Acute Aortic Dissection

Risk stratification can be aided by the Aortic Dissection Detection Risk Score (ADD-RS), used in conjunction with a D-dimer level. Though ADD-RS is validated, its combination with D-dimer (e.g., the ADvISED algorithm) is not externally validated and should be used cautiously. Imaging remains essential for diagnosis.

• Stanford Type A dissections require surgery urgently. Untreated, mortality increases by 1% per hour, reaching 50% at 48 hours.
• Stanford Type B dissections are less lethal and may be managed medically unless complications necessitate intervention.

Classification

The Stanford classification is most commonly used:

• Type A: Proximal dissections, where there is involvement of the ascending aorta, regardless of the site of entry..
• Type B: Distal dissections, all dissections not involving the ascending aorta, therefore arch and      descending.

Pathophysiology

Predisposing factors include:

1. Hypertension (most important in older adults)
2. Familial aortic disease
3. Age (17-59: 27%, 60-74: 40%, >75: 33%)
4. Connective tissue diseases (Marfan, Ehlers-Danlos, Turner syndrome)
5. Autoimmune vasculitis
6. Pregnancy
7. Aortic valve disease (e.g., bicuspid valve)
8. Aortic manipulation
9. Aneurysms
10. Iatrogenic causes (catheterization)
11. Cocaine/methamphetamine use

Complications:

• Transmural rupture with haemorrhage (fatal)
• Proximal dissection: Three main life-threatening complications – cardiac tamponade, aortic incompetence, coronary artery occlusion
• Aortic branch occlusion: stroke, limb ischemia, renal or GI ischemia. Any aortic branch may become occluded due progressive dissection of the intimal flap
• Chronic dissection with aneurysm formation

Clinical Features

Note that many “classic” findings of aortic dissection are frequently absent. A high index for suspicion must therefore be maintained in those patients who are most at risk.

History:

• Sudden chest/back pain (95% of cases)
• Pain is sharp, tearing, or ripping
• Radiation: anterior chest (ascending aorta), interscapular (descending aorta), jaw/neck (arch), back (abdominal aorta)
• Pain can be migratory, transient, or absent
• Syncope (20%) – more common with Type A
• Aortic branch occlusion symptoms (neurological, GI, renal) with considerable clouding of clinical picture
• Precipitating stressor or adrenergic surge

Examination:

• BP often elevated; hypotension = ominous (signifying a proximal dissection with cardiac tamponade or aortic transmural rupture)
• Pulse/BP discrepancies may exist
  • Carotid, radial, femoral pulses should be compared to each side
  • Limb pulse and blood pressure discrepancies may occur and may be transient.
  • A systolic blood pressure deficit of  > 20 mg Hg in the upper limbs is considered a significant finding. 
  • These signs have low sensitivity however and their absence cannot rule out     the possibility of aortic dissection
• New aortic regurgitation murmur
  • Acute onset of aortic incompetence with anterior chest/neck/jaw/facial pain is     very suggestive of a proximal aortic dissection
• Tamponade (Beck’s triad): hypotension, JVP, muffled heart sounds
• Neurological signs with chest/back pain = red flag

Differential Diagnoses

• Acute coronary syndrome
• Pulmonary embolism
• Pericarditis/myocarditis
• Oesophageal rupture

Risk Stratification (ADD-RS)

Three high-risk categories:

1. Predisposing Conditions
   • Marfan/connective tissue disorders
   • Aortic disease/family history
   • Aortic valve disease
   • Recent manipulation
   • Aneurysm
2. Pain Characteristics
   • Chest, back or abdominal pain that is described as:
     • Abrupt/severe AND
     • Sharp/tearing
3. Examination Findings
   • Perfusion deficits (pulse/BP/neuro)
   • New murmur
   • Hypotension/shock

Score:

• 0: Low risk (~4% of AD)
• 1: Moderate (~36%)
• 2-3: High (~60%)

Management by ADD-RS and D-dimer:

• Score 0-1 and D-dimer < 500 ng/mL → Stop workup
• Score 0-1 and D-dimer ≥ 500 ng/mL → Consider CTA
• Score ≥2 → Consider CTA

Investigations

Blood Tests:

• FBE (low Hb = leak/rupture)
• U&Es/glucose
• Coags
• Troponin (rare elevation)
• D-dimer (elevated in AD, useful for risk stratification)

ECG:

• May be normal or show non-specific changes
• LVH and strain (due to pre-existing long term hypertension)
• Myocardial infarction due to involvement of coronary vessels is described but is rare
• ST elevation rare

CXR:

May be normal, hence a CXR cannot exclude aortic dissection. Additionally there is wide inter-observer variation in the diagnosis of aortic dissection based on the CXR alone. Suggestive features of aortic dissection include:

• Widened mediastinum
• Loss of the normal contour of the aortic arch and/ or descending aorta.
• Central displacement of aortic intimal calcification (> 5 mm).
• Pleural effusion (hemothorax) an ominous sign

Advanced Imaging

CT Angiogram (First choice):

This in most cases will be the best first up investigation

• Fast, widely available
• Full aorta (chest to pelvis)
• Can detect proximal PE if protocolled correctly

The clinical question frequently arises concerning the possibility of pulmonary embolism verses acute aortic dissection

• A CT aortogram is the betterinvestigation when both questions are being asked, providing the scan is performed in a specific way, and so it is important to communicate with the radiographer / radiologist.
• A CT aortogram has a reasonable chance of also detecting larger, more proximal pulmonary emboli – although it cannot definitely exclude smaller more peripheral pulmonary emboli. 
• A CTPA on the other hand is not useful for detecting the presence of an aortic dissection.    
• Ultimately, if clinical suspicion requires definitive exclusion of both conditions, then both a CT angiogram and a CTPA will be required. 

MRI/MRA:

• Sensitive/specific for aortic dissection
• Alternative to CT (contrast allergy, renal failure)
• Not for unstable patients
• Note: For patients with severe renal failure (and not on dialysis) the gadolinium used in the MRI may put the patient at risk of Nephrogenic Systemic Fibrosis – however this is a rare complication,

TTE:

Advantages:

• Non-invasive and can be done at the bedside.
• Evaluates aortic valve/tamponade

Disadvantages:

• Requires an experienced operator and high-end equipment
• Unable to adequately visualize the distal ascending aorta or beyond.

TOE:

• Best for proximal dissection
• Can be used in unstable patients
• Operator-dependent

Coronary Angiography:

• Not recommended for suspected AD

Management

1. ABCs and large bore IV access
2. Monitoring (pulse ox, ECG continuous, arterial line if possible)
3. Hypotension – Most patients with AD have elevated blood pressure, hypotension is an ominous sign
   • IV fluids may provide some temporizing benefit in the hypotensive patient.
   • Inotropes and vasopressors may aggravate the shear forces on the aortic wall
   • Urgent definitive surgical intervention is the only potentially lifesaving treatment.
4. Analgesia: IV opioids
5. Beta Blockers: Esmolol infusion (preferred), metoprolol
   • Essential part of management and should be instituted as soon as the diagnosis is made, unless there is an absolute contraindication to its use.
6. Vasodilators (GTN, nitroprusside): Only after BBs
7. Surgery
   • Type A: Urgent surgery
   • Type B: ICU, medical or endovascular management unless complicated

Disposition

• Type A: Transfer for cardiac surgery
• Type B: ICU management under vascular and critical care teams

All patients with type A aortic dissection, and who are suitable candidates for surgery, will need transfer to a hospital with facilities for cardiac surgery.

Those with type B aortic dissections who are suitable for medical management and endovascular stenting, may be managed in ICU under the close care of a Vascular surgeon as well as the Intensivist.

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References

Publications

• Thrumurthy SG, Karthikesalingam A, Patterson BO, Holt PJ, Thompson MM. The diagnosis and management of aortic dissection. BMJ. 2011 Jan 11;344:d8290.
• Nazerian P, Mueller C, Soeiro AM, Leidel BA, Salvadeo SAT, Giachino F, Vanni S, Grimm K, Oliveira MT Jr, Pivetta E, Lupia E, Grifoni S, Morello F; ADvISED Investigators. Diagnostic Accuracy of the Aortic Dissection Detection Risk Score Plus D-Dimer for Acute Aortic Syndromes: The ADvISED Prospective Multicenter Study. Circulation. 2018 Jan 16;137(3):250-258.
• Jelinek GA, Bugeja LC, Spanos PA, Neate SL, Bergman RL, Ranson DL. Collaboration between the coroner and emergency physicians: efforts to improve outcomes from aortic dissection. Med J Aust. 2014 Nov 17;201(10):607-9.

FOAMed

• Nickson C. Acute Aortic Dissection. LITFL
• Nickson C. Aortic Dissection Echocardiography. LITFL
• Beech G. CT Case 006. LITFL
• Lam L. CT Case 034. LITFL
• Nazerian P. Aortic Dissection Detection Risk Score (ADD-RS). MDCalc