Aortic dissection overview

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Aortic dissection Microchapters
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Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Aortic dissection from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
Diagnostic Study of Choice
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
Echocardiography and Ultrasound
CT scan
MRI
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
Special Scenarios
Management during Pregnancy
Case Studies
Case #1

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

Aortic dissection is a tear in the wall of the aorta that causes blood to flow between the layers of the wall of the aorta and force the layers apart. Aortic dissection is a medical emergency and can quickly lead to death, even with optimal treatment. If the dissection tears the aorta completely open (through all three layers) massive and rapid blood loss occurs. Aortic dissections resulting in rupture have a 90% mortality rate even if intervention is timely.

Acute aortic dissection is the most common fatal condition that involves the aorta. The mortality rate has been estimated to be as high as 1% per hour during the first 48 hours. Because of the diverse clinical manifestations of aortic dissection, one needs to maintain a high index of suspicion in patients with not just chest pain, but also those with stroke, congestive heart failure, hoarseness, hemoptysis, claudication, superior vena cava (SVC) syndrome, excruciating abdominal pain or upper airway obstruction. Despite the fact that a noninvasive diagnosis can be made in up to 90% of cases, the correct antemortem diagnosis is made less than 50% of the time. Recognition of the condition and vigorous pre-operative management are critical to survival.

Historical Perspective

DeBakey and Cooley reported the first successful operation for resection and graft replacement of the ascending aorta using cardiopulmonary bypass in 1956.

Classification

Several different classification systems have been used to describe aortic dissections. The systems commonly in use are either based on either the anatomy of the dissection (proximal, distal) or the duration of onset of symptoms (acute, chronic) prior to presentation.

There are two systems used to classify Aortic Dissection: Stanford and DeBakey classifications.

Stanford classification (classification on the basis of location of dissection): Type A involves ascending aorta, Type B involves descending aorta

DeBakey Classification (classification on the basis of origin of dissection): Type 1 origin from ascending aorta and goes till aortic arch, Type 2 originated and ends in ascending aorta, Type 3 origin in descending aorta and travels distally.

Pathophysiology

Aortic dissection begins as a tear in the aortic wall in > 95% of patients. The tear is usually transverse, extends through the intima and halfway through the media and involves ~50% of the aortic circumference. A inherent weakness in the tunica media layer predisposes patients to develop tear in the intima layer. Two thirds of dissections originate in the ascending aorta, and 20% are in the proximal descending aorta.

Causes

Age related changes due to atherosclerosis and uncontrolled hypertension are associated with spontaneous dissection, while blunt trauma injury and sudden deceleration in a motor vehicle accident is a major cause of aortic dissection.

Differentiating Aortic Dissection from other Diseases

Aortic dissection is a life threatening entity that must be distinguished from other life threatening entities such as cardiac tamponade, cardiogenic shock, myocardial infarction, and pulmonary embolism. An aortic aneurysm is not synonymous with aortic dissection. Aneurysms are defined as a localized permanent dilation of the aorta to a diameter > 50% of normal. Aortic Intramural Hematoma can also progress to dissection if blood pressure is not well controlled,

Epidemiology and Demographics

There are approximately 2,000 cases of aortic dissection in the US per year, and aortic dissection accounts for 3-4% of sudden deaths. The peak incidence is in the sixth and seventh decades, and males predominate 2:1.

Risk Factors

Aging, atherosclerosis, diabetes, hypertension and trauma are common risk factors for aortic dissection. Uncommon risk factors include aortic surgery, bicuspid aortic valve, cocaine, coarctation of the aorta, cystic medial necrosis, Ehlers-Danlos syndrome, giant cell arteritis, heart surgery, Marfan’s syndrome, Pseudoxanthoma elasticum, Turner's syndrome, tertiary syphilis and the third trimester of pregnancy.

Screening

Screening guidelines state that an EKG should be obtained for all patients who present with symptoms suspicious for aortic dissection. A chest x ray should be obtained for patients determined to be in low-risk, and moderate-risk categories, and for patients in high-risk categories, TEE, CT Angiography or MRI Angiography should be obtained.

Natural History, Complications and Prognosis

Aortic dissection carries a very poor prognosis. 90% of patients who are untreated will be dead at one year. Type A dissection is associated with a worse prognosis than type B dissection. Aortic dissection can be complicated by extension to the coronary arteries resulting in myocardial infarction, involvement of the aortic arch to cause stroke, dilation of the route to cause aortic insufficiency, extension into the pericardium to cause pericardial tamponade, and heart failure, and aortic rupture.

Diagnosis

History and Symptoms

67% of patients with aortic dissection present with acute symptoms (<2 weeks), and 33% with chronic symptoms (>= 2 weeks). 74% of patients who survive the initial tear typically present with the sudden onset of severe tearing pain in the chest or abdominal area depending on the area of involvement. The pain typically radiates to the back and occasionally radiates to the groin area in cases when dissection is progressing distally.

Physical Examination

Aortic dissection is commonly associated with varying blood pressure (pseudohypotension or hypertension or hypotension), wide pulse pressure (if the aortic root is involved causing aortic insufficiency), tachycardia, pulsus paradoxus, swollen face due to superior vena cava compression (superior vena cava syndrome). Radial-radial delay or radio-femoral delay (deficit) in pulse can be seen in patients depending on the location of dissection. Pulse deficit is commonly seen in females. In proximal dissections involving aortic root, aortic insufficiency is a complication, and on physical examination an early diastolic decrescendo murmur, which is best heard in the right second intercostal space is noted.

Laboratory Findings

Routine blood work is usually not helpful and should not delay definitive diagnostic studies such as a CT Angiography scan and treatment. Hemolysis can be present as a result of blood in the false lumen. The presence of an elevated CK MB may indicate the presence of concomitant acute myocardial infarction (often a right coronary artery occlusion due to occlusion of the ostium of the RCA by the dissection). Hematuria may be present and may indicate the presence of renal infarction.

Electrocardiogram

ST elevation myocardial infarction (MI) due to occlusion by the dissection of the coronary artery at its ostium may be present. The right coronary artery tends to be involved more frequently than the left coronary artery. Electrical alternans may be present in the setting of a pericardial effusion or cardiac tamponade should the dissection have extended into the pericardium.

Imaging in Acute Aortic Dissection

There are a wide variety of imaging studies that can be used to diagnose aortic dissection, but in general, transesophageal imaging is the imaging modality of choice in the acutely ill patient and CT Angiography, MRI is the imaging modality of choice in the assessment of longstanding aortic disease in a patient who has chronic chest pain who is hemodynamically stable or for the evaluation of a chronic dissection.

Chest X-ray

An increased aortic diameter is the most common finding on chest X ray, and is observed in up to 84% of patients. A widened mediastinum is the next most common finding, and is observed in 15-20% of patients. The chest X-Ray is normal in 17% of patients. A pleural effusion (hemothorax) in the absence of congestive heart failure can be another sign of aortic dissection.

CT

A CT scan can be used to diagnose aortic dissection if neither a TEE nor MRI is available in a timely fashion, or if there is a contraindication to their performance. An example would be after hours in an emergency room setting. If the results of the CT scan are non-diagnostic, then TEE or MRI should be performed to confirm the diagnosis.

MRI

MRI is the imaging modality of choice in the assessment of longstanding aortic disease in a patient who has chronic chest pain who is hemodynamically stable or for the evaluation of a chronic dissection.

Echocardiography

In the management of the acute patient with suspected aortic dissection, a transesophageal echo performed acutely in the emergency room is the preferred approach. If the patient is hemodynamically unstable, then a transesophageal echo can be performed in the operating room as the patient after the patient has been induced and is being prepared for surgery.

Aortography

Aortography is rarely used in the modern era. It can be used of the other imaging modalities are not available or are inconclusive.

Coronary Angiography

Pre-operative angiography has not been associated with improved outcomes in retrospective analyses. Often times when patient present with coronary occlusion secondary to dissection, EKG changes suggestive of myocardial ischemia,

patient end up getting coronary angiography.

Treatment

Medical Therapy

Type A dissections of the proximal aorta are generally managed with operative repair. The repair can be done via open surgery vs endovascular repair depending on the extent of dissection.

Type B dissections of the descending aorta are generally managed medically. Even patients who are undergoing operative repair require optimal medical management. The two goals in the medical management of aortic dissection are to reduce blood pressure and to reduce the oscillatory shear on the wall of the aorta (the shear-force dP/dt or force of ejection of blood from the left ventricle). The target blood pressure should be a mean arterial pressure (MAP) of 60 to 75 mmHg.

Aortic dissection is the only hypertensive emergency where target BP is less than 120/80 within first four hours of presentation. Ideally, target is to control the heart rate to less than 60 per minute. The first line of agents are beta blockers, esmolol continuous infusion is used preferably as it is short acting and works for blood pressure as well as heart rate. IV Labetalol or PO propranolol or metoprolol can also be used. Addition of other IV continuous nitroprusside can also be used.Cyanide toxicity is a concern when nitroprusside is used for more than 24 hour.

Surgery

Any dissection that involves the ascending aorta is considered a surgical emergency, and urgent surgical consultation is recommended. There is a 90% 3-month mortality among patients with a proximal aortic dissection who do not undergo surgery. These patients can rapidly develop acute aortic insufficiency (AI), tamponade or myocardial infarction (MI).

Secondary Prevention

Proper treatment and control of hardening of the arteries (atherosclerosis) and high blood pressure may reduce risk of aortic dissection. It is very important for patients at risk for dissection to tightly control their blood pressure. Taking safety precautions to prevent injuries can help prevent dissections. Many cases of aortic dissection cannot be prevented. If diagnosed with Marfan or Ehlers-Danlos syndrome, regular follow-up is advisable.

References