Abdominal Aortic Dissection

Dissection that arises in the abdominal aorta without a thoracic tear.

The entry tear is most often distal to the renal arteries, the false lumen may thrombose or stay patent, and the dissection may extend into the iliac vessels.

It makes up about 1 to 4% of all aortic dissections.

Causes: hypertension and atherosclerosis (commonest), iatrogenic injury (angiography catheters, intra aortic balloon pump, aortic or renal artery intervention, endovascular repair, clamping at surgery), blunt abdominal trauma and seat belt injury, aortic aneurysm, connective tissue disease (Marfan, vascular Ehlers-Danlos and Loeys-Dietz syndromes), fibromuscular dysplasia, cocaine or amphetamine use, pregnancy and arteritis.

Mean age is about 60 to 70 years, with a male predominance; patients with iatrogenic injury, trauma or connective tissue disease are younger.

Natural history: most patients stabilise on medical therapy, but a substantial minority (roughly 20 to 40%) develop aneurysmal dilatation of the false lumen or aorta over years, and rupture is uncommon. In hospital mortality is about 5 to 10% in uncomplicated disease and much higher with rupture or visceral ischaemia. Evidence is limited because the condition is rare.

• Sudden abdominal, back, flank or groin pain (often tearing), though many patients have mild pain or none, and the dissection is found on imaging.

• Hypertension is common. Signs: pulse deficit or cool leg, abdominal tenderness, pulsatile mass if aneurysmal, renal infarction with flank pain and haematuria, new or worsening hypertension from renal artery involvement, bowel ischaemia, and rarely spinal cord ischaemia (paraparesis).

Differential diagnosis: ruptured abdominal aortic aneurysm, acute mesenteric ischaemia, renal colic, pancreatitis, perforated viscus, lumbar disc disease, acute limb ischaemia from embolism, retroperitoneal haemorrhage, and extension of a thoracic dissection downward.

Complications: limb, renal or visceral malperfusion, rupture, aneurysmal dilatation, thrombosis of the false lumen with occlusion of branches, acute kidney injury, refractory hypertension and recurrence.

• CT angiography of the whole aorta from chest to pelvis (to exclude thoracic involvement and define the entry tear, extent, false lumen perfusion, branch vessel origin from true or false lumen, and diameter). MR angiography or duplex ultrasonography is used for follow up and when contrast is a concern.
• Blood tests: creatinine, lactate, creatine kinase, troponin, full blood count, coagulation, D-dimer (greater than 0.5 micrograms/mL supports an acute aortic syndrome), liver enzymes, group and crossmatch of 4 units if unstable. ECG to exclude coronary involvement.
• Genetic testing and family imaging when the patient is under 50, has syndromic features, or has a family history of aortic disease.

• Admit to a high dependency unit with vascular surgery input.
• Analgesia and impulse control:
  • Morphine 2 to 5 mg IV or fentanyl 25 to 50 micrograms IV increments.
  • Target heart rate 60 to 70 beats/min and systolic pressure 100 to 120 mmHg, starting with rate control: 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) or infusion 0.5 to 2 mg/min.
  • If systolic pressure stays greater than 120 mmHg after rate control: nicardipine 5 to 15 mg/h or glyceryl trinitrate 5 to 100 micrograms/min. Never start a vasodilator before rate control.
  • If beta blockers are contraindicated (asthma, heart block): diltiazem 0.25 mg/kg IV then 5 to 15 mg/h.
  • Avoid anticoagulants, antiplatelet drugs and thrombolytics unless a clear indication exists.
• Uncomplicated disease (medical 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 resting heart rate 60 to 70 beats/min.
  • Atorvastatin 40 to 80 mg daily for atherosclerosis, aspirin 75 to 100 mg daily only when atherosclerotic disease needs it, smoking cessation, avoidance of fluoroquinolones, stimulants and heavy isometric lifting.
• Indications for intervention:
  • Rupture or contained leak, limb, renal or visceral malperfusion, refractory pain or hypertension, rapid growth (more than 5 mm in 6 months), maximal diameter 50 to 55 mm or more, extension toward the thoracic aorta, or saccular aneurysmal change.
  • Endovascular repair with a stent graft covering the entry tear is preferred (technical success greater than 90%; 30-day mortality about 5 to 10%); fenestrated or branched grafts for suprarenal disease; stenting or fenestration of a compressed branch vessel for malperfusion; open graft replacement when anatomy is unsuitable (mortality about 10 to 20%).
  • At endovascular repair give unfractionated heparin 70 to 100 units/kg IV and cefazolin 2 g IV at induction.
  • Rupture: permissive hypotension with systolic pressure about 70 to 90 mmHg while mentation holds, blood transfusion, avoid large crystalloid volumes, and emergency repair.
  • Complications of repair: spinal cord ischaemia (about 1 to 3%), endoleak, renal injury, access site injury, stent graft thrombosis.
  • Iatrogenic catheter related dissection without flow limitation usually heals with medical therapy and surveillance.
• Special groups:
  • Pregnancy: rare; use labetalol 100 to 400 mg twice daily and nifedipine retard 10 to 20 mg twice daily; avoid ACE inhibitors, ARBs and atenolol; deliver when the fetus is viable and the aorta is unstable.
  • Connective tissue disease: earlier intervention (45 to 50 mm), losartan 50 to 100 mg daily in Marfan syndrome, genetic counselling.
  • Cocaine and amphetamine users: lorazepam 2 mg IV, vasodilators, and labetalol with caution.
  • Elderly and frail: favour endovascular repair.
  • Renal impairment: limit contrast volume, hydrate, and use MR or ultrasound for follow up where possible.
• Red flags: new or worsening pain, hypotension, cold or pulseless limb, haematuria or oliguria, abdominal pain with rising lactate, paraparesis.
• Follow up: CT or MR angiography at 1, 3, 6 and 12 months, then yearly for life; blood pressure and heart rate at each visit; duplex ultrasonography as an interval check in stable patients.