Aortic Dissection

Essentials of Diagnosis

• Sudden searing chest pain with radiation to back, abdomen, or neck in a hypertensive patient

• Widened mediastinum on chest radiograph

• Pulse discrepancy in the extremities

• Acute aortic regurgitation may develop

General Considerations

• Occurs when a spontaneous intimal tear develops and blood dissects into the media of the aorta

• Tear probably results from repetitive torque applied to ascending and proximal descending aorta during the cardiac cycle

• Blood entering the intimal tear may extend the dissection into the

  • Abdominal aorta

  • Lower extremities

  • Carotid arteries

  • Subclavian arteries (less commonly)

• Hypertension is important component

• Abnormalities of smooth muscle, elastic tissue, or collagen are more common in patients without hypertension

• Both absolute pressure levels and the pulse pressure are important in propagation of dissection

• Type A dissection

  • Involves the arch proximal to the left subclavian artery

  • Death may occur within hours, due to rupture of dissection into pericardial sac or dissection into the coronary arteries, resulting in myocardial infarction

  • Rupture into plural cavity also possible

  • Flap of aortic wall created by the dissection may occlude major aortic branches, resulting in ischemia of brain, intestines, kidney, or extremities

• Type B dissection typically occurs in the proximal descending thoracic aorta just beyond the left subclavian artery

• Conditions associated with increased risk of dissection

  • Pregnancy

  • Bicuspid aortic valve

  • Coarctation

Symptoms and Signs

• Sudden onset of severe persistent chest pain

  • Characteristically radiates down the back or possibly into the anterior chest

  • May also radiate into the neck

• Dissections may occur with minimal pain

• Hypertension

• Syncope

• Hemiplegia

• Paralysis of lower extremities

• Intestinal ischemia or kidney injury

• Peripheral pulses may be diminished or unequal

• A diastolic murmur may develop as a result of a dissection in the ascending aorta close to the aortic valve, causing valvular regurgitation, heart failure, and cardiac tamponade

Differential Diagnosis

• Myocardial infarction

• Pulmonary embolism

• Arterial embolism

Imaging Studies

• Multiplanar CT scanning

  • Immediate diagnostic imaging modality of choice

  • Should be obtained in any hypertensive patient with chest pain and equivocal findings on ECG

  • Should include both the chest and abdomen to fully delineate the extent of the dissected aorta

• MRI

  • Excellent imaging modality for chronic dissections

  • The longer imaging time and the difficulty of monitoring patients in the scanner make CT scanning preferable in acute situations

• Chest radiographs may reveal

  • An abnormal aortic contour

  • Widened superior mediastinum

• Transesophageal echocardiography

  • An excellent diagnostic imaging method

  • However, it is not readily available in the acute setting

Diagnostic Procedures

• ECG findings

  • May be normal in some patients

  • Left ventricular hypertrophy from long-standing hypertension often present

  • Acute changes suggesting myocardial ischemia do not develop unless dissection involves the coronary artery ostium

  • Classically, inferior wall abnormalities predominate since dissection leads to compromise of the right rather than the left coronary artery

• Aortic dissection is a true emergency; requires immediate control of blood pressure to limit extent

• Use aggressive measures to lower blood pressure when dissection is suspected, even before diagnostic studies have been completed

• Treatment requires a simultaneous reduction of the systolic blood pressure to 100–120 mm Hg and pulse pressure

• Indications for late aneurysm repair are determined by aneurysm size (6 cm or larger), similar to undissected thoracic aneurysms

Medications

• Beta-blockers

  • Should be first-line therapy

  • Have the most desirable effect of reducing the left ventricular ejection force that continues to weaken the arterial wall

  • Should be used with antihypertensive regimen in long-term medical care of patients

• Labetalol

  • Both an alpha- and beta-blocker

  • Lowers pulse pressure and achieves rapid blood pressure control

  • Give 20 mg over 2 minutes by intravenous injection

  • Additional doses of 40–80 mg intravenously can be given every 10 minutes (maximum dose 300 mg) until the desired blood pressure has been reached

  • Alternatively, 2 mg/min may be given by intravenous infusion, titrated to desired effect

• Esmolol

  • Has short half-life

  • Reasonable choice in patients who have asthma, bradycardia, or other conditions that require the patient's reaction to beta-blockers be tested

  • Give loading dose of 0.5 mg/kg over 1 minute followed by an infusion of 0.0025–0.02 mg/kg/min

  • Titrate the infusion to a goal heart rate of 60–70 beats/min

• Nitroprusside may be added if beta-blockade alone does not control the hypertension

  • 50 mg in 1000 mL of 5% dextrose water, infused at a rate of 0.5 mL/min for a 70-kg person (0.3 mcg/kg/min)

  • Infusion rate is increased by 0.5 mL every 5 minutes until adequate control of the pressure has been achieved

• Calcium-channel antagonists

  • No data supporting use in patients with asthma

  • However, diltiazem and verapamil are potential alternatives to beta-blockers

• Morphine sulfate is appropriate for pain relief

Surgery

• Type A dissections

  • Urgent intervention is required

  • Procedure involves grafting and replacing the diseased portion of the arch and brachiocephalic vessels as necessary

  • Replacement of the aortic valve may be required with reattachment of the coronary arteries

• Type B dissections with malperfusion

  • Urgent surgery is required if there is aortic branch compromise resulting in malperfusion of the renal, visceral, or extremity vessels

  • The immediate goal of surgical therapy is to restore flow to the ischemic tissue which is most commonly accomplished via a bypass

  • Endovascular stenting of the entry tear at the level of the subclavian artery may result in obliteration of the false lumen and restore flow into the branch vessel from the true lumen; however, results are unpredictable

• Type B dissections without malperfusion: early thoracic stent graft repair improves

  • Long-term aortic-specific survival

  • Late aneurysm formation rates, especially in healthy patients with high-risk anatomic features (aortic diameter > 4 cm or partial false lumen thrombosis)

Follow-Up

• Yearly CT scans are required to monitor for aneurysm development

Prognosis

• Type A dissections

  • Mortality rate for untreated type A dissections

    • Approximately 1% per hour for 72 hours

    • Over 90% at 3 months

• Type B dissections

  • Mortality is also extremely high for untreated type B dissections with malperfusion or rupture

  • For acute type B dissections without malperfusion, evidence shows that long-term aortic-specific survival and late aneurysm formation rates are improved with early thoracic stent graft repair

• Surgical and endovascular options are technically demanding and require an experienced team to achieve perioperative mortalities of < 10%

• Aneurysmal enlargement of the residual false lumen may develop despite adequate antihypertensive therapy

When to Admit

• All patients with an acute dissection should be admitted

• Any dissection involving the aortic arch (type A) should be immediately repaired

• Acute type B dissections require repair only when there is evidence of rupture or major branch occlusion