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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. 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 BP 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 or, for patients with congenital connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome), at age 20 to 40.
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.
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.
The Stanford system is simpler.
Although dissection may originate anywhere along the aorta, it occurs most commonly 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). Rarely, dissection is confined to individual arteries (eg, coronary or carotid arteries), typically in pregnant or postpartum women.
Aortic dissection always occurs in the setting of preexisting degeneration of the aortic media. Causes include connective tissue disorders and injury (see Table: Conditions Contributing to Aortic Dissection).
Conditions Contributing to Aortic Dissection
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.
Dissections may communicate back with the true aortic lumen through intimal rupture at a distal site, maintaining systemic blood flow. But serious consequences are common:
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.
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.
Occasionally, patients present with symptoms of stroke, MI, intestinal infarction, paraparesis or paraplegia due to interruption of the blood supply to the spinal cord, or ischemic limb due to acute distal arterial occlusion.
About 20% of patients have partial or complete deficits of major arterial pulses, which may wax and wane. Limb BPs 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.
Aortic dissection must be considered in any patient with chest pain, thoracic back pain, unexplained syncope or abdominal pain, stroke, or acute-onset heart failure, especially when pulses or BPs 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 MI, 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 MI), 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. If TEE is unavailable, CTA is recommended; 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. Assays for soluble elastin compounds and smooth-muscle myosin heavy-chain protein are being studied; they look promising but are not routinely available. Serum CK-MB and troponin may help distinguish aortic dissection from MI, except when dissection causes MI.
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.
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.
Patients who do not immediately die of aortic dissection should be admitted to an ICU with intra-arterial (see Vascular Access : Procedure) BP monitoring; an indwelling urethral catheter is used 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.
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 β-blocker is usually used first. 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 α- and β-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 β-blockers include Ca 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 β-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 β-blocker or Ca channel blocker, because reflex sympathetic activation in response to vasodilation can increase ventricular inotropy and aortic shear stress, worsening the dissection.
A trial of drug therapy alone is appropriate for uncomplicated, stable dissection confined to the descending aorta (type B) and for stable, isolated dissection of the aortic arch. Surgery is virtually always indicated if dissection involves the proximal aorta. Surgery is also indicated for limb or visceral ischemia, uncontrolled hypertension, continued aortic enlargement, extension of the dissection, and evidence of aortic rupture, regardless of dissection type. Surgery may also be best for acute distal dissections in patients with Marfan syndrome.
The goal of surgery is to obliterate entry into the false channel and reconstitute the aorta with a synthetic graft. If present, significant 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.
All patients, including those treated by surgery or endovascular methods, are given long-term antihypertensive drug therapy, usually including β-blockers, Ca channel blockers, and ACE inhibitors. Almost any combination of antihypertensives is acceptable; exceptions are those that act mainly by vasodilation (eg, hydralazine, minoxidil) and β-blockers that have intrinsic sympathomimetic action (eg, acebutolol, pindolol). Avoidance of strenuous physical activity is often recommended. MRI may be done before discharge and repeated at 6 mo and 1 yr, then every 1 to 2 yr.
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.
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 β-blockers and other drugs as needed to control BP.
Drug therapy alone is appropriate for uncomplicated, stable dissection confined to the descending aorta or the aortic arch; other cases require surgery.
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