Aortic dissection
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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]
Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [3] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.
Overview
Epidemiology and Demographics
Risk Factors
Pathophysiology
Aneurysm vs Dissection:
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. Cystic medial necrosis is the most common risk factor for the development of ascending aneurysms, and atherosclerosis is the commonest risk factor for descending aneurysms.
- The natural history of thoracic aneurysms depends on the size. Rupture is the most common cause of death, and the frequency of rupture is much higher in dissecting aneurysms than in non-dissecting ones.
- Thoracic aneurysms enlarge at a more rapid rate than abdominal aneurysms (0.42 vs. 0.28 cm/yr), with aneurysms of the aortic arch growing at ~ 0.56 cm/yr. Aneurysms that are 5-6cm in diameter have a faster rate of growth and a greater tendency to rupture than smaller ones.
Etiology
Classification systems
Natural History
Differential diagnosis of entities to distinguish from aortic dissection
Diagnosis
History and Symptoms
About 96% of individuals with aortic dissection present with severe pain that had a sudden onset. It may be described as tearing in nature, or stabbing or sharp in character. 17% of individuals will feel the pain migrate as the dissection extends down the aorta. The location of pain is associated with the location of the dissection. Anterior chest pain is associated with dissections involving the ascending aorta, while intrascapular (back) pain is associated with descending aortic dissections. If the pain is pleuritic in nature, it may suggest acute pericarditis due to hemorrhage into the pericardial sac.
While the pain may be confused with the pain of a myocardial infarction (heart attack), aortic dissection is usually not associated with the other signs that suggest myocardial infarction, including heart failure, and ECG changes. Also, individuals suffering from an aortic dissection usually do not present with diaphoresis (profuse sweating).
Individuals with aortic dissection who do not present with pain have chronic dissection.
Less common symptoms that may be seen in the setting of aortic dissection include congestive heart failure (7%), syncope (9%), cerebrovascular accident (3-6%), ischemic peripheral neuropathy, paraplegia, cardiac arrest, and sudden death. If the individual had a syncopal episode, about half the time it is due to hemorrhage into the pericardium leading to pericardial tamponade.
Neurologic complications of aortic dissection (i.e., cerebrovascular accident (CVA) and paralysis) are due to involvement of one or more arteries supplying portions of the central nervous system.
If the aortic dissection involves the abdominal aorta, compromise of the branches of the abdominal aorta are possible. In abdominal aortic dissections, compromise of one or both renal arteries occurs in 5-8% of cases, while mesenteric ischemia (ischemia of the large intestines) occurs 3-5% of the time.[1] [2] [3] [4]
Blood pressure changes
While many patients with an aortic dissection have a history of hypertension, the blood pressure is quite variable at presentation with acute aortic dissection, and tends to be higher in individuals with a distal dissection. In individuals with a proximal aortic dissection, 36% present with hypertension, while 25% present with hypotension. In those that present with distal aortic dissections, 70% present with hypertension while 4% present with hypotension.
Severe hypotension at presentation is a grave prognostic indicator. It is usually associated with pericardial tamponade, severe aortic insufficiency, or rupture of the aorta. Accurate measurement of the blood pressure is important. Pseudohypotension (falsely low blood pressure measurement) may occur due to involvement of the brachiocephalic artery (supplying the right arm) or the left subclavian artery (supplying the left arm).
Aortic insufficiency
Aortic insufficiency (AI) occurs in 1/2 to 2/3 of ascending aortic dissections, and the murmur of aortic insufficiency is audible in about 32% of proximal dissections. The intensity (loudness) of the murmur is dependent on the blood pressure and may be inaudible in the event of hypotension.
There are multiple etiologies for AI in the setting of ascending aortic dissection. The dissection may dilate the annulus of the aortic valve, so that the leaflets of the valve cannot coapt. Another mechanism is that the dissection may extend into the aortic root and detach the aortic valve leaflets. The third mechanism is that if there was an extensive intimal tear, the intimal flap may prolapse into the LV outflow tract, causing intimal intussusception into the aortic valve preventing proper valve closure.
Myocardial infarction
Myocardial infarction (heart attack) occurs in 1-2% of aortic dissections. The etiology of the infarction is involvement of the coronary arteries (the arteries that supply the heart) in the dissection. The right coronary artery is involved more commonly than the left coronary artery. If the myocardial infarction is treated with thrombolytic therapy, the mortality increases to over 70%, mostly due to hemorrhage into the pericardial sac causing pericardial tamponade.
Because aortic dissection may present to the emergency room physician similar to a myocardial infarction, the physician must be careful to make the proper diagnosis prior to initiating treatment for myocardial infarction, since the treatment regimen for myocardial infarction can be lethal to an individual presenting with aortic dissection.
Pleural effusion
A pleural effusion (fluid collection in the space between the lungs and the chest wall or diaphragm) can be due to either blood from a transient rupture of the aorta or fluid due to an inflammatory reaction around the aorta. If a pleural effusion were to develop due to an aortic dissection, it is more commonly in the left hemithorax rather than the right hemithorax.
- 74% of patients who survive the initial tear typically present with the sudden onset of severe tearing pain. 92% of patients with anterior chest pain as their major source of pain have either type I or type II dissections, and only 8% have type III. Neck, throat, jaw, and unilateral face pain are also seen more commonly in those with type I or type II dissection. 52% of patients with type III dissection have the majority of their pain in the back, and 67% of these patients have some degree of back pain.
- Up to 15 – 55 % of patients can have painless dissection. Dissection should therefore be included in the differential in patients with unexplained syncope, stroke or congestive heart failure (CHF).
- 4% of patients present with out of hospital cardiac arrest.
- Unusual symptoms include:
- Hoarseness
- Hemoptysis
- Claudication
- Superior vena cava (SVC) syndrome
- Upper gastrointestinal (UGI) bleed
- Upper airway obstruction.
Physical Examination
- Cardiac tamponade, hemothorax, Horner syndrome, and hoarseness (due to compression of the left recurrent laryngeal nerve) can also be seen.
- Descending dissection can lead to splanchnic ischemia, renal insufficiency
Heart
- Aortic regurgitation is present in approximately 40 – 66 % of patients and is almost always seen in those with type I or type II dissection. The murmur of aortic insufficiency (AI) due to aortic dissection is best heard at the R 2nd intercostal space (ICS), as compared with the lower left sternal border for AI due to primary aortic valvular disease.
Lungs
Rales may be present due to cardiogenic pulmonary edema
Extremities
Diminution or absence of pulses is found in up to 40% of patients, and occurs due to occlusion of a major aortic branch. For this reason it is critical to assess the pulse and blood pressure in both arms.
Neurologic
- Neurologic deficits such as coma, altered mental status, Cerebrovascular accident (CVA) and vagal episodes are seen in up to 20%.
- There can also be focal neurologic signs due to occlusion of a spinal artery. This condition is known as Anterior spinal artery syndrome or "Beck's syndrome".
Laboratory Findings
Electrolyte and Biomarker Studies
- Routine blood work is usually not helpful, although one can see evidence of hemolysis from the blood in the false leumen. There has been one report using a smooth muscle myosin heavy chain immunoassay to help diagnose aortic dissection. They report that a level > 10 ng/ml within the first 12h is 90% sensitive and 97% specific. This needs to be confirmed in other trials however.
- The presence of an elevated CK MB may indicate the presence of concomitant MI (often an right coronary artery occlusion due to occlusion of the ostium of the RCA by the dissection).
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.
Chest X Ray
- Chest X-Ray Abnormalities:
- An increased aortic diameter is the most common CXR finding, seen in up to 84% of patients.
- A widened mediastinum is the next most common finding, seen in 15-20%.
- Normal in 17%.
- Pleural effusion (hemothorax) in the absence of CHF can also be another clue to dissection.
Computed tomography angiography
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Aortic dissection Type Stanford A -
Aortic dissection Type Stanford A - '1 Aorta ascendens, true Lumen - 2 false Lumen - 3 Pulmonary artery - 4 Aorta descendens - 5 thoracic vertebra -
Another example of Stanford A type dissection
Computed tomography angiography is a fast non-invasive test that will give an accurate three-dimensional view of the aorta. These images are produced by taking rapid thin cut slices of the chest and abdomen, and combining them in the computer to create cross-sectional slices. In order to delineate the aorta to the accuracy necessary to make the proper diagnosis, an iodinated contrast material is injected into a peripheral vein. Contrast is injected and the scan performed using a Bolus Tracking method. This is a type of scan timed to an injection, in order to capture the contrast as it enters the aorta. The scan will then follow the contrast as it flows though the vessel.
It has a sensitivity of 96 - 100% and a specificity of 96 to 100%. Disadvantages include the need for iodinated contrast material and the inability to diagnose the site of the intimal tear.
CT scanning with contrast has a reported sensitivity of 94% and a specificity of 87%. Unfortunately, the intimal flap is seen in < 75% of cases. Additionally, one can not assess the coronary arteries or for the presence of AI. Over the past few years, spiral CT and ultrafast CT (electron beam CT) have substantially improved the accuracy in the diagnosis of aortic dissection.
Differentiating a true lumen from the false lumen
- Beak sign: In the false lumen, there will be an acute angle between the dissection flap and the arterial wall.
- Aortic cobwebs: In the false lumen, there may be fibroelastic bands.
- Size: False lumen is usually larger than the true lumen.
- Diplaced intimal calcification: Usually faces the true lumen.
Labeled CT images shown below are courtesy of Radswiki and copylefted:
MRI
Magnetic resonance imaging (MRI) is currently the gold standard test for the detection and assessment of aortic dissection, with a sensitivity of 98% and a specificity of 98%. An MRI examination of the aorta will produce a three-dimensional reconstruction of the aorta, allowing the physician to determine the location of the intimal tear, the involvement of branch vessels, and locate any secondary tears. It is a non-invasive test, does not require the use of iodinated contrast material, and can detect and quantitate the degree of aortic insufficiency.
The disadvantage of the MRI scan in the face of aortic dissection is that it has limited availability and is often located only in the larger hospitals, and the scan is relatively time consuming. Due to the high intensity of the magnetic waves used during MRI, an MRI scan is contraindicated in individuals with metallic implants. In addition, many individuals succumb to claustrophobia while in the MRI scanning tube.
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MRI of an aortic dissection. 1 Aorta descendens with dissection. 2 Aortic isthmus.
Echocardiography
The transesophageal echocardiogram (TEE) is a relatively good test in the diagnosis of aortic dissection, with a sensitivity of up to 98% and a specificity of up to 97%. It is a relatively non-invasive test, requiring the individual to swallow the echocardiography probe. It is especially good in the evaluation of AI in the setting of ascending aortic dissection, and to determine whether the ostia (origins) of the coronary arteries are involved. While many institutions give sedation during transesophageal echocardiography for added patient-comfort, it can be performed in cooperative individuals without the use of sedation. Disadvantages of the TEE include the inability to visualize the distal ascending aorta (the beginning of the aortic arch), and the descending abdominal aorta that lies bellow the stomach. A TEE may be technically difficult to perform in individuals with esophageal strictures or varices.
Transthoracic (TTE) unfortunately does not provide pretty pictures of the distal ascending, transverse and descending aorta in a small number of patients. Its use is limited to assess cardiac complications of dissection including AI, tamponade and LV function.
Transesophageal (TEE), however, is a portable technique that can be brought to the emergency department and establish a diagnosis in < 5 minutes of starting the test. It can identify true and false lumens, the intimal flap, thrombosis in the false lumen, pericardial effusion, AI, and the proximal coronaries. Although monoplane TEE has a sensitivity of 98%, its specificity is only 77%. This can be increased to a sensitivity and specificity of 99% and 98% respectively with combined use of TTE and TEE. Biplane and multiplane imagine however have been shown to be 98% sensitive and 95% specific for aortic dissection.
In general, it is recommended to perform bedside multiplane TEE in patients with acute symptoms or clinically unstable, and MRI in patients with a more chronic presentation if they are hemodynamically stable.
CT angio is reserved for patients whom TEE or MRI is unavailable or contraindicated. Aortography is required if the tests listed above are non-diagnostic.
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Aortic Dissection Type A Example 1
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Aortic Dissection Type A Example 2
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Aortic Dissection Type A Example 3
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Aortic Dissection Type A Example 4
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Aortic Dissection Type A Example 5
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Aortic Dissection Type A Example 6
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Aortic Dissection Type B Example 1
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Aortic Dissection Type B Example 2
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Other Imaging Findings
Aortogram
An aortogram involves placement of a catheter in the aorta and injection of contrast material while taking x-rays of the aorta. The diagnosis of aortic dissection can be made by visualization of the intimal flap and flow of contrast material in both the true lumen and the false lumen.
The aortogram was previously considered the gold standard test for the diagnosis of aortic dissection, with a sensitivity of up to 88% and a specificity of about 94%. It is especially poor in the diagnosis of cases where the dissection is due to hemorrhage within the media without any initiating intimal tear.
The advantage of the aortogram in the diagnosis of aortic dissection is that it can delineate the extent of involvement of the aorta and branch vessels and can diagnose aortic insufficiency.
The disadvantages of the aortogram are that it is an invasive procedure and it requires the use of iodinated contrast material.
Although aortography has a sensitivity of 88% and a specificity of 94% in experienced hands, it has largely been replaced by noninvasive diagnostic techniques. It is helpful however, in determining the site of dissection, the relationship of the dissection the major aortic branches, as well as identifying the true and false lumens. Additionally, coronary angiography can be preformed at the same time. False negatives occur if the false leumen is already thrombosed, or when there is simultaneous opacification of both lumens.
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Aorta: Dissection, Cystic Medial Degeneration
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Treatment
The risk of death due to aortic dissection is highest in the first few hours after the dissection begins, and decreases afterwards. Because of this, the therapeutic strategies differ for treatment of an acute dissection compared to a chronic dissection. An acute dissection is one in which the individual presents within the first two weeks. If the individual has managed to survive this window period, his prognosis is improved. About 66% of all dissections present in the acute phase.
In all individuals with aortic dissections, medication should be used to control high blood pressure, if present.
In the case of an acute dissection, once diagnosis has been confirmed, the choice of treatment depends on the location of the dissection. For ascending aortic dissection, surgical management is superior to medical management. On the other hand, in the case of an uncomplicated distal aortic dissections (including abdominal aortic dissections), medical management is preferred over surgical treatment [5]
Individuals who present two weeks after the onset of the dissection are said to have chronic aortic dissections. These individuals have been self-selected as survivors of the acute episode, and can be treated with medical therapy as long as they are stable.
Medical management is appropriate in individuals with an uncomplicated distal dissection, a stable dissection isolated to the aortic arch, and stable chronic dissections. Patient selection for medical management is very important. Stable individuals who present with an acute distal dissection (typically treated with medical management) still have an 8 percent 30 day mortality.
VIDEO - What is New in the Treatment of Type B Aortic Dissection?, Girma Tefera, MD, speaks at the University of Wisconsin School of Medicine and Public Health.
Medical management
The prime consideration in the medical management of aortic dissection is strict blood pressure control. The target blood pressure should be a mean arterial pressure (MAP) of 60 to 75 mmHg. Another factor is to reduce the shear-force dP/dt (force of ejection of blood from the left ventricle).
To reduce the shear stress, a vasodilator such as sodium nitroprusside should be used with a beta blocker, such as esmolol, propranolol, or labetalol. The alpha-blocking properties of labetalol make it especially attractive in this situation.
Calcium channel blockers can be used in the treatment of aortic dissection, particularly if there is a contraindication to the use of beta blockers. The calcium channel blockers typically used are verapamil and diltiazem, because of their combined vasodilator and negative inotropic effects.
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.
Surgical management
Indications for the surgical treatment of aortic dissection include an acute proximal aortic dissection and an acute distal aortic dissection with one or more complications. Complications include compromise of a vital organ, rupture or impending rupture of the aorta, retrograde dissection into the ascending aorta, and a history of Marfan's syndrome.
The objective in the surgical management of aortic dissection is to resect (remove) the most severely damaged segments of the aorta, and to obliterate the entry of blood into the false lumen (both at the initial intimal tear and any secondary tears along the vessel). While excision of the intimal tear may be performed, it does not significantly change mortality.
Some methods of repair are:
- Replacement of the damaged section with a tube graft (often made of dacron) when there is no damage to the aortic valve.
- Bentall procedure - Replacement of the damaged section of aorta and replacement of the aortic valve.
- David procedure - Replacement of the damaged section of aorta and reimplantation of the aortic valve.
A number of comorbid conditions increase the surgical risk of repair of an aortic dissection. These include:
- Prolonged pre-op evaluation (increased length of time prior to surgery)
- Advanced age
- Comorbid disease states (e.g.: coronary artery disease)
- Aneurysm leakage
- Cardiac tamponade
- Shock
- Past history of myocardial infarction or CVA
- History of renal failure (either acute or chronic renal failure)
Long term follow-up
The long term follow-up in individuals who survive aortic dissection involves strict blood pressure control. 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 pressure below 130 mmHg.
The risk of death is highest in the first two years after the acute event, and individuals should be followed closely during this time period. 29% of late deaths following surgery are due to rupture of either the dissecting aneurysm or another aneurysm. In additions, there is a 17 to 25% incidence of new aneurysm formation. This is typically due to dilatation of the residual false lumen. These new aneurysms are more likely to rupture, due to their thinner walls.
Serial imaging of the aorta is suggested, with MRI being the preferred imaging technique.
- DeBakey and Cooley reported the first successful operation for resection and graft replacement of the ascending aorta using cardiopulmonary bypass in 1956.
- Any dissection that involves the ascending aorta is considered a surgical emergency. Without surgery, there is a 90% 3-month mortality. These patients can rapidly develop acute aortic insufficiency (AI), tamponade or myocardial infarction (MI). 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.
- Operative mortality for ascending dissections is surgeon dependant, and averages ~ 5 – 20 %. This however, is well below the 50% mortality when these cases are managed with medical therapy.
- Factors that increase surgical risk include renal insufficiency, visceral ischemia, tamponade and underlying pulmonary disease.
- Surgical therapy involves excision of the intimal tear, obliteration of the proximal entry site into the false leumen, 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).
- Dissections involving the descending aorta only can be managed medically unless there is progression or continued hemorrhage into the pleural or retroperitoneal space. The major surgical complication in descending dissections is spinal cord ischemia and paralysis.
- Medical management centers around blood pressure control and decreasing the velocity of left ventricular contraction with the goal of decreasing aortic shear stress. Pain control with morphine is also extremely important. For patients with DeBakey III or Daily B dissections, medical therapy offers an > 80% survival rate.
- The systolic blood pressure is kept at the lowest level tolerated. Initial treatment usually involves either Labetalol (20mg bolus f/b 20-80mg q10min to a total dose of 300mg, or as an infusion of 0.5 – 2 mg/min) or Propranolol (1 – 10 mg load f/b 3mg/hr) with the goal heart rate ~ 60 BPM. Lopressor and Verapamil can also be used.
- If the heart rate is controlled, and the systolic blood pressure (SBP) is > 100 mmHg with adequate mentation and urine output, Sodium Nitroprusside is added (0.25 – 0.5 ug/kg/min). Nitroprusside should never be used prior to beta blockade, as the hypotension can result in a reflex tachycardia.
- All patients should have an arterial line in the arm with the higher BP for accurate monitoring.
Pathological Findings
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Dissecting Aneurysm: Gross fixed tissue external view of heart aortic arch and descending aorta showing dilated first and second portion of arch from anterior projection.
Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
References
- ↑ Saner, H.E., et al., Aortic dissection presenting as Pericarditis. Chest, 1987. 91(1): p. 71-4. PMID 3792088
- ↑ Rosman, H.S., et al., Quality of history taking in patients with aortic dissection. Chest, 1998. 114(3): p. 793-5. PMID 9743168
- ↑ Hagan, P.G., et al., The International Registry of Acute Aortic Dissection (IRAD): new insights into an old disease. JAMA, 2000. 283(7): p. 897-903. PMID 10685714
- ↑ von Kodolitsch, Y., A.G. Schwartz, and C.A. Nienaber, Clinical prediction of acute aortic dissection. Arch Intern Med, 2000. 160(19): p. 2977-82. PMID 11041906
- ↑ Suzuki T, Mehta RR, Ince H, Nagai R, Sakomura Y, Weber F, Sumiyoshi T, Bossone E, Trimarchi S, Cooper J, Smith D, Isselbacher E, Eagle K, Nienaber C. "Clinical profiles and outcomes of acute type B aortic dissection in the current era: lessons from the International Registry of Aortic Dissection (IRAD)". Circulation. 108 Suppl 1: II312–7. PMID 12970252.
Acknowledgements
The content on this page was first contributed by: David Feller-Kopman, MD and C. Michael Gibson M.S., M.D.