Aortic dissection overview
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Aortic dissection Microchapters |
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Diagnosis |
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Treatment |
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Special Scenarios |
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Case Studies |
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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, 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.
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. 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 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.
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 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.
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.
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). 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 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 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 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.
Medical Therapy
Type A dissections of the proximal aorta are generally managed with operative repair whereas 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.
Step 1: Urgent Surgical Consultation
- Simultaneous with the initiation of medical therapy as described below, urgent surgical consultation should be required regarding the potential need for operative repair of the dissection. Type A dissections of the proximal aorta are generally managed with operative repair whereas Type B dissections of the descending aorta are generally managed medically. Even patients who are undergoing operative repair require optimal medical management as described in the steps below.
Step 2: Rate Control
- The initial step in the medical management of the patient with aortic dissection is rate control. Rate control reduces oscillatory sheer stress as well as blood pressure. Rate control should be accomplished before vasodilators are administered in so far as vasodilators can increase oscillatory sheer stress.
- All patients should have an arterial line in the arm with the higher BP for accurate monitoring.
- Intravenous beta blockers can be administered and titrated to a heart rate of 60 bpm or less. The systolic blood pressure is kept at the lowest level that maintains adequate perfusion. Labetalol is an ideal agent in so far as it has both alpha and beta blocking properties. Initial treatment usually involves either labetalol (a 20 mg bolus followed by 20-80mg every 10 minutes to a total dose of 300 mg, or as an infusion of 0.5 to 2 mg/min) or Propranolol (1 to 10 mg load followed by 3mg/hr) with the goal being a heart rate of 60 beats per minutes. Lopressor can also be administered.
- If there is an absolute contraindication to the administration of beta blockers than a nondihydropyridine calcium channel–blocking can be administered as an alternative for rate control. The calcium channel blockers typically used are verapamil and diltiazem, because of their combined vasodilator and negative inotropic effects.
- If aortic insufficiency is present, then beta blocker administration should be undertaken carefully as prolonging the diastolic filling period may increase the magnitude of aortic regurgitation.
- Pain control with morphine is important in so far as it reduces sympathetic tone, heart rate and blood pressure.
Step 3: Blood Pressure Control
- Vasodilator administration should only be undertaken after the heart rate is controlled. If the heart rate is not controlled, the administration of vasodilators may cause reflex tachycardia, and cause further expansion of the dissection.
- If the systolic blood pressure remains above 120 mm Hg, then an angiotensin-converting enzyme inhibitor should be administered to further reduce the blood pressure. If this is ineffective, then the administration of parenteral vasodilators should be considered.
- If the heart rate is controlled, and the systolic blood pressure (SBP) is > 100 mmHg with adequate mentation and urine output, Sodium nitroprusside can be administered at a dose of 0.25 – 0.5 ug/kg/min. Nitroprusside should never be administered prior to beta blockade, as the hypotension can result in a reflex tachycardia.
- The target blood pressure should be a mean arterial pressure (MAP) of 60 to 75 mmHg.
- If the individual has refractory hypertension (persistent hypertension on the maximum doses of three different classes of antihypertensive agents), involvement of the renal arteries in the aortic dissection plane should be considered.
Step 4: Operative Repair Versus Medical Therapy
- Acute thoracic aortic dissection of the proximal ascending aorta (Type A dissections) should be urgently evaluated for emergent surgical repair given the increased risk of associated morbid/ mortal complications such as aortic rupture.
- Acute thoracic aortic dissection of the descending aorta (Type B dissection) should be managed medically unless and of the following morbid/ mortal complications develop:
- Malperfusion syndrome
- Further propagation of the dissection
- Further rapid aneurysm expansion
- Blood pressure lability suggestive of renal artery involvement
- For patients with DeBakey III or Daily B dissections, medical therapy offers an > 80% survival rate.
Step 5: Chronic Therapy
- In order to prevent recurrence and improve the patient's long term prognosis, smoking cessation, aggressive blood pressure control, and aggressive lipid- lowering therapy are essential. The relative risk of late rupture of an aortic aneurysm is 10 times higher in individuals who have uncontrolled hypertension, compared to individuals with a systolic blood pressure below 130 mmHg.
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).
Contraindications to the Operative Repair of a Type A Dissection
Even acute MI in the setting of dissection is not a surgical contraindication. Acute hemorrhagic stroke is, however, a relative contraindication, due to the necessity of intraoperative heparinization.
Surgical Indications for Operative Repair of a Type B Dissection
Dissections involving only the descending aorta can generally be managed medically, but indications for surgery include the following:
- Progression of the dissection
- Continued hemorrhage into the pleural or retroperitoneal space
Surgical Complications Following Repair of a Type B Dissection
- Spinal cord ischemia and paralysis.
Surgical Risk Factors
Risk factors associated with increased surgical mortality include the following:
- Renal insufficiency
- Mesenteric ischemia
- Renal ischemia
- Pericardial tamponade
- Underlying pulmonary disease
Surgical Procedure
Surgical therapy involves excision of the intimal tear, obliteration of the proximal entry site into the false lumen, and reconstitution of the aorta with placement of a synthetic graft. AI can be corrected by resuspension of the native valve, or by aortic valve replacement (AVR).