Acute Aortic Syndrome

Acute aortic syndrome is the group of life threatening acute aortic wall disorders presenting with pain: aortic dissection, intramural haematoma and penetrating atherosclerotic ulcer, with or without rupture. Type A involves the ascending aorta and type B the descending aorta distal to the left subclavian artery.

Epidemiology. Incidence is about 3 to 6 cases in 100,000 each year. Mortality of untreated type A dissection is about 1 to 2% each hour in the first 48 hours. Peak age is 60 to 70 years, with younger patients having genetic disease.

Risk factors. Hypertension (most), connective tissue disease (Marfan, Ehlers-Danlos vascular type, Loeys-Dietz), bicuspid aortic valve, Turner syndrome, aortic aneurysm, vasculitis (giant cell arteritis, Takayasu), cocaine and amphetamine use, pregnancy, cardiac surgery or catheterisation, trauma and fluoroquinolone use.

Pathophysiology. An intimal tear lets blood enter the media and create a false lumen. Intramural haematoma arises from vasa vasorum rupture, and penetrating ulcer from an atherosclerotic erosion. Complications are rupture, tamponade, aortic regurgitation, branch vessel malperfusion (coronary, cerebral, spinal, mesenteric, renal, limb) and heart failure.

Presentation is abrupt, severe chest, back or abdominal pain, maximal at onset, often tearing, migrating, or sharp. Others are syncope, stroke, paraplegia, limb ischaemia, pulse deficit or blood pressure difference between arms of over 20 mmHg, new aortic regurgitation murmur, hypotension and shock. Hypertension is common in type B, and hypotension suggests type A with tamponade or rupture.

Red flags.

• Sudden severe pain with pulse deficit, neurological deficit or syncope.
• Hypotension, tamponade or new regurgitation murmur.
• Widened mediastinum on radiograph, or known connective tissue disease.

Assess pretest probability by risk markers (high risk condition, pain features, examination features). CT angiography of the aorta (with ECG gating for the ascending aorta) is the first test for most patients. Transoesophageal echocardiography at the bedside in the unstable patient, and MRI when CT is contraindicated.

D-dimer under 500 nanogram/mL can exclude dissection only in patients with a low pretest probability (aortic dissection detection score of 0 or 1). ECG, troponin (coronary involvement or infarction mimic), chest radiograph, lactate, creatinine, full blood count and group and crossmatch.

Differential diagnosis. Acute coronary syndrome, pulmonary embolism, pericarditis, oesophageal rupture, pneumothorax, musculoskeletal pain and pancreatitis.

Analgesia and monitoring. Fentanyl 25 to 50 microgram IV, or morphine 2 to 4 mg IV, titrated to pain relief. Continuous arterial pressure, ECG and urine output. Two large bore cannulae.

Impulse control (reduce shear stress). Target heart rate under 60 beats/min first, then systolic pressure 100 to 120 mmHg (the lowest that maintains organ perfusion).

• Esmolol 500 microgram/kg IV bolus then 50 to 300 microgram/kg/min.
• 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 beta blockers are contraindicated (severe asthma, bradycardia, block): diltiazem 0.25 mg/kg IV then 5 to 15 mg/h, or verapamil 5 to 10 mg IV.
• Then add a vasodilator if pressure remains high: nicardipine 5 mg/h titrated by 2.5 mg/h every 5 to 15 minutes (maximum 15 mg/h), or nitroprusside 0.3 to 0.5 microgram/kg/min (maximum 10 microgram/kg/min, short term, with cyanide and thiocyanate monitoring). Never give a vasodilator without prior rate control.

Avoid. Anticoagulants, antiplatelets and thrombolytics. In hypotension, give blood and avoid large crystalloid volumes (permissive pressure of 80 to 90 mmHg), and think of tamponade or rupture.

Type A (ascending). Emergency open surgery (replacement of the ascending aorta, with valve and arch repair as needed). Pericardiocentesis in tamponade only to bridge to theatre, with minimal drainage.

Type B.

• Uncomplicated: medical therapy with impulse control, and early transition to oral antihypertensives (beta blocker, plus ACE inhibitor or calcium channel blocker) and surveillance imaging.
• Complicated (rupture, malperfusion, refractory pain or hypertension, rapid expansion): thoracic endovascular aortic repair, with open surgery or fenestration in selected cases.

Intramural haematoma and ulcer. Type A haematoma is managed like dissection, and type B by medical therapy with imaging at 1 week, 1 month, 3 and 6 months, and repair if it progresses. Symptomatic ulcers with rupture risk need endovascular repair.

Long term care. Blood pressure under 130/80 mmHg, beta blocker, lifelong imaging, avoidance of fluoroquinolones and heavy lifting, genetic testing and family screening.

Monitoring. Arterial pressure, heart rate, pain, neurological and limb perfusion checks, urine output and lactate.

Referral and escalation. Cardiac or vascular surgery at once. Transfer to an aortic centre without delay.

Special groups. In pregnancy, third trimester dissection requires combined obstetric and cardiac surgical planning. In connective tissue disease, restrict physical exertion and treat with beta blockers or losartan.