Thoracic Aortic Dissection
Physical disruption of the intima of the aorta (flap) with degeneration of the media resulting in a dissection plane through which blood flows into a false lumen.
Can lead to:
- Compression of branches of the aorta
- Malperfusion
- Cardiac complications – such as aortic regurgitation, coronary ischemia, tamponade
- Rupture
- Death
Causes - Direct Mechanical – Trauma, Iatrogenic (e.g. Aortic cannulation)
- Repetitive insult and intimal breakdown due to hypertension
- Intimal disruption due to atherosclerotic plaque ulceration
- Intramural Hematomas – absence of either a definable flap or communication between the true and thrombosed false lumen of the aorta. These are thought to be secondary to rupture of the vasa vasorum
Epidemiology
- Most common acute disease of the aorta.
- Usually within the 5th – 7th decade of life
- M:F ratio is approximately 2:1
- Hypertension, Bicuspid Aortic Valve, and Connective tissue disorders, such as Marfan's syndrome and Ehlers-Danlos Syndrome, all have higher incidence of aortic dissection.
Classification
- This is very important for deciding treatment options as treatment is based on involvement of the ascending aorta or not, or if dissection is limited to the descending aorta (distal to the left subclavian artery).
- The most commonly used are the Stanford, DeBakey classifications. In the UK the Stanford is used more often.
Stanford Classification
Type A - involves the ascending aorta and arch, even is the descending aorta is also involved.
Type B - involves only the descending aorta (distal to the left subclavian artery).
DeBakey classification:
I - invovles the ascending aorta and arch of the aorta
II - involves the ascending aorta only
III - involves the descending aorta only (IIIa - descending thoracic aorta only; IIIb - descending thoracic and abdominal aorta)
- Aortic Dissections are also classified as acute or chronic –
- Acute – symptoms presenting within 2weeks
- Chronic – symptoms lasting over 2 weeks
Presentation
- Presentation is largely dependent on either hemorrhage, or aortic branches compressed or sheared off
- Severe tearing pain in chest and back is very common
- Up to 40% die immediately.
- Hemorrhage produces hypotension and shock
- Branches sheared off or compressed result in a myriad of signs and symptoms depending on branch(s) affected – stroke, renal ischaemia, visceral ischaemia, coronary ischaemia can thus result
- Sudden death – if tamponade due to rupture into pericardium
Diagnosis
- If the clinical picture suggests aortic dissection then always maintain a high index of suspiscion
- Timely diagnosis and treatment is essential to reduce mortality and morbidity
- The major differntials include - Acute Coronary Syndrome and Pumonary Embolus
- Imaging is key –
- CXR – shows widened mediastinum, but usually not much more can be deduced from it
- Angiography in the form of CT Angiogram (CTA) or MRA, with or without 3D reconstruction, – is the best
- Echocardiogram – is usually a very welcome addition, especially to asses aortic root and valve, pericardium and the heart. However, due to the emergent state of this condition this may not always be available.
- In emergency – the combination of a CTA and intra-operative transoesophageal echocardiography is the most commonly used.
Treatment
- Generally the classification dictates treatment, particularly in the acute setting
- Stanford Type A – requires immediate operative intervention
- Stanford B Type – is treated medically, at least initially
Stanford Type A:
- Control blood pressure and attain hemodynamic stability
- Adequate imaging is essential - CTA/MRA
- Prompt surgical repair
- Choice of approach depends on - expertise, associated valve or coronary artery involvement, and proximity of branches to the intimal tear. However, approach is almost always via a median sternotomy.
- Goals of surgery are to
- Excise/Exclude intimal tear to arrest dissection
- Replace ascending aorta/flap segment in order to prevent rupture
- If associated aortic incompetence then either
- Replace the aortic valve +/- the aortic Root, or
- Repair/Resuspension of the aortic valve
- Aortic arch replacement if malperfusion of great vessels
- CABG – if the coronaries are involved. This is usually the right coronary, as left main stem involvement is usually fatal
Stanford Type B:
- Initial management is medical and the aim is to
- Control blood pressure, and
- Prevent propagation of the dissection
- In the acute setting – IV beta-blockers are most commonly used. Vasodilators such as nitroprusside may be added if the beta-blockers prove inadequate
- Surgery or EVAR is employed if –
- Failure of medical therapy, and/or
- Complicated descending aorta dissection (e.g. Malperfusion)
Outcomes
- Type A
- Operative Mortality of Type A repair – 10 – 20%
- Survival – 55% at 5 years and 37 – 46% at 10 years
- Type B survival, if medically treated –