1. Answer: B. The size of the ascending aorta correlates with several anthropometric measures. Aortic size correlates most closely with height, body surface area, gender and increasing age. Aortic size correlates less well with body weight as an isolated factor. In a majority of individuals, the aortic root, proximal and mid portion of the tubular ascending aorta can be adequately imaged from the transthoracic left parasternal window from various intercostal spaces. The right parasternal view can be helpful when visualization is inadequate in the left parasternal views. Correlation between computed tomography or magnetic resonance angiography of the ascending aorta at the aortic root, proximal and mid ascending aorta is good when TTE image quality is adequate. Because it is subject to pulsatile blood flow, the aortic size varies between systole and diastole. Thus if the aorta can be imaged adequately throughout the cardiac cycle, it should be ideally imaged during diastole. M-mode is used primarily for assessing the size of the aortic root whereas two-dimensional echocardiography can be used to visualize the aortic root and tubular ascending aorta. See Figure 26-19 showing normal thoracic aortic sizes by echocardiography.

2. Answer: A. The American Society of Echocardiography (ASE) Pediatric Guidelines recommend measuring the aorta by two-dimensional imaging in systole using an inner edge to inner edge convention. This convention, which is in contrast to the leading edge to leading edge end-diastolic measurement recommended in adults, was chosen since it is believed to correlate best with prognosis especially in disease states such as Marfan syndrome. In systole the aorta is exposed to the highest wall stress and therefore systolic measurements may be more predictive of aortic complications such as aortic dissection. There are separate guidelines from the ASE pertaining to adults that recommend measurements be made in end diastole not in systole. Since these guidelines are not aligned, it is important to recognize that measurement differences may occur when individuals transition from pediatric to adult echocardiography laboratories. In general, measurements made in systole may be 1-2 mm greater than those made in diastole for younger individuals with compliant aortas.

3. Answer: D. The term “bovine aortic arch” refers to a common anatomic variant pattern of the aortic arch. Although a common misnomer (the human bovine aortic arch variant does not resemble the aortic arch pattern found in cattle), it remains a widely used descriptive term in the medical literature. In the common configurations referred to as bovine aortic arch, the innominate artery and the left common carotid artery have a common origin (Fig. 26-20). These aortic configurations occur in about 9%-13% of individuals. The aortic arch and great vessels are not visualized from the standard parasternal window but can be best imaged from the suprasternal notch.

4. Answer: D. Complex aortic atheromas are usually defined as ≥4 mm thickness or mobile. These characteristics are most strongly associated with embolic risk including stroke and peripheral embolization and can be defined by TEE. Complex aortic atheromas are most often seen in the descending aorta followed by the aortic arch and ascending aorta in decreasing prevalence. TEE is not adequate to visualize the innominate artery although complex atheromas are infrequent in this region.

5. Answer: C. A potential limitation of TEE for the evaluation of the thoracic aorta is the so-called “blind spot.” This area encompasses an approximately 3 cm portion of the distal ascending aorta and proximal arch. The “blind spot” is caused by the interposition of air most commonly from the trachea or left main bronchus causing acoustic interference between the transducer and the aorta. The “blind spot” is not caused by interference from the right main bronchus or azygos vein. Although a hiatal hernia may interfere with cardiac imaging from the mid to lower TEE windows, it is not the cause of the aortic “blind spot.” Despite the potential for the “blind spot” to interfere with aortic imaging, the diffuse processes of the aorta infrequently render it a significant limitation. During cardiac surgery the “blind spot” can be overcome by epiaortic imaging or by placing a fluid-filled balloon in the trachea to enhance ultrasound transmission to the aorta.

6. Answer: D. TEE may provide a rapid and accurate diagnosis of traumatic aortic injury. Most traumatic aortic injuries are the result of abrupt deceleration resulting in shearing of the aorta in the region of the isthmus. The aortic isthmus is the region between the left subclavian artery and the first intercostal arteries where the aorta is fixed to the thoracic cage by the ligamentum arteriosum and intercostal arteries. Although many patients experience complete transection of the aorta after motor vehicle accidents and do not survive, some with less severe injuries may be rapidly diagnosed and undergo life-saving surgery. Findings seen with aortic deceleration injuries include: (1) a localized flap in the region of the aortic isthmus; (2) a thick wall flap that runs perpendicular to the aortic wall unlike what is seen with spontaneous aortic dissection; (3) absence of two channels or a typical true and false lumen with differential flow in the lumens; (4) turbulent blood flow above the dissection flap; (5) disruption of the aortic wall; (6) a localized pseudoaneurysm in the region of the dissection; and (7) a mediastinal hematoma.

7. Answer: C. Distinguishing the true from the false lumen in patients with aortic dissection has important surgical and prognostic implications. With TEE it may be possible to determine if the false lumen provides flow to aortic arch vessels thus compromising flow. The true lumen is generally the smaller lumen that receives brisk systolic antegrade flow and expands during systole. Flow communication into the false lumen may occur. In contrast the false lumen is generally the larger lumen but is compressed during systole and receives reduced systolic antegrade flow which is delayed and lower in velocity. Thrombosis of the false lumen not the true lumen may occur and may be complete or partial. Partial thrombosis of the false lumen in type B aortic dissection has been demonstrated to have a worse prognosis than complete thrombosis or a patent false lumen without thrombosis.

8. Answer: A. Aneurysmal dilatation of an artery such as the aorta is a localized or diffuse increase in diameter to at least 1.5 times greater than the normal expected size. That is, if the ascending aorta is normally 3.0 cm in diameter for a given patient based on age, gender and body surface area, an aortic aneurysm would be present if the maximal diameter was equal to or greater than 4.5 cm or at least 50% greater than the expected size. Dilatation of less than 1.5 times the normal expected size is generally referred to as aortic ectasia.

9. Answer: D. Marfan syndrome is a systemic disorder of connective tissue characterized primarily by aortic aneurysms and other cardiovascular, skeletal, and ocular abnormalities. The condition is caused by a genetic mutation in the FBN1 gene. A principal manifestation (major criteria) for diagnosis of Marfan syndrome is dilatation/aneurysms of the ascending aorta involving at least the sinuses of Valsalva. This is the most common site for aneurysm formation. Dilatation/aneurysms of the aortic arch, descending thoracic and thoracoabdominal aorta are also common and can develop in the absence of coexisting ascending aortic aneurysms. Isolated abdominal aortic aneurysms are however, relatively rare.

10. Answer: B. The two most common types of rightsided aortic arches are: mirror image and nonmirror image (aberrant left subclavian artery). Mirror image type is commonly associated with congenital heart disease (most often tetralogy of Fallot) whereas nonmirror image type is infrequently associated with other congenital cardiac malformations. In mirror-image right aortic arch, the innominate artery originates as the first branch (from patient left to right), followed by right carotid artery and right subclavian artery (Fig. 26-21A). In nonmirror image right aortic arch, the sequence of branching (from patient left to right) is left carotid artery, right carotid artery, right subclavian artery, and then left subclavian artery (Fig. 26-21B). The left (aberrant) subclavian artery originates from the proximal descending aorta often with a prominent diverticulum (diverticulum of Kommerell) at its origin. The artery courses behind the esophagus and trachea and can produce a vascular ring with esophageal compression.

11. Answer: A. Normal aortic dimensions and correlates of size have been established and are shown in Figure 26-19. In addition, the normal shape of the aorta is also well established and characterized by sinus of Valsalva diameter > sinotubular junction diameter and sinus of Valsalva diameter > tubular ascending aortic diameter. In general, the diameter at the sinus of Valsalva is approximately 0.2 cm in men and 0.1 cm in women greater in size than the tubular ascending aortic diameter. Thus the presence of a tubular ascending aorta of greater size than the sinus of Valsalva size is the most likely choice to represent a pathologic process despite normal overall dimensions.

12. Answer: B. Shone complex is a rare congenital heart disease comprised typically of four obstructive left heart lesions: supravalvular mitral ring, parachute-like mitral valve, subaortic stenosis, and aortic coarctation. Valvular aortic stenosis with a bicuspid aortic valve may also occur. Turner syndrome has commonly recognized cardiac malformations. The most common cardiac defects are coarctation of the aorta and a bicuspid aortic valve. Other abnormalities associated with Turner’s can include aortic aneurysms and dissection. Noonan syndrome is a genetic disease typified by facial anomalies, short stature, webbed neck, undescended testes and congenital heart defects. The classic cardiac malformations reported in Noonan’s are pulmonary stenosis and hypertrophic cardiomyopathy. Down syndrome (or trisomy 21) is frequently associated with congenital heart defects the most common of which are atrioventricular septal defects.

13. Answer: C. An aorta that is anterior to the pulmonary artery associated with atrioventricular concordance and ventricular-arterial discordance refers to the anatomic configuration of D-transposition of the great arteries. D-transposition (complete or uncorrected transposition) is a cyanotic congenital heart defect in which the aorta is anterior and to the right of the pulmonary artery. It is characterized by the aorta arising from the morphologic right ventricle and the pulmonary artery arising from the morphologic left ventricle resulting in two separate circulatory systems. The condition is often diagnosed in utero by ultrasound, but if not, cyanosis upon birth will immediately lead to the diagnosis.

An aorta that is anterior to the pulmonary artery associated with atrioventricular discordance and ventricular-arterial discordance refers to L-transposition or congenitally corrected transposition. L-transposition is an acyanotic congenital heart defect in which the aorta is anterior and to the left of the pulmonary artery. It is characterized by double discordance (a “double switch”) where the atrial and ventricular connections are discordant and the ventricular to great artery connections are discordant. Blood flow is from the right atrium into the right-sided morphologic left ventricle through the pulmonary artery to the lungs. From the lungs blood flow returns from the pulmonary veins into the left atrium, to the left-sided morphologic right ventricle and to the aorta. Since circulation is physiologically corrected patients survive into adulthood.

An aorta overriding the ventricular septum with a malalignment ventricular septal defect describes tetralogy of Fallot. This cyanotic heart defect is classically described by four malformations: a ventricular septal defect, pulmonary stenosis, an overriding aorta, and right ventricular hypertrophy. The degree of pulmonary stenosis varies and is the main determinant of disease severity and degree of cyanosis. This condition is often diagnosed at birth or during the first year of life depending on cyanosis severity. A periductal aorta-pulmonary connection with normal pulmonary pressure refers to a patent ductus arteriosus. When a patent ductus remains untreated, depending on its size, pulmonary hypertension and heart failure can develop. In the absence of pulmonary hypertension the condition is well tolerated and can persist into adulthood.

14. Answer: A. Bicuspid aortic valves are associated with ascending aortic dilatation with a prevalence ranging greater than 50%. The tubular ascending aorta is usually the region with the greatest degree of dilatation. The underlying predisposition is likely related to genetic abnormalities of connective tissue along with flow-related stress which render the aorta susceptible to dilatation, aneurysm and aortic dissection. When presenting for aortic valve surgery, the ACC/AHA guidelines recommend elective aortic repair when the aortic size reaches >4.5 cm.

Patterns and classifications of ascending aortic dilatation in patients with bicuspid aortic valves have been proposed. Figure 26-22 demonstrates some of the more common variations. Figure 26-22A shows an aortic root predominant pattern which is in fact relatively uncommon. Figure 26-22B shows a pattern of relative sparing of the aortic root with tubular ascending aortic predominance and aortic arch sparing. Figure 26-22C shows a pattern of diffuse involvement of the aortic root, tubular ascending aorta, and aortic arch. Other patterns are possible with aortic arch dilatation common but usually not to the degree that requires surgical intervention.

Coarctation of the aorta is a commonly associated congenital malformation which develops in patients with bicuspid aortic valves. It occurs in ˜5% of all bicuspid aortic valve patients. Conversely, in those patients with coarctation of the aorta, a bicuspid aortic valve is present >50% of the time.

15. Answer: D. Several classification systems have been developed to describe aortic dissection involving the thoracic aorta. There are three classifications commonly in use and are based either on the location/extent of the dissection or on the underlying pathophysiology. The DeBakey classification has types I, II, IIIa, and IIIb and is based on the location/extent of aortic dissection. The Stanford classification has types A and B and is based on whether the dissection is in the proximal or distal aorta. The Svensson classification has classes 1-5 and is based on the pathophysiology of aortic syndrome.

The patient described has a DeBakey type 2/Stanford A with a variant form limited, iatrogenic hematoma. DeBakey type 2 refers to the ascending aortic location, Stanford A similarly locates the dissection in the ascending aorta or arch and by Svensson classification there is a class 5 iatrogenic intramural hematoma (Table 26-1).

16. Answer: D. The TEE image depicts a large pedunculated aortic thrombus in the distal aortic arch/proximal descending thoracic aorta. Although most sources of emboli from the aorta are related to complex atherosclerotic plaques, large aortic thrombi may also occur. A majority of these thrombi develop in areas of diffuse atheromatous disease but they may also occur in regions with minimal or no apparent atherosclerosis. An alternative etiology of aortic thrombus is an underlying thrombophilic state such as antiphospholipid antibody syndrome or malignancy. Treatment for aortic thrombi has not been well established although anticoagulant therapy is supported by some studies. If recurrent embolic events occur, surgical removal of the aortic thrombi may be necessary.

Aortic thrombi do not predispose to aortic dissection although they may be seen at the site of traumatic aortic disruption. Aortic aneurysms may be a site for aortic thrombus formation but usually they appear as mural and layered and not pedunculated. Bacteremia may lead to mycotic aneurysms or atheromatous plaques with superimposed infection but not usually isolated infective masses.

17. Answer: D. The TEE X-plane echocardiographic image of the upper descending thoracic aorta depicts severe aortic atheromatous plaque of >0.5 mm, grade 4. There are no apparent mobile or ulcerated components. Plaque size can be graded based on intimal or atheroma thickness. There are a few published grading systems for atheroma with small differences in cut-off ranges for atheroma severity. The grading system endorsed by the 2015 multimodality imaging of thoracic aorta in adults guidelines and standards is shown in Table 26-2.

Distinguishing intimal thickening from atheroma is not always easily characterized. Intimal thickening is typically diffuse, homogeneous, mild, and without significant calcification.

18. Answer: C. The continuous-wave Doppler profile is consistent with coarctation of the aorta with a high-velocity systolic and diastolic flow (continuous flow, sawtooth pattern). The simplified Bernoulli equation typically overestimates the peak gradient obtained at cardiac catheterization. This occurs because the precoarctation velocity is often elevated due to flow acceleration and bicuspid aortic valve disease. However, using the modified Bernoulli equation, (P = 4 V₂² – V₁²) where the proximal velocity V₁ is accounted for results in a good correlation between Doppler echocardiography and cardiac catheterization.

19. Answer: C. The suprasternal notch view by TTE provides visualization of the distal ascending aorta, aortic arch and branch vessels and upper descending aorta. Recognition of normal anatomy in this view is important. The structures labeled are: 1—innominate vein; 2—right pulmonary artery; 3—innominate artery; 4—left atrium. The proximal portion of the left subclavian and left carotid artery can be seen in most individuals. The vessel border between the innominate vein and artery may be confused for a dissection flap if normal anatomy is not known. Typically continuous low-velocity flow is seen in the innominate vein with flow direction opposite to that in the aortic arch.

20. Answer: C. As previously discussed, ascending aortic size correlates best with several anthropometric measures. The best determinants are age, gender, body height, and body surface area. Normal reference sizes are shown in Figure 26-19. In addition, cut-off values for indexed aortic sizes correcting for body surface area are reported and also shown in Figure 26-19. In this individual, the indexed aortic size at the level of the aortic root would be (4.2/2.5 = 1.68 cm/m²) which is within normal. Furthermore, the shape of the ascending aorta appears normal without effacement of the sinotubular junction.