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Ashley EA, Niebauer J. Cardiology Explained. London: Remedica; 2004.

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Cardiology Explained.

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Chapter 12Aneurysm and dissection of the aorta

Aortic aneurysm

Aneurysms of the thoracic aorta (see Figure 1) are not as common as those affecting the abdominal portion, but carry a higher risk of rupture. Both share the same primary cause: atherosclerosis. In the past, ascending aortic aneurysms were typically caused by syphilis, but nowadays hypertension or Marfan's syndrome are more likely to be responsible. Symptoms result from the acute painful tear felt as central chest pain, which radiates to the back, and from the compression of surrounding structures:

Figure 1. A typical aneurysm of the thoracic aorta at surgery.

Figure 1

A typical aneurysm of the thoracic aorta at surgery.

  • dysphagia (esophagus)
  • dyspnea (bronchi; pericardial effusion)
  • upper thorax/neck swelling (superior vena cava)

Standard radiology and echocardiography can be useful in monitoring the progression of aneurysms. Computed tomography (CT) is the gold standard and should be carried out annually in patients with known disease that does not yet require surgery or percutaneous placement of an aortic prosthesis/stents. However, magnetic resonance imaging (MRI) is increasingly being used.

Management

The central feature of management is rigorous control of blood pressure (BP). Therapy should include a β-blocker and be aimed at keeping systolic pressure <120 mm Hg.

Marfan's syndrome

Described by Bernard Marfan in 1896, this autosomal dominant single-gene disorder results from a mutation of the fibrillin gene on chromosome 15. The key clinical features are:

  • arachnodactyly (long spindly fingers)
  • high-arched palate
  • pectus excavatum
  • an armspan greater than height
  • upward lens dislocation
  • aortic root dilatation and aortic incompetence
  • mitral valve prolapse

Abraham Lincoln

Abraham Lincoln was both tall (6 ft 4 in) and thin (160–180 lb). He had long arms and legs, and large, narrow hands and feet. Contemporary descriptions of his appearance indicate that he was stoop-shouldered, loose-jointed, and walked with a shuffling gait. In addition, he wore eyeglasses to correct a visual problem. It is not surprising then that many have concluded that he suffered from Marfan's syndrome. Certainly, he shared a great-great-grandfather with a man who had a confirmed diagnosis of Marfan's. In fact, this observation, reported by Dr Harold Schwartz in 1959, was the beginning of a mystery that has taxed historians and doctors ever since. However, Lincoln showed few other signs of Marfan's. He had visual problems, but examination of his eyeglasses reveals he was farsighted and not nearsighted – a classic symptom of Marfan's. Also, a cast of his hands has shown that they were muscular and powerful, and not the slender hands of someone with Marfan's syndrome. Although the fun of the mystery is often in the debate and not in the answer, this is one theory that could be tested: a limited amount of bone fragments and hair from Lincoln was retained by the attending physician at the time of his assassination. Molecular testing using these samples could end the debate in an instant.

The key differential diagnosis is homocystinuria, a recessively inherited defect in amino-acid metabolism, which has similar skeletal features. Homocystinuria is associated with low IQ and typically causes downward dislocation of the lens. However, it does not affect the heart.

Marfan's patients should undergo annual echo screening of the aortic root and prophylactic replacement should be considered when the diameter reaches 55 mm (a normal diameter is 40 mm). Beta-blockade can retard the rate of dilatation, but patients who do not have the replacement die in the fourth or fifth decade from aortic dissection or cardiac failure secondary to aortic regurgitation.

Sinus of Valsalva

A congenital aneurysm of the sinus of Valsalva is a rare cause of arteriovenous shunt. It is formed because of a weak connection between the aortic valve and the aortic fibrous ring. This enlarges during childhood and usually ruptures in adulthood into the right ventricle, creating a volume shunt from the left to the right side of the heart. The diagnosis is confirmed by aortography. Without surgical repair, biventricular failure results.

Aortic dissection

Dissection, which is usually caused by atherosclerosis, is the development of a tear in the aortic intima that creates a false lumen through the aortic media for a variable distance (see Figures 2 and 3).

Figure 2. The adventitia, media, and intima of the aortic wall.

Figure 2

The adventitia, media, and intima of the aortic wall.

Dissection is classified according to whether it includes the ascending aorta (type A) or not (type B) (see Figure 3). Type A dissection is a surgical emergency because of the high risk of proximal extension, rupture, and sudden death. If a type A dissection is confirmed by CT or MRI, the patient should be operated on immediately. The highly specialized repair operation can involve replacement of the aortic root with a vascular graft, reimplantation of the coronary arteries, and resuspension of the aortic valve. In some cases it may be necesssary to replace the valve.

Figure 3. Classification of dissection.

Figure 3

Classification of dissection.

In contrast, type B dissection is managed medically by aggressive antihypertensive treatment. In the acute situation, the systolic BP should be lowered to <110 mm Hg using intravenous (IV) β-blockade (eg, labetalol). Beta-blockade, as well as reducing the BP, reduces the BP's rate of rise and for this reason it is preferred to sodium nitroprusside as the first-line IV agent. If β-blockers are contraindicated then rate-limiting calcium-channel blockers, such as diltiazem or verapamil, can be used.

Dissection typically presents with a severe tearing central chest pain that radiates to the back. A patient with such a history should be referred urgently to a specialist center since the ascending aorta might be involved. Immediate investigations include:

  • CT or MRI scan (see Figures 4 and 5, previous page)
  • transesophageal echo to assess possible aortic regurgitation (see Figure 6, previous page)
  • transthoracic echo for pericardial effusion
  • preoperatively, coronary artery disease must be ruled out by coronary angiography

Figure 4. Computed tomography scans showing dissection of the aorta.

Figure 4

Computed tomography scans showing dissection of the aorta.

Figure 5. Magnetic resonance images showing separation of the dissected membrane.

Figure 5

Magnetic resonance images showing separation of the dissected membrane. AA: ascending aorta; F: false lumen; I: intimal flap; P: pulmonary artery; S: subclavian artery; T: true lumen.

Figure 6. Transesophageal echocardiograms showing separation of the dissecting membrane.

Figure 6

Transesophageal echocardiograms showing separation of the dissecting membrane. AV: aortic valve; F: false lumen; I: intimal flap; LA: left atrium; T: true lumen.

A physical examination can prove useful diagnostically, but should not delay the above emergency investigations. It should include:

  • measurement of the BP in both arms (unequal BP is a sign, though not a reliable sign)
  • documentation of all peripheral pulses (lack of peripheral pulses may be the only sign if the dissection spares the ascending aorta)
  • close attention to heart sounds (aortic regurgitation and tamponade are possible with proximal extension)
  • neurologic examination (hemiplegia or paraplegia can result from occlusion of the carotid arteries and anterior spinal arteries, respectively)

Other potentially useful investigations are:

  • assessment of renal function, including urine microscopy and catheterization for accurate measurement of renal output
  • a chest x-ray, which often shows a distended aorta or generalized widening of the mediastinum (see Figures 7 and 8)

Figure 7. (a,b) Chest x-rays.

Figure 7

(a,b) Chest x-rays. A dissected aorta can be seen in (b) (arrow).

Figure 8. Chest x-ray showing extreme dissection of the aorta (arrows).

Figure 8

Chest x-ray showing extreme dissection of the aorta (arrows).

Further reading

  1. Erbel R, Alfonso F, Boileau C. et al. ; Task Force on Aortic Dissection, European Society of Cardiology. Diagnosis and management of aortic dissection. Eur Heart J. 2001;22:1642–81. [PubMed: 11511117]
  2. Khan IA, Nair CK. Clinical, diagnostic, and management perspectives of aortic dissection. Chest. 2002;122:311–28. [PubMed: 12114376]
Copyright © 2004, Remedica.
Bookshelf ID: NBK2210

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