Aortic Dissection

Aortic Dissection is a mimic! - Acute dissection requires a tear in the aortic intima with blood passing through the tear separating the intima from the media or adventitia, creating a false lumen or channel. As blood is diverted into this channel, circulatory volume decreases, and the channel expands and creates either an expanding mass or a heamatoma from coagulating blood. Propagation of the dissection can proceed in anterograde or retrograde fashion from the initial tear involving side branches and causing complications such as malperfusion syndromes (cardiac, spinal, cerebral, renal, coeliac, mesenteric, iliac, or femoral arteries), tamponade, or aortic valve regurgitation. As circulatory volume decreases, cardiac output also decreases, resulting in end - organ failure.

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There are 2 main classification – DeBakey and Stanford, the latter more commonly used in Australia.

The Stanford classification system classifies dissections into two groups,

# Type A, which affects the ascending aorta- (62%) , and

# Type B, which affects only the descending aorta, beginning distal to the left subclavian artery (38%).

De Bakey has 3 stratified categories Type I, Type II and Type III.

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What about checking of differences in Blood Pressure between both arms?

Often we can see that > 10mmHg differences are abnormal but studies have shown that it is common for normotensive, hypertensive and in those with peripheral vascular disease to have significant systolic and diastolic differences between both arms. One review quoted studies showing a systolic difference of > 20 in 25-34%, 18-60% and 10-20% of the above groups respectively, whilst they had diastolic differences of > 10 in 15-30% and 15-40% of the first 2 groups.

That is blood pressure difference has no role unless significant enough to cause a pulse deficit. Pulse deficits (as defined by a weak or absent brachial, carotid or femoral pulse) described in 19- 30% of patients with an acute type A dissection compared with 9- 21% with a type B dissection.

However, if absent this does not rule out dissection: one meta-analysis found a pooled sensitivity of pulse deficits is 31%. Remember also to consider checking BPs in arms and legs if there is hypotension in both arms as there may be occlusion of the vessels supplying the arms without femoral involvement in type A (known as pseudohypotension).

Just like intussuseption in paediatric surgery, Aortic dissection can present as a spectrum of pain descriptions, locations and severities, and dissection may mimic other disorders such as stroke, myocardial infarction , vascular embolisation and abdominal pathology. Common misdiagnoses included acute coronary syndrome (19%), musculoskeletal pain (20%), pneumonia/pulmonary embolism (20%), pericarditis (12%), gastrointestinal (GI) pain (9%), and other causes (20%).

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Reference

Clark CE, Taylor RS, Shore AC, Campbell JL. The difference in blood pressure readings between arms and survival: primary care cohort study. BMJ. 2012;344:e1327. Published 2012 Mar 20. doi:10.1136/bmj.e1327

Merck Manual - https://www.merckmanuals.com/professional/cardiovascular-disorders/diseases-of-the-aorta-and-its-branches/aortic-dissection

Woods, S. L., Froelicher, E. S. S., & Motzer, S. A. (2000). Cardiac nursing. Philadelphia: Lippincott Williams & Wilkins.