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Aortic Dissection

By Mark A. Farber, MD, FACS, Professor of Surgery and Radiology, Division of Vascular Surgery;Director University of North Carolina Aortic Network, University of North Carolina;University of North Carolina ; Thaniyyah S. Ahmad, MD, MPH, University of North Carolina

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Aortic dissection is the surging of blood through a tear in the aortic intima with separation of the intima and media and creation of a false lumen (channel). The intimal tear may be a primary event or secondary to hemorrhage within the media. The dissection may occur anywhere along the aorta and extend proximally or distally into other arteries. Hypertension is an important contributor. Symptoms and signs include abrupt onset of tearing chest or back pain, and dissection may result in aortic regurgitation and compromised circulation in branch arteries. Diagnosis is by imaging tests (eg, transesophageal echocardiography, CT angiography, MRI, contrast aortography). Treatment always involves aggressive blood pressure control and serial imaging to monitor progression of dissection. Surgical repair of the aorta and placement of a synthetic graft are needed for ascending aortic dissection and for certain descending aortic dissections. Endovascular stent grafts are used for certain patients, especially when dissection involves the descending thoracic aorta. One fifth of patients die before reaching the hospital, and up to one third die of operative or perioperative complications.

Evidence of dissection is found in 1 to 3% of all autopsies. Blacks, men, the elderly, and people with hypertension are especially at risk. Peak incidence occurs at age 50 to 65 in the general population and at age 20 to 40 for patients with congenital connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome).

Classification of aortic dissection

Aortic dissections are classified anatomically.

The DeBakey classification system is most widely used.

  • Type I (50% of dissections): These dissections start in the ascending aorta and extend at least to the aortic arch and sometimes beyond.

  • Type II (35%): These dissections start in and are confined to the ascending aorta (proximal to the brachiocephalic or innominate artery).

  • Type III (15%): These dissections start in the descending thoracic aorta just beyond the origin of the left subclavian artery and extend distally or, less commonly, proximally. Type IIIa dissections originate distal to the left subclavian artery and are confined to the thoracic aorta. Type IIIb dissections originate distal to the left subclavian artery and extend below the diaphragm.

The Stanford system is simpler.

  • Type A: These dissections involve the ascending aorta.

  • Type B: These dissections are confined to the descending thoracic aorta (distal to the left subclavian artery).

Although dissection may originate anywhere along the aorta, it occurs most commonly at areas of greatest hydraulic stress, which are the

  • Right lateral wall of the ascending aorta (within 5 cm of the aortic valve)

  • Proximal segment of the descending aorta (just beyond the origin of the left subclavian artery)

Rarely, dissection is confined to individual arteries (eg, coronary or carotid arteries), typically in pregnant or postpartum women.

Etiology

Aortic dissections often occur in patients with preexisting degeneration of the aortic media. Causes and risk factors include connective tissue disorders, atherosclerotic disease, and injury (see Table: Conditions Contributing to Aortic Dissection).

Conditions Contributing to Aortic Dissection

Category

Examples

Atherosclerotic risk factors

Cocaine

Smoking

Connective tissue disorders, acquired

Connective tissue disorders, congenital or hereditary

Bicuspid aortic valve

Cystic medial necrosis

Familial thoracic aortic aneurysm

Iatrogenic

Aortic catheterization

Aortic valve surgery

Trauma

Deceleration injuries

Atherosclerotic risk factors, notably hypertension, contribute in more than two thirds of patients. After rupture of the intima, which is a primary event in some patients and secondary to hemorrhage within the media in others, blood flows into the media, creating a false channel that extends distally or, less commonly, proximally along the artery.

Pathophysiology

The pathophysiologic sequence of aortic dissections involves aortic wall inflammation, apoptosis of vascular smooth muscle cells, degeneration of aortic media, elastin disruption, and then vessel dissection. Dissections may communicate back with the true aortic lumen through intimal rupture at a distal site, maintaining systemic blood flow.

Serious consequences are common and include

  • Compromise of the blood supply of arteries that branch off the aorta (including coronary arteries)

  • Aortic valvular dilation and regurgitation

  • Heart failure

  • Fatal rupture of the aorta through the adventitia into the pericardium, right atrium, or left pleural space

Acute dissections and those present < 2 wk are most likely to cause these complications. Risk decreases at 2 wk if evidence indicates thrombosis of the false lumen and loss of communication between the true and false lumina.

Variants of aortic dissection include separation of the intima and media by intramural hematoma without a clear intimal tear or flap, intimal tear and bulge without hematoma or false lumen, and dissection or hematoma caused by ulceration of atherosclerotic plaque. These variants are thought to be precursors of classic aortic dissection.

Symptoms and Signs

Typically, excruciating precordial or interscapular pain, often described as tearing or ripping, occurs abruptly. The pain frequently migrates from the original location as the dissection extends along the aorta. Up to 20% of patients present with syncope due to severe pain, aortic baroreceptor activation, extracranial cerebral artery obstruction, or cardiac tamponade. Hypotension and tachycardia could indicate active bleeding.

Occasionally, patients present with symptoms of malperfusion (stroke, myocardial infarction, intestinal infarction, renal insufficiency, paraparesis, or paraplegia) due to interruption of the blood supply to a particular vascular bed, including the spinal cord, brain, heart, kidneys, intestine, or extremities. The interruption in blood supply is most often due to acute distal arterial obstruction by the false lumen.

About 20% of patients have partial or complete deficits of major arterial pulses, which may wax and wane. Limb blood pressures may differ, sometimes by > 30 mm Hg; this finding suggests a poor prognosis. A murmur of aortic regurgitation is heard in about 50% of patients with proximal dissection. Peripheral signs of aortic regurgitation may be present. Rarely, heart failure results from severe acute aortic regurgitation. Leakage of blood or inflammatory serous fluid into the left pleural space may lead to signs of pleural effusion. Occlusion of a limb artery may cause signs of peripheral ischemia or neuropathy. Renal artery occlusion may cause oliguria or anuria. Cardiac tamponade may cause pulsus paradoxus and jugular venous distention.

Pearls & Pitfalls

  • Only about 20% of patients with aortic dissection have pulse deficits.

Diagnosis

  • Transesophageal echocardiography (TEE), CT angiography (CTA), or magnetic resonance angiography (MRA)

Aortic dissection must be considered in any patient with chest pain, thoracic back pain, unexplained syncope, unexplained abdominal pain, stroke, or acute-onset heart failure, especially when pulses or blood pressures in the limbs are unequal. Such patients require a chest x-ray; in 60 to 90%, the mediastinal shadow is widened, usually with a localized bulge signifying the site of origin. Left pleural effusion is common.

Patients presenting with acute chest pain, ECG changes of acute inferior myocardial infarction, and a previously undocumented murmur of aortic insufficiency (AI) are of particular concern for a type I aortic dissection into the right coronary artery (causing inferior myocardial infarction), and the aortic valve (causing AI).

If chest x-ray suggests dissection, TEE, CTA, or MRA is done immediately after the patient is stabilized. Findings of an intimal flap and double lumina confirm dissection.

Multiplanar TEE is 97 to 99% sensitive and, with M-mode echocardiography, is nearly 100% specific. It can be done at the bedside in < 20 min and does not require contrast agents. However, CTA is typically the first-line imaging modality because it is often available more rapidly and widely than TEE. The sensitivity of CTA exceeds 95% and it has a positive predictive value of 100% and a negative predictive value of 86%.

MRA has nearly 100% sensitivity and specificity for aortic dissection. But it is time-consuming and ill-suited for emergencies. It is probably best used for stable patients with subacute or chronic chest pain when dissection is suspected.

Contrast aortography is an option if surgery is being considered. In addition to identifying the origin and extent of dissection, severity of aortic regurgitation, and extent of involvement of the aorta’s major branches, aortography helps determine whether simultaneous coronary artery bypass surgery is needed. Echocardiography should also be done to check for aortic regurgitation and thus determine whether the aortic valve should be repaired or replaced concomitantly.

ECG is nearly universally done. However, findings range from normal to markedly abnormal (in acute coronary artery occlusion or aortic regurgitation), so the test is not diagnostically helpful for dissection itself. Assays for soluble elastin compounds and smooth-muscle myosin heavy-chain protein are being studied; the data appears promising, but the assays are not routinely available. Serum CK-MB and troponin may help distinguish aortic dissection from myocardial infarction, except when dissection causes myocardial infarction.

Routine laboratory tests may detect slight leukocytosis and anemia if blood has leaked from the aorta. Increased LDH may be a nonspecific sign of celiac or mesenteric arterial trunk involvement.

A cardiothoracic surgeon should be consulted early during the diagnostic evaluation.

Prognosis

About 20% of patients with aortic dissection die before reaching the hospital. Without treatment, mortality rate is 1 to 3%/h during the first 24 h, 30% at 1 wk, 80% at 2 wk, and 90% at 1 yr.

Hospital mortality rate for treated patients is about 30% for proximal dissection and 10% for distal. For treated patients who survive the acute episode, survival rate is about 60% at 5 yr and 40% at 10 yr. About one third of late deaths are due to complications of the dissection; the rest are due to other disorders.

Treatment

  • Beta-blockers and other drugs to control BP

  • Usually surgery (endovascular or open repair)

Patients who do not immediately die of aortic dissection should be admitted to an ICU with intra-arterial blood pressure monitoring and an indwelling urethral catheter to monitor urine output. Blood should be typed and cross-matched for 4 to 6 units of packed RBCs when surgery is likely. Hemodynamically unstable patients should be intubated.

Medical management

Drugs to decrease arterial pressure, arterial shear stress, ventricular contractility, and pain are started immediately to maintain systolic BP at ≤ 110 mm Hg or the lowest level compatible with adequate cerebral, coronary, and renal perfusion.

A beta-blocker is usually the first-line drug for BP control. Options include metoprolol 5 mg IV up to 4 doses 15 min apart, esmolol 50 to 200 mcg/kg/min in a constant IV infusion, and labetalol (an alpha- and beta-adrenergic blocker) 1 to 2 mg/min in a constant IV infusion or 5 to 20 mg IV initial bolus with additional doses of 20 to 40 mg given q 10 to 20 min until BP is controlled or a total of 300 mg has been given, followed by additional 20- to 40-mg doses q 4 to 8 h prn.

Alternatives to beta-blockers include calcium channel blockers (eg, verapamil 0.05 to 0.1 mg/kg IV bolus or diltiazem 0.25 mg/kg [up to 25 mg] IV bolus or 5 to 10 mg/h by continuous infusion).

If systolic BP remains > 110 mm Hg despite use of beta-blockers, nitroprusside in a constant IV infusion can be started at 0.2 to 0.3 mcg/kg/min and titrated upward (often to 200 to 300 mcg/min) as necessary to control BP. Nitroprusside should not be given without a beta-blocker or calcium channel blocker, because reflex sympathetic activation in response to vasodilation can increase ventricular inotropy and aortic shear stress, worsening the dissection.

Pearls & Pitfalls

  • To manage BP in aortic dissection, do not use a vasodilator (eg, nitroprusside) without a beta-blocker or calcium channel blocker because the vasodilator causes reflex sympathetic activation, which increases aortic shear stress.

Surgical repair

For the descending aorta, a trial of drug therapy alone is appropriate for an uncomplicated, stable dissection confined to the descending aorta (type B). Endovascular repair is warranted in patients with complications (malperfusion, persistent hypertension and pain, rapidly enlarging aortic diameter, extension of the dissection, and rupture). Surgery is also best for acute distal dissections in patients with Marfan syndrome.

For the ascending aorta, surgery is virtually always indicated due to the risk of life-threatening complications and usually involves open repair and replacement, although endovascular therapy is gaining support in certain circumstances.

The extent of repair depends upon the reason for repair and the anatomic nature of the dissection.

The goal of surgery is to obliterate entry into the false channel and reconstitute the aorta with a synthetic graft. If present, severe aortic regurgitation must be treated by resuspending the aortic leaflets or replacing the valve. Surgical outcomes are best with early, aggressive intervention. Mortality rate ranges from 7 to 36%. Predictors of poor outcome include hypotension, renal failure, age > 70, abrupt onset of chest pain, pulse deficit, and ST-segment elevation on ECG.

Stent grafts that seal entry to the false lumen and improve patency of the true lumen, balloon fenestration (in which an opening is made in the dissection flap that separates the true and false lumina), or both may be less invasive alternatives for patients with type B dissection if peripheral ischemic complications develop. Currently, there are no endovascular stent grafts approved for routine use in type A dissections. However, some endovascular devices are available for compassionate use in patients with type A dissections who have contraindications to open surgical repair.

Complications of surgery include death, stroke (due to emboli), paraplegia (due to spinal cord ischemia), renal failure (especially if dissection includes renal arteries) and endoleak (leakage of blood back into the aneurysmal sac). The most important late complications include redissection, formation of localized aneurysms in the weakened aorta, and progressive aortic regurgitation. These complications may require surgical or endovascular repair.

Long-term management

All patients, including those treated by surgery or endovascular methods, are given long-term antihypertensive drug therapy, usually including beta-blockers, calcium channel blockers, and ACE inhibitors. Almost any combination of antihypertensives is acceptable; exceptions are those that act mainly by vasodilation (eg, hydralazine, minoxidil) and beta-blockers that have intrinsic sympathomimetic action (eg, acebutolol, pindolol). Avoidance of strenuous physical activity is often recommended. CT may be done before discharge and repeated at 6 mo and 1 yr, then every 1 to 2 yr.

After repair of a dissection, the aorta should be monitored for the rest of the patient's life. The weakened aorta may develop aneurysmal degeneration above or below the surgical repair or re-dissect. For these reasons, continued surveillance is indicated.

Key Points

  • Aortic dissection may originate anywhere along the aorta but is most common at the proximal ascending aorta (within 5 cm of the aortic valve) or the descending thoracic aorta just beyond the origin of the left subclavian artery.

  • Dissection requires preexisting degeneration of the aortic media (eg, caused by connective tissue disorders, injury) but hypertension is commonly also involved.

  • Patients typically have excruciating, tearing precordial or interscapular pain.

  • Other manifestations depend on whether the aortic root and/or branches of the aorta are affected, and the presence and location of any rupture; heart failure, organ ischemia, and hemorrhagic shock may occur.

  • Diagnose using TEE, CTA, or MRA.

  • Immediately give beta-blockers and other drugs as needed to control blood pressure.

  • Drug therapy alone is appropriate for uncomplicated, stable dissection confined to the descending aorta; other cases require surgery.

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* This is the Professional Version. *