Расслоение аорты

Около 96% людей с БА испытывают внезапную сильную боль. Боль может быть описана как разрывающая, колющая или острая боль. ^[4] Около 17% людей чувствуют миграцию боли по мере того, как расслоение распространяется вниз по аорте. ^[5] Местоположение боли связано с местом расслоения. ^[6] Боль в передней части грудной клетки связана с расслоением восходящей аорты, а межлопаточная боль в спине связана с расслоением нисходящей аорты. Если боль носит плевритный характер, это может указывать на острый перикардит, вызванный кровотечением в мешочек, окружающий сердце . Это особенно опасный случай, предполагающий, что острая тампонада перикарда может быть неизбежной. Тампонада перикарда - наиболее частая причина смерти от БА. ^[7]

Хотя боль можно спутать с сердечным приступом , AD обычно не ассоциируется с другими предполагающими признаками, такими как сердечная недостаточность и изменения ЭКГ . Менее распространенные симптомы, которые могут наблюдаться при БА, включают застойную сердечную недостаточность (7%), обмороки (9%), инсульт (6%), ишемическую периферическую невропатию , параплегию и остановку сердца . ^[8] Если человек теряет сознание, примерно в половине случаев это связано с кровотечением в перикард, которое приводит к тампонаде перикарда. Неврологические осложнения расслоения аорты, такие как инсульт и паралич , возникают из-за поражения одной или нескольких артерий, снабжающих кровью части центральной нервной системы . ^{[ необходима цитата ]}

Если AD затрагивает брюшную аорту, поражение одной или обеих почечных артерий происходит в 5–8% случаев, в то время как ишемия кишечника возникает примерно в 3% случаев. ^{[9] [10]}

Артериальное давление

Люди с БА часто имеют в анамнезе высокое кровяное давление . Артериальное давление весьма непостоянно при острой болезни Альцгеймера. Как правило, он выше у людей с дистальным расслоением. У лиц с проксимальным AD у 36% имеется гипертензия, а у 25% - гипотензия . Проксимальный AD обычно связан с ослаблением сосудистой стенки из-за кистозной медиальной дегенерации . У пациентов с дистальной (Стэнфордский тип B) АД 60–70% имеют высокое кровяное давление, а 2–3% - низкое кровяное давление . ^[11]

Тяжелая гипотензия при поступлении - серьезный прогностический показатель. Обычно это связано с тампонадой перикарда, тяжелой аортальной недостаточностью или разрывом аорты. Важно точное измерение артериального давления. Псевдогипотония (ложно низкое измерение артериального давления) может возникать из-за поражения брахиоцефальной артерии (кровоснабжающей правую руку) или левой подключичной артерии (кровоснабжающей левую руку). ^{[ необходима цитата ]}

Аортальная недостаточность

Аортальная недостаточность (AI) возникает от половины до двух третей восходящей АД, а диастолический шум в сердце при аортальной недостаточности слышен примерно в 32% проксимальных расслоений. Интенсивность (громкость) шума зависит от артериального давления и может быть неслышной при низком артериальном давлении. ^{[ необходима цитата ]}

Существует несколько причин для ИИ в настройке восходящего AD. Расслоение может привести к расширению фиброзного кольца аортального клапана , предотвращая копирование створок клапана. Расслоение может распространяться на корень аорты и отделять створки аортального клапана. В качестве альтернативы, после обширного разрыва интимы лоскут интимы может выпадать в выводной тракт левого желудочка , вызывая инвагинацию интимы в аортальный клапан, тем самым препятствуя надлежащему закрытию клапана. ^{[ необходима цитата ]}

Инфаркт миокарда

Инфаркт возникает в 1-2% случаев расслоения аорты. Инфаркт вызывается поражением коронарных артерий , которые снабжают сердце насыщенной кислородом кровью, при расслоении. Правая коронарная артерия поражается чаще, чем левая коронарная артерия. Если инфаркт миокарда лечится тромболитической терапией, смертность увеличивается до более чем 70%, в основном из-за кровотечения в перикардиальный мешок, вызывающего тампонаду сердца . ^{[ необходима цитата ]}

Плевральный выпот

Плевральный выпот (сбор жидкости в пространстве между легким и грудной стенкой или диафрагмой ) может быть обусловлены либо кровями из переходного разрыва аорты или из - за жидкости к воспалительной реакции вокруг аорты. Если плевральный выпот развился из-за БА, он чаще встречается в левом гемитораксе, чем в правом. ^{[ необходима цитата ]}

Aortic dissection is associated with hypertension (high blood pressure) and many connective tissue disorders. Vasculitis (inflammation of an artery) is rarely associated with aortic dissection. It can also be the result of chest trauma. About 72 to 80% of individuals who present with an aortic dissection have a previous history of hypertension. Illicit drug use with stimulants such as cocaine and methamphetamine is also a modifiable risk factor for AD.^[12][13] It can also be caused by smoking.

A bicuspid aortic valve (a type of congenital heart disease involving the aortic valve) is found in 7–14% of individuals who have an aortic dissection. These individuals are prone to dissection in the ascending aorta. The risk of dissection in individuals with bicuspid aortic valve is not associated with the degree of stenosis of the valve.^{[citation needed]}

Connective tissue disorders such as Marfan syndrome, Ehlers-Danlos syndrome, and Loeys–Dietz syndrome increase the risk of aortic dissection.^[11] Similarly, vasculitides such as Takayasu's arteritis, giant cell arteritis, polyarteritis nodosa, and Behcet's disease have been associated with a subsequent aortic dissection.^[11][12] Marfan's syndrome is found in 5–9% of individuals who had an aortic dissection. In this subset, the incidence in young individuals is increased. Individuals with Marfan syndrome tend to have aneurysms of the aorta and are more prone to proximal dissections of the aorta.^[14]

Turner syndrome also increases the risk of aortic dissection, by aortic root dilatation.^[15]

Chest trauma leading to aortic dissection can be divided into two groups based on cause: blunt chest trauma (commonly seen in car accidents) and iatrogenic. Iatrogenic causes include trauma during cardiac catheterization or due to an intra-aortic balloon pump.^{[citation needed]}

Aortic dissection may be a late sequela of heart surgery. About 18% of individuals who present with an acute aortic dissection have a history of open-heart surgery. Individuals who have undergone aortic valve replacement for aortic insufficiency are at particularly high risk because aortic insufficiency causes increased blood flow in the ascending aorta. This can cause dilatation and weakening of the walls of the ascending aorta.^{[citation needed]}

Syphilis only potentially causes aortic dissection in its tertiary stage.^[16]

Blood penetrates the intima and enters the media layer.

As with all other arteries, the aorta is made up of three layers, the intima, the media, and the adventitia. The intima is in direct contact with the blood inside the vessel, and mainly consists of a layer of endothelial cells on a basement membrane; the media contains connective and muscle tissue, and the vessel is protected on the outside by the adventitia, comprising connective tissue.^[17]

In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure rips the tissue of the media apart along the laminated plane splitting the inner two-thirds and the outer one-third of the media apart.^[18] This can propagate along the length of the aorta for a variable distance forward or backwards. Dissections that propagate towards the iliac bifurcation (with the flow of blood) are called anterograde dissections and those that propagate towards the aortic root (opposite of the flow of blood) are called retrograde dissections. The initial tear is usually within 100 mm of the aortic valve, so a retrograde dissection can easily compromise the pericardium leading to a hemopericardium. Anterograde dissections may propagate all the way to the iliac bifurcation of the aorta, rupture the aortic wall, or recanalize into the intravascular lumen leading to a double-barrel aorta. The double-barrel aorta relieves the pressure of blood flow and reduces the risk of rupture. Rupture leads to hemorrhaging into a body cavity, and prognosis depends on the area of rupture. Retroperitoneal and pericardial ruptures are both possible.^{[citation needed]}

The initiating event in an aortic dissection is a tear in the intimal lining of the aorta. Due to the high pressures in the aorta, blood enters the media at the point of the tear. The force of the blood entering the media causes the tear to extend. It may extend proximally (closer to the heart) or distally (away from the heart) or both. The blood travels through the media, creating a false lumen (the true lumen is the normal conduit of blood in the aorta). Separating the false lumen from the true lumen is a layer of intimal tissue known as the intimal flap.^{[citation needed]}

The vast majority of aortic dissections originate with an intimal tear in either the ascending aorta (65%), the aortic arch (10%), or just distal to the ligamentum arteriosum in the descending thoracic aorta (20%).^{[clarification needed]}

As blood flows down the false lumen, it may cause secondary tears in the intima. Through these secondary tears, the blood can re-enter the true lumen.^{[citation needed]}

While it is not always clear why an intimal tear may occur, quite often it involves degeneration of the collagen and elastin that make up the media. This is known as cystic medial necrosis and is most commonly associated with Marfan syndrome and is also associated with Ehlers-Danlos syndrome.^{[citation needed]}

In about 13% of aortic dissections, no evidence of an intimal tear is found. In these cases, the inciting event is thought to be an intramural hematoma (caused by bleeding within the media). Since no direct connection exists between the true lumen and the false lumen in these cases, diagnosing an aortic dissection by aortography is difficult if the cause is an intramural hematoma. An aortic dissection secondary to an intramural hematoma should be treated the same as one caused by an intimal tear.^{[citation needed]}

Diagnostic algorithm of aortic dissection

Because of the varying symptoms of aortic dissection, the diagnosis is sometimes difficult to make. Concern should be increased in those with low blood pressure, neurological problems, and an unequal pulses.^[19]

While taking a good history from the individual may be strongly suggestive of an aortic dissection, the diagnosis cannot always be made by history and physical signs alone. Often, the diagnosis is made by visualization of the intimal flap on a diagnostic imaging test. Common tests used to diagnose an aortic dissection include a CT scan of the chest with iodinated contrast material and a transesophageal echocardiogram. The proximity of the aorta to the esophagus allows the use of higher-frequency ultrasound for better anatomical images. Other tests that may be used include an aortogram or magnetic resonance angiogram of the aorta. Each of these tests has pros and cons, and they do not have equal sensitivities and specificities in the diagnosis of aortic dissection.^{[citation needed]}

In general, the imaging technique chosen is based on the pretest likelihood of the diagnosis, availability of the testing modality, patient stability, and the sensitivity and specificity of the test.^{[citation needed]}

D-dimer

A measurement of blood D-dimer level may be useful in diagnostic evaluation. A level less than 500 ng/ml may be considered evidence against a diagnosis of aortic dissection,^[1][20] although this guideline is only applicable in cases deemed "low risk"^[21] and within 24 hours of symptom onset.^[22] The American Heart Association does not advise using this test in making the diagnosis, as evidence is still tentative.^[23]

Chest X-ray

Chest radiography may although demonstrate a change in the morphology of the thoracic aorta which can be seen in aortic dissection. Classically, new widening of the mediastinum on radiograph is of moderate sensitivity for detecting an ascending aortic dissection; however, this finding is of low specificity, as many other conditions can cause apparent widening of the mediastinum.^{[citation needed]}

There are several other associated radiographic findings:^{[citation needed]}

• The "calcium sign" describes an apparent separation of the intimal calcification from the outer aortic margin by greater than 10 mm.
• Pleural effusions, more commonly in descending aortic dissections, and typically left sided.
• Other: obliteration of the aortic knob, depression of the left mainstem bronchus, loss of the paratracheal stripe, and tracheal deviation.

Importantly, about 12 to 20% of aortic dissections are not detectable by chest radiograph; therefore, a "normal" chest radiograph does not rule out aortic dissection. If there is high clinical suspicion, a more sensitive imaging test (CT angiogram, MR angiography, or transesophageal echo) may be warranted.^{[citation needed]}

Computed tomography

Computed tomography angiography is a fast, noninvasive test that gives 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. 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 type of scan is timed to an injection to capture the contrast as it enters the aorta. The scan then follows the contrast as it flows through the vessel. It has a sensitivity of 96 to 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.^{[citation needed]}

• 

  CT with contrast demonstrating aneurysmal dilation and a dissection of the ascending aorta (type A Stanford)

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  Chest CT with descending (type B Stanford) aortic dissection (red circle)

• Type A dissection with pericardial effusion as a result.

MRI

Magnetic resonance imaging (MRI) is also used for the detection and assessment of aortic dissection, with a sensitivity of 98% and a specificity of 98%. An MRI examination of the aorta produces a three-dimensional reconstruction of the aorta, allowing the physician to determine the location of the intimal tear and the involvement of branch vessels, and to locate any secondary tears. It is a noninvasive test, does not require the use of iodinated contrast material, and can detect and quantitate the degree of aortic insufficiency.^{[citation needed]}

The disadvantage of the MRI scan in the face of aortic dissection is that it may be available only in larger hospitals, and the scan is relatively time-consuming, which could be dangerous in people who are already very unwell. Due to the high-intensity magnetic fields used during MRI, it cannot be used on individuals with metallic implants. In addition, some individuals experience claustrophobia while surrounded by the MRI magnet.^{[citation needed]}

Ultrasound

The transesophageal echocardiogram (TEE) is a good test in the diagnosis of aortic dissection, with a sensitivity up to 98% and a specificity up to 97%. It has become the preferred imaging modality for suspected aortic dissection. It is a relatively noninvasive 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 TEE include the inability to visualize the distal ascending aorta (the beginning of the aortic arch), and the descending abdominal aorta that lies below the stomach. A TEE may be technically difficult to perform in individuals with esophageal strictures or varices.^{[citation needed]}

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  Aortic dissection with an intramural hematoma as seen on TEE