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Acute Aortic Syndrome & Blunt Traumatic Aortic Injury

MCh / CTVS Level Notes

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PART 1: ACUTE AORTIC SYNDROME (AAS)

Definition

1. Aortic Dissection (AD)
2. Intramural Haematoma (IMH)
3. Penetrating Atherosclerotic Ulcer (PAU)

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Pathological Relationships

Three-quarters of AAS presentations are aortic dissection; 10-20% are IMH; a small proportion are PAU.

• Grainger & Allison, p.2061

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Clinical Presentation of AAS

• Classic: Abrupt onset severe tearing or ripping chest pain, often interscapular
• Pain may be anterior, abdominal, or migratory
• A small proportion have clinically silent dissection

• Cerebrovascular accident (arch vessel occlusion)
• Renal failure
• Acute bowel or limb ischaemia (branch vessel occlusion - malperfusion syndrome)
• Myocardial infarction (coronary ostial involvement)
• Acute aortic regurgitation (aortic root involvement)
• Pericardial tamponade
• Massive haemothorax with shock (rupture)
• Progression to aneurysm

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AAS Classification: Stanford / DeBakey

• Acute: < 14 days
• Subacute: 14 days - 2 months
• Chronic: > 2 months

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1A. Aortic Dissection

• Incidence: 5-10 per 100,000/year, increasing with ageing population
• Risk factors: Hypertension (most common), Marfan syndrome, Ehlers-Danlos, bicuspid aortic valve, pre-existing TAA, vasculitides

• 20% die before reaching hospital
• Type A: ~1-3% mortality per hour for first 48 hours; 30-day mortality ~50% with medical therapy, ~17% with surgery
• Type B (uncomplicated): 30-day mortality ~10%; complications occur in 30% (20% mortality at 48 h, 30% at 30 days)

• High-dependency environment, invasive monitoring
• Heart rate target: <60 bpm
• Systolic BP target: <120 mmHg
• IV β-blockade (e.g. esmolol, labetalol) + IV nitrates
• Pain control

• Indicated in all patients - immediate surgical repair
• Fatal complications if delayed: aortic rupture, cardiac tamponade, acute AR, AMI
• Arch vessel involvement: high neurological complication risk
• Requires CPB with or without DHCA

• Uncomplicated: Medical therapy alone OR TEVAR + medical (INSTEAD trial: TEVAR improves 5-year aorta-specific survival and delays disease progression)
• Complicated type B: Urgent intervention (TEVAR preferred)

• False lumen expansion rate >1 cm/year
• False lumen diameter >2.2 cm
• Early combined diameter >4 cm
• Entry tear diameter >1 cm
• Partial false lumen thrombosis

• Coverage of the main proximal entry tear with a stent-graft to depressurise the false lumen (FL) and allow true lumen (TL) re-expansion
• Goal: complete FL collapse or thrombosis (protects against rupture and aneurysm)
• Adjunctive branch stenting or fenestration for static vessel occlusion

• In-hospital mortality: 4% (TEVAR) vs 40% (open surgery) vs 33% (medical)
• Survival at 5 years: 79% (TEVAR) vs 44% (surgery/medical)
• Grainger & Allison, p.2062-2063

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CT Imaging of Aortic Dissection

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Branch Vessel Occlusion in Dissection

• Dynamic occlusion: Flap prolapses across ostium - treated by FL depressurisation (TEVAR covers entry tear)
• Static occlusion: Dissection extends into branch vessel - requires additional branch stenting or fenestration

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1B. Intramural Haematoma (IMH)

• Definition: Intramural haemorrhage from vasa vasorum (no intimal tear identifiable)
• More commonly involves descending thoracic aorta; older patients
• CT appearance: Crescent-shaped high-density thickening of aortic wall (no contrast in haematoma)
• Can evolve: IMH → PAU (develops over days-weeks) → dissection or rupture
• Management: Broadly similar to dissection by Stanford type
• Type A IMH: Surgery
• Type B IMH (complicated): TEVAR covering involved segment
• Grainger & Allison, p.2061

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1C. Penetrating Atherosclerotic Ulcer (PAU)

• Definition: Ulcerating atheromatous plaque eroding through intima into media
• Usually in markedly atheromatous segments, most commonly descending thoracic aorta
• CT: Eccentric outpouching with adjacent wall hyperdensity (IMH)
• Risk: More prone to rupture than dissection (penetrates deeper layers)
• Management: Treat PAU as the "entry tear" - short stent-grafts; acute persistent pain is an indication for treatment

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AAS - Diagnostic Imaging

• Normal CXR does NOT exclude AAS
• May show widened mediastinum, aortic knob abnormality, pleural effusion
• Useful to confirm alternative diagnosis in low-risk patients

• Demonstrates dissection flap, true/false lumen, entry/re-entry tears
• Identifies complications: branch vessel occlusion, pericardial effusion, haemothorax
• Essential for treatment planning

• TOE: excellent for proximal aorta, intraoperative guidance
• Rapid, bedside - suited to unstable patients
• Can show IMH as crescentic wall thickening, dissection flap, pericardial effusion, AR

• Best for IMH dating and characterisation
• Limited access in emergency

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PART 2: BLUNT TRAUMATIC AORTIC INJURY (TAI)

Epidemiology

• Blunt aortic injury is the second most common cause of death from blunt trauma (after head injury)
• In USA: ~40,000 motor vehicle deaths/year; 20% caused by aortic rupture
• In UK: ~15% of road traffic accident fatalities involve thoracic aorta
• On arrival to hospital: only 25% of patients with blunt TAI are alive
• Prognosis of untreated survivors:
  • 30% die within 6 hours
  • 50% die within 24 hours
  • 90% die within 4 months
• Miller's Anesthesia, p.7775; Grainger & Allison, p.2063

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Mechanism of Injury

• Especially at speeds >30 mph
• Rapid traction on the relatively immobile aortic isthmus (fixed by ligamentum arteriosum)
• Isthmus = distal to L. subclavian artery, proximal to 3rd intercostal artery
• Ligamentum arteriosum acts as a hinge for arch movement → maximum shearing force at isthmus
• 50-70% of traumatic ruptures occur at the isthmus

• Torsion from heart displacement leftwards during AP compression (ascending aorta near innominate; from vertical falls >10 ft)
• "Osseous pinch" - compression between sternum and vertebral column (transverse force through full aortic wall thickness)

• Isthmus: 50-70% (90% in some series)
• Ascending aorta / arch: 18%
• Distal thoracic aorta: 14%

• Subintimal haemorrhage (intimal tear only)
• IMH confined to media
• Traumatic dissection
• False aneurysm / pseudoaneurysm (laceration into adventitia - which is the only remaining intact layer)
• Complete transection → exsanguination at scene

In 80-90% there is complete aortic rupture with death at the scene. Survivors have partial-thickness injuries with at least the adventitia intact; periaortic haemorrhage is almost always present.

• Grainger & Allison, p.2063

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CT Grading of TAI (Presley Trauma Center System)

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Clinical Diagnosis

• Often difficult due to lack of specific symptoms (obtunded from head injury, confounding injuries)
• Symptoms when present: anterior chest pain, interscapular pain, dyspnoea, hoarseness (haematoma compression of recurrent laryngeal nerve), dysphagia

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Imaging of TAI

Chest X-ray (initial screening)

• Sensitivity 80-90% for mediastinal haemorrhage - useful screening tool
• Signs of TAI on CXR:
  • Widened superior mediastinum (M/C ratio >0.25 or >8 cm absolute)
  • Deviation of trachea to the right of midline
  • Widened right paratracheal stripe
  • Loss / obscuring of aortic knuckle contour
  • Displacement of nasogastric tube by haematoma (most specific indirect sign)
  • Left pleural effusion / apical cap
• Important: Normal CXR does NOT exclude significant TAI
• Supine position makes mediastinal width interpretation unreliable, especially in obese patients

CT Aortography (investigation of choice)

• Diagnostic accuracy approaches 100%
• First-line investigation in all patients stable enough to transfer
• Allows assessment of entire thorax, abdomen and head in single examination
• Direct CT signs of TAI:
  • Contrast extravasation
  • Defined pseudoaneurysm (most common finding)
  • Dissection flap
  • Focal aortic calibre change
  • Small aortic contour abnormality (intimal/medial disruption)
  • IMH
• Indirect signs:
  • Periaortic mediastinal haematoma
  • Haemothorax
• False positives: ductus diverticulum, severe atherosclerosis, double density from overlapping vessels, superior intercostal vein, bronchial artery infundibulum, motion artefacts
• Equivocal cases: IVUS can resolve (aortography adds little)

TOE (Trans-Oesophageal Echocardiography)

• Sensitivity 91%, specificity 98% for isthmic injuries
• Can be performed bedside in 15-20 minutes in unstable patients
• Identifies: intimal flap, mural thickening, periaortic blood
• Gap >7 mm between probe and aorta at proximal descending thoracic level + pleural blood = strongly suggests aortic disruption
• Contraindications: severe facial injuries, unstable cervical spine fractures
• Limitations: entire aortic circumference not visualised in ~30%; aortic arch poorly seen
• Role: screening in unstable patients; intraoperative guidance for stent-graft deployment

Aortography (largely historical)

• Sensitivity 84-96%; specificity imperfect
• Replaced by CT; no longer preferred; no additional benefit over CT

MRI

• Accuracy approaching 100%; can date IMH
• Limited by availability and time constraints in trauma settings

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TAI CT + TEVAR Images

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Management of TAI

Pre-operative / Initial Resuscitation

1. ATLS principles - manage other life-threatening injuries first (TAI rarely requires immediate repair if the adventitia is intact)
2. Aggressive blood pressure and heart rate control (mandatory to prevent complete rupture):
   • Systolic BP <100 mmHg (Miller) / <120 mmHg (Grainger)
   • HR <100 bpm
   • β-Blockers (esmolol, labetalol) - reduce dP/dt (rate of pressure rise)
   • IV nitroglycerin or sodium nitroprusside infusion
3. Allow time to manage: haemorrhage, sepsis, hypothermia, coagulopathy, acidosis
4. Controlled hypotension allows elective scheduling of definitive repair (days to weeks later)

Emergency TEVAR for TAI is now the exception, not the rule.

• Grainger & Allison, p.2063

Definitive Management

• STS Class I recommendation; Level of Evidence B
• Preferred over open surgery whenever technically feasible
• Requires minimum 15 mm proximal landing zone (normal aorta) distal to last great vessel
• Left subclavian artery (LSA) frequently covered to extend landing zone:
  • Most patients tolerate this (adequate collaterals via circle of Willis + left vertebral artery)
  • Carotid-to-subclavian bypass not routinely required
  • Risk of adverse central neurological events after LSA coverage without revascularisation: ~10%

• Ascending aorta or arch injuries: CPB ± DHCA required
• Descending thoracic aorta: Open repair of short segment; partial left heart bypass (PLHB) for spinal cord and visceral protection without full heparinisation
• Reserved for cases not amenable to TEVAR or endovascular failure

Anaesthetic / Intraoperative Considerations (Miller's Anesthesia)

• Full stomach precautions
• Monitoring: arterial line, CVP, large-bore IV access
• TEE for intraoperative guidance
• Avoid wide swings in BP during induction and laryngoscopy - prepare esmolol and nitroglycerin in advance
• Controlled postoperative ventilation with ICU transfer

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Associated Injuries to Consider

• Head injury (CT head)
• Pneumothorax / haemothorax
• Pulmonary contusion
• Rib fractures, flail chest
• Cardiac contusion (ECG, troponin)
• Diaphragmatic injury
• Intra-abdominal solid organ injury

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SUMMARY TABLE: AAS vs Blunt TAI

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KEY SUMMARY BOX: Acute Aortic Syndrome

Diagnosis is usually by cross-sectional imaging. Three-quarters of AAS is dissection; 10-20% is IMH; small proportion is PAU. Dissection involves ascending aorta and arch in three-quarters of cases. IMH more commonly involves descending thoracic aorta. PAU usually in markedly atheromatous segments (descending thoracic aorta).

• Grainger & Allison, p.2061

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• Grainger & Allison's Diagnostic Radiology, Chapters 17 and 79 (pp. 431-432, 443, 2061-2063)
• Miller's Anesthesia 10e, Chapter (pp. 7774-7777)
• Braunwald's Heart Disease (pp. 841-845, 3469-3472)