Acute Type A Aortic Dissection Case File

Acute Type A Aortic Dissection Case File

Eugene C. Toy, Md, Michael d . Faulx, Md

Case 27

A 28-year-old man with no medical history presents with acute chest pain. The pain started suddenly approximately 2 hours ago, and he describes it as a severe (rated at 10/ 10) tearing sensation radiating to the back between the scapulae. He never experienced this pain before. His family history is unremarkable. He doesn’t smoke, use alcohol, or take illicit drugs. On presentation, vitals were as follows: heart rate 120 bpm, blood pressure in left arm 100/ 40 mmHg and in right arm 105/ 40 mmHg, respiratory rate 25 breaths/min, temperature 37.2°C (98.96°F), and his oximetry (O2 saturation) was 96% on 2 L/min of oxygen. His height is 2 m (6.56 ft) and weight 100 kg (220 lb). Physical examination revealed a tall, young gentleman in moderate distress. Cardiac examination revealed a regular rhythm with tachycardia, jugular venous pressure at 9 cm H2O, III/ IV diastolic murmur with highest intensity in the left lower sternal border, and no rubs. Chest exam revealed pectus carinatum and mild bibasilar crackles. His neurological exam is intact. Other features included mild scoliosis and arachnodactyly in his fingers. His presenting ECG and chest x-ray are shown in Figures 27-1 and 27-2. Laboratory data were normal except for an elevated CK, CK-MB, and troponin T.

• What is the most likely diagnosis?
• What is the best next diagnostic step?
• What is the best next step in therapy?

Figure 27-1. ECG for main subject of this case. Note the ST segment elevation in the inferior leads.

Figure 27-2. PA Chest x-ray for main subject of this case.

Answer to Case 27:

Acute Type A Aortic Dissection

• Most likely diagnosis: Acute type A aortic dissection complicated by severe aortic regurgitation and inferior myocardial infarction.
• Next diagnostic step: CT angiogram of the aorta.
• Next step in therapy: Emergent surgery.

ANALYSIS

Objectives

1. Know the different types of acute aortic dissection, the diagnostic approach, and how to manage them.
2. Understand the etiology, pathophysiology, and risk factors of different types of aortic aneurysms.
3. Be familiar with the different strategies of surveillance and management of aortic aneurysms according to their type and size.

Considerations

The patient is young and presents with sudden-onset severe and tearing chest pain radiating to his back. This presentation is classic for an acute aortic dissection. He also has skeletal features suggestive of Marfan’s syndrome. Patients with Marfan’s syndrome are at higher risk for developing thoracic aortic aneurysms and dissection. Marfan’s syndrome is an autosomal dominant disease, but he has no family history of Marfan’s syndrome. Remember that up to one-third of patients with Marfan’s syndrome develop the mutation in the Fibrillin-1 gene spontaneously so absence of family history does not preclude the diagnosis. The patient’s physical exam shows signs of type A aortic dissection with complications. There is no differential blood pressure between both arms because the dissection starts proximally and involves the right brachiocephalic and left subclavian arteries. The patient has a wide pulse pressure and a diastolic murmur heard at the left lower sternal border suggestive of aortic insufficiency, which occurs with proximal type A dissection involving the aortic root. The chest x-ray shows a widened mediastinum. In addition, he has an inferior ST elevation myocardial infarction suggestive of dissection into the ostium of the right coronary artery. He is tachycardic with borderline low blood pressure, jugular venous distention, and bibasilar crackles, which are all signs of acute heart failure due to the severe aortic insufficiency and inferior myocardial infarction. The clinician should be vigilant about recognizing these complications because they determine the next steps in management.

Although this patient has abnormal vitals, he is relatively stable and the next step would be to get a cardiac gated CT aortogram to diagnose the aortic dissection, determine its type, and identify the origin of the dissection flap as well as the degree of involvement of other major vessels. Cardiothoracic surgery should be consulted emergently in this case. The mortality rate for aortic dissection involving the ascending aorta is around 20% and increases by 1% per hour during the first 48 hours until the patient undergoes surgery. While waiting to go to the OR, initial medical management should focus on stabilizing the patient by controlling heart rate and blood pressure using intravenous beta-blockers and intravenous arterial vasodilators if needed. The beta-blockers should be given before the administration of direct-acting vasodilator therapy to reduce aortic wall strain, and the dose should be titrated to a target a heart rate between 55 and 65 bpm. However, beta-blocker therapy in this patient is relatively contraindicated because of the presence of severe aortic regurgitation and physical exam findings consistent with acute heart failure.

Approach To:

Aortic Diseases

DEFINITIONS

Ascending thoracic aorta: The ascending segment of the aorta extending from the aortic root to the aortic arch.

Aortic Arch: The aortic segment that gives rise to the major vessels of the head and arms (right brachiocephalic, left common carotid, and left subclavian); it represents the transition from the ascending aorta to the descending aorta.

Descending thoracic aorta: Aortic segment extending from just distal to the left subclavian artery until the diaphragmatic crura.

Abdominal Aorta: The part of the aorta distal to the diaphragmatic crura

Aortic Aneurysm: Pathologic weakening in the aortic wall leading to an increase in the diameter of the aorta by >50% of that expected for age- and sexmatched individuals.

Aortic dissection: A tear in the aortic wall between the tunica intima and media creating a false lumen compromising the integrity of the aorta and its branches.

CLINICAL APPROACH

Pathophysiology

A dissection usually results from a tear in the vascular intima, causing it to separate from the media with creation of a false lumen. Less commonly, it can result from rupture of the vasa vasorum (arterioles and capillary network supplying the aortic wall) with subsequent hemorrhage into the aortic wall. The high pressure in the aorta causes the false lumen to expand and propagate in an antegrade fashion, thus compromising the true lumen and branching vessels and causing end-organ damage. The tear can result from either pathologic weakness of the aortic wall or extremely high blood pressure.

Epidemiology

Aortic dissection involving the ascending aorta is the most common aortic emergency with an estimated prevalence of 5–30 cases per million. It usually affects older adults between 50 and 70 years of age. Presentation in younger individuals should raise suspicion for genetic or congenital disorders. Prevalence is 2–3 times more common in men than women. It is associated with very high mortality. estimated at 20% and then 1% per hour in the first 24–48 hours if surgery is not performed.

Risk Factors

Hypertension is present in 75% of individuals with dissection and represents the most prevalent risk factor for aortic dissection. Older age, atherosclerosis, and tobacco use are also common risk factors for dissection.

Genetic diseases also contribute to the risk of aortic dissection and dissections in younger patients should prompt some investigation for an underlying predisposing disorder. Marfan's syndrome is an autosomal dominant defect in the Fibrillin-1 gene that regulates extracellular matrix and TGF-B. It is associated with ocular and musculoskeletal manifestations in addition to aortic pathology. Loeys-Dietz syndrome is also an autosomal disorder with a defect in the TGFBR1 or TGFBR2 gene that encodes TGF-B receptors. It is associated with hypertelorism and bifid uvula and tends to involve the aortic root. Ehlers-Danlos type IV is an autosomal dominant defect in the COL3A1 gene, which encodes procollagen 3. Other clinical manifestations include easy bruising and uterine rupture. Certain congenital disorders are also associated with an increased risk for aortic dissection such as bicuspid aortic valve (BAV), coarctation of the aorta, Turner’s syndrome, and tetralogy of Fallot.

Other causes of aortic dissection include cocaine abuse and chest trauma, including recent surgical or procedural instrumentation. Inflammation of aortic tissue can also cause aortic dissection including infections such as tertiary syphilis and inflammatory vasculitides such as Takayasu’s arteritis, giant cell arteritis, and Behçet disease.

Classification

Aortic dissections are classified in several ways based on their anatomical features (see Figure 27-3). An acute dissections are by definition is <2 weeks old; otherwise it is classified as chronic.

Clinical Features, Diagnosis, and Management

See Table 27-1 for a detailed approach to the management of aortic dissection.

Clinical Approach to Aortic Aneurysms

Aortic aneurysms are classified as thoracic aortic aneurysms (TAAs), abdominal aortic aneurysms (AAAs), or thoracoabdominal aortic aneurysms (TAAAs). The Crawford classification system of aortic aneurysms is shown in Figure 27-4.

Abdominal Aortic Aneurysms (AAAs)

Pathophysiology: The pathologic dilation of the aorta occurs due to degeneration and inflammation in the aortic wall causing loss of elasticity with subsequent aneurismal dilation. The larger the aneurysm, the more rapidly it will expand, 

Figure 27-3. Stanford and DeBakey classification of aortic dissections. (Reproduced, with permission,

from Doherty GM. Current Diagnosis & Treatment: Surgery, 13th ed. New York: McGraw-Hill Education, 2010. Figure 19-16.)

according to Laplace’s law. Aneurysms >6 cm have >20% per year risk of rupture. Smaller (5–6-cm) aneurysms have 6% yearly risk of rupture. Rupture most commonly occurs in the left retroperitoneal space and is contained.

Epidemiology: AAA is more common than TAA. Of all aneurysm cases reported, 75% involve the abdominal aorta. Incidence of all aortic aneurysms in men is approximately 5% and women 1–2% in those aged more than 65 years. Also, 95% of AAAs are infrarenal. Rupture of AAA is associated with very high mortality. The “rule of quarters” applies to the outcome of aortic rupture—onequarter die before reaching the hospital, a second quarter die before surgery, and a third quarter die perioperatively while undergoing surgery, making overall survival rate after rupture about 25%.

Etiology and risk factors: Older age, current or past history of smoking, male gender, hypertension, hyperlipidemia, and atherosclerosis in other vascular beds are all associated with an increased risk for aortic aneurysms. Approximately one-quarter of AAA patients have a first-degree relative with an AAA. Firstdegree male relatives of patients with AAA have a 12 times greater risk of having an AAA. Infections such as salmonella and Staphylococcus aureus can cause mycotic aneurysms. Large-vessel vasculitides such as Takayasu’s arteritis, giant cell arteritis, or Behçet’s syndrome can also lead to aneurysm formation. As with dissections, blunt external or internal iatrogenic trauma can predispose to the development of aneurysms.

Clinical Presentation: The majority of AAAs are discovered incidentally during routine care or imaging for other reasons and are asymptomatic. Symptoms are usually associated with large aneurysms or those with rapid growth. Patients can present with sudden, constant, sharp, or dull back pain, which may radiate to the legs, flanks, or buttocks. Shock, pallor, abdominal distention, and signs of

Figure 27-4. Crawford classification system for aortic aneurysms. (Reprinted, with permission, from Edmunds LH Jr, ed. Cardiac Surgery in the Adult. New York: McGraw-Hill; 1997).

end-organ damage could all be signs of uncontained ruptured aneurysms. Complications of AAA include formation of arteriovenous fistula between AAA and the inferior vena cava as well as aortoenteric fistula between AAA and the intestines, causing gastrointestinal bleeding, and these are all indications for surgical intervention.

Physical exam findings: A palpable, pulsatile abdominal mass can be felt in many patients with large AAAs. Deep palpation should be avoided in patients with a known large aneurysm to prevent aneurysmal rupture. Auscultation could reveal an abdominal bruit. Bruits in other vessels are also common because these patients usually have atherosclerosis in multiple major arteries. Absent pulses or cold extremities could be signs of distal embolization from a mural thrombus in the wall of the aneurysm.

Diagnostic Testing: Abdominal ultrasound is the most commonly used screening tool for AAA, and it is widely available with no radiation exposure or need for IV contrast. It is cost-effective and accurate for aneurysms up to 4.5 cm in diameter. It can be used for surveillance as well. However, it is not a good modality for evaluating the branches of the aorta, and thus further imaging is needed for better delineation of detailed aortic anatomy prior to surgical intervention if indicated. CT aortography provides accurate measurement of aneurysm size, shape, and involvement of branching vessels. It is better than ultrasound for aneurysms >4.5 cm, and it allows for assessment of extravasated blood and the extent of rupture. Magnetic resonance angiography (MRA) is also accurate for assessing aneurysm size and pathology and is well suited for the assessment of suprarenal and ileofemoral involvement. Conventional aortography is invasive and can cause underestimation of aneurysm size if there is mural thrombus.

Screening: The US Preventative Services Task Force recommends one-time ultrasound screening for AAA for men 65–75 years of age with a history of smoking. The Society for Vascular Surgery recommends AAA screening also in men and women with a family history of AAAs.

Management: Management is dictated by whether the patient is symptomatic, the size of the aneurysm, and associated complications or end-organ involvement. (See Tables 27-2, 27-3, and 27-4 for more information regarding management.)

Thoracic Aortic Aneurysms (TAAs)

Pathophysiology: TAA is most commonly caused by cystic medial degeneration characterized by loss of the elastic lamina and smooth muscles in the tunica media and replacement with cysts with basophilic ground substance, leading to a cystic appearance. It can also be caused by atherosclerosis and inflammation in the aortic wall as in AAA. Genetic diseases can cause TAA by various mechanisms such as defects in collagen, procollagen, and TGF-B production pathways.

Etiology and risk factors: Older age, current or past history of smoking, male gender, hypertension, hyperlipidemia, and atherosclerosis in other vascular beds

are all risk factors for TAA. Genetic diseases such as Marfan’s, Loeys-Dietz, and

Ehlers Danlos type IV syndromes are also risk factors. Infections such as syphilis

affecting the aortic root or mycotic bacterial aneurysms can also result in TAA

formation. Large-vessel vasculitides, trauma, and remodeling of chronic aortic dissections are also risk factors for TAA.

Clinical Presentation: Most TAAs are discovered incidentally during routine care or imaging for other reasons and are asymptomatic. Symptoms usually develop when the TAA is large or ruptured, causing sudden-onset, severe, sharp chest or back pain. They rupture into the left pleural space more commonly but can also rupture into the pericardium, causing cardiac tamponade, or into the esophagus, causing hematemesis. Large aneurysms can also compress other structures in the thorax. This, in turn, can cause superior vena cava compression syndrome, dysphagia due to esophageal compression, hoarseness due to laryngeal nerve compression, or dyspnea and cough due to trachea or main bronchi compression. Large aortic root aneurysms can cause severe aortic insufficiency with heart failure. They can also compress the coronary vessels, causing myocardial ischemia; they can also cause aortic dissection.

Physical exam findings: The physical exam is not always helpful in patients with TAA. Rarely, a suprasternal pulsatile mass can be felt. Detailed cardiovascular examination is necessary to evaluate for complications of TAA such as aortic regurgitation, cardiac tamponade, or thromboembolic phenomena. The physician must complete a full body exam to detect signs of end-organ compromise due to the TAA.

Diagnostic testing: Chest x-ray can show a widened mediastinum, trachea or bronchial displacement, or unusual aortic borders. Computed tomography angiography (CTA) and MRA are very sensitive and specific for the assessment

Abbreviations: DREAM, Dutch randomized endovascular aneurysm management (trial); EVAR, endovascular aortic repair; OVER, open versus endeovascular repair.

of TAA. CTA is the most commonly used modality. MRA provides better assessment of the aortic root, aortic valve, and pericardium. TEE is of limited benefit to evaluate the aortic root, valve, and ascending aorta, and conventional aortography is occasionally reserved for preoperative planning occasionally.

Management: For details regarding the management of TAA, see Tables 27-4 and 27-5.

CASE CORRELATION

• See also Case 1 (acute coronary syndrome/STEMI), Case 2 (acute coronary syndrome/NSTEMI), Case 3 (cardiogenic shock), Case 6 (acute valvular regurgitation), Case 21 (chest pain), and Case 22 (syncope).

COMPREHENSION QUESTIONS

27.1 Which of the following is an indication to undergo emergent aortic surgery?

A. Acute type B aortic dissection

B. Abdominal aortic aneurysm 4.5 cm in diameter

C. Chronic type A aortic dissection

D. Ruptured aortic aneurysm 5 cm in diameter

27.2 A 65-year-old gentleman with history of uncontrolled hypertension and smoking had a screening abdominal ultrasound last year showing an infrarenal abdominal aortic aneurysm 4 cm in diameter. He says he has been taking his blood pressure medications, but his blood pressure in clinic today is 170/90 mmHg. He continues to smoke. He is here today for a repeat abdominal ultrasound that shows the aneurysm to be 5.2 cm in diameter. In addition to counseling him to quit smoking, what is the best next step in this patient’s management?

A. Optimize blood pressure control only

B. Optimize blood pressure control and refer to vascular surgery for surgical repair

C. Repeat an ultrasound in 3 months

D. Repeat an ultrasound in 1 year

E. Make no changes or referrals at this time

27.3 A 55-year-old man presents with worsening shortness of breath and exercise tolerance for the past 6 months. He has also been noticing worsening lower extremity edema, orthopnea, and paroxysmal nocturnal dyspnea. His medical history is significant only for being told that his thoracic aorta might be larger than average 5 years ago when he had a chest x-ray. One of his cousins had problems with one of his heart valves when he was young. No other significant family history. Physical examination reveals a blood pressure of 120/40 mmHg and a heart rate of 120 bpm. He has a II/IV diastolic murmur heard over the left lower sternal border and Corrigan’s pulse. He has no abnormal skeletal, occular, or morphologic features. What is the most likely diagnosis?

A. Bicuspid aortic valve and aortic root dilation causing aortic insufficiency

B. Aortic insufficiency and aortic root dilation due to Marfan’s syndrome

C. Patent foramen ovale with right-to-left shunt

D. Infective endocarditis causing tricuspid valve stenosis

ANSWERS

27.1 D . Ruptured aortic aneurysm is a life-threatening emergency, especially when the rupture is not contained, and is an indication to undergo emergent surgery. It has very high mortality rate.

27.2 B. Optimize blood pressure control and refer to vascular surgery for surgical repair because his abdominal aneurysm has expanded at a rate of >1 cm per year. This patient also needs to stop smoking and needs better blood pressure control.

27.3 A. The patient clearly has aortic insufficiency, evident by symptoms of progressive heart failure, diastolic murmur at the left lower sternal border, wide pulse pressure, and Corrigan’s pulse. He has no morphologic features to suggest Marfan’s. His age of presentation is typical of bicuspid aortic valve disease. Bicuspid aortic valve can itself cause aortic insufficiency, but it also predisposes to ascending aortic aneurysms, causing dilation of the root and aortic insufficiency.

CLINICAL PEARLS

• Acute aortic dissection presents with sharp chest pain radiating to the back.
• Type A acute aortic dissection is a surgical emergency. Type B aortic dissections should be managed medically unless surgery is indicated for rupture or vascular compromise of end organs.
• Aortic aneurysms are generally asymptomatic and discovered incidentally. Asymptomatic aneurysms should be monitored periodically until they reach a size of ≥5.5 cm, and then surgery is indicated. Surgery is indicated also for symptomatic patients.
• Endovascular aortic repair (EVAR) performs as well as open-heart surgery in randomized controlled trials, where it has lower perioperative mortality, but the long-term mortality is similar. However, EVAR requires certain criteria that are available in only 30–60% of patients.
• Screening with an abdominal ultrasound is recommended for male patients 65–75 years old with a history of smoking.

References

Baverman AC, Thompson RW, Sanchez LA. Diseases of the aorta. In: Bonow O, Braunwald E, eds. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Philadelphia, PA: Elsevier, Saunders; 2012:1309–1337. 

Blankensteijn J, de Jong SECA, Prinssen M, et al. Two-year outcomes after conventional or endovascular repair of the abdominal aortic aneurysms. N Engl J Med. 2005;352:2398–2405. 

Bunte MC, Thamilarasan M. Aortic aneurysm and aortic dissection. In: Griffin BP, ed. Textbook of Cardiovascular Medicine. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2013:459–480. 

EVAR Trial Participants. Comparison of endovascular aneurysm repaire with open repair in patients with abdominal aortic aneurysm (EVAR 1 trial), 30-day operative mortality results: randomised controlled trial. Lancet. 2004;364:843–848. 

EVAR Trial Participants. Endovascular aneurysm repair and outcome in patients unfit for open repair of abdominal aortic aneurysm (EVAR trial 2): randomised controlled trial. Lancet. 2005;365:2187–2192. 

Fleming C, Whitlock EP, Beil TL, et al. Screening for abdominal aortic aneurysm: a best-evidence systematic review for the U.S. Preventative Services Task Force. Ann Intern Med. 2005;142:203–211. 

Greenhalgh RM, Brown LC, Powell JT, Thompson SG, Epstein D, Sculpher MJ; United Kingdom EVAR Trial Investigators. Endovascular versus open repair of abdominal aortic aneurysm. N Engl J Med. 2010;362:1863–1871. 

Rooke TW, Hirsch AT, Misra S, et al. 2011 ACCF/AHA focused update of the guideline for the management of patients with peripheral arterial disease (updating the 2005 guideline). J Am Coll Cardiol. 2011;58(19):2020–2045. 

Svensson LG, Khitin L. Aortic cross-sectional area/height ratio timing of aortic surgery in asymptomatic patients with Marfan syndrome. J Thorac Cardiovasc Surg. 2002;123:360–361. 

Svensson LG, Kim KH, Lytle BW, et al. Relationship of aortic cross-sectional area to height ratio and the risk of aortic dissection in patients with bicuspid aortic valves. J Thorac Cardiovasc Surg. 2003;126:892–893.

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