Aortic Dissection

Aortic dissection is a tear in the aortic intima that allows blood to enter the media, creating a false lumen that propagates along the aorta. It is the commonest catastrophic aortic emergency, with an incidence of 3 to 6 per 100,000 per year. Without treatment, mortality in acute type A dissection rises by 1 to 2% per hour in the first 48 hours, reaching over 50% at 1 week.

Classification

• Stanford type A: involves the ascending aorta, regardless of origin of the tear. Surgical emergency.
• Stanford type B: confined to the descending aorta distal to the left subclavian artery.
• DeBakey: type I (ascending to arch and beyond), type II (ascending only), type III (descending only: IIIa above the diaphragm, IIIb extending below).
• Timing: hyperacute (under 24 hours), acute (up to 14 days), subacute (15 to 90 days), chronic (over 90 days).
• Related acute aortic syndromes: intramural haematoma (haemorrhage in the wall without intimal tear) and penetrating atherosclerotic ulcer.

Risk factors

• Hypertension (in about 70%).
• Age 60 to 70 years, male sex (about 2:1).
• Connective tissue disease: Marfan, Loeys-Dietz, vascular Ehlers-Danlos syndrome, Turner syndrome, familial thoracic aortic aneurysm and dissection.
• Bicuspid aortic valve, coarctation, pre-existing aneurysm, aortitis (giant cell arteritis, Takayasu arteritis, syphilis).
• Cocaine and amphetamine use, fluoroquinolone exposure, heavy weightlifting.
• Pregnancy (third trimester and postpartum), especially with Marfan syndrome.
• Iatrogenic: cardiac catheterisation, cardiac surgery, aortic cross-clamping, intra-aortic balloon pump, aortic valve interventions.
• Trauma: deceleration injuries.

Complications determining prognosis

• Aortic regurgitation, coronary malperfusion (right coronary mostly), pericardial tamponade and rupture (type A).
• Branch malperfusion (cerebral, spinal cord, mesenteric, renal, limb), rupture, and aneurysmal degeneration of the false lumen in the chronic phase.
• Hospital mortality of medically managed acute type B dissection is 10%, and with complications (malperfusion, rupture) is 20% or more. Surgical mortality in type A is 15 to 25%.

Pain is the cardinal symptom (about 95%), described as abrupt in onset, severe from the outset ("maximal at onset"), sharp, tearing or ripping:

• Type A: anterior chest pain, with radiation to the neck and jaw.
• Type B: interscapular or back pain, with radiation to the abdomen and legs.
• Migrating pain suggests propagation. Painless dissection occurs in 5 to 10%, commonly in older patients, those with diabetes, and those with neurological presentations.

Findings

• Blood pressure: hypertension at presentation in about 70% of type B and 35% of type A, and hypotension in type A with tamponade, rupture or acute regurgitation.
• Pulse deficit and blood pressure differential of more than 20 mmHg between arms (in 15 to 30%).
• New aortic regurgitation murmur (in 40% of type A) and signs of heart failure.
• Syncope (about 10%), from tamponade, arrhythmia or cerebral hypoperfusion.
• Neurological deficit: stroke, spinal cord ischaemia (paraplegia, anterior spinal artery syndrome), ischaemic neuropathy, hoarseness (recurrent laryngeal compression), Horner syndrome.
• Myocardial ischaemia and ST elevation (inferior MI from right coronary involvement) in 1 to 2%.
• Mesenteric ischaemia: abdominal pain, lactic acidosis, bloody stools.
• Renal: oliguria, acute kidney injury, refractory hypertension.
• Limb ischaemia.
• Pleural effusion, haemothorax, haemoptysis, or haematemesis (rupture).

Aortic Dissection Detection Risk Score (ADD-RS) counts one point for each category

• High-risk conditions (Marfan syndrome, family history, known aortic valve disease or aneurysm, previous aortic manipulation).
• High-risk pain features (abrupt, severe, ripping or tearing).
• High-risk examination features (pulse deficit, systolic blood pressure differential, focal neurological deficit with pain, new aortic regurgitation murmur with pain, hypotension or shock).

Scores of 0 with D-dimer under 500 ng/mL effectively exclude the diagnosis. A score of 1 with a normal D-dimer is also low risk. Scores of 2 or more need immediate imaging.

Differential diagnosis: acute coronary syndrome, pulmonary embolism, pericarditis, oesophageal rupture, pneumothorax, acute pancreatitis, cholecystitis, musculoskeletal pain, and non-dissecting thoracic aneurysm.

Initial tests

• ECG in all (to detect ischaemia, which may coexist). Do not give anticoagulants or thrombolytics before excluding dissection in chest pain with ST elevation if there is any suspicion.
• Chest radiograph: widened mediastinum (in about 60%), abnormal aortic contour, pleural effusion, displaced calcification (calcium sign). It is normal in 10 to 20%, so it cannot exclude dissection.
• D-dimer: less than 500 ng/mL has a negative predictive value of 97 to 99% in low-risk patients. It cannot rule out dissection in high-risk patients, and is raised in many other conditions.
• Bedside echocardiography: pericardial effusion, aortic regurgitation, dilated root, intimal flap in the root. Used for rapid triage.
• Laboratory tests: CBC, troponin, creatinine, lactate, liver enzymes, coagulation, and cross-match 4 to 6 units.

Definitive imaging

• CT angiography (ECG-gated when possible) of the chest, abdomen and pelvis is the first-line test (sensitivity and specificity about 98 to 100%). It shows the entry tear, intimal flap, true and false lumens, extent, branch vessel involvement, haemopericardium, rupture and aneurysm.
• Transoesophageal echocardiography: bedside, in unstable patients, with sensitivity of about 98%. Requires sedation and blood pressure control, and has a blind spot in the distal ascending aorta and arch.
• MR angiography: high accuracy, used for stable patients and follow-up, but less practical in the acute setting.
• Intramural haematoma shows crescentic wall thickening over 5 mm on non-contrast CT (hyperdense) without a flap, and penetrating atherosclerotic ulcer shows a contrast-filled outpouching.
• Catheter aortography is no longer a diagnostic tool.

Immediate stabilisation (all patients, before and after diagnosis)

• Resuscitation area with arterial line (right radial preferred, or the arm with the higher pressure), continuous ECG, urinary catheter.
• Analgesia: fentanyl 25 to 50 micrograms IV titrated, or morphine 2 to 4 mg IV. Pain control reduces sympathetic drive.
• Impulse control (anti-impulse therapy): lower the heart rate to 60 beats/minute or below first, then lower the systolic blood pressure to 100 to 120 mmHg (or the lowest tolerated with adequate end-organ perfusion), as soon as possible.
• Esmolol 500 micrograms/kg IV bolus over 1 minute, then 50 micrograms/kg/min infusion, increasing by 50 micrograms/kg/min every 4 minutes to 200 micrograms/kg/min.
• Labetalol 20 mg IV over 2 minutes, then 20 to 80 mg every 10 minutes to a total of 300 mg, or infusion 0.5 to 2 mg/min.
• Add vasodilator only after adequate beta blockade (to avoid reflex tachycardia that increases shear stress): nicardipine 5 to 15 mg/h, clevidipine 1 to 21 mg/h, or sodium nitroprusside 0.25 to 0.5 micrograms/kg/min (up to 10 micrograms/kg/min), with cyanide toxicity risk with prolonged use or renal failure.
• Non-dihydropyridine calcium channel blockers (diltiazem 0.25 mg/kg IV, then 5 to 15 mg/h) when beta blockers are contraindicated (severe asthma, acute aortic regurgitation requiring tachycardia).
• In suspected acute severe aortic regurgitation, avoid beta blockers if heart failure develops, and use inotropes cautiously.
• Hypotension: assess for tamponade, rupture and acute regurgitation rather than treating with vasopressors. Give blood and volume, and take the patient to theatre urgently.
• Avoid anticoagulants, antiplatelets and thrombolysis.

Type A dissection

• Emergency open surgery is the standard of care, ideally within hours of diagnosis. Repair includes resection of the entry tear and replacement of the ascending aorta (supracoronary graft), with hemiarch or total arch replacement as needed, root replacement (Bentall or valve-sparing) for root involvement, or valve resuspension, plus coronary reimplantation or bypass if indicated.
• Cardiopulmonary bypass with arterial cannulation through the axillary artery and antegrade cerebral perfusion, with moderate or deep hypothermic circulatory arrest.
• Operative mortality is 15 to 25% (higher with malperfusion, shock, age over 80 and coronary involvement).
• Pericardial tamponade: urgent surgery. Pericardiocentesis is avoided or limited to small volume drainage to maintain systolic pressure of 90 mmHg in pre-arrest states, since release of tamponade may precipitate rupture.
• Selected patients with extensive irreversible organ damage or a very poor prognosis may be managed palliatively.
• Malperfusion syndromes may require preoperative or concurrent revascularisation (stenting, fenestration) before or after central repair.
• Intramural haematoma in the ascending aorta is treated as type A, with urgent surgery in the presence of high-risk features (diameter over 5 cm, haematoma thickness over 11 mm, pericardial effusion, aortic regurgitation).

Type B dissection

• Uncomplicated: medical therapy with anti-impulse therapy in the intensive care unit for 24 to 48 hours, then transition to oral agents. Routine thoracic endovascular aortic repair in the subacute phase (14 to 90 days) is considered in patients with high-risk anatomic features (maximum aortic diameter over 40 mm, false lumen diameter over 22 mm, entry tear over 10 mm, proximal tear location, circumferential false lumen, patent false lumen, rapid growth), as it promotes aortic remodelling and improves long-term survival.
• Complicated (rupture, malperfusion, refractory pain or hypertension, rapid expansion, extension, early aneurysm): urgent TEVAR to cover the primary entry tear and reperfuse true lumen branches. Fenestration or stenting of branch vessels for malperfusion persistence. Open surgery is for unsuitable anatomy or retrograde type A extension.
• Complications include stroke (3 to 5%), spinal cord ischaemia (2 to 5%), retrograde type A dissection (1 to 2%), and access vessel injury. Spinal protection with CSF drainage in selected patients.

Oral therapy and secondary prevention

• Lifelong blood pressure target below 130/80 mmHg (some advocate below 120/80 mmHg), heart rate below 70 beats/minute.
• Beta blocker (metoprolol succinate 50 to 200 mg daily, propranolol 40 to 160 mg twice daily, bisoprolol 2.5 to 10 mg daily, or labetalol 100 to 400 mg twice daily), plus ACE inhibitor or ARB (losartan 50 to 100 mg daily) and amlodipine 5 to 10 mg as required. Three or more agents are often required.
• Avoid fluoroquinolones, stimulants and heavy isometric exercise.
• Smoking cessation, statin if atherosclerosis is present, and sleep apnoea treatment.
• Genetic evaluation and family screening.

Surveillance

• Imaging (CT angiography or MR angiography) before discharge, at 1, 3, 6 and 12 months, and annually thereafter (every 6 months with a false lumen larger than 4.5 to 5.5 cm). Indications for later intervention include aneurysmal growth (over 5.5 cm, or over 5 mm per 6 months), recurrent symptoms, malperfusion and rupture.
• Residual dissected aorta after type A repair needs lifelong imaging.

Special situations

• Pregnancy: beta blockers throughout, labetalol and nifedipine for blood pressure, surgery for type A (with fetal viability considered, caesarean delivery before repair beyond 28 weeks), and TEVAR in selected type B cases.
• Intramural haematoma and penetrating ulcer: managed according to location and complications, with early imaging at 1 to 4 weeks.
• Iatrogenic dissection (catheter-related): often conservative if localised.