over half of all AAA possess anatomy favorable for stentgraft placement.
Data are still forthcoming on the long-term success of endovascular stent grafting. In randomized trials thus far, it appears that endovascular repair incurs a lower operative mortality compared to open AAA surgery, but no benefit in total mortality in the long term has been demonstrated. Nonetheless, the procedure remains an attractive alternative to conventional surgical repair, but is usually limited to patients with significant comorbid medical conditions who are at high surgical risk.
ATHEROMATOUS AORTIC DISEASE
Atherosclerotic plaques in the aorta can give rise to cerebral and peripheral embolic events (Fig. 48.8).
TEE, in particular, has been a valuable imaging modality in assessing the presence, composition, and extent of these plaques.
Plaques >4 mm in thickness, or those with mobile or ulcerated components, appear to be strongly associated with subsequent embolic events.
Treatment strategies for patients with such plaques have not been evaluated in sufficient numbers in a prospective randomized fashion. However, there is evidence that lipidlowering therapy with a statin is a reasonable treatment option, and anticoagulation with warfarin or antiplatelet therapy may benefit some patients.
FIGURE 48.8 TEE in a short-axis view identifying a protruding thick (>4-mm) atheroma in the descending thoracic aorta.
Earlier reports of a potential association between warfarin and the cholesterol embolization syndrome have produced some reluctance to use such anticoagulant therapy in these patients, and further study is thus needed. The potential role of aortic replacement or removal of atheroma remains to be defined.
It has become increasingly common for cardiac surgeons to assess the aorta before the institution of cardiopulmonary bypass. The presence of significant plaque may alter the cross-clamp site or may even lead to endarterectomy or aortic replacement at the time of surgery.
Cholesterol Embolization Syndrome
The cholesterol embolization syndrome can be seen in patients undergoing diagnostic angiography, but can also occur spontaneously. There is a reported association between warfarin anticoagulation and these events.
The syndrome represents a showering of emboli, typically from the descending aorta. Patients most often present with the skin findings of livedo reticularis and blue toes, in the presence of palpable pulses. Renal insufficiency may occur, and may not be reversible. Transient eosinophilia is often present, and treatment is supportive.
If the atheroma arose from an AAA, then surgical intervention can help prevent future events.
INFLAMMATORY AORTITIS
Giant Cell Arteritis
Giant cell arteritis is an inflammatory disease that affects the temporal arteries, producing local tenderness and headaches. Patients affected are typically over the age of 55 years, and women are affected twice as frequently as men.
The most devastating consequence is blindness. Although temporal arteritis is the hallmark of this disorder, there may be involvement of the thoracic aorta and the great vessels. This can lead to branch vessel occlusion, aneurysm formation, or even dissection.
Corticosteroid treatment is the mainstay of therapy. With the development of advanced aortic involvement, surgical treatment may be required.
Takayasu Arteritis
Takayasu arteritis is an inflammatory disorder of the aorta that typically affects women under age 40 years. Its prevalence is greater in Asian and African populations than in those of European or North American descent.
A subacute inflammatory illness phase is manifested by constitutional symptoms. Later, there is occlusive inflammation of the aorta and branch vessels, with segmental narrowing apparent. Symptoms of arterial insufficiency will be present, depending on the vessels involved. Acquired coarctation can occur, leading to hypertension, as can aneurysm formation.
Treatment is corticosteroids. For occlusive lesions that do not respond to steroids, surgical bypass may be warranted.
Syphilitic Aortitis
Syphilitic aortitis represents a manifestation of tertiary syphilis, which may occur 10 to 30 years after the initial infection. This inflammation results in a weakening of the vessel wall and can lead to aneurysm formation, usually saccular.
Syphilitic aortitis most commonly affects the ascending aorta, and hence can result in aortic insufficiency. The arch may also be affected. Involvement of the descending aorta occurs less often.
Other Inflammatory Aortitis
Aortitis can also be seen in other systemic inflammatory diseases such as reactive arthritis, ankylosing spondylitis, rheumatoid arthritis, Wegener granulomatosis, and enteropathic arthropathies.
A common genetic underpinning of these conditions is the HLA-B27 genotype, which should be considered in cases of lone aortic regurgitation, ascending aortic dilatation, and conduction system disease.
Treatment involves addressing the underlying disorder, with surgery as needed for aneurysmal or aortic valvular complications.
Mycotic Aneurysms
Bacteremia (from endocarditis, trauma, intravenous drug abuse) can result in infection within the weakened aneurysmal arterial wall. Persistent fevers after treatment of the inciting event should raise concern for an infected aneurysm.
Mycotic aneurysms more commonly involve the abdominal aorta. Atheromatous plaques can also become infected (bacterial aortitis), serving as a nidus for infection requiring prolonged antibiotic therapy.
ESSENTIAL FACTS
Aortic Dissection
The hallmark of aortic dissection is an intimal flap.
Increasing aortic size and aneurysm formation is a harbinger of aortic dissection.
Proximal (ascending) aortic dissections are treated with surgery.
In cases of cardiac tamponade, evacuation of hematoma should be performed in the operating room under cardiopulmonary bypass support.
Distal (descending) aortic dissections are treated medically, with surgery guided by a complication-specific approach.
Congenital bicuspid aortic valve, Marfan syndrome, Loeys-Dietz syndrome, prior aortic surgery, and the peripartum period represent risk factors for aortic dissection in the young.
A negative surface echocardiogram, absence of pulse deficits, or a normal mediastinum on chest x-ray does not exclude the presence of aortic dissection.
Anti-impulse medical therapy with intravenous beta-blockade followed by sodium nitroprusside is the mainstay of medical treatment.
Intramural Hematoma and Penetrating Aortic Ulcer
Penetrating aortic ulcers arise more commonly in areas of atheromatous disease such as the thoracoabdominal aorta.
Penetrating aortic ulcers that involve the ascending aorta are treated surgically.
Intramural hematomas that involve the ascending aorta are generally treated surgically, although recent publications have raised some controversy and suggest that medical management may be an option in some populations.
Neither of the aortic dissection variants involves an intimal dissection flap.
Aortic Aneurysm
Indications for surgery:
1. Symptoms
2. Inflammatory or infectious
3. Rapidly expanding 0.5 cm/year, even if asymptomatic
4. >5.0 to 5.5 cm diameter for ascending thoracic
5. >6.0 to 6.5 cm diameter for descending thoracic
6. >5.0 to 5.5 cm diameter for abdominal
Earlier surgical intervention (>4.5 to 5.0 cm) is recommended in Marfan syndrome, Loeys-Dietz syndrome, and bicuspid aortic valve patients.
Beta-adrenergic blockade may slow the progression of aortic dilatation.
Atheromatous Aortic Disease
Mobile, ulcerated, or thick atheromatous plaques (>4 mm) identified by TEE are associated with embolic events.
SUGGESTED READINGS
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QUESTIONS AND ANSWERS
Questions
1. A 70-year-old man presents with the sudden onset of tearing chest pain. On presentation, he has a heart rate of 130 beats/min (bpm) with a systolic blood pressure of 80 mm Hg. A bedside transesophageal echocardiography (TEE) demonstrates the presence of a proximal aortic dissection. A pericardial effusion with partial diastolic collapse of the right ventricle is also present. Significant respiratory variation is noted across mitral and tricuspid Doppler inflows. Appropriate treatment is:
a. Immediate percutaneous pericardiocentesis to relieve the tamponade, followed by surgery to replace the ascending aorta
b. To proceed immediately to the operating room
c. Emergency angiography to define coronary anatomy, followed by surgery
d. Intra-aortic balloon pump to stabilize the hemodynamics, followed by surgery
2. A 60-year-old hypertensive man presents with tearing back pain. MRI confirms the presence of a descending thoracic dissection originating beyond the left subclavian artery. Appropriate initial treatment includes:
a. Immediate surgery to replace the descending aorta
b. Intravenous nitroprusside followed by immediate surgery
d. Intravenous nitroprusside alone; surgery for persistent pain, or for involvement of renal or mesenteric arteries
e. Intravenous beta-blockade and nitroprusside; surgery for persistent pain, or for involvement of renal or mesenteric arteries
3. A 56-year-old man presents for screening physical examination. He is asymptomatic. Vital signs reveal a heart rate of 80 bpm with a blood pressure of 160/90 mm Hg. His exam is remarkable only for a pulsatile mass in the abdomen. Ultrasound reveals the presence of a 3.9-cm abdominal aortic aneurysm (AAA). Appropriate management includes
a. Immediate referral for surgery:
b. Start a beta-blocker and repeat ultrasound in 6 months
c. Refer for stenting of the AAA
4. A 76-year-old woman with hypertension presents with severe chest pain. Her blood pressure is 200/110 mm Hg. Electrocardiogram reveals nonspecific ST–T changes. Chest x-ray is unremarkable. CT scan demonstrates the presence of a penetrating ulcer in the ascending aorta. No dissection flap is seen. Appropriate management includes:
a. Start intravenous beta-blocker and nitroprusside while plans are being made for surgery
b. Intravenous beta-blocker and nitroprusside, with surgery only if complications develop
c. Intravenous nitroprusside alone, with surgery only if complications develop
5. A 23-year-old patient with Marfan syndrome presents for routine evaluation. He is asymptomatic. Workup includes a CT scan that reveals the presence of a 4.2-cm ascending aorta. Appropriate management includes:
a. Refer for surgery
b. Start on beta-blocker and reimage in 6 to 12 months
c. Reimage in 6 to 12 months
6. The same patient returns for follow-up in 12 months. The aorta now measures 5.0 cm in size. He remains asymptomatic. Appropriate management includes:
a. Refer for surgery
b. Continue beta-blocker, reassess in 6 months
c. Reassess in 3 months
7. Which of the following disorders is associated with involvement of the aorta?
a. Marfan syndrome
b. Giant cell arteritis
c. Ankylosing spondylitis
d. Syphilis
e. All of these disorders can have aortic involvement.
8. Which of the following statements regarding transesophageal findings of aortic atheroma is not true?
a. Plaques >2 mm in the ascending aorta are associated with increased risk of stroke.
b. Plaques >4 mm in the ascending aorta are associated with increased risk of stroke.
c. Mobile components are associated with an increased risk of stroke.
d. Limited data suggest that these patients may benefit from anticoagulation therapy with warfarin.
Answers
1. Answer B: This patient should be taken to the operating room immediately. Percutaneous drainage has been associated with increased mortality in this setting. Given the hemodynamic status, there is no time to proceed with angiography first. Balloon pumps are contraindicated with aortic dissection.
2. Answer D: Initial therapy for descending aortic dissection is medical, with surgery reserved for special circumstances. The goal of treatment is reduction in blood pressure, as well as reduction in dp/dt. Both beta-blockade, started immediately, and nitroprusside should be used.
3. Answer B: Asymptomatic aneurysms of 3.9 cm have a very small risk of rupture. The patient should be followed by serial examination to assess size and rate of expansion. Control of his hypertension with beta-blockers may delay the growth of the aneurysm. There are no data as of yet that endovascular stent grafts will lower the threshold for intervention for these aneurysms.
4. Answer A: Penetrating aortic ulcers involving the ascending aorta are generally treated like dissections, with prompt referral for surgery.
5. Answer B: The patient’s aorta has not yet reached a size that would be considered for surgery in the absence of symptoms. There are data that beta-blockers can slow the rate of expansion of these aneurysms and improve survival.
6. Answer A: There has been rapid growth in the size of the aneurysm (0.8 cm in 1 year). The patient should be referred for surgery.
7. Answer E: All of the disorders listed can include involvement of the aorta.
8. Answer A: Plaques >4 mm have been associated with cerebral embolic events. The role of anticoagulation needs to be more clearly defined, but there are some data to support its use.