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Acute Aortic Syndromes
Basic Principles
Incidence and Predisposing Factors
Among patients with acute chest pain, a cardiac cause (most often acute myocardial infarction) is responsible for less than 20% of cases ( Fig. 32.1 ). Aortic disease accounts for less than 1% of patients with acute chest pain and is 20 times less common than acute myocardial infarction, with an estimated prevalence of only 3 to 4 cases per 100,000 persons per year. , However, aortic disease is important to recognize because prompt surgical intervention is lifesaving.
Ascending aortic dissections have higher mortality rates than dissection limited to the descending thoracic aorta. Among patients with an acute aortic syndrome involving the ascending aorta, 20% to 40% suffer instant death, possibly accounting for up to 7% of out-of-hospital cardiac arrest cases ( Fig. 32.2 ). Among those who survive to hospital admission, outcomes remain poor, with an estimated mortality rate of 1% per hour for ascending aortic dissection, a surgical mortality rate between 5% and 20%, and continued excess deaths over longer-term follow-up. ,
An acute aortic syndrome may be the initial presentation of a patient with no known cardiac or aortic disease, but it occurs more often in patients with underlying conditions associated with an increased risk of aortic aneurysm and dissection (see Chapter 33 ). In patients older than 40 years of age, the most common predisposing factors for an acute aortic syndrome are hypertension (72%), atherosclerosis (31%), and prior cardiac or aortic surgery. In younger patients, aortic dissection usually is related to an underlying connective tissue disorder (e.g., Marfan syndrome, Loeys-Dietz syndrome), bicuspid aortic valve disease, or drugs that acutely increase blood pressure (e.g., cocaine, methamphetamines) ( Table 32.1 ).
TABLE 32.1
Patient Populations at Risk for Aortic Dissection.
Modified from Bolger AF. Aortic dissection and trauma: value and limitations of echocardiography. In: Otto CM, ed. Practice of Clinical Echocardiography . 5th ed. Philadelphia: Elsevier; 2017:677–691.
| Predisposing Factors | Comments |
|---|---|
| Degenerative Diseases | |
| Hypertension Atherosclerotic vascular disease
|
Most common cause ascending aortic dissection in older adults |
| Genetic: Pathologic Single-Gene Variants | |
| Marfan syndrome Loeys-Dietz syndrome Familial aortic aneurysm Ehlers-Danlos syndrome, vascular form Osteogenesis imperfecta |
Consider when there is effacement of the sinotubular junction and sinus dilation, a family history, or other phenotypic features (see Chapter 33 ) |
| Genetic: Chromosomal Defects | |
| Turner syndrome Noonan disease |
Dissection can occur even without a BAV. |
| Congenital Conditions | |
| BAV Aortic coarctation |
The population prevalence of BAV is 1%–2%, and it is associated with an increased risk of aortic dissection. Less than 10% of patients with BAV have an aortic coarctation, although 50%–75% of patients with a coarctation have a BAV (see Chapter 22 ). |
| Trauma | |
| Deceleration injury Penetrating injury |
— |
| Cardiac Surgery | |
| Cannulation Cross-clamping Aortic valve replacement Catheter-based procedures Transcatheter aortic valve implantation |
— |
| Systemic Inflammatory Disease | |
| Takayasu arteritis Giant cell arteritis Spondyloarthropathies Behçet disease |
Dissection may be the first clinical manifestation of disease. |
| Infective Aneurysms | |
| Syphilis Bacterial, fungal, viral |
Rare in Europe and the United States |
| Other Precipitating Factors | |
| Pregnancy Weightlifting Cocaine use Discontinuation of β-blockers Polycystic kidney disease |
— |
BAV , Bicuspid aortic valve.
Pathophysiology
The most common type of acute aortic syndrome is aortic dissection (80% of cases). Less common presentations include aortic intramural hematoma (IMH; ≈15% of cases), penetrating ulcer in the aortic wall (≈5% of cases), and traumatic aortic injury.
Anatomically, an aortic dissection is characterized by separation of the aortic intima from the adventitia, which results in two aortic lumens separated by a thin, mobile flap of tissue. It remains controversial whether dissection is initiated by a tear in the intima or by hemorrhage into the media with subsequent disruption of the intima, but blood flow through the intimal tear propagates downstream, with further separation of the flow into two lumens extending from the initiation site to the arch, descending thoracic, and abdominal aorta. ,
An IMH occurs when there is hemorrhage into the aortic wall without an identifiable entry site, intimal flap, or false lumen, resulting in the appearance of a crescent-shaped thickening (≥5 mm) in the aortic wall on short-axis views. Among patients presenting with an IMH, progression to frank dissection with an intimal flap and/or aortic rupture is common. ,
A penetrating ulcer is an atherosclerotic plaque that disrupts the aortic wall’s elastic lamina, often with a localized IMH but without propagation distally. Penetrating ulcers most often occur in the descending thoracic aorta and sometimes in the arch or abdominal aorta, but they rarely occur in the ascending aorta. Most patients with a penetrating ulcer are older (>70 years) and have extensive atherosclerotic vascular disease.
Blunt thoracic trauma, particularly a deceleration injury resulting from a motor vehicle accident, can cause aortic dissection or transection, typically at the aortic isthmus just distal to the left subclavian artery.
Iatrogenic causes of aortic dissection include direct injury to the aorta during cardiac surgery or injury related to catheter interventions for coronary disease, structural heart disease, and electrophysical procedures.
Classification
Acute aortic syndromes are classified as type A if the ascending aorta is involved and type B if the dissection or IMH is limited to the descending thoracic aorta. Other, more complex classifications of acute aortic syndromes are useful for surgical planning, but the key element in diagnosis and management is whether the ascending aorta is involved in the disease process as the site of the initial tear or by retrograde dissection from a more distal intimal tear.
Management of type A dissection includes prompt surgical intervention with graft replacement of the ascending aorta. Type B dissections usually are treated medically with blood pressure control. Surgical or transcatheter intervention is considered only later in the disease course if needed for progressive changes in aortic size or branch vessel involvement.
Complications
Dissections can propagate retrogradely into the aortic sinuses, with rupture into the pericardium that produces tamponade physiology, distortion of normal aortic valve anatomy causing aortic regurgitation (AR), extension into a coronary artery resulting in acute infarction, or frank aortic rupture into the mediastinum ( Fig. 32.3 ). More often, the dissection extends distally into the descending thoracic aorta, the abdominal aorta, the iliofemoral arteries, and other branch vessels, resulting in vascular compromise and clinical symptoms ( Fig. 32.4 ).
Clinical Presentation and Diagnostic Approach
Most patients present within 24 hours of the initiating event. Symptoms of severe chest or back pain occur in about 90% of patients. Pain is often described as “tearing,” with radiation to the back or upper abdomen. Patients also can present with hypotension or shock due to partial rupture into the mediastinum or pleural cavities. The location of chest or back pain depends to some extent on the location of the dissection; the patient may notice the pain migrating to different locations as the dissection propagates downstream. For example, anterior chest pain may resolve and be replaced by upper back, then lower back, and then abdominal pain. A patient may present with only upper abdominal pain. For patients at risk for acute aortic dissection who present with atypical symptoms, it is important to consider this diagnosis and proceed with appropriate imaging. , , ,
In patients with a suspected acute aortic syndrome, the first steps are based on the clinical history, physical examination findings, and serum D-dimer measurements. The number of high-risk clinical features determines the aortic dissection risk score, which ranges from 0 to 3 based on the predisposing conditions (i.e., Marfan, family history, and aortic valve disease), pain characteristics (i.e., abrupt onset, severity intensity, and tearing description), and physical examination findings (i.e., pulse deficit or differential, AR murmur, and hypotension). A score of 0 indicates a low risk, a score of 1 indicates an intermediate risk, and a score of 2 or greater is considered high risk. Measurement of serum D-dimer levels is helpful for patients with a low risk score but for whom there is concern about an acute aortic syndrome.
Multimodality imaging is the key to diagnosis of acute aortic syndromes. When clinical features suggest the possibility of an acute aortic syndrome, most centers use computed tomographic angiography (CTA) as the initial imaging approach. , , CTA usually is the imaging modality of choice because of its accuracy for this diagnosis and the ability to obtain imaging quickly at any time in most emergency departments ( Table 32.2 ). CTA images should be gated to the electrocardiographic (ECG) tracing to avoid artifacts ( Fig. 32.5 ) and can be reconstructed in 3D or with the centerline approach for surgical planning ( Fig. 32.6 ).
TABLE 32.2
American Society of Echocardiography Recommendations for Choice of Imaging Modality for Aortic Dissection.
From Goldstein SA, Evangelista A, Abbara S, et al. Multimodality imaging of diseases of the thoracic aorta in adults: from the American Society of Echocardiography and the European Association of Cardiovascular Imaging: endorsed by the Society of Cardiovascular Computed Tomography and Society for Cardiovascular Magnetic Resonance. J Am Soc Echocardiogr . 2015;28(2):119–182.
| Modality | Recommendation | Advantages | Disadvantages |
|---|---|---|---|
| CT | First-line | Initial study for > 70% of patients Widely available, quickest diagnostic times Very high diagnostic accuracy Relatively operator independent Allows evaluation of entire aorta, including arch vessels, mesenteric vessels, and renal arteries |
Ionizing radiation exposure Requires iodinated contrast media Pulsation artifact in ascending aorta (can be improved with ECG gating) |
| TEE | First- and second-line | Very high diagnostic accuracy in thoracic aorta Widely available, portable, convenient, fast Excellent for pericardial effusion and for presence, degree, and mechanisms of AR and LV function Can detect involvement of coronary arteries Safely performed in critically ill patients, even those on ventilators Optimal procedure for guidance in OR |
Depends on skill of operator Blind spot for upper ascending aorta, proximal arch Not reliable for cerebral vessels, celiac trunk, SMA, and others. Reverberation artifacts can potentially mimic dissection flap (can be differentiated from flaps in most cases) Semi-invasive |
| TTE | Second-line | Often initial imaging modality in ED Provides assessment of LV contractility, pericardial effusion, RV size and function, PA pressure Presence and severity of AR |
Sensitivity not sufficient distal to aortic root Descending thoracic aorta imaged less easily and less accurately Misses IMH and PAU |
| MRI | Third-line | 3D multiplanar and high resolution Very high diagnostic accuracy Does not require ionizing radiation or ICM Appropriate for serial imaging over many years |
Less widely available Difficult monitoring in critically ill patients Not feasible in emergent or unstable clinical situations Longer examination time Caution with use of gadolinium in patients with renal failure |
| Angiography | Fourth-line | Rarely necessary | Often misses IMH (up to 10%–20% of ADs) Long diagnostic time Requires iodinated contrast media Increased morbidity Less sensitivity than CT, TEE, and MRI |
AD , Aortic dissection; AR , aortic regurgitation; CT , computed tomography; ECG , electrocardiographic; ED , emergency department; IMH , intramural hematoma; MRI , magnetic resonance imaging; OR , operating room; PA , pulmonary artery; PAU , penetrating atherosclerotic ulcer; SMA , superior mesenteric artery.
Bedside transthoracic echocardiography (TTE) followed by transesophageal echocardiography (TEE) is recommended only if CTA is not available or is contraindicated due to patient instability or contrast allergy ( Fig. 32.7 ). However, some investigators suggest that more widespread use of point-of-care ultrasound would lead to the diagnosis of patients who might otherwise be missed. Other imaging approaches, such as cardiac catheterization with aortic and coronary angiography, may be considered in some situations, depending on the other possible diagnoses for that patient. Currently, the major role for TEE evaluation of patients with acute aortic syndromes is for evaluation of the aortic valve and root in those undergoing emergency surgical intervention (discussed later). Imaging guidelines for patients with a suspected aortic dissection have been published by the American Heart Association (AHA) and the European Society of Cardiology (ESC) , ( Table 32.3 ).
TABLE 32.3
Imaging Guidelines for Patients With a Clinical Presentation Suggesting Acute Aortic Syndrome.
| Guideline | AHA 2010 | ESC 2014 |
|---|---|---|
| Acute Presentation | ||
| Chest radiography | Chest radiography is indicated in patients with low to intermediate risk to evaluate alternative causes of symptoms or the need for prompt additional imaging (class I). A negative chest x-ray study should not delay definitive aortic imaging in high-risk patients (class III). |
Chest radiography may be considered for low-risk patients (class IIb). |
| TTE | — | Recommended as the initial imaging investigation in patients with suspected acute aortic syndrome (class I) |
| Aortic imaging with TEE, CTA, or MRI | Urgent advanced imaging is recommended for all patients at high risk for aortic dissection (class I). | For unstable patients, TEE or CTA is recommended (class I). |
| — | In stable patients, CTA, MRI (class 1), or TEE (class IIa) is recommended. | |
| A second imaging study should be obtained if initial imaging study is negative but clinical suspicion is high (class I). | A second imaging study should be obtained if initial imaging is negative but clinical suspicion is high (class I). | |
| — | CTA is recommended for diagnosis of traumatic aortic injury (class I) with TEE if CTA not available (class IIa). | |
| — | CTA is recommended for diagnosis of contained thoracic aortic rupture (class I). | |
| Choice of imaging modality | Imaging modality is based on patient variables, institutional capabilities, and immediate availability (class I). | Imaging modality is chosen based on local availability and expertise. |
| Intraoperative Study | ||
| TEE | TEE monitoring is reasonable for all open surgical repairs and endovascular thoracic aortic procedures (class IIa). | — |
| Postprocedure Surveillance | ||
| CT or MRI | Imaging of the thoracic aorta is reasonable after type A or B aortic dissection (class IIa). | — |
| Imaging interval | Imaging at 1, 3, 4, and 12 months after dissection is reasonable. Using the same modality at the same institution allows side-by-side comparison of images (class IIa). | — |
AHA , American Heart Association; ESC , European Society of Cardiology.
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