81 DISSECTING AORTIC ANEURYSM
Laurence H. Brinckerhoff M.D., David N. Campbell M.D.

1. Why is the term dissecting aortic aneurysm really incorrect?

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The correct term should be dissecting aortic hematoma because the lesion is not an aneurysm. Blood dissects between the middle and outer layers of the media and adventitia of the aorta (specifically, there does not need to be an intimal tear, although there usually is).

2. When should the diagnosis be entertained?

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Suspicion is the most important factor because no one feature is common to patients presenting with aortic dissections. In any patient who presents with severe knifelike, ripping chest and back pain, the diagnosis of aortic dissection should be considered.

3. After the diagnosis is entertained, how should the patient be managed?

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Two thirds of patients are hypertensive, so blood pressure must be controlled. The other diagnosis to be strongly considered is acute myocardial infarction (MI). An electrocardiogram often rules out MI, but some aortic dissections tear off a coronary artery; thus, both acute infarction and aortic dissection occur concurrently (this patient group is in big trouble).

4. What is the most significant diagnostic clue on physical examination?

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A new aortic valvular diastolic murmur, indicating aortic valvular regurgitation caused by distortion of the valve structure by the mural hemotoma. In addition, the dissecting hematoma can encircle the lumen or actually cleave the takeoff of the subclavian or femoral vessels, resulting in the loss of pulses. Neurologic findings, including paraplegia and hemiplegia, may also be present because of similar flap occlusion of the great vessels.

5. Which chest radiograph findings are helpful in diagnosis?

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Widened mediastinum and loss of aortic knob silhouette-a hematoma surrounding the aorta makes the aortic outline blurry-are helpful findings.

6. How is the diagnosis confirmed? What are the best diagnostic studies?

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The literature reports the high accuracy of transesophageal echocardiography (TEE) and computed tomography angiography (CTA) in the diagnosis of aortic dissections. Some institutions rely solely on one of these diagnostic tool (both studies are operator dependent). However, the aortogram is still the gold standard, but it requires more time. If time allows and the patient is stable, an aortogram should be obtained to confirm the diagnosis, type of dissection (ascending versus descending), status of the aortic valve, and status of the coronary arteries. In fact, the modalities may be complementary: whereas the TEE or CTA confirms the diagnosis, the aortogram defines location and evaluates the status of the aortic valve and coronary arteries.

7. What are the types of dissection?

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The following classification has both therapeutic and prognostic value:

* Ascending (type A) involves only the ascending or both the ascending and descending aorta.
* Descending (type B) involves only the descending aorta.

8. Who cares whether a dissection involves the ascending (type A) or descending (type B) aorta?

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Ascending dissections require early surgical correction to avoid extension into the coronary or carotid arteries, rupture into the pericardium (tamponade), or both.
Descending dissections do not involve the ascending aorta and may be managed medically or surgically (see Controversies).

9. What is the key to medical management?

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The blood pressure (BP) should be lowered to 100-110 mmHg (systolic) with a combination of sodium nitroprusside and propranolol. Propranolol is particularly important because it decreases the contractility of the myocardium (dp/dt), thereby decreasing the shearing force that prevents propagation of the dissection down the aorta. Conceptually, the BP should be lowered as much as possible, but the patient must continue to perfuse the end organs (i.e., make urine).

10. What are the principles and advantages of surgical management?

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1. Ascending dissectionTo close off the hematoma by obliterating the most proximal intimal tear
2. To restore competency of the aortic valve
3. To restore flow to any branches of the aorta that have been sheared off and receive blood flow from a false lumen
4. To protect the heart during these maneuvers and to restore coronary blood flow if a coronary artery has been sheared off
5. To look for tears in the transverse aortic arch

Technique: Use of deep hypothermia circulatory arrest with or without retrograde cerebral perfusion is in vogue at present. This technique allows the arch to be inspected and the distal anastomosis of the Dacron graft to be sewn accurately to the distal ascending aorta in an open fashion. Whether to replace or repair the aortic valve is controversial.

1. Descending dissectionTo close off the hematoma by obliterating the most proximal intimal tear
2. To restore blood flow to branches of the aorta fed by the false channel

Technique: Surgery is performed using partial cardiopulmonary bypass, or the “clamp and run” technique, in which the aorta is cross-clamped and the graft is sewn in as fast as possible (see Controversies).
KEY POINTS: DISSECTING AORTIC ANEURYSM

1. The correct term should be dissecting aortic hematoma because the lesion is not an aneurysm.
2. A new aortic valvular diastolic murmur, indicating aortic valvular regurgitation caused by distortion of the valve structure by the mural hematoma.
3. Ascending dissections require early surgical correction to avoid extension into the coronary or carotid arteries, rupture into the pericardium, or both.
4. Descending dissections may be managed medically; blood pressure should be lowered to 100-110 mmHg with a combination of sodium nitroprusside and propranolol.

11. What are the operative complications?

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* Hemorrhage (20%): very common because of the use of heparin and the poor quality of aortic tissue (like wet Kleenex)
* Renal failure (20%)
* Pulmonary insufficiency (30% higher in repair of descending dissections)
* Paraplegia: often presents before operation; as a surgical complication, it usually occurs only with descending dissections (11%)
* Acute MI or low cardiac output (30%)
* Bowel infarction (5%)
* Death (15%): higher for acute than chronic dissections and higher for repair of ascending dissections

12. What are the long-term results?

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Of patients who survive the operation, two thirds die within 7 years because of comorbid cardiac and cerebrovascular disease.