Acute Aortic Dissection

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Definition

Dissection of the aorta is an event that results in the separation of the layers of the media by blood, producing a false channel with variable proximal and distal extension.

1. Etiology
· Cystic medial necrosis - 20%
· Marfan syndrome - 20-40%
· Other causes: hypertension, bicuspid aortic valve/aortic stenosis, atherosclerosis, coarctation, pregnancy, trauma, aortic cannulation, aortic cross-clamping, cardiac catheterization

2. Morphology
· Blood leaves the normal aortic channel through intimal tear, rapidly dissecting through the media to produce a false channel
· The intimal tear is sometimes absent; possible rupture of vasa vasorum with medial hemorrhage
· Usually the dissection proceeds distally; 38% dissect proximally and 10% in the transverse arch
· Dissection may shear off or extend into branch arteries
· False channel characteristics:
1) Thickens and gradually enlarges with time
2) May interrupt blood supply of branches by ext ernal compression
3) Outer wall thin - media + adventitia
4) May rupture to pericardium or pleural space
5) May thrombose

3. Classification
· Acute = less than 2 weeks, chronic = greater than 2 weeks

DeBakey I	Ascending + arch	Stanford A
DeBakey II	Ascending only	Stanford A
DeBakey IIIa	Descending only	Stanford B
DeBakey IIIb	Descending + abdom	Stanford B

4. Clinical Features
1) Severe pain - tearing, interscapular, precordial, neck, migrating, persisting

2) Signs of occlusion of major vessel
· Arch - stroke, syncope
· Intercostal - paraplegia
· Renal - oliguria-anuria
· Iliac - ischemic leg

3) Sudden death
· Rupture to pericardium, pleural, peritoneal space
· Shear off coronary artery

4) Hypovolemic Shock
· Blood in periaortic tissues
· Acute aortic valve insufficiency
· Cardiac tamponade

5.. Diagnosis
1) Imaging
· Chest X-ray - widened mediastinum, cardiomegaly, pleural effusion, intimal calcification seperated more than 6mm from the edge
· Echo - identifies intimal flap/false channel, noninvasive, no contrast media, performed at bedside
· TEE is best for the descending aorta; TTE best for the ascending aorta and arch
· Aortography - conventional method of diagnosis (gold standard), shows origin of arteries from true or false lumen
· CT Scan - identifies intimal flap rapidly, requires contrast media
· MRI - multiple planes, cine for AI

2) Main points of interest
· Involvement of the ascending aorta
· Location of the intimal tear
· Status of perfusion in the major branches
· Size of the aorta and presence of AI
· Extent of the false lumen
· Pericardial effusion

6. Treatment Overview
· Type A and complicated type B dissections are managed surgically
· Uncomplicated type B dissections are managed medically
· The goals of surgical therapy are to prevent extension, excise the intimal tear, and replace the segment of aorta which is susceptible to rupture
· The goals of medical therapy are to prevent extension, control blood pressure, and relieve pain

7. Treatment - Ascending Aorta
· Immediate operation is indicated because rupture is likely
· Contraindications: ? advanced age, incurable coexisting disease, paraplegia
· Note: new stroke may resolve, not a contraindication
· Replace ascending aorta and the aortic valve if insufficient; the valve may be worth preserving if normal
· Replace arch if false channel leaking or site of tear

· Operative strategy (elephant trunk)
1) Use circulatory arrest if indicated
2) Incise in a longitudinal fashion, avoiding the phrenic and recurrent nerves
3) Follow the dissection from inside the aorta to determine extent and remove damaged intima and media
4) Invert the graft into the distal aorta and approximate only the aortic adventitia to the inside of the graft
5) Pull the graft out and anastomose the arch vessels as a group
6) Once the distal repair is completed, the proximal portion can be performed off pump

8. Treatment - Descending Aorta
1) Medical treatment indicated unless complications of dissection have occurred
· NTP + beta-blocker to maintain normal blood pressure
· 80% survive 1 year
· Close follow-up required, 50% die in 3-5 years

2) Complications dictate immediate operation (interposition graft or fenestration)
· Hemothorax, persisting pain, limb ischemia, acute renal failure, paraparesis (malperfusion syndrome)
· Paraplegia NOTan indication for operation because not likely to resolve

9. Results After Operation
1) Early (hospital) death
· Ascending aorta - 5-10% (up to 30%)
· Arch - 10-25% (up to 50%)
· Descending - 10% (up to 25-60%)

2) 10 year survival - 46%
· 1/3 late death related to residual old false channel or redissection

3) Aneurysm of false channel
· Uncontrolled hypertension - 50%
· Controlled blood pressure - 10-20%

4) Redissection - 10% (Marfan higher)