Aortic Dissection: Lecture notes

Epidemiology

Incidence: 3 cases per 100 000 people per year; up to 25% missed diagnosis ante-mortem. ‘Typical’ case 60-80 years old M>F. Overall in-hospital mortality 27%.
Risk factors:
- Inherited disease (especially younger patients < 40 yrs) – Marfan’s syndrome (fibrillin gene mutations), Ehlers-Danlos syndrome type IV (collagen defects), Turner syndrome, annulo- aortic ectasia and familial aortic dissection.
- Aortic wall stress: Hypertension (72%), previous cardiovascular surgery, bicuspid or unicommisural aortic valve, aortic coarctation, iatrogenic, infection (syphilis), arteritis such as Takayasu’s or giant cell, aortic dilatation / aneurysm, wall thinning, ‘crack’ cocaine (abrupt catecholamine-induced hypertension).
- Reduced resistance aortic wall: Increasing age, pregnancy (debatable).

Golledge J, Eagle K. Acute aortic dissection. Lancet 2008;372:55-66. [Reference]
European Society of Cardiology. Diagnosis and management of aortic dissection. Eur Heat J 2001;22:1642-81. [Reference PDF]

Clinical Presentation (with incidence %)

Severe or ‘worst ever’ (90%), abrupt (90%), sharp (64%) or tearing (50%) retrosternal or interscapular pain, migrating (16%), down the back (46%), maximal at onset (not crescendo build up, as in an AMI).
Complications:
- Aortic incompetence (32%), cardiac tamponade, myocardial ischaemia (although only 2-5% of ECG’s mimick AMI). Different BP >20 mmHg in arms, or missing pulse (15%).
- Pleural rub or effusion, haemothorax.
- Altered consciousness, syncope (13 %), hemiplegia (5%), paraplegia.
- Abdominal pain (43% descending, 22% ascending), intestinal ischaemia, bowel infarct.
- Oliguria, haematuria.

Diagnosis

CXR – Widened mediastinum (56-63%), abnormal aortic contour (48%), aortic knuckle double calcium sign >5mm (14%), pleural effusion (L>R), tracheal shift, left apical cap. ‘Normal’ in 11-16%.
Echocardiography – Transthoracic 75% diagnostic Type A (ascending), 40% descending (Type B). Transoesophageal (TOE). Much higher sensitivity / specificity, though operator-dependent, need sedation, and is less available. Useful in ICU / perioperative.
Helical CT – Useful screen for widened mediastinum. Newer multiplane/slice scanners may now negate additional need for TOE or aortography to plan operative management.
Aortography – Was the traditional gold standard, delineating aortic incompetence and associated branch vessel involvement as well.
MRI / MRA – Excellent sensitivity and specificity limited by availability.

Hayter R, Rhea J, Small A et al. Suspected aortic dissection and other aortic disorders: multi-detector row CT in 373 cases in the emergency setting. Radiology 2006;238:841-52. [Reference]

Management

Ascending Type A – Immediate blood pressure control prior to transfer for operation using IV beta blocker (propranolol, esmolol or labetalol) combined with SNP (or GTN) as vasodilators aiming for SBP 100-120 mmHg, and surgery or endovascular stenting.
Descending Type B – Medical control of BP with beta blockers, with surgery or endovascular stent grafting for selected patients with an unfavourable outlook.

Reed K, Curtis L. Aortic Emergencies: Part 1 – thoracic dissections and aneurysms. Emergency Medicine Practice 2006;8(2):1-24. EB Medicine
Eggebrecht H et al. Endovascular stent-graft placement in aortic dissection: a meta-analysis. Eur Heart J 2006;27:489-98. [Reference]
Nienaber C et al. Aortic dissection: new frontiers in diagnosis and management: Part 1: from etiology to diagnostic strategies. Circulation 2003;108:628-35. [Reference]
Hagan PG, Nienaber CA, Isselbacher EM et al. The International Registry of Acute Aortic Dissection (IRAD). JAMA 2000; 283:897-903. [Reference]