Thoracic Aortic Dissection

A tear in the aortic intima allows blood to enter the media and create a false lumen. Incidence is about 3 to 6 per 100,000 per year, men more than women (about 2:1), mean age 60 to 65 years (younger with connective tissue disease, bicuspid valve, cocaine use and pregnancy).

• Type A involves the ascending aorta (about 60%); type B involves the descending aorta distal to the left subclavian artery (about 35 to 40%). Acute is up to 14 days, subacute 15 to 90 days, chronic more than 90 days.
• Risk factors: hypertension (about 70%), atherosclerosis, bicuspid valve, Marfan, vascular Ehlers-Danlos and Loeys-Dietz syndromes, Turner syndrome, aortic coarctation, pregnancy (third trimester and postpartum), cocaine and amphetamines, giant cell arteritis, Takayasu arteritis, syphilis, fluoroquinolone use, trauma and aortic catheterisation, and heavy weightlifting.
• Mechanism: intimal tear with propagation of the false lumen in both directions, causing aortic rupture, tamponade, aortic regurgitation, coronary or branch vessel obstruction (malperfusion), and stroke.
• Untreated type A: mortality rises by about 1 to 2% per hour in the first 24 to 48 hours, and about half die within a week. Surgical in hospital mortality for type A is about 15 to 25%. Uncomplicated type B has about 5 to 10% early mortality with medical therapy, rising to about 20% when complicated.

• Abrupt severe chest, back or abdominal pain, tearing or ripping in about half, maximal at onset and sometimes migrating. Syncope (5 to 10%).
• Signs: hypertension (common, especially type B) or hypotension and shock (tamponade, rupture, acute aortic regurgitation); pulse deficit or a blood pressure difference greater than 20 mmHg between arms (about 20% of type A); diastolic murmur of aortic regurgitation (about 40 to 50% of type A); signs of tamponade; stroke; spinal cord ischaemia with paraplegia; mesenteric, renal or limb ischaemia; Horner syndrome and hoarseness.
• Differential diagnosis: acute coronary syndrome (type A can obstruct the right coronary ostium and cause inferior infarction), pulmonary embolism, pericarditis, pneumothorax, oesophageal rupture, pancreatitis, leaking aortic aneurysm, intramural haematoma, penetrating aortic ulcer and musculoskeletal pain.
• Complications: tamponade, rupture, acute aortic regurgitation and heart failure, myocardial infarction, stroke, spinal cord ischaemia, mesenteric ischaemia, acute kidney injury, limb ischaemia, and late aneurysmal dilatation of the false lumen (about 20 to 50% over years).

• ECG (may show ischaemia or be normal; never give thrombolysis or anticoagulation for ST elevation until dissection is excluded), troponin, D-dimer (greater than 0.5 micrograms/mL has high sensitivity of about 95%; a normal value excludes dissection in low risk patients), chest X-ray (mediastinal widening in 60 to 90%, normal in up to 20%), lactate, full blood count, creatinine, liver enzymes, coagulation and a crossmatch of 4 to 6 units.
• Bedside echocardiography for pericardial effusion, aortic root size and aortic regurgitation.
• ECG-gated CT angiography of the whole aorta (chest, abdomen and pelvis) is the usual definitive test; transoesophageal echocardiography in the unstable patient; MRI in stable and chronic disease.
• Define: entry tear, extent, false lumen patency, branch vessel involvement, maximal diameter, and coronary and valve involvement.
• After stabilisation: genetic testing and family imaging when the patient is young (under 50), has syndromic features, or has a family history.

• Resuscitation and heart rate and pressure control in intensive care or resuscitation area (do not delay for imaging in high probability patients):
  • Analgesia: fentanyl 25 to 50 micrograms IV increments or morphine 2 to 5 mg IV.
  • Heart rate 60 to 80 beats/min and systolic pressure 100 to 120 mmHg within the first hour. Start rate control first: esmolol 500 micrograms/kg IV over 1 minute then 50 to 300 micrograms/kg/min (increase by 50 micrograms/kg/min every 4 minutes), or labetalol 20 mg IV over 2 minutes then 20 to 80 mg every 10 minutes (maximum 300 mg) or infusion 0.5 to 2 mg/min.
  • If systolic pressure remains greater than 120 mmHg after rate control: nicardipine 5 to 15 mg/h, glyceryl trinitrate 5 to 100 micrograms/min, or sodium nitroprusside 0.25 to 10 micrograms/kg/min. Never use a vasodilator before rate control, because reflex tachycardia raises shear stress.
  • If beta blockers are contraindicated (asthma, severe aortic regurgitation, heart block): diltiazem 0.25 mg/kg IV (maximum 20 mg) then 5 to 15 mg/h.
  • Hypotension: look for tamponade, rupture, acute regurgitation or blood loss. Give fluids in 250 mL boluses, use noradrenaline or phenylephrine to restore pressure (avoid inotropes that raise the rate of pressure rise), transfuse blood, and proceed to emergency surgery. In tamponade, drain only the minimum needed to keep systolic pressure at about 90 mmHg, because over drainage causes rebleeding.
  • Avoid anticoagulants, antiplatelet drugs and thrombolytics.
• Type A (emergency surgery as soon as the diagnosis is made):
  • Replacement of the ascending aorta with or without hemiarch under hypothermic circulatory arrest with cerebral perfusion; composite valve and root replacement (valved conduit with coronary reimplantation) when the root is destroyed, diameter is 45 mm or more, or there is connective tissue disease; valve sparing root replacement in selected young patients; total arch replacement with frozen elephant trunk in selected patients with arch tears or malperfusion.
  • Mortality about 15 to 25%. Medical therapy alone is reserved for patients with devastating neurological injury, irreversible coma or prohibitive comorbidity.
• Uncomplicated type B (medical therapy):
  • Intensive care for 24 to 48 hours with esmolol 500 micrograms/kg IV over 1 minute then 50 to 300 micrograms/kg/min, or labetalol 20 mg IV then 20 to 80 mg every 10 minutes (maximum 300 mg), targeting heart rate 60 beats/min and systolic pressure 100 to 120 mmHg, then oral therapy: bisoprolol 2.5 to 10 mg daily, ramipril 2.5 to 10 mg daily, amlodipine 5 to 10 mg daily, spironolactone 25 to 50 mg daily as needed. Target blood pressure less than 130/80 mmHg and heart rate 60 to 70 beats/min.
  • Consider thoracic endovascular aortic repair in the subacute phase (14 to 90 days) for high risk features: maximal aortic diameter greater than 40 mm, false lumen diameter greater than 22 mm, entry tear greater than 10 mm, entry tear on the inner curve, recurrent pain, or refractory hypertension; the aim is to prevent late aneurysm.
• Complicated type B (urgent endovascular repair):
  • Indications: rupture or impending rupture (haemothorax, periaortic haematoma), malperfusion (limb, mesenteric, renal), refractory pain or hypertension, rapid expansion.
  • Thoracic endovascular aortic repair covering the primary entry tear with a landing zone of at least 20 mm in healthy aorta (revascularise the left subclavian artery if it must be covered). Technical success greater than 90%; 30-day mortality about 8 to 10%; stroke about 3 to 5%; spinal cord ischaemia about 3% (use cerebrospinal fluid drainage and keep mean arterial pressure at 80 mmHg or more in high risk patients); retrograde type A dissection about 1 to 2%.
  • Malperfusion: aortic fenestration or branch stenting; fasciotomy for limb compartment syndrome; bowel assessment and resection for infarction after perfusion is restored. Open repair for failed endovascular treatment.
  • Acute kidney injury: avoid nephrotoxins, maintain perfusion, and dialyse for refractory hyperkalaemia, acidosis, fluid overload or uraemic complications.
• Chronic dissection and aneurysm: repeat imaging; operate when the descending aorta is 55 to 60 mm (50 to 55 mm in connective tissue disease), grows more than 5 mm in 6 months, or becomes symptomatic.
• Long term care:
  • Lifelong blood pressure control (less than 130/80 mmHg), heart rate control, losartan 50 to 100 mg daily in Marfan syndrome, atorvastatin 40 to 80 mg daily for atherosclerosis, smoking cessation.
  • Avoid fluoroquinolones, stimulants, decongestants and heavy isometric exercise; allow moderate aerobic exercise.
  • Imaging with CT or MRI before discharge, at 1, 3, 6 and 12 months, then yearly.
  • Screen first degree relatives with aortic imaging and genetic testing where indicated.
• Special groups:
  • Pregnancy: type A with a viable fetus (28 weeks or more): caesarean section first, then aortic repair; before viability, repair with bypass (fetal loss about 20 to 30%). Use labetalol 100 to 400 mg twice daily and nifedipine retard 10 to 20 mg twice daily; avoid ACE inhibitors, ARBs and atenolol.
  • Marfan and other connective tissue disease: root replacement at 45 to 50 mm or less with risk factors; avoid contact sport.
  • Bicuspid valve: replace the ascending aorta at 55 mm (50 mm with risk factors, or 45 mm if valve surgery is planned).
  • Cocaine and amphetamine use: give lorazepam 2 mg IV, use vasodilators for pressure control, and use labetalol cautiously.
  • Giant cell arteritis: prednisolone 1 mg/kg/day (maximum 60 mg) with specialist care. Syphilitic aortitis: benzathine benzylpenicillin 2.4 million units IM weekly for 3 weeks.
  • Elderly: more atherosclerotic complications and higher surgical risk; favour endovascular treatment for type B.
  • Renal impairment: reduce contrast volume; accept the imaging risk for diagnosis.
• Red flags: hypotension, syncope, new neurological deficit, pulse deficit, abdominal or limb pain, fall in urine output, new diastolic murmur, recurrent pain.
• Follow up: CT or MRI at 1, 3, 6 and 12 months, then yearly; blood pressure and heart rate at each visit; echocardiography of the aortic root and valve yearly after type A repair.