Introduction
- Arturo A. Evangelista, MD
Aortic diseases are a major cause of cardiovascular morbidity and mortality. Aortic aneurysm, aortic dissection, intramural hematoma, penetrating aortic ulcer, and blunt chest or iatrogenic aortic trauma contribute to the whole spectrum of aortic diseases. Although the atherosclerotic process, mainly systemic arterial hypertension, plays a pivotal role in several of these entities, the relationships between aortic diseases and genetic disorders is becoming more evident.
In healthy adults, ascending aortic diameters do not usually exceed 40 mm. The diameter is influenced by several factors, including age, gender, body size (height, weight, body surface area), and blood pressure. The aorta expansion rate is around 0.9 mm in men and 0.7 mm in women for each decade of life. Although normal aortic dimensions should be normalized to body size and age, upper normal values of 21 mm/m 2 and 16 mm/m 2 for ascending and descending aorta, respectively, could be applied in the general clinical practice.
Imaging techniques in aorta assessment
In the last decade, remarkable advances have been made in noninvasive imaging of aortic diseases. Multiple modalities, including computed tomography (CT), magnetic resonance imaging (MRI), echocardiography, and aortography, are well suited for imaging the thoracic aorta ( Table 155.1 ).
| Advantages of Modality | TTE | TEE | CTA | MRA | Angio |
|---|---|---|---|---|---|
| Readily available | +++ | ++ | +++ | + | + |
| Quickly performed | +++ | ++ | ++ | + | + |
| Performed at bedside | +++ | +++ | – | – | – |
| Noninvasive | +++ | + | +++ | +++ | – |
| No iodinated contrast | +++ | +++ | – | +++ | – |
| No ionizing radiation | +++ | +++ | – | +++ | – |
| Overall aorta segments assessment | + * | ++ † | +++ | +++ | +++ |
| Left ventricular function | +++ | +++ | – | +++ | +++ |
| Presence of aortic regurgitation | +++ | +++ | – | ++ | +++ |
| Presence of pericardial effusion | +++ | +++ | ++ | ++ | + |
| Branch vessel involvement | + | + | +++ | ++ | +++ |
| Periaortic hematoma | – | + | +++ | +++ | – |
* Very positive in aortic root, and positive in arch and abdominal aorta.
† Very positive in aortic root and descending thoracic aorta, and positive in arch.
Transthoracic Echocardiography
Although transthoracic echocardiography (TTE) is not the technique of choice for overall assessment of the aorta, it is useful for the diagnosis and follow-up of some aortic segments and should routinely be included as part of the standard echocardiographic examination. , The aortic root and proximal ascending aorta are best imaged in the left parasternal view. In some patients, the right parasternal long-axis view can provide supplementary information. The suprasternal view depicts the aortic arch and the three major supraaortic vessels (innominate, left carotid, and left subclavian arteries), with variable lengths of the ascending and descending aorta. From this window, aortic coarctation can be detected with continuous wave Doppler; a persistent ductus arteriosus may also be identified with color Doppler. The entire thoracic descending aorta is not well visualized by TTE. A short-axis view of the descending aorta can be imaged posterior to the left atrium in the parasternal long-axis view and in the four-chamber view. In contrast, the abdominal descending aorta is relatively easily visualized to the left of the inferior vena cava in sagittal subcostal views. The lower abdominal aorta, below the renal arteries, can be visualized to rule out abdominal aortic aneurysms.
Transesophageal Echocardiography
Proximity of the esophagus to the thoracic aorta permits high-resolution images from higher frequency transesophageal echocardiography (TEE) transducers. , However, TEE is semiinvasive, and it requires intravenous sedation and a more operator experience than TTE. The most important TEE views of the ascending aorta, aortic root, and aortic valve are the high long-axis (at 120 to 150 degrees) and short-axis (at 30 to 60 degrees) views. A short segment of the distal ascending aorta is in a blind spot behind the right bronchus. The descending aorta is easily visualized in short-axis (0 degrees) and long-axis (90 degrees) views from the celiac trunk to the left subclavian artery. Further withdrawal of the probe shows the aortic arch. However, the subclavian artery is the only supraaortic artery usually visualized. TEE is accurate in the diagnosis of acute aortic syndrome and also adds important information on mechanisms and severity of aortic regurgitation or the entry tear location and size of the aortic dissection. Intraoperative TEE is essential for planning surgical treatment and guiding thoracic endovascular therapy. However, the accuracy of TEE depends largely on operator skill for image acquisition and interpretation. Real-time three-dimensional transesophageal echocardiography (3D TEE) appears to offer some advantages over two-dimensional TEE in revealing some aortic dissection findings.
Computed Tomography
CT, a well-established and widely used technique for the diagnosis of aortic diseases, has several advantages. It is widely available and can be used to rapidly obtain a complete 3D dataset with a wide field of view of the entire aorta Electrocardiographically (ECG)-gated acquisition protocols permit the generation of motion-free images of the aortic root and ascending aorta. Unenhanced CT followed by contrast-enhanced angiography is the recommended protocol, particularly when intramural hematoma is suspected. CT aortography (CTA) remains one of the most frequently used imaging techniques for the diagnosis and follow-up of aortic conditions in both acute and chronic presentations.
Important features of aortic disease that are crucial for diagnosis and treatment can be visualized by CT. These include the location of the diseased segment; maximum diameter of dilatation; and the presence of atheroma, thrombus, intramural hematoma, penetrating ulcers, and calcifications. In select cases, CT can be used to detect the presence of coronary artery disease. In aortic dissection, CT can define the presence and extent of a dissection flap, detect areas of compromised perfusion, and may aid the planning of surgical or endovascular repair procedures.
Magnetic Resonance Imaging
MRI is a noninvasive imaging technique that permits the most complete study of aortic disease. It offers morphologic and functional information. This imaging modality can be used to define the location and extent of aneurysms, and aortic wall ulceration and dissections; it can also demonstrate areas of wall thickening related to aortitis or intramural hematoma. Conventional ECG-gated spin echo imaging and cine gradient echo imaging have earned MRI the reputation of being the ideal tool for evaluating the aorta. Contrast-enhanced 3D MR angiography permits rapid acquisition and multiplanar imaging with minimal dephasing artifacts. Phase-contrast imaging is another technique that enables flow in the great vessels to be evaluated with accurate quantification of peak velocity and forward and regurgitant flow. MR contrast-enhanced angiography can provide a 3D dataset of the aorta and branch vessels, allowing complex anatomy and postoperative changes to be depicted through postprocessing techniques such as maximum intensity projection and multiplanar reformatting. ,
Multimodality imaging in aortic diseases
Selecting the most appropriate imaging modality for aortic disease assessment should be based on the patient´s clinical presentation, aortic disease suspected, segment of the aorta to be analyzed, and specific diagnostic questions to be answered. TTE permits adequate assessment of several aortic segments, particularly the aortic root and proximal ascending aorta. However, the technique is less consistent in imaging the distal ascending aorta, aortic arch, and descending thoracic aorta. CTA and MRA are the preferred techniques for assessing these segments. Aortography is rarely used for routine imaging of thoracic aortic disease, because it is invasive, visualizes only the aortic lumen, and does not permit accurate measurements. Neither is TEE preferred for routine aortic imaging, because it is semiinvasive and relatively unpleasant for the patient. It also does not permit full visualization of the aorta and vessels or easy identification of landmarks when consecutive exams are compared. In the follow-up of aortic aneurysms, it is better to use the same imaging modality for greater accuracy in identifying changes based on comparative data obtained by the same technique. CT is better than the other imaging techniques for the measurement of segments distal to the sinotubular junction; however, it is reasonable to change imaging modalities to spare the patient cumulative radiation exposure over many years of follow-up.
Echocardiography, CT, and MRI are all excellent imaging techniques for assessing the thoracic aorta. Test selection should be based on consideration of the patient´s presentation, the diagnostic information sought, and local institutional factors such as expertise and availability.
Aortic Atherosclerosis and Embolic Events
- Itzhak Kronzon, MD
- Paul A. Tunick, MD
Nearly 150 years ago, Panum suggested that atherosclerotic material within the aorta can embolize to peripheral arteries. In a 1945 paper based on an autopsy, Flory showed that arterial occlusion was the result of aortic atherosclerotic plaque. However, modern imaging technologies, which include contrast angiography, computed tomography, magnetic resonance imaging, and transthoracic and transesophageal echocardiography, are required to evaluate aortic atherosclerosis in vivo. At present, two- and three-dimensional (3D) transesophageal echocardiography (TEE) provides accurate, high-resolution images of the thoracic aortic wall. This technique has also established the correlation among severe aortic plaque, stroke, and peripheral aortogenic embolism. Box 156.1 shows various names used in the medical literature to define this aortic pathology. For the sake of simplicity, we will use the term aortic plaque .
Aortic plaque
Complex aortic plaque
Eroded atheromatous plaque
Arteriosclerotic plaque
Aortic atheroma
Atheromatous aorta
Protruding atheroma
Aortic atherosclerosis
Atherosclerotic atheromatosis
Atherosclerotic debris
Transesophageal echocardiography and aortic plaque
Almost the entire thoracic aorta can be visualized during transesophageal examination. Multiplane views permit the visualization of each aortic segment except for a short segment at the junction of the aortic arch and the ascending aorta, which is masked by the air column in the trachea. Normally the aortic intima is smooth and thin ( Fig. 156.1 , A ). There is no evidence of irregularity, protrusion, calcification, or ulceration. Aortic plaque is considered mild when intimal thickness is 3 mm or less (see Fig. 156.1 , B ). Severe plaque is determined by intimal thickness of equal or more than 4 mm (see Fig. 156.1 , C ). If the plaque is unstable, there may be rupture and thrombus formation (seen as a mobile mass, see Fig. 156.1 , D , and Videos 156.1, 156.2, and 156.3). Plaques can also show calcification ( Fig. 156.1 , E ) or ulcerations (see Fig. 156.1 , F ). Three-dimensional echocardiography may provide detailed topographic images of aortic plaque, including exact location, shape and thickness (see Fig. 156.1 , G , and Video 156.4).
Plaques with thickness of 4 mm or more and/or those that contain ulceration or clot are defined as complex plaques . Many investigators have shown that complex plaques are associated with stroke and embolic events. Noncomplex plaques (i.e., < 4 mm with no evidence of ulceration or clot) are significantly less dangerous. The amount of aortic plaque (also known as atherosclerotic burden) increases from the ascending aorta distally. It is also obvious that aortic plaques are only one manifestation of atherosclerosis and therefore are associated with a higher prevalence of coronary artery disease, carotid artery disease, renal artery stenosis, abdominal aortic aneurysms, and all the atherosclerotic risk factors.
Other imaging modalities
Transthoracic echocardiography occasionally demonstrate ascending aortic plaques. The aortic arch can be evaluated for plaques using the suprasternal window. The descending aorta may be visualized from the apical window. The quality of these images is frequently suboptimal. Computed tomography (CT) with contrast and magnetic resonance imaging (MRI) have been used to evaluate aortic plaques when TEE was not available or possible. Both technologies can demonstrate the entire aorta, including the proximal arch (which may not be seen on TEE), the abdominal aorta, and the aortic branches. CT can assess aortic wall calcification ( Fig. 156.1 , H ), whereas MRI can provide information about the composition of the plaque (e.g., fibrous vs. fatty) ( Fig. 156.1 , I ).
Clot embolization versus cholesterol embolization
Aortic atherosclerosis is associated with two different embolic syndromes. The first is clot embolization. It is estimated that 99% of all embolization cases associated with aortic plaque are embolization of clot that was superimposed on the plaque. The embolus occludes large to mid-sized arteries and causes stroke due to significant brain infarct and infarct in other organs such as the spleen, kidney, or limb.
The second embolic syndrome, cholesterol crystal embolization, is much less common. It is estimated that only 1% of all aortic plaque–related embolic events are associated with cholesterol embolization. In this syndrome, spontaneous or iatrogenic rupture of a plaque is responsible for the embolization of its content, which includes showers of cholesterol crystals. Such embolization may lead to bilateral blue toe syndrome, renal failure, and diffuse cerebral dysfunction.
High-risk plaque
The risk of embolization is directly related to plaque thickness. The odds ratio for embolization of plaque less than 4 mm in thickness was found in one study to be 4, whereas the odds ratio for plaques with a thickness of 4 mm or more was 13.8. Naturally, the distribution of the emboli is directly related to the plaque site within the thoracic aorta, and thus strokes are likely to occur in patients with plaques in the ascending aorta and the aortic arch and not in patients with isolated descending aortic plaques. The incidence of embolic stroke in patients with aortic arch complex plaques was found by three different studies to be 12% in the first year. Plaque morphology may contribute to the embolization risk. Noncalcified plaques have the highest stroke risk. Also, when a higher proportion of plaque is occupied by lipid (which appears hypoechoic by echocardiography) or when a plaque is thrombosed, embolic risk is higher as well.
Aortic plaque and embolic events in heart surgery and invasive intravascular procedures
Cardiac catheterization carries a low but definite risk for embolic stroke (less than 1:1,000). Other embolic vascular complications (lower extremity, gut, spleen, kidney, etc.) are also known. During percutaneous transcatheter coronary angioplasty (PTCA), the rate of stroke is 0.2%. Most of these strokes occur in patients who have aortic plaque. Patients at a higher risk for stroke during cardiac catheterization or intervention are those with previously known severe ascending aorta and aortic arch plaque or those who have a previous history of embolic stroke. The right brachial artery approach in those patients may decrease the risk of embolic stroke by avoiding negotiation of the more distal arch (and also avoid other embolic events related to plaque in the abdominal and thoracic aorta). However, to date, there are no data showing that this approach can indeed prevent stroke.
Stroke is not uncommon in patients who undergo cardiac surgery. The risk of stroke in those patients may reach 7%. Of patients who undergo coronary artery bypass grafting, 25% have complex aortic arch plaque, and it has been demonstrated that cannulation of the arch in those patients may be the culprit for this devastating outcome. The risk of embolic complication and death in a patient undergoing open-heart surgery is sixfold higher in patients with complex aortic arch plaque. It appears that off-pump coronary artery bypass done with full sternotomy or minimally invasive surgery (mini-thoracotomy), which prevents any manipulation of the aorta (no aortic cannulation or cross-clamping), is associated with a lower incidence of intraoperative stroke.
Management options
The optimal treatment of aortic plaque is not known. However, statins appear to be of value in long-term prevention of recurrent embolic events in those patients. No prospective, randomized study has yet established the value of anticoagulants and antiplatelet agents. Several small, retrospective studies suggest that anticoagulation with warfarin was superior to that with aspirin in decreasing morbidity and mortality in patients with complex plaque. However, multicenter studies in progress may address this issue in the near future. Avoiding the aorta during coronary bypass decreases the rate of complications and the number of strokes.
Aortic Aneurysm
- Arturo A. Evangelista, MD
Aortic dilation is defined by a size measurement of the aorta that exceeds normal range for a given age and body size, and an aneurysm by an increase of more than 50% above the normal diameter range. From a practical point of view, an aortic aneurysm is diagnosed when diameters exceed 50 mm in ascending and 40 mm in descending aorta. The estimated incidence of thoracic aortic aneurysm is 5.6 to 10.4 cases per 100,000 patient-years. Sixty percent involve the aortic root and/or ascending aorta, 40% involve the descending aorta, 10% involve the arch, and 10% involve the thoracic abdominal aorta, with some involving more than one segment. Abdominal aortic aneurysms are much more common than thoracic aortic aneurysms. Screening of subgroups at risk (i.e., males ≥ 65 years, smokers, and those with a family history) shows the prevalence to be on average 5.5%. The etiology, natural history, and treatment of thoracic aneurysms differ for each segment.
Etiology
Formation and expansion of thoracic aneurysms is multifactorial and involves interplay of genetic predisposition, cellular imbalances, and hemodynamic factors. Etiologies of thoracic aneurysms are listed in Table 157.1 . In older patients, the most common etiology is a degenerative process associated with hypertension, hyperlipidemia, or smoking. However, a genetic cause should be suspected in young patients or in those without cardiovascular risk factors.
| D egenerative | Associated with age, hypertension With atherosclerotic risk factors, frequently involves descending aorta With aortic valve disease, involves ascending aorta |
| Genetically Triggered Diseases | |
| Marfan syndrome | Aortic root dilatation in > 75% of cases Annuloaortic ectasia Descending aorta dilation is infrequent |
| Loeys-Dietz syndrome | Aggressive vasculopathy Arterial tortuosities Higher risk of dissection than Marfan syndrome |
| Bicuspid aortic valve | Ascending aorta dilation in > 50% of cases Valsalva sinus involvement in > 20% of cases Faster growth rate than tricuspid valves |
| Turner syndrome, Ehlers-Danlos syndrome | More common in ascending aorta |
| Familial nonsyndromic aneurysms | New mutations: ACTA-II, etc. May involve various aortic segments |
| A ortitis | |
| Infectious | Syphilis, Salmonella , Mycobacterium , others |
| Inflammatory | Giant cell and Takayasu arteritis, others |
| T rauma | Typical location at the aortic isthmus |
Morphology
Aneurysms of the aorta can be classified in two morphologic types: fusiform and saccular. Morphologic shapes of the aortic root and ascending aorta are (1) annuloaortic ectasia, characterized by a “pear-shaped” aortic root with dilatation localized to the annulus and sinuses of Valsalva; (2) dilation involving the annulus, sinuses of Valsalva, and the tubular part of the ascending aorta; and (3) dilation beginning at the sinotubular junction, but sparing the aortic annulus and sinuses of Valsalva ( Fig. 157.1 , Video 157.1).
Annuloaortic ectasia is common in patients with Marfan syndrome ; however, this entity may also be present in patients with no other conditions. Other cases of ascending aorta aneurysm are associated with an underlying bicuspid aortic valve, with dilation localized most frequently at the level of the tubular portion of the ascending aorta in 44%, but another 20% at the sinus level. Proximal atherosclerotic aneurysms are typically fusiform and may extend into the arch. This etiology is the predominant cause of aneurysm of the descending thoracic and abdominal aorta.
Diagnosis
Thoracic aortic enlargement is often diagnosed on imaging studies performed for unrelated indications. An abnormal contour of the superior mediastinum on chest x-ray may raise the suspicion. Transthoracic echocardiography (TTE) is very useful for the diagnosis and follow-up of aortic root aneurysms, which is crucial for patients with annuloaortic ectasia or Marfan syndrome. Because the predominant area of dilation is in the proximal aorta, TTE often suffices for screening. This is the technique of choice in the serial measurement of maximum aortic root diameters, evaluation of aortic regurgitation, and timing of elective surgery. Aortic root dimensions are assessed at end-diastole in the parasternal long-axis view at four levels: annulus, sinuses of Valsalva, supraaortic ridge, and proximal ascending aorta. Measurements should be made perpendicular to the long axis of the aorta with the use of the leading edge method. Although some experts , favor inner-edge-to-inner-edge to match the method used by magnetic resonance imaging (MRI) and computed tomography (CT) scanning, the 3 to 4 mm of underestimation of diameter size using this method may constitute a risk because surgical recommendations were established with the leading-edge technique. Both TTE and transesophageal echocardiography (TEE) have limitations for the adequate measurement of distal ascending aorta size. In some cases, the right parasternal window permits better visualization of this aortic segment. However, contrast-enhanced CT and MRI may visualize the entire aorta and its major branches and accurately detect the size of thoracic aortic aneurysms. The multiplanar capacity of multidetector CT, together with its submillimeter spatial resolution, offers the best information for thoracic aortic aneurysms. This technique permits easy identification of the maximum aortic diameter plane, which must be doubly orthogonal to the longitudinal plane of the aortic segment. Using the parasagittal plane, the oblique maximum intensity projection (MIP) plane is reproducible and comparable in follow-up studies. ,
The information provided by MR angiography in aortic aneurysm assessment is similar to that offered by CT. It is recommended to conduct a functional study through the aortic valve using cine-MR sequences to rule out associated valvular disease that may be related to aortic dilation. Recently, MRI has been established as an accurate noninvasive tool for the assessment of aortic distensibility and pulse wave velocity. These methods have been used to assess aortic elasticity in patients with Marfan syndrome, bicuspid aortic valve, or aortic aneurysms. , Recently, some authors have shown that ascending aorta flow patterns as assessed by four-dimensional (4D)-MRI are a major contributor to aortic dilatation in bicuspid aortic valve disease.
Natural history and complications
The size of the aorta is the principal predictor of aortic rupture or dissection, the risk of which is almost 7% per year for a diameter greater than 60 mm. The odds ratio for rupture increase 27-fold compared with lower values. Davies and colleagues showed aortic size index to be a significant predictor of aortic rupture with a moderate risk when the aortic size index is greater than 2.75 cm/m . The growth rate was significantly greater for aneurysms of the descending aorta, 3 mm/yr, than for ascending aorta, 1 mm/yr. The rate of aneurysmal expansion is not constant, however, as growth rates accelerate as the aneurysm enlarges. Risk factors for increased growth of thoracic aortic aneurysms include older age, female sex, chronic obstructive pulmonary disease, hypertension, and a positive family history. A growth rate greater than 5 mm/yr is associated with an increased risk of rupture.
Serial imaging
Careful follow-up of maximum aortic diameter is paramount for correct therapeutic management. Aneurysms affecting the aortic root can be correctly followed by TTE if the echocardiographic window is adequate. The excellent reproducibility of measurements at this level and information from other parameters such as aortic regurgitation severity and ventricular function facilitate appropriate follow-up.
Serial follow-up evaluation of proximal ascending aorta diameters should be made by echocardiography every 6 to 12 months depending on aortic dimensions, rate of expansion, and aortic valve dysfunction. However, it is advisable to perform a CT/MRI study when aortic root or ascending aortic diameter is 45 mm by TTE to confirm measurement agreement, rule out aortic section asymmetry, and obtain a basal measurement to compare when enlargement nears surgical indication. CT or MRI are the techniques of choice in the follow-up of aortic aneurysms located in the upper part of the ascending aorta or more distal segments. Use of the same modality at the same institution should be considered so that similar images of matching anatomic segments can be compared side by side. In patients with nephropathy or in young patients, MRI is a reasonable alternative to CT. For correct monitoring, it is necessary to measure aortic diameter in the same location and the same spatial plane. In asymptomatic patients with aortic aneurysm, imaging controls should be performed at 6-month intervals until aortic size remains stable, in which case the controls may be annual. However, when aortic size is near to indicating surgery, it is advisable to perform the test every 6 months.
Surgical indication
The clinical significance of maximum aortic diameter in the indication of prophylactic surgical treatment implies taking measurements as accurately as possible , , ( Fig. 157.2 ). Indications for surgery are based mainly on aortic diameter and derived from findings on natural history regarding the risk of complications versus the risk of elective surgery. Although several modalities serves for this purpose, CT is frequently used because it offers comprehensive imaging of the entire aorta, provides high spatial resolution data, and permits assessment of coronary abnormalities, which reduces the need for invasive coronary angiography ( Fig. 157.3 ). The surgical options for repair of ascending aortic aneurysms depend on the presence of aortic valve disease, dilation of the sinuses of Valsalva, and distal extension of the aneurysm into the aortic arch. Intraoperative TEE (Videos 157.2, 157.3, and 157.4) is useful for evaluating the aortic valve to determine if valve-sparing surgery is feasible, to define the aortic valve annular diameter in relation to the diameter of the sinotubular junction to establish the need for aortic root replacement, and to detect and quantify the presence of aortic regurgitation after valve repair.
Sinus of Valsalva Aneurysm
- Farouk Mookadam, MD, MSc(HRM)
The sinuses of Valsalva are cuplike dilatations in the aortic wall just above the three cusps of the aortic valve. These sinuses function in part to suspend the aortic valve between the valve annulus and the sinotubular ridge. In addition the left and right sinuses house the ostia of the left and right coronary arteries ( Fig. 158.1 ). Aneurysm of the sinus of Valsalva was first described by Hope in 1839. In 1840, the first six cases were described by Thurnam , with a description that aneurysms of the sinuses of Valsalva usually protrude into one of the cardiac chambers. Subsequently, Smith described sinus of Valsalva aneurysms (SOVAs) found during postmortem examination. Aneurysms of the sinus of Valsalva are thought to result from incomplete fusion of the medial layer of the aorta with the annulus fibrosis of the aortic valve. The medial layer lacks an elastic lamella, which creates a weakness in the aortic wall that makes it susceptible to dilatation and aneurysm formation, especially in the presence of hypertension.
Clinical significance
In general, sinuses of Valsalva are rare and may be due to acquired conditions or congenital conditions ( Table 158.1 ). SOVAs are not infrequently associated with other cardiac congenital abnormalities such as ventricular septal defect, anomalous coronary arteries, or abnormal aortic valve cusps (bicuspid and quadricuspid). In instances of bicuspid aortic valve, not only does the congenitally abnormal valve result in complications, such as regurgitation or stenosis, but a concomitant aortopathy may coexist. The aortopathy most commonly affects the ascending aorta; however, SOVA may also be an accompaniment of bicuspid or quadricuspid aortic valve.
| Congenital | Acquired |
|---|---|
| Bicuspid aortic valve | Endocarditis |
| Connective tissue disease Marfan disease Ehlers-Danlos syndrome | Iatrogenic post aortic valve surgery or cardiac catheterization Atherosclerotic degeneration |
Clinical presentation will vary depending on the site, size, and whether compressive symptoms or rupture into a cardiac chamber or extracardiac site occurs. Hence, with sinus of Valsalva causing right ventricular inflow or outflow tract obstruction, right-sided heart failure symptoms will predominate. A fistula into the right atrium (RA) or right ventricle (RV) will present the same, whereas fistula into the left atrium may present with predominantly left-sided heart failure ( Fig. 158.2 ).
The sinuses of Valsalva characteristically will rupture into an adjacent chamber as shown in Table 158.2 and Figure 158.2 . The etiology is generally thought to be congenital, due to abnormal ultrastructural change in the medial layer of the sinus wall, but may also be acquired in endocarditis or rarely may be iatrogenic after coronary angiography or after aortic valve surgery. In known connective tissue disease abnormalities such as Marfan syndrome or in patients with a bicuspid aortic valve, quadricuspid aortic valve, or coarctation of the aorta, the association with abnormal elastic tissue may be seen.
| Ruptured Sinuses | Unruptured Sinuses |
|---|---|
| RSOVA may rupture into RA, RV, or adjacent main pulmonary artery | RSOVA can cause RVOT obstruction |
| LSOVA will rupture into LA, RA | LSOVA can cause LA compression |
| RSOVA may result in right coronary artery dissection or compression and acute myocardial infarction | RSOVA may compress conduction system and cause heart block |
| RSOVA may rupture into the pericardium with tamponade |
In the presence of a membranous ventricular septal defect (VSD), prolapse of the noncoronary cusp or the right coronary cusp into the VSD by a windsock mechanism may occur. In one large study of SOVA spanning almost half a century, 63% of subjects were male; asymptomatic incidental murmur was noted in 20%; fatigue was noted in 45%; dyspnea and chest pain were noted in 36% and 19% respectively; and palpitations were noted in 5%. Symptoms in SOVA largely depend on which sinus dilates and the size and the relationship with adjacent structures. Symptoms may be due to compressive aneurysms on the coronary arteries or obstructive to right ventricular inflow or right ventricular outflow tract (RVOT) outflow; may be due to left-to-right or left-to-left shunting; or, less commonly, may cause conduction system abnormalities by impinging on conduction fibers in the interventricular septum or atrial ventricular node. Extracardiac rupture within the pericardium or mediastinum is extremely uncommon. Aneurysms arose from the right coronary sinus in 70%; the noncoronary sinus in 25%; and the left coronary sinus in 5% of patients. The aneurysms had ruptured in 29 of the patients (34%). Twenty percent ruptured into the RV and 13% into the RA. All the ruptured aneurysms arose from the right coronary sinus (76%) or the noncoronary sinus (24%). Aneurysms originating in the noncoronary sinus tended to rupture into the RA (86%), and those originating in the right coronary sinus tended to rupture into the RV ( 73%). Most right coronary sinus aneurysms rupture into the RV, either into the body or into the outflow tract. In the Mayo series, 20% of all SOVAs opened into the RV and 13% into the RA. Of the right coronary sinus aneurysms, most (73%) opened into the RV. Aneurysms of the noncoronary sinus ruptured into the RA in 86% of patients. Rarely, rupture may occur into the left ventricle, left atrium, pulmonary artery, pericardium, interventricular septum, or superior vena cava. It is safe to say that approximately two thirds of SOVAs arise from the right sinus of Valsalva; two thirds will rupture into the RV; two thirds are in males; one third arise from the noncoronary sinus of Valsalva; one third rupture into the RA; one third will present with rupture; and 20% to 25% will be asymptomatic and discovered incidentally. Approximately 6% will have endocarditis. Not infrequently, the presentation may be insidious with gradual symptom presentation over several years. The SOVA may be discovered incidentally on imaging or clinically through a continuous murmur. The subacute or insidious presentation is that of congestive heart failure from volume overload or RVOT obstruction.
With regard to clinical presentation, it generally may be acute with chest pain or more commonly with heart failure. Symptoms of acute or subacute dyspnea on exertion or right-sided heart failure symptoms if the aneurysm results in right-sided volume overload by rupture into the RA or RV, or if RVOT obstruction or tricuspid valve inflow obstruction occurs. Figure 158.3 outlines some examples of a right and noncoronary SOVA and the putative chamber into which it may enlarge. Of note, the relationship of the SOVA and coronary arteries (see Fig. 158.3 ) displays the mechanism for coronary artery compression and angina-type pain or acute coronary syndrome that may result.
Diagnosis
The physical examination may reveal a wide pulse pressure, especially if significant aortic regurgitation is present, and a long diastolic murmur from aortic regurgitation or a continuous murmur if a sinus to cameral (aortocameral shunt) is present. The 12-lead electrocardiogram shows no pathognomonic findings, but LV hypertrophy is a common finding. The chest x-ray may show unfolding of the aorta or, more commonly, cardiomegaly and features of congestive heart failure.
Transesophageal echocardiography (TEE), two-dimensional or real-time three-dimensional (3D) TEE can increasingly make the diagnosis, including size and site of rupture, more easily and with better information regarding site, size, and receiving chamber into which the sinus protrudes or communicates. Echocardiography plays an important role in diagnosing sinus of Valsalva aneurysms and rupture. According to the published case reports from the past, more than 90% cases were diagnosed by color Doppler echocardiography. Two-dimensional echocardiography demonstrates the site of aneurysm and its relation to adjacent structures ( Figs. 158.4 and 158.5 ). Figure 158.6 , right panel, shows a parasternal long-axis view with an RSOVA that ruptures into the RV, and the left panel shows color Doppler of a high-velocity jet into the RV. Color Doppler shows turbulent flow across the site of rupture, and spectral Doppler confirms a high-velocity continuous shunt throughout the cardiac cycle. The high-velocity continuous nature of the jet spanning the entire cardiac cycle helps distinguish aneurysm rupture into the right ventricle from a ventricular septal defect, where the flow is restricted mainly to the systolic phase ( Fig. 158.7 ). Although in some adult patients with ventricular septal defect and increased left ventricular end-diastolic pressure, diastolic left-to-right shunt can be present, the diastolic flow velocity is usually low (< 2 m/sec) as left ventricular diastolic pressure is much lower than diastolic pressure in the ascending aorta. With large ruptures, Doppler interrogation in the descending aorta can also demonstrate diastolic flow reversal. In patients with abnormal aortic valve anatomy, echocardiography is also important for the long-term follow-up and monitoring of patients. In the example shown in Figure 158.8 , the upper panel shows a parasternal short-axis view of a bicuspid aortic valve in a 39-year-old man who at age 12 underwent surgery for repair of coarctation of the aorta. Routine transthoracic echocardiography now reveals aneurysm of the sinuses of Valsalva involving the right and non-coronary cusps (see Fig. 158.8 , lower panel). In addition, echocardiography is the modality of choice when following patients known to have SOVAs to look for changes in size or complications such as aortic regurgitation. TEE defines the anatomy with greater clarity. 3D live imaging is increasingly available to improve visualization of the sinuses, rupture, and adjacent structures.
Cardiac computed tomographic angiography can be beneficial in both diagnosis as well as surgical planning. More importantly, percutaneous closure may benefit from a combined echocardiography and thoracic aortogram information. Similarly, cardiac magnetic resonance imaging may be used with appropriate protocols in the assessment of SOVA.
Heretofore, it was felt that angiography was the gold standard; however, cardiac computer tomographic angiography or cardiac magnetic resonance imaging has been increasingly used as adjunctive tools in confirming the diagnosis and aiding surgical management. Further delineation of the anatomy of aneurysms can be obtained by cardiac magnetic resonance and electrocardiogram-gated contrast-enhanced computed tomography. These techniques also provide much better spatial resolution of cardiac structures and give detailed anatomic depiction of the Valsalva aneurysms in relation to surrounding structures. Cardiac CT is also helpful in identifying coronary anomalies that may accompany abnormal aortic valve morphology or aortic abnormalities such as coarctation of the aorta.
Treatment
In general, treatment is surgical for both ruptured and unruptured SOVA, if it is associated with symptoms. Asymptomatic SOVAs, depending on the size, may also require surgery to avoid complications such as acute rupture, which can be devastating when accompanied by hemodynamic compromise and may even result in death. The SOVA also can be complicated by endocarditis or thrombus formation with central or peripheral embolization. More recently, and increasingly, transcatheter repair is being used with increasing success. 3D live imaging is an emergent and important tool that is readily available to delineate the features of SOVA, which is important for intraprocedural guidance of surgical or transcatheter repair. , Cardiac computed tomographic angiography can be beneficial in both diagnosis as well as surgical planning. More importantly, percutaneous closure may benefit from a combined echocardiography and thoracic aortogram information. Similarly, cardiac magnetic resonance imaging may be used with appropriate protocols in the assessment of SOVA.
This recent series supports percutaneous closure with good safety and efficacy in experienced hands. The procedure is especially beneficial to high-risk surgical patients with comorbidities and multiple prior sternotomies, especially if the SOVA is the sole abnormality requiring attention. Selection of patients in skilled hands makes this an attractive alternative to surgery with very good short-term and mid-term outcomes.
When left untreated, ruptured SOVAs have a high 1-year mortality, with an estimated mean survival time after diagnosis of 3.9 years. Hence, a ruptured SOVA almost always mandates surgical intervention. When an unruptured SOVA is symptomatic with heart failure, conduction system aberrations, arrhythmia, or compressive symptoms on the right ventricular inflow of the coronary arteries or RVOT, or when there is suspicion for endocarditis, these are also reasons for surgical intervention. Asymptomatic unruptured SOVA may be monitored closely. In the event of symptoms or significant aortic valvular regurgitation or evidence that rapid growth ensues or severe enlargement occurs with or without fistulous communication, surgery may be indicated with similar criteria used for ascending aortic aneurysms. There are few data to support this approach, but it provides a framework for clinical decision making. If during follow-up of these patients, rupture or compressive symptoms or infections supervene, then surgical intervention is again recommended. The operative mortality rate is low at less than 1% in uncomplicated SOVA; however, in the presence of endocarditis or acute hemodynamic collapse, the mortality rate may be higher. Long-term survival is excellent with surgery for SOVA repair, with 5- to 10-year survival between 82% and 97%. ,
Acute Aortic Syndrome
- Muhamed Saric, MD, PhD
- Itzhak Kronzon, MD
Acute aortic syndrome (AAS) encompasses several life-threatening clinical entities with overlapping features including acute onset of chest pain, disruption of the aortic wall media, and a need for urgent medical care ( Fig. 159.1 ). The term “acute aortic syndrome” was first proposed in 2001 by the Spanish physicians Vilacosta and San Román. The following three entities were originally included in the spectrum of acute aortic syndrome: aortic dissection, intramural hematoma (IMH), and penetrating atherosclerotic ulcer (PAU). Traumatic aortic rupture (TAR; transection) due to blunt deceleration trauma as well as aortic aneurysm leak and rupture may also be included the spectrum of AAS.
Aortic dissection—the most common clinical presentation of AAS—is discussed in this chapter; the other forms of AAS are described elsewhere in this book. The cardinal features of an aortic dissection are: (1) intimal tear (which may be primary or secondary); (2) abnormal blood flow from the aortic lumen into the media, which is typically already weakened by chronic hypertension, connective tissue disorders, or trauma (medial degeneration); (3) longitudinal cleavage of aortic wall by blood flow, leading to creation of a false lumen separated from the true lumen by an intimomedial dissection flap; (4) development of complications such as tamponade, aortic regurgitation, and malperfusion in the territories of aortic branch vessels; and (5) long-term changes in the aortic anatomy (such as false-lumen thrombosis and aneurysm formation).
History
Elements of what we now refer to as acute aortic syndrome have been observed as early as 1555 by the European anatomist Andreas Vesalius (1514-1564), who described antemortem a traumatic abdominal aortic aneurysm in a man who had fallen from a horse; the patient’s autopsy in 1557 by Vesalius’s colleagues confirmed the diagnosis. An intimal tear, the hallmark of aortic dissection, might have been first noted on autopsy by the German anatomist Daniel Sennert (1572-1637, Latinized to Sennertus) and published posthumously in 1650. The British royal physician Frank Nichols (1699-1778) provided the first unequivocal description of aortic dissection on autopsy of the English king George II, who had died in 1760 of an ascending aortic dissection after straining on a commode. Nichols described the aortic pathology as “a transverse fissure” of the aortic trunk.
The term “dissection” appears to have been first applied to blood vessels and the aorta in 1802 by the Swiss surgeon Jean Pierre Maunoir (1768-1861). , A few years later, in 1826, the French physician René Laennec (1781-1826) introduced the term dissecting aneurysm (anévrysme disséquant). Until the introduction of aortography in 1929 by the Portuguese physician Reynaldo dos Santos (1876-1970), aortic dissection was exclusively a postmortem diagnosis. Aortography remained the primary means of diagnosing aortic dissection until the introduction of the modern imaging techniques of echocardiography, computed tomography (CT), and magnetic resonance imaging in the second half of the 20th century. The first successful surgical repair of a dissection in the descending aorta was reported in 1955 by Michael DeBakey (1908-2008), an American surgeon of Lebanese origin, and his colleagues. The first successful surgical repair of an ascending aorta dissection was reported in 1962 by the American surgeons Frank Spencer and Hu Blake.
As further discussed later, DeBakey and Stanford are the two major classifications of aortic dissection. DeBakey proposed his classification in 1966 ; the alternative classification was published in 1970 by researchers from Stanford University in California. Because aortic dissection is a rare diagnosis and the number of patients seen at any one hospital is small, the International Registry of Acute Aortic Dissection (IRAD) was established in 1996 to pool data from leading centers in North America, Europe, and Asia. At the turn of the 21st century, methods for percutaneous endovascular repair of aortic dissection are being developed.
Classifications of aortic dissection
Classifications of aortic dissection take into account both temporal and special aspects.
Temporal
Dissections that are diagnosed within the first 2 weeks of presentation are termed acute; once the 2-week mark is passed, they are referred to as chronic dissections.
Spatial
Stanford and DeBakey are the two most commonly used spatial classifications ( Fig. 159.2 ). In Stanford classification, all dissections are either type A or type B. Any involvement of the ascending aorta classifies the dissection as type A irrespective of whether the dissection is contained within the ascending aorta or extends further distally into the aortic arch, descending thoracic aorta, abdominal aorta, and beyond. Type B dissections are confined to the descending aorta.
The DeBakey classification is more detailed than the Stanford one. Dissections contained within the ascending aorta are termed DeBakey II, whereas those extending any length distally from the ascending aorta are classified as DeBakey I. Thus DeBakey types I and II correspond to Stanford type A. Dissections limited to the descending aorta are labeled DeBakey III; this term is thus equivalent to Stanford type B. DeBakey III dissections that are confined to the descending thoracic aorta are labeled as IIIa; those extending into the abdominal aorta are called IIIb.
Epidemiology
Aortic dissection is the most common form of catastrophic aortic disease and comprises approximately two thirds to three fourths of all AAS cases. The overall incidence of aortic dissection is low and is estimated at 0.5 to 4.0 annual cases per 100,000 individuals. Thus there are only a few thousand new aortic dissection cases diagnosed worldwide each year. Men are approximately twice as likely as women to develop aortic dissection. Aortic dissections originate in the ascending aorta much more commonly than in the descending aorta; in the initial IRAD database, Stanford type A comprised approximately two thirds and Stanford type B approximately one third of all aortic dissections.
The prevalence of aortic dissection has a bimodal distribution with one cluster in younger patients (around 40 years of age) and the other in older patients (around 60 years of age). In younger patients, connective tissue disorders (such as Marfan, Loeys-Dietz, Ehlers-Danlos type 4, Turner syndrome, and bicuspid valve aortopathy) are the predominant risk factor, whereas hypertension is particularly prevalent among older patients with aortic dissection.
Risk factors mediate the pathogenesis of aortic dissection either by triggering initial events (intimal tear or vasa vasorum rupture) or by promoting chronic medial degeneration that facilitates subsequent dissection.
Systemic hypertension promotes both intimal tear formation and chronic medial denegation. Hypertension is the most commonly observed risk factor in patients with aortic dissection. It is present in about three fourths of patients with aortic dissection. Dissections in the setting of cocaine use are at least in part related to systemic hypertension. Interestingly, cocaine use is associated preferentially with type B dissections.
Certain inherited connective tissue disorders are the strongest risk factor for the development of aortic dissections, especially type A. Except for Turner syndrome, these disorders tend to have an autosomal dominant pattern of inheritance. They include Marfan syndrome (due to mutations in the fibrillin gene), Loeys-Dietz syndrome (mutation in the genes encoding transforming growth factor beta receptor 1 and 2), Ehlers-Danlos syndrome type 4 (mutations in the collagen gene), congenital aortic wall abnormalities associated with bicuspid aortic valve (mutations in, e.g., the NOTCH1 gene), and aortic coarctation (e.g., chromosome X monosomy in Turner syndrome). Although these disorders are rare, they account for a disproportionately high percentage of aortic dissections, especially before the age of 40. For instance, the prevalence of Marfan syndrome in the general population is about 0.02% (1 in 5000), yet Marfan syndrome accounts for about 5% of all aortic dissections in the original IRAD series.
For unknown reasons, pregnancy is a risk factor for aortic dissection, particularly in Marfan syndrome and bicuspid aortic valve aortopathy. About half of all aortic dissections in women younger than 40 years occur during pregnancy, especially during the last trimester and in the early postpartum period. Occasionally, aortic dissection is iatrogenic in origin following either aortic cannulation (as during arteriography or insertion of intraaortic balloon pumps) or surgery (primarily as a result of aortic valve surgery). Atherosclerosis, although implicated in many other forms of aortic disease, is generally considered not to be a direct risk factor for aortic dissection unless associated with a penetrating atherosclerotic ulcer.
Pathophysiology
The aortic wall consists of three layers. The media, a thick middle layer filled with strong elastic fibers, is bounded by the thin intima, which lines the aortic lumen, and the adventitia, which covers the outer wall of the aorta and provides most of the wall’s tensile strength. The wall is nourished through vasa vasorum, small arteries that penetrate the wall from the adventitial side. Pathophysiology of aortic dissection consists of three elements: basic features, complications, and long-term changes in the aortic wall.
Basic Features
Aortic dissection occurs when the normal intraluminal blood flow in the aorta gains access to the aortic media and cleaves it longitudinally in either antegrade or retrograde direction. The cleavage creates an intimomedial flat that separates the abnormal false lumen in the media from the normal aortic lumen (true lumen). The intimomedial flap is frequently but incorrectly referred to as an “intimal flap” despite the fact that the bulk of the flap originates from the cleaved media.
Disruption of the media may then lead to a variety of complications whose clinical presentation depends on the location of aortic dissection. Type A dissection may lead to tamponade, aortic regurgitation, and malperfusion of coronary or cerebral circulation. Type B dissection may lead to malperfusion in spinal and visceral arterial circulation.
In the classic form of aortic dissection, an intimal tear starting at the luminal side is the primary event, which starts the cascade of subsequent blood flow–driven longitudinal cleavage of the aortic wall and attendant complications. The higher the amplitude and the rate of rise in systolic blood pressure, the larger the cleaving force within the aortic media.
Preexisting structural abnormalities of the media (such as connective tissue disorders or chronic hypertension) greatly enhance the propagation of cleavage. Historically, the medial change that predisposes to aortic dissection was described as cystic medial necrosis. Such a term is inaccurate as the change is neither cystic nor necrotic. Medial degeneration is probably a better term.
Although an intimal tear may affect any portion of the aorta, it typically occurs at one of the two sites with highest shear stress: (1) the right side of the ascending aorta just distal to the ostium of the right coronary artery in type A dissection; and (2) just distal to the ostium of the subclavian artery and close to the attachment of the ligamentum arteriosum in type B dissection.
Intramural hematoma may be considered a variant of aortic dissection in which the initial event is rupture of the vasa vasorum leading to wall hematoma that erodes into the lumen, creating an intimal tear from the medial site into the aortic lumen. Thus, with intramural hematoma, an intimal tear is not a primary event (as in classic dissection) but rather a secondary phenomenon. The concept that aortic dissection may be initiated by an intramural hematoma is not a recent one; it was described on autopsies as least since 1920.
Penetrating atherosclerotic ulcer, first described in 1934, may also lead to aortic dissection, although contained rupture is a more common presentation of such an ulcer.
Irrespective of how an aortic dissection starts, the intimomedial flap may have additional entry and exit points along the dissection path.
Complications
Aortic dissection may be complicated by malperfusion syndromes, aortic regurgitation, and rupture into an adjacent cavity. Malperfusion syndromes in the territories of aortic side branches may lead to coronary and cerebral ischemia in type A dissection, or spinal, limb, and/or abdominal ischemia in type A or B dissections. Aortic insufficiency is a possible complication of a type A dissection. The mechanism of aortic valvular regurgitation is multifactorial including effacement of the sinotubular junction and loss of leaflet support, as well as prolapse of the intimal flap through the aortic valve into the left ventricle. Aortic dissection may rupture into the pericardial, pleural, and/or peritoneal space, leading to hemorrhagic effusions. Pericardial tamponade is believed to be the most common cause of death in type A dissection. Urgent surgical repair of the aortic dissection rather than pericardiocentesis is the treatment of choice for such a complication.
Long-Term Changes
If the patient survives and no surgical intervention is performed within 2 weeks of dissection onset, aortic dissection enters a chronic phase in which the false lumen either undergoes thrombosis or remains permanently patent. Thrombosis obliterates the true lumen and allows for reestablishment of physiologic flow confined to the true lumen. False-lumen thrombosis is preceded by blood stasis, which is visualized by echocardiography as spontaneous echocardiographic contrast (“smoke”) in the false lumen. Permanent patency of the false lumen is enhanced by the presence of reentry fenestrations. The cleaved media of the chronically patent false lumen may endothelialize to give rise to the so-called double-barrel aorta. In addition, progressive weakening of the false lumen’s adventitial wall may give rise to a secondary aortic aneurysm.
Diagnosis of aortic dissection
The diagnosis of aortic dissection requires a high index of suspicion given the low prevalence of the disease. Classically, aortic dissection presents with severe, often migratory chest pain that is tearing or ripping in nature. Physical diagnosis is notoriously unreliable in establishing the diagnosis; pathognomonic physical findings (such as pulse deficits or focal neurological signs) occur in one third of cases or fewer.
Four imaging techniques are used in diagnosing aortic dissection: echocardiography, computed tomography (CT) ( Fig. 159.3 , A and B ), magnetic resonance imaging (MRI) (see Fig. 159.3 , C and D ), and aortography. Either transesophageal echocardiography or computer tomography is the initial diagnostic test of choice for acute dissections. Note that although one can occasionally establish the diagnosis of aortic dissection on transthoracic echocardiography ( Fig. 159.4 /Video 159.4, A-D ), this imaging technique does not have sufficient sensitivity or specificity for the diagnosis of aortic dissection and thus should be used only as a rough screening tool.
Magnetic resonance imaging is best suited for chronic dissections. Aortography, the most invasive of the four imaging techniques, typically adds no incremental value in the diagnosis of aortic dissection compared to noninvasive techniques. However, aortography is still useful during attempts to treat or palliate aortic dissection, such as during stent placement or creation of iatrogenic fenestrations in the intimomedial tear.
Echocardiography in aortic dissection
The principal goal of aortic dissection imaging by echocardiography, CT, or MRI is to identify the three fundamental features of aortic dissection: basic findings, complications, and long-term changes. Transesophageal echocardiography ( Figs. 159.5 and 159.6 ) is the echocardiographic test of choice for the diagnosis of aortic dissection, because transthoracic echocardiography lacks sensitivity and specificity in diagnosing this disorder. Nonetheless, transthoracic echocardiography may be invaluable in visualization of complications of aortic dissection.
On echocardiography, the dissection flap separating the true lumen from the false lumen appears as an undulating membrane parallel to the long axis of the aorta. The intimomedial flap is often easier to visualize in the short axis than in the long axis of the aorta. The linear reverberation artifact in the ascending aorta should not be mistaken for type A dissection. Similarly, the band of tissue separating a prominent azygos vein from the descending thoracic aorta should not be misinterpreted as a dissection flap ( Fig. 159.7 /Videos 159.7, A-C ).
The true lumen expands with systole and shrinks with diastole and is often smaller than the false lumen. Because the true lumen is lined by the intima and the false lumen by the cleaved media, the presence of intimal atherosclerotic changes helps identify the true lumen. The false lumen is also more likely to feature blood stasis, giving rise to spontaneous echo contrast (“smoke”) and thrombus formation. Microbubble contrast may help in distinguishing the true from the false lumen, as the contrast typically fills the true lumen before the false lumen ( Fig. 159.8 /Video 159.8).
Entry sites from the true lumen into the false lumen are best visualized by color Doppler jets extending from the true lumen into the false lumen at predilection sites (a few centimeters distal to the right coronary cusp in type A dissections, or in the descending thoracic aorta just distal to the origin of the left subclavian artery in type B dissections). Similarly, exit holes may be seen on the distal portions of the dissection flap, with color jets exiting the false lumen into the true lumen.
Complications of aortic dissection are easily visualized by standard transesophageal and transthoracic echocardiographic techniques: aortic insufficiency; segmental left ventricular wall motion in case of dissection into coronary arteries; echolucent space around the heart indicative of pericardial effusion; and extension of the dissection flap into aortic branch vessels. Even though transthoracic echocardiography is inadequate for the diagnosis of aortic dissection per se, visualization of known complications on transthoracic echocardiography is an important diagnostic clue that the patient might have aortic dissection.
Long-term changes in the false lumen start with development of spontaneous echocardiographic contrast in the false lumen, which eventually leads to clot formation and obliteration of the false lumen ( Fig. 159.9 /Video 159.9, A-C ). Transesophageal echocardiography may also be used for serial monitoring of possible aortic aneurysm formation after aortic dissection.
The major drawback of transesophageal echocardiography is its inability to visualize the portion of the thoracic aorta around the origin of the brachiocephalic trunk; this region is a blind spot due to interposition of the trachea and the left main bronchus between the aorta and the esophagus. This region, however, can often be well visualized on suprasternal transthoracic imaging.
Therapy and prognosis
Type A aortic dissection is an absolute medical emergency requiring prompt surgical repair, as likelihood of survival decreases with each passing hour. Up to 90% of unoperated patients with type A dissection die within 3 months of presentation. For type B dissections, medical therapy on average has a lower mortality than surgical repair. Thus, medical therapy is the preferred choice in treating type B dissections unless complications develop. Percutaneous endovascular stent-graft placement is becoming an alternative to surgical repair of type B dissections. Medical therapy is used in all patients irrespective of whether they are operated or not. A multidrug regimen including a beta-blocker is recommended to control the systemic blood pressure and to decrease the rate of rise of systemic blood pressure.
Conclusions
Aortic dissection occurs when blood enters the aortic media and tears it longitudinally. Acute aortic dissection is an absolute medical emergency requiring prompt diagnosis and, often, urgent surgery. Transesophageal echocardiography and contrast-enhanced CT are preferred diagnostic modalities in the acute setting, whereas MRI is better suited for chronic dissections. The triad of diagnostic features of aortic dissection visualized by these imaging techniques consists of (1) basic findings (intimal flap; false lumen; true lumen; entry and reentry tears); (2) signs of complications (aortic insufficiency, malperfusion of aortic branches; pericardial or pleural effusions); and (3) long-term changes (thrombosis of the false lumen; double-barrel aorta; secondary aortic aneurysm).
Penetrating Atherosclerotic Ulcer and Intramural Hematoma
- Raimund Erbel, MD
- Sofia Churzidse, MD
- Riccardo Gorla, MD
- Alexander Janosi, MD
- Sofia Churzidse, MD
Penetrating atherosclerotic ulcer
The term penetrating aortic ulcer (PAU) describes a condition in which the ulceration of an atherosclerotic lesion penetrates the aortic internal elastic lamina into the aortic media ( Fig. 160.1 ). Although the clinical presentation of PAU is similar to that of classic aortic dissection, PAU is considered to be a disease of the intima (i.e., atherosclerosis), whereas aortic dissection and intramural hematoma (IMH) are predominantly diseases of the media that involve degenerative changes of the elastic fibers and smooth muscle cells.
