AORTIC DISSECTION

AORTIC DISSECTION - Jeremy Golding, MD
BASICS
DESCRIPTION
• Intimal tear in aorta resulting in hematoma formation. Accumulating blood in false lumen of arterial wall leads to propagation of this dissection.
• DeBakey classification: Based on origin site
- Type I: Originates in ascending aorta, propagates at least as far as aortic arch
- Type II: Involves only ascending aorta
- Type III: Originates in descending aorta, may propagates proximately or distally
• Stanford classification: More widely used
- Type A: Involves ascending aorta and aortic arch regardless of site of intimal tear
- Type B: Involves descending aorta
• New classification, subdivisions of DeBakey or Stanford
- 1. Classic
- 2. Medial disruption with hematoma formation
- 3. Discrete without hematoma
- 4. Plaque rupture, ulceration
- 5. Iatrogenic
• Synonym(s): Dissecting aneurysm
GENERAL PREVENTION
• Long-term control of hypertension
• Surveillance of aortic root and replacement when appropriate in patients with collagen disorders (e.g., Marfan, Ehlers-Danlos)
EPIDEMIOLOGY
• Predominant age: Depends on cause; commonly present in patients with Marfan syndrome in 3rd and 4th decades; otherwise most common between 6th and 8th decades
• Predominant sex: Male > Female (3:1)
• Mean age: Men 60 years, women 67 years
Incidence
2000 new cases diagnosed annually
Prevalence
US
• Diagnosed in 1 in 10,000 patients admitted to hospital
• Found in 1 in 350 patients at autopsy
RISK FACTORS
• Hypertension in 70% of patients
• Cystic medial necrosis
• Collagen abnormalities
- Marfan syndrome
- Ehlers-Danlos syndrome
• Inflammatory aortitis
• Takayasu arteritis
• Giant cell arteritis
• Congenital abnormalities
- Bicuspid aortic valve
- coarctation
• Pregnancy
• Chest trauma
• Cocaine use
• Cardiovascular surgery
• Elderly
• MDMA (ecstasy) use
• 1-Antitrypsin deficiency
• Smoking
Genetics
Increased incidence among family members
ETIOLOGY
• Cystic medial necrosis
• Iatrogenic during arterial catheterization
ASSOCIATED CONDITIONS
• Ehlers-Danlos syndrome
• Marfan syndrome
• Aortic stenosis
• Coarctation of aorta
• Bicuspid valve
• Turner syndrome
• Osteogenesis imperfecta
• Syphilis
• Relapsing polychondritis
• During pregnancy: Possibly cystic medionecrosis of pregnancy; unclear whether pregnancy is originating factor or contributes to worsening of a pre-existing condition


DIAGNOSIS
SIGNS AND SYMPTOMS
• Abrupt onset of sharp or tearing pain
• Shearing anterior chest pain radiating to interscapular region
• Back pain
• Syncope
• Symptoms of CHF
• Stroke
• Limb ischemia
• Abdominal pain
• Acute myocardial infarction/angina
• Spinal cord syndromes/deficits
• Hypotension or hypertension
• Wide pulse pressure
• Murmur of aortic insufficiency
• Features of tamponade
• Dullness in left lung base (effusion)
• Pulse deficits or asymmetry
• Fever
• 96% of acute aortic dissections can be identified by abrupt onset of sharp thoracic or abdominal pain in the presence of mediastinal widening on chest radiograph and asymmetry of pulses
History
Typical patient is a hypertensive man in his 60s with abrupt onset of severe chest pain.
TESTS
• Electrocardiogram
- Left ventricular hypertrophy
- Nonspecific ST-T changes
- Electrical alternans (in cardiac tamponade)
• Echocardiogram
- Dilated aortic root
- Increased aortic posterior or anterior wall thickness
- Pericardial effusion
- Oscillating intimal flap
Imaging
Chest radiograph, in stable patients
• Widening of superior mediastinum
• Left pleural effusion
• Haziness or enlargement of aortic knob
• Double density of descending aorta
• Irregular aortic contour: >5 mm separation of intimal calcification from outer aortic contour
• Rightward displacement of trachea
• Cardiomegaly
Diagnostic Procedures/Surgery
• (Sensitivity/specificity is indicated for each.)
• Chest CT (88/100%)
- Demonstration of 2 lumens with hematoma formation
- Detection of intimal flap
- Differential flow between 2 lumens
- Compression of true lumen by false lumen
• Spiral CT aortography; more sensitive and specific (99/99%)
• Aortogram (88/94%)
- Demonstration of 2 lumens
- Detection of intimal flap
- Compression of true lumen
- Ulcer-like projections of contrast
- Altered flow patterns
• Transesophageal echocardiography (99/98%): Test of choice for unstable patients
• MRI: If available and patient hemodynamically stable, test of choice for delineation of vascular anatomy (>99/99%)
• Intravascular ultrasonography: May detect with negative transesophageal echocardiography
Pathological Findings
• ~60% of intimal tears occur in proximal ascending aorta. Remainder are between origin of left subclavian artery and ligamentum arteriosum, descending aorta (20%), aortic arch (10%), and abdominal aorta.
• Although medionecrosis is found in normal aging aortas, it is more extensive in patients who develop aortic dissection.
• Cystic medial necrosis is seen in patients with defects in elastin and connective tissue organization (e.g., Marfan, Ehlers-Danlos).
• Death usually is due to rupture and tamponade.
DIFFERENTIAL DIAGNOSIS
• Myocardial infarction
• Pulmonary embolism
• Pneumonia
• Pleurisy
• Pericarditis
• Pneumothorax
• Angina
• Acute pancreatitis
• Penetrating duodenal ulcer
TREATMENT
GENERAL MEASURES
• Admit to ICU for assessment of hemodynamic stability, pain control, BP control
• Intubate; hemodynamically unstable patients
• Medical therapy
- Treatment of choice for descending dissections without complications (Type III)
- Based on decreasing BP and shearing forces of myocardial contractility (dp/dt) to decrease intimal tear and hematoma propagation
- Survival is 60-80% at 4-5 years
• Arterial BP monitoring is critical.
• Careful observation for changes in mentation, neurologic signs, or evidence of organ dysfunction
• Foley catheter to follow urine output
• Swan-Ganz catheterization may be helpful in monitoring cardiac performance and filling pressures during use of vasoactive and cardiodepressive drugs.
• Pain control difficult despite use of narcotics.
Diet
NPO until surgical evaluation is complete and patient classified as medical therapy only
Activity
Bed rest
MEDICATION (DRUGS)
First Line
• Propranolol plus nitroprusside; dosing
- Propranolol: 0.5-1 mg IV q5min until heart rate 60-70 bpm and
- Nitroprusside: Titrated to reduce systolic BP to 100-110 mm Hg (13.3-14.6 kPa)
• Contraindications
- Propranolol
 Bronchial asthma
 Diabetes mellitus
 Raynaud disease
 Sinus bradycardia
 A-V heart block >1st degree
 In presence of MAOIs
 Cardiogenic shock
 Acute CHF
 Right ventricular failure from pulmonary hypertension
- Nitroprusside
 In treatment of compensatory hypertension, that is, arteriovenous shunt
 In patients with inadequate cerebral circulation
 For use during emergency surgery in moribund patients
• Precautions
- Propranolol
 Use cautiously in patients with angina pectoris, cardiac failure, impaired renal or hepatic function, thyrotoxicosis, pre-excitation syndromes, diabetes, or nonallergic bronchospasm.
 Propranolol may produce bradycardia, heart block, or hypotension. Patients should not be suddenly withdrawn from -blockers.
- Nitroprusside
 May not lower BP adequately; another agent may be required.
 In patients with renal or hepatic insufficiency, may cause cyanide toxicity through excessive production of serum thiocyanate. Confusion and hyper-reflexia are early signs of thiocyanate toxicity. Thiocyanate inhibits uptake and binding of iodine; caution with hypothyroidism. Check thiocyanate levels after 48 hours.
 Administration via infusion pump.
 Methemoglobinemia may be seen rarely.
• Significant possible interactions
- Propranolol: Adenosine, albuterol, alfentanil, amiodarone, barbiturates, bromazepam, chlorothiazide, chlorpromazine, chlorpropamide, chlorprothixene, cimetidine, clonidine, dextroamphetamine, diazoxide, dihydroergotamine, diltiazem, disopyramide, tricyclic antidepressants, encainide, epinephrine, flecainide, fluvoxamine, furosemide, glipizide, halofenate, haloperidol, heparin, ibuprofen, indomethacin, insulin, isoniazid, isoproterenol, lidocaine, lidoflazine, methacholine, methyldopa, metoclopramide, naproxen, nifedipine, phenylpropanolamine, procainamide, quinidine, reserpine, rifampin, ritodrine, sulfonylureas, theophylline, thioridazine, tocainide, tubocurarine, verapamil, and warfarin
- Nitroprusside: Clonidine and other antihypertensives may have hypotensive effects.
Second Line
• Labetalol: 10-20 mg IV bolus to a maximum of 300 mg total, then titrated to response with infusion
• Trimethaphan: Infusion rate 1-2 mg/min
• Reserpine: 0.5-2 mg IM q4-8h; onset of action 1-3 hours
• Methyldopa: 250-500 mg q6h; onset of action of 4-6 hours; duration 1-12 hours
SURGERY
• Treatment of choice for all ascending aortic dissections
• Surgical indications for Type III
- Increasing size of hematoma
- Impending rupture
- Inability to control pain
- Bleeding into pleural space
• Endovascular stents, fenestration, and stent grafting
FOLLOW-UP
PROGNOSIS
• Mortality, untreated
- 24 hours: 33%
- 2 weeks: 60%
- 3 months: 90%
• Hospital survival estimate, treated medically and surgically: 70%
• Mortality, ascending dissection treated early surgically: 29-38%
• 10-year survival, treated surgically (all): 40%
• Redissection risk
- 5 years: 13%
- 10 years: 23%
COMPLICATIONS
• Redissection
• Localized saccular aneurysm
• Cardiac tamponade
• Aortic valvular insufficiency
• Progressive aortic enlargement
PATIENT MONITORING
• Maintain systolic BP at 120 mm Hg (16 kPa) or below, as tolerated.
• Routine chest films and/or chest CT may be helpful for patient treated medically long term.
• Follow-up visit at 1 month, then at 3-month intervals. During follow-up, pay careful attention to signs and symptoms of aortic insufficiency, chest or back pain, and development of saccular aneurysms as displayed on chest films.
REFERENCES
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