Aortic Dissection

Intro:

-- Pathophysio

1. Risk Factors

2. Signs and symptoms

3. Blood Ix-initial preliminary ddx

4. ECG

5. Radiology 

6. Management

-- summary

Pathophysio

AD occurss when there is violation of the intimal layer of the aorta. This allows blood to dissect between the intimal and adventitial layers, causing the blood to flow into the media.

There are 3 possibilities as to how the blood enters the media:

1. Atherosclerotic ulcer leading to intimal tear
2. Disruption of vasa vasorum causing intramural haematoma
3. De novo intimal tear

Following dissection, blood flow into the media may cause:

• extension up or down
• rupture
• vessel branch occlusion
• aortic regurgitation
• pericardial effusion / tamponade

Risk Factors

1. inherited diseases: Marfan's
2. Underlying comorbidities: Hypertension, Hyperlipidemia, artherosclerosis
3. Others: Infection, history of cardiovascular surgery, arteritis, aortic dilation, aneurysm, pregnancy, trauma, old age
4. Iatrogenic: recent cadiac catheterization

Symptoms

1. severe pain at chest/back/abdomen/leg, depends on where the origin of aneurysm

2. signs: heart failure and hypotension

- unequal BP in the arms 20mmHg (suggest the presence of artery-clogging plaque in the vessel in limb with lower pressure)

- cold pallor /absent peripheral pulses in limbs 

- stroke/paraplegia

- anuria

- Aortic regurgitation

- left pleural effusion

 Murmurs

AR- early diastolic murmur

delayed distal pulse

Blood Ix

• FBC：leukocytosis
• Cr elevation with renal artery involvement
• Tropnonin elevated : if dissection causes myocardial ischaemia
• D-dimer – if negative --> dissection is very unlikely, but not sufficient to rule out
• Cross-match: just in case there are excessive blood loss, in need of transfusion
• Various biomarkers being investigated (e.g. elastin fragments, d-dimer, smooth muscle myosin heavy-chain protein)- if indicated

ECG

Results can be

• normal
• inferior ST elevation (right coronary dissection) but can be any STEMI (0.1% of STEMIs are dissections)
• pericarditis changes, electrical alternans (tamponade)

example:

https://www.medscape.com/viewarticle/775982_2

The ECG shows findings of STEMI with right ventricular involvement (ST depression in lead I and elevation in VI). This could be a complication of an acute proximal aortic dissection, which can extend retrogradely, catching the proximal right coronary artery (RCA), either by a dissecting hematoma compressing the RCA lumen or a transsection of the proximal RCA. In either situation, an acute inferior STEMI can result as a complication of a proximal aortic dissection.

Radiology

• Chest X-Ray
• CT angiogram
• Ultrasound

Chest X-Ray

** to always compare to old X-ray

** Loss of the aortic knob/aortic-pulmonary window and the calcium sign.

** widened mediastinum

** sometimes there are hemothorax /pleural effusion / loss of costophrenic angle (due to rupture)

**pericardial effusion/tamponade/cardiomegaly

                                                            CT Angiogram (gold standard)

reference CTA: 

http://www.svuhradiology.ie/case-study/thoracic-aortic-dissection-ct/

POCUS

abdominal aortic dissection ultrasound

Differential:

Types of Aortic Dissection

• Is it Stanford A / B

TYPE A: 

• severe and sharp chest pain 
• --> surgical intervention

• Involves ascending aorta. Can extend distally ad infinitum. Surgery usually indicated.

TYPE B: back pain 

•     (usually with malperfusion, ongoing progression, inability to control BP, and perforation.)
• --> medical intervention

• Involves descending aorta, aorta beyond left subclavian artery. Often managed medically with BP control.

Management:

Step 1:

• O2
• wide bore IV access (Swan sheath)
• invasive monitoring
• warn blood bank (x-match 6U + need for other products: FFP, PLT concentration, cryo) - depends on situation
• correct coagulopathy

Step 2:

• control Pain

Step 3:

• control HR and BP (aim for P 60-80 and BP 100-120 SBP) target BP <120/80
• Nitroprusside 0.25-0.5 mcg/kg/min then titrate or Nicardipine 5mg/hr
• IV propanolol 0.5-1mg q5min till HR 60-80
• Warning: Beware of pseudohypotension! of the bilateral BPs use the higher BP reading. if hypotensive, might lead to tamponade. resus with IV fluid and stop all anti-hpertensive agents

• HR control:
• IV beta blocker (propranolol, esmolol or labetalol) combined with vasodilators (e.g. GTN, labetalol, SNP)
• start b-blocker first to avoid increased aortic wall stress from reflex tachycardia

Step 4: 

• call cardiothoracic surgeon if indicated

https://www.longdom.org/open-access/a-contemporary-review-of-acute-aortic-dissection-2165-7548-1000274.pdf

Sample case for practice

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6682226/

other cases: 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3856285/

Reference:  

1. type B AD

2. https://emergencymedicinecases.com/aortic-dissection-em-cases-course/

3. https://twitter.com/ManualOMedicine/status/1266758102667460609/photo/1