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| == Pathophysiology== | | == Pathophysiology== |
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| ===Aneurysm vs Dissection:=== | | ===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.
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| :* 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.
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| :* 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.
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| ==Etiology== | | ==Etiology== |
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| ==== Echocardiography ==== | | ==== Echocardiography ==== |
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| 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 (medical)|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]].
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| 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.
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| 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.
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| 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.
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| 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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| [[Image:Aortic dissection - Echocardiogram - Longitudinal view.jpg|420px|thumb|left|Echocardiogram of an aortic dissection]]
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| [[Image:Aortic dissection - Echocardiogram - Longitudinal view - Color.jpg|420px|thumb|left|Echocardiogram of an aortic dissection]]
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| <youtube v=nD8DrZCPFBI/>
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| Aortic Dissection Type A Example 1
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| <googlevideo>-1580944144837691434&hl=en </googlevideo>
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| Aortic Dissection Type A Example 2
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| <googlevideo>-3610218405615821421&hl=en</googlevideo>
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| Aortic Dissection Type A Example 3
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| <googlevideo>-8461290621229660122&hl=en</googlevideo>
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| Aortic Dissection Type A Example 4
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| <googlevideo>-8561147882050584609&hl=en</googlevideo>
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| Aortic Dissection Type A Example 5
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| <googlevideo>2157100999251300976&hl=en</googlevideo>
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| Aortic Dissection Type A Example 6
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| <googlevideo>698950344523479477&hl=en</googlevideo>
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| Aortic Dissection Type B Example 1
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| <googlevideo>3238725821918795498&hl=en</googlevideo>
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| {{-}}
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| Aortic Dissection Type B Example 2
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| <googlevideo>197658671308723787&hl=en</googlevideo>
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| {{-}}
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| ==== Other Imaging Findings ==== | | ==== Other Imaging Findings ==== |
| ====Aortogram====
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| 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.
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| The aortogram was previously considered the [[gold standard (test)|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.
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| 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]].
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| The disadvantages of the aortogram are that it is an invasive procedure and it requires the use of iodinated contrast material.
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| 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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| <googlevideo>-1291385681032114503&hl=en</googlevideo>
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| ==Aorta: Dissection, Cystic Medial Degeneration==
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| <youtube v=t9WVLNi7zXk/>
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| == Treatment == | | == 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.
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| In all individuals with aortic dissections, medication should be used to control [[hypertension|high blood pressure]], if present.
| | === Medical Therapy === |
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| 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 <ref>{{cite journal | author = 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 | title = Clinical profiles and outcomes of acute type B aortic dissection in the current era: lessons from the International Registry of Aortic Dissection (IRAD). | journal = Circulation | volume = 108 Suppl 1 | issue = | pages = II312-7 | year = | id = PMID 12970252}}</ref>
| | === Surgical Therapy === |
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| 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.
| | === Follow-up === |
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| 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.
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| [http://videos.med.wisc.edu/videoInfo.php?videoid=264 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.
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| === Medical management ===
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| 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]]).
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| 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.
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| [[Calcium channel blocker]]s 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.
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| 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.
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| === Surgical management ===
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| 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]].
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| 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.
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| Some methods of repair are:
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| * Replacement of the damaged section with a tube graft (often made of dacron) when there is no damage to the [[aortic valve]].
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| * [[Bentall procedure]] - Replacement of the damaged section of aorta and replacement of the aortic valve.
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| * [[David procedure]] - Replacement of the damaged section of aorta and reimplantation of the aortic valve.
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| A number of comorbid conditions increase the surgical risk of repair of an aortic dissection. These include:
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| * Prolonged pre-op evaluation (increased length of time prior to surgery)
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| * Advanced age
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| * Comorbid disease states (e.g.: [[coronary artery disease]])
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| * Aneurysm leakage
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| * [[Cardiac tamponade]]
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| * [[Shock (medical)|Shock]]
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| * Past history of [[myocardial infarction]] or [[cerebrovascular accident|CVA]]
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| * History of [[renal failure]] (either acute or chronic renal failure)
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| === 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.
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| 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.
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| Serial imaging of the aorta is suggested, with [[MRI]] being the preferred imaging technique.
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| *DeBakey and Cooley reported the first successful operation for resection and graft replacement of the ascending aorta using cardiopulmonary bypass in 1956.
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| *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.
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| :*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.
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| :*Factors that increase surgical risk include renal insufficiency, visceral ischemia, tamponade and underlying pulmonary disease.
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| :*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).
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| :*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.
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| :*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.
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| :*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.
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| :*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.
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| :*All patients should have an arterial line in the arm with the higher BP for accurate monitoring.
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| ==Pathological Findings== | | ==Pathological Findings== |
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| <div align="left">
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| <gallery heights="225" widths="225">
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| Image:Aortic dissection 1.jpg|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. <br> <small> [http://www.peir.net Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology] </small>
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| </gallery>
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| </div>
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| == References == | | == References == |