Aortic Insufficiency In Plax Color Flow

Fig. 1. Parasternal long-axis (PLAX) view showing aortic root dissection flap that prolapses into the left ventricular outflow tract during diastole. It was accompanied by new onset aortic regurgitation. (Please see companion DVD for corresponding video.)

Fig. 1. Parasternal long-axis (PLAX) view showing aortic root dissection flap that prolapses into the left ventricular outflow tract during diastole. It was accompanied by new onset aortic regurgitation. (Please see companion DVD for corresponding video.)

filling the space within the media between the intimal flap and the adventitia (Fig. 3). The initiating event is generally felt to be rupture of the intima with the subsequent dissection through the media, although primary hemorrhage within the media with subsequent intimal perforation is a potential alternative mechanism. Shear forces may lead to further tears in the intimal flap, which may function as additional entry sites for blood into and from the false lumen.

Etiology of Aortic Dissection

Acute aortic dissection usually occurs in association with medial degeneration (Table 1). The great majority of patients have a history of hypertension. Several connective tissue disorders are also associated with aortic dissection, such as Marfan and Ehlers-Danlos syndromes. Marfan syndrome is responsible for the majority of aortic dissection in patients under 40 yr old. Bicuspid aortic valve, coarctation, Turner's and Noonan's syndromes, polycystic kidney disease, and family histories ofdissection have been associated with a higher risk of dissection. Pregnancy is another condition that increases the risk of dissection, especially during the third trimester or during labor. Direct or indirect trauma such as deceleration owing to a motor vehicle accident may cause aortic dissection; usually this occurs

Fig. 2. Transesophageal descending thoracic aorta short-axis in the same patient in Fig. 1A,B. Color flow Doppler shows systolic flow within the true lumen (TL). Compare this to the false lumen (FL). (Please see companion DVD for corresponding video.)

Polycyctic Kidney Disease Aortic

Fig. 2. Transesophageal descending thoracic aorta short-axis in the same patient in Fig. 1A,B. Color flow Doppler shows systolic flow within the true lumen (TL). Compare this to the false lumen (FL). (Please see companion DVD for corresponding video.)

in the aortic isthmus distal to the ligamentum arterio-sum. Cardiac surgery is also associated with a risk of aortic dissection, in particular bypass surgery and aortic valve replacement. Patients with Takayasu's disease and other inflammatory collagen vascular diseases are also at increased risk. Corticosteroid use has also been associated with increased risk of dissection. Aortic dissection has also been reported to occur in association with cocaine use, particularly crack cocaine, presumably owing to abrupt elevations in systemic blood pressure.

Location of Dissection

It is important to distinguish proximal from distal dissection for prognostic and therapeutic reasons (Fig. 4).

Proximal dissections involve the aortic root. Acute proximal dissections are an acute cardiovascular emergency requiring immediate surgical correction. Distal dissections commence after the origin of the left subclavian artery and propagate distally without aortic root involvement. These distal lesions can usually be managed medically.

Associated Findings in Aortic Dissection

The marked increased morbidity and mortality associated with proximal aortic dissection is secondary to the potentially morbid sequelae of dissection. Dissection proximally toward the heart represents one of the most morbid complications of dissection. Dissections that

Fig. 3. Pathological specimen showing a large intramural hematoma in a patient with acute aortic dissection. This 54-yr-old male presented to the emergency department with severe neck pains. His had a history of bicuspid aortic valve with aortic stenosis and regurgitation. (Image courtesy of Robert Padera, MD, Brigham and Women's Hospital.)

Aortic Valve Plax

Fig. 3. Pathological specimen showing a large intramural hematoma in a patient with acute aortic dissection. This 54-yr-old male presented to the emergency department with severe neck pains. His had a history of bicuspid aortic valve with aortic stenosis and regurgitation. (Image courtesy of Robert Padera, MD, Brigham and Women's Hospital.)

Table 1

Factors Predisposing to Aortic Dissection

Predisposing factors for AD

• Bicuspid aortic valve disease (7-14%)

• Cystic medial degeneration (e.g., Marfan syndrome [5-9% of all AD cases], Ehlers-Danlos syndrome)

• Iatrogenic trauma: intra-arterial catheterization and coronary angiography, cardiac surgery (aortic cannulation site), intra-aortic balloon pump cardiopulmonary bypass); before cardiac surgery (up to 18% of all AD)

• Direct trauma

• Pregnancy (third trimester)

• Cocaine abuse

• Coarctation of the aorta

• Takayasu's disease

• Polycystic kidney disease

• Family history of AD

• Corticosteriods (prolonged use)

• Turner's and Noonan's syndromes

involve the aortic root can extend into the coronary arteries causing an acute coronary syndrome; similarly, dissections that involve the aortic arch can extend into the great vessels causing stroke or transient ischemic attack. Dissections extending into the aortic root can also involve the aortic valve itself resulting in acute aortic insufficiency. Dissections extending to the heart can also extend into the pericardial space resulting in pericardial effusion or even acute tamponade. Finally, dissections are associated with marked weakening of the aortic lining and can be associated with catastrophic rupture of the aorta itself.

Transthoracic Imaging

Transthoracic imaging (TTE) has a sensitivity of 59-85% and specificity of 63-96% for the diagnosis of aortic dissection. This low sensitivity is mainly secondary to the suboptimal visualization of the ascending aorta beyond the sinotubular junction and poor visualization of the aortic arch (Fig. 5). However, TTE is a highly valuable tool for identifying complications of dissection. Aortic regurgitation and aortic root dilatation are frequent findings and easily seen by TTE (Fig. 6; please see companion DVD for corresponding video). Wall motion abnormalities caused by occlusion of the coronary arteries by the dissecting flap may be occasionally identified. Furthermore, TTE is the preferred modality to assess pericardial effusion and tamponade caused by rupture of the dissected aorta into the pericardial space (Table 2). TTE is also useful in the initial evaluation of suspected aortic dissection involving the proximal abdominal aorta (Fig. 7).

Plax Aortic Dissection Ultrasound

Fig. 4. The Debakey and Stanford classifications of aortic dissection. The Stanford classification is the most commonly used. Type A dissections involve the ascending aorta and aortic arch irrespective of the number or location of entry sites. Type A dissections are generally surgical emergencies. Type B dissections, beginning distal to the subclavian, are most often managed medically.

Fig. 4. The Debakey and Stanford classifications of aortic dissection. The Stanford classification is the most commonly used. Type A dissections involve the ascending aorta and aortic arch irrespective of the number or location of entry sites. Type A dissections are generally surgical emergencies. Type B dissections, beginning distal to the subclavian, are most often managed medically.

Tte Dissection Images

Fig. 5. Visualization of the aorta on transthoracic echocardiography (TTE). Limited acoustic windows leave gaps in the TTE examination of the aorta and renders relatively low sensitivity (59-85%) of TTE in the diagnosis of aortic dissection. TTE is nonetheless valuable in assessing related complications of aortic dissection (e.g., wall motion abnormalities, pericardial effusion, or tamponade, or evaluating other conditions that mimic aortic dissection).

Fig. 5. Visualization of the aorta on transthoracic echocardiography (TTE). Limited acoustic windows leave gaps in the TTE examination of the aorta and renders relatively low sensitivity (59-85%) of TTE in the diagnosis of aortic dissection. TTE is nonetheless valuable in assessing related complications of aortic dissection (e.g., wall motion abnormalities, pericardial effusion, or tamponade, or evaluating other conditions that mimic aortic dissection).

In general, TTE is of limited diagnostic value in the initial assessment of aortic dissection and should be used as an initial screening test among patients in whom the clinical suspicion for aortic dissection is very low. In this group of patients, the absence of direct and indirect signs of dissection makes the diagnosis highly unlikely. On the other hand, TTE is highly specific and the visualization of the typical echocardiography findings of aortic dissection, particularly in patients with proximal dissections, confirms the diagnosis (Table 3).

One of the most important uses of TTE in the evaluation of a patient with suspected aortic dissection is to rule out other conditions that mimic aortic dissection (Table 4). These include acute coronary syndrome and myocardial infarction (might be associated with a regional wall motion abnormality), acute pulmonary embolism (might be associated with right ventricular dysfunction). In addition, TTE can be very useful in diagnosing associated conditions seen in conjunction with or as complications of aortic dissection. These include acute aortic insufficiency, pericar-dial effusion or tamponade caused by dissection into the pericardium.

Transesophageal Imaging (see Chapter 23,

TEE Primer)

Early recognition of aortic dissection is critical because the mortality rate is very high if left untreated. Thus, diagnostic accuracy is of crucial importance when selecting an initial diagnostic test to evaluate a patient with suspected aortic dissection. There are a number of noninvasive approaches to rapid diagnosis of suspected aortic dissection. Although contrast-enhanced computed tomography scanning has become the method of choice in many institutions (Table 5), TEE is a good alternative

Fig. 6. Two-dimensional guided M-mode showing aortic root dilatation in a 44-yr-old female with Marfan syndrome. (Please see companion DVD for corresponding video.)

Echo Images Marfan Syndrome

Fig. 6. Two-dimensional guided M-mode showing aortic root dilatation in a 44-yr-old female with Marfan syndrome. (Please see companion DVD for corresponding video.)

Table 2

Possible Transthoracic Echocardiography Findings in Aortic Dissection

1. Mobile dissection (intimal) flap within:

a. Aortic root (PLAX, PSAX)

b. Sino-tubular junction and ascending aorta (high PLAX)

c. Aortic arch (SSN)

d. Descending thoracic aorta (PLAX, A2C)

e. Proximal abdominal aorta (SC)

2. Flail aortic leaflet(s) (PLAX, PSAX, apicals)

3. Aortic root dilatation

4. Acute aortic insufficiency (PLAX, PSAX, apicals)

5. Wall motion abnormality (left ventricle)

6. Pericardial effusion or tamponade (SC, PLAX, SAX)

7. Differential color Doppler flow patterns within true and false lumen (PLAX, SSN, SC, apicals)

8. Pulse Doppler examination of flow at entry/exit sites and within true and false lumen (SSN, SC, apicals)

Apicals, apical five-chamber and apical (long-axis) five-chamber view, Apical two-Chamber (A2C); PLAX, parasternal long-axis views; PSAX, parasternal short-axis views; SC, subcostal views; SSN, suprasternal notch views. TTE, transthoracic echocardiography.

choice (Table 6). TEE offers several advantages when compared to other noninvasive methods: it is highly accurate, fast, relatively safe, and inexpensive. Because it can be performed at the bedside, it is often preferred among intubated and critically ill patients. Moreover,

TEE is the only diagnostic modality that can be used in the operating room during aortic dissection repair to monitor flow in the thoracic aorta during cardiopulmonary bypass, and to evaluate the need for further surgical interventions such as aortic valve replacement in patients with aortic dissection complicated by significant aortic regurgitation.

The aortic valve, aortic root, proximal ascending, distal aortic arch, descending thoracic, and proximal abdominal aortas are all well visualized with this approach (Figs. 8 and 9). However, the region of the distal ascending aorta and proximal aortic arch (TEE blind areas) is subopti-mally visualized by this technique owing to the interposition of the trachea and bronchi between the transducer in the esophagus and the aorta. One potential limitation of the technique because of this "blind spot" is that dissections that begin at the site of aortic cannulation following bypass surgery and travel distally can be missed.

In several studies, the sensitivity and specificity of TEE has consistently been high, ranging from 97 to 100% and 95 to 98%, respectively, for the diagnosis of aortic dissection. The echocardiographic finding considered diagnostic of an aortic dissection is the presence of an undulating linear density (intimal flap) within the aortic lumen separating the true and false channels (Figs. 10-12 [please see companion DVD for corresponding video for Figs. 10 and 11]; Table 7). The flap usually has independent motion from that of the

Echocardiography Images

Fig. 7. Transthoracic echoardiography (TTE) can provide information on aortic dissection involving the proximal abdominal aorta. This 54-yr-old female patient presented with a history of back pains. Two-dimensional, M-mode, and Color flow Doppler images of her dissection appear below. Note the differential flow patterns between the true lumen (TL) and the false lumen (FL).

Table 3

Utility of Transthoracic Echocardiography in Aortic Dissection

Advantages/disadvantages of TTE in Aortic Dissection

Advantages

Rapid diagnosis (for sinotubular and abdominal aortic dissection)

Best utility for complications accompanying aortic dissection (e.g., aortic, myocardical, and pericardial involvement) Portable (bedside or operating room) Safe

Inexpensive

Requires no sedation or anesthesia

Disadvantages

Suboptimal visualization of thoracic aorta

Limited diagnostic value for initial diagnosis and assessment

Relatively low sensitivity (59-85%) and specifity (63-96%)

TTE, transthoracic echocardiography.

heart and aortic walls and its presence should be sought in different planes. Color flow Doppler confirms the presence of two lumina by the demonstration of differential color flow patterns between the true and the false lumen with the true lumen usually displays pulsatile

Table 4

Conditions Mimicking Acute Aortic Dissection

Differential diagnosis of acute aortic dissection

1. Acute coronary syndromes and myocardial infarction

2. Acute pulmonary embolism

3. Acute pericarditis

4. Acute pleurisy

5. Esophageal spasm

6. Other causes of acute chest pain syndromes

7. Other causes of the acute abdomen (for abdominal aortic dissection)

systolic flow. Identification of the entry site of the dissection may also help in the identification of the true lumen from the false one (Figs. 13 and 14; please see companion DVD for corresponding video for Fig. 13). TEE can identify the spatial extent of dissection and sites of intimal tears. TEE can also detect and characterize complications of potential prognostic and therapeutic importance such as pericardial effusion, aortic regurgitation, and dissection into the right ventricle or the right atrium creating aorta-to-right ventricle or atrium fistulas. TEE may provide additional information useful to the surgeon such as whether the intimal flap

Table 5

Imaging Modalities and Diagnostic Performance in Suspected Aortic Dissection

Table 5

Imaging Modalities and Diagnostic Performance in Suspected Aortic Dissection

Diagnostic performance

Transesophageal echocardiography

Angiography

Computed tomography

Magnetic resonance imaging

Sensitivity

+++

++

+++

+++

Specificity

+++

+++

+++

+++

Site of internal tear

++

++

+

+++

Presence of thrombus

+

+++

++

+++

Presence of aortic

+++

+++

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