Aortic Dissection

Aortic dissections often occur in patients with preexisting degeneration of the aortic media. Causes and risk factors include connective tissue disorders, atherosclerotic disease Atherosclerosis Atherosclerosis is characterized by patchy intimal plaques (atheromas) that encroach on the lumen of medium-sized and large arteries. The plaques contain lipids, inflammatory cells, smooth muscle... read more , and injury (see table Conditions Contributing to Aortic Dissection Conditions Contributing to Aortic Dissection ).

Atherosclerotic risk factors, notably hypertension Hypertension Hypertension is sustained elevation of resting systolic blood pressure (≥ 130 mm Hg), diastolic blood pressure (≥ 80 mm Hg), or both. Hypertension with no known cause (primary; formerly, essential... read more , 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.

The pathophysiologic sequence of aortic dissections involves

Dissections may communicate back with the true aortic lumen through intimal rupture at a distal site, maintaining systemic blood flow.

Serious consequences of aortic dissection are common and include

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

Variants of dissection are thought to be precursors of classic aortic dissection. Variants of aortic dissection include

Typically in aortic dissection, 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 (ischemia due to the obstruction resulting from dissection), such as stroke Symptoms and Signs Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more , myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more , 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 Symptoms and Signs Aortic regurgitation (AR) is incompetency of the aortic valve causing backflow from the aorta into the left ventricle during diastole. Causes include valvular degeneration and aortic root dilation... read more may be present. Rarely, heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular (LV) failure causes shortness of breath and fatigue, and right ventricular (RV) failure causes peripheral and abdominal... read more results from severe acute aortic regurgitation. Cardiac tamponade Cardiac Tamponade Cardiac tamponade is accumulation of blood in the pericardial sac of sufficient volume and pressure to impair cardiac filling. Patients typically have hypotension, muffled heart tones, and distended... read more may cause pulsus paradoxus and jugular venous distention.

Leakage of blood or inflammatory serous fluid into the left pleural space may lead to signs of pleural effusion Pleural Effusion Pleural effusions are accumulations of fluid within the pleural space. They have multiple causes and usually are classified as transudates or exudates. Detection is by physical examination and... read more .

Occlusion of a limb artery may cause signs of peripheral ischemia or neuropathy.

Renal artery occlusion Renal Artery Stenosis and Occlusion Renal artery stenosis is a decrease in blood flow through one or both of the main renal arteries or their branches. Renal artery occlusion is a complete blockage of blood flow through one or... read more may cause oliguria or anuria.

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, electrocardiography (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 minutes 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.

Electrocardiography (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 appear promising, but the assays are not routinely available. Serum creatine kinase-MB and troponin levels 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 lactate dehydrogenase 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%/hour during the first 24 hours, 30% at 1 week, 80% at 2 weeks, and 90% at 1 year.

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 years and 40% at 10 years. 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 intensive care unit with intra-arterial blood pressure monitoring Arterial Catheterization A number of procedures are used to gain vascular access. Most patients’ needs for IV fluid and drugs can be met with a percutaneous peripheral venous catheter. If blind percutaneous placement... read more and an indwelling urethral catheter to monitor urine output. Blood should be typed and cross-matched for 4 to 6 units of packed red blood cells when surgery is likely. Hemodynamically unstable patients should be intubated.