Index
It occurs when an injury to the innermost layer of the aorta allows blood to flow between the aortic wall layers, forcing the layers to separate.
In most cases, this is associated with a sudden onset of severe chest or back pain, often described as “tearing” in character. In addition, vomiting, sweating, and lightheadedness may occur.
Other symptoms may result from decreased blood supply to other organs, such as stroke or mesenteric ischemia. Aortic dissection can quickly lead to death due to insufficient blood flow to the heart or rupture of the aorta.
Aortic dissection is more common in those with a history of high blood pressure and several connective tissue diseases that affect the strength of the blood vessel wall, such as Marfan syndrome, a bicuspid aortic valve, and previous heart surgery.
Severe trauma, smoking, cocaine use, pregnancy, a thoracic aortic aneurysm, inflammation of the arteries, and abnormal lipid levels are also associated with an increased risk.
The diagnosis is suspected based on symptoms with medical imaging, such as CT scan, MRI, or ultrasound, used to confirm further and evaluate the dissection. The two main types are Stanford type A, which involves the first part of the aorta, and type B, which does not.
Prevention is by controlling blood pressure and not smoking. Treatment of aortic dissection depends on the part of the aorta involved. Dissections that affect the first part of the aorta usually require surgery.
Surgery can be done through an opening in the chest or endovascular aneurysm repair, carried out from within the blood vessels.
Dissections involving the second part of the aorta can usually be treated with medications that lower blood pressure and heart rate unless complications.
Aortic dissection is relatively rare, occurring at an estimated rate of three per 100,000 people per year. It is more common in men than women. At diagnosis, the typical age is 63, and approximately 10% of cases occur before age 40.
Without treatment, about half of people with type A die within three days, and about 10% of people with type B die within a month.
The first case of aortic dissection described was in the examination of King George II of Great Britain after his death in 1760. Surgery for aortic dissection was introduced in the 1950s by Michael E. DeBakey.
Signs and symptoms
About 96% of people with aortic dissection have severe pain that had a sudden onset. The pain can be described as a tearing, stabbing, or sharp sensation; 17% of people feel that the pain migrates as the dissection spreads through the aorta.
The location of the pain is associated with the site of the dissection. Anterior chest pain is associated with dissections involving the ascending aorta, whereas interscapular (back) pain is associated with descending aortic dissections.
If the pain is pleuritic, it may suggest acute pericarditis caused by bleeding in the pericardial sac. This is a particularly dangerous eventuality, meaning that acute pericardial tamponade may be imminent.
Pericardial tamponade is the most common cause of death from aortic dissection.
While the pain can be confused with myocardial infarction (heart attack), aortic dissection is generally not associated with the other myocardial infarction signs, including heart failure and EKG changes.
People with aortic dissection who do not have pain have a chronic dissection.
Less common symptoms that may be seen in the setting of aortic dissection include congestive heart failure (7%), fainting (9%), stroke (6%), ischemic peripheral neuropathy, paraplegia, and cardiac arrest.
Half the time, if the individual has a fainting episode, it is due to bleeding into the pericardium leading to pericardial tamponade.
The neurologic complications of aortic dissection (i.e., stroke and paralysis) are due to the involvement of one or more arteries supplying parts of the central nervous system.
If the aortic dissection involves the abdominal aorta, involvement of the abdominal aorta branches is possible.
In abdominal aortic dissections, involvement of one or both renal arteries occurs in 5-8% of cases, while mesenteric ischemia (ischemia of the intestines) occurs in approximately 3%.
Blood pressure
People with an aortic dissection often have a history of high blood pressure; blood pressure is quite variable at presentation with acute aortic dissection and tends to be higher in individuals with distal dissection.
In individuals with proximal aortic dissection, 36% have hypertension, while 25% have hypotension. Proximal aortic dissections tend to be more associated with the weakening of the vascular wall due to medial cystic degeneration.
In those presenting with distal aortic dissections (type B), 60-70% present with high blood pressure, while 2-3% current with low blood pressure.
Severe hypotension at presentation is a powerful prognostic indicator. It is usually associated with pericardial tamponade, severe aortic regurgitation, or aortic rupture. Accurate blood pressure measurement is essential.
Pseudohypotension (falsely low blood pressure measurement) can occur due to the involvement of the brachiocephalic artery (supplying the right arm) or the left subclavian artery (supplying the left arm).
Aortic insufficiency
Aortic regurgitation (AI) occurs in half to two-thirds of ascending aortic dissections, and the diastolic heart murmur of aortic regurgitation is audible in approximately 32% of proximal dissections.
The intensity (volume) of the murmur depends on blood pressure and maybe inaudible with low blood pressure.
There are multiple causes for AI in the context of ascending aortic dissection. Dissection can dilate the annulus of the aortic valve so that the valve leaflets cannot cooperate. Another mechanism is that the dissection may extend to the aortic root and detach the fly from the aortic valve.
The third mechanism is that if there was an extensive intimal tear, the intimal flap might prolapse into the left ventricular outflow tract, causing intimal intussusception in the aortic valve that prevents valve closure.
Myocardial infarction
Myocardial infarction (heart attack) occurs in 1-2% of aortic dissections. The cause of the infarction is the participation of the coronary arteries, which supply the heart with oxygenated blood, in the dissection.
The right coronary artery is more commonly involved than the left coronary artery. If the myocardial infarction is treated with thrombolytic therapy, mortality increases to more than 70%, mainly due to bleeding in the pericardial sac causing cardiac tamponade.
Because aortic dissection can present to the emergency physician similar to myocardial infarction, the physician must take care to make a proper diagnosis before starting treatment for myocardial infarction as the myocardial infarction regimen can be lethal for an individual with aortic dissection.
Pleural effusion
A pleural effusion (accumulation of fluid in the space between the lungs and the chest wall or diaphragm) may be due to blood from a transient rupture of the aorta or fluid due to an inflammatory reaction around the aorta.
If a pleural effusion develops due to an aortic dissection, it is more common in the left hemithorax than in the right.
Causes
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 trauma to the chest.
About 72 to 80% of people who present with an aortic dissection have a previous history of hypertension. Illicit drugs with stimulants such as cocaine and methamphetamine are also a modifiable risk factor for aortic dissection. It can also be caused by smoking.
A bicuspid aortic valve (a type of congenital heart disease that involves the aortic valve) is found in 7-14% of people who have an aortic dissection. These people are prone to dissection in the ascending aorta.
The risk of dissection in individuals with a bicuspid aortic valve is not associated with the degree of valve stenosis.
Connective tissue disorders such as Marfan syndrome, Ehlers-Danlos syndrome, and Loeys-Dietz syndrome increase the risk of aortic dissection.
Similarly, vasculitis such as Takayasu’s arteritis, giant cell arteritis, polyarteritis nodosa, and Behcet’s disease have been associated with posterior aortic dissection.
Marfan syndrome is found in 5-9% of people who have had an aortic dissection. In this subset, the incidence in young individuals increases. People with Marfan syndrome tend to have aortic aneurysms and are more prone to proximal aortic dissections.
The Turner syndrome also increases the risk of dissection by dilating the aortic root. Trauma to the chest leading to aortic dissection can be divided into two groups based on the cause: blunt chest trauma (commonly seen in car accidents) and iatrogenic.
Iatrogenic causes include trauma during cardiac catheterization or an intra-aortic balloon pump. Aortic dissection can be a late sequel to cardiac surgery. About 18% of people who present with an acute aortic dissection have a history of open-heart surgery.
People who have undergone aortic valve replacement for aortic regurgitation are at exceptionally high risk because aortic regurgitation causes the increased blood flow in the ascending aorta.
This can cause dilation and weakening of the walls of the ascending aorta. Syphilis only causes aortic dissection in its tertiary stage.
Pathophysiology
As with all other arteries, the aorta comprises three layers, the intima, the media, and the adventitia.
The intima is in direct contact with the blood within the vessel and consists mainly of a layer of endothelial cells on a basement membrane; the medium contains connective and muscular tissue, and the ship is protected on the outside by the adventitia, which comprises the connective tissue.
In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure separates the tissue from the media along the laminated plane that divides the inner two-thirds and the outer third of the independent press.
This can spread along the aorta for a variable distance forward or backward. Dissections that spread to the iliac bifurcation (with the flow of blood) are called antegrade dissections, and those that spread to the aortic root (opposite the flow of blood) are called retrograde dissections.
The initial tear is generally within 100 mm of the aortic valve, so a retrograde dissection can easily compromise the pericardium leading to a hemopericardium.
Antegrade dissections can spread to the iliac bifurcation of the aorta, rupture the aortic wall, or recanalize into the intravascular lumen, leading to a double-barreled aorta.
The double-barreled aorta relieves blood flow pressure and reduces the risk of rupture. The rupture leads to bleeding into the body cavity, and the prognosis depends on the break area. Retroperitoneal and pericardial cracks are both possible.
The initiating event in 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 rupture.
The force of the blood entering the medium causes the tear to spread. It can extend proximally (closer to the heart) or distally (away from the heart).
Blood travels through the media, creating a false light (the true light is the average blood conduit in the aorta). The separation of false light from true light is a layer of intimal tissue known as the intimal fin.
The vast majority of aortic dissections originate with a rupture of the intima in the ascending aorta (65%), the aortic arch (10%), or only distal to the ligament arteriosus in the descending thoracic aorta (20%).
As blood flows through the false light, it can cause secondary tears in the intima. Through these secondary tears, the blood can re-enter the true light.
While it is not always clear why an intimal rupture can occur, it often involves degeneration of the collagen and elastin that make up the media. This is known as medial cystic necrosis and is most commonly associated with Marfan syndrome and is also associated with Ehlers-Danlos syndrome.
In approximately 13% of aortic dissections, there is no evidence of an intimal rupture. In these cases, the inciting event is believed to be an intramural hematoma (caused by bleeding within the medium).
Since there is no direct connection 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 way as one caused by an intimal rupture.
Diagnosis
Due to the different symptoms of aortic dissection, the diagnosis is sometimes difficult to make. Concern should increase in those with low blood pressure, neurological problems, and irregular pulses.
While taking a good history of the individual can be highly suggestive of an aortic dissection, the history and physical signs cannot always make the diagnosis alone.
Diagnosis is often made by viewing the intimal flap on an imaging test.
Standard 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 higher frequency ultrasound to obtain better anatomical images. Other tests that may be used include an aortogram or MRI angiogram of the aorta.
Each of these tests has pros and cons, and they do not have the same sensitivities and specificities in diagnosing aortic dissection.
In general, the imaging technique chosen is based on the probability of the diagnosis before the test, the availability of the test modality, the stability of the patient, and the sensitivity and specificity of the test.
D-dimer
A measurement of the D-dimer level in the blood can be helpful in the diagnostic evaluation. A level below 500 ng/ml can be evidence against a diagnosis of aortic dissection. However, this guide is only applicable in cases considered “low risk” and within 24 hours of the onset of symptoms.
The American Heart Association does not advise using this test to make the diagnosis, as the evidence is still tentative.
Chest x-ray
The chest radiograph may show a change in the morphology of the thoracic aorta that can be seen on aortic dissection.
Classically, the new widening of the mediastinum on radiography is moderately sensitive for detecting an ascending aortic dissection; however, this finding is of low specificity since many other conditions can cause an apparent widening of the mediastinum.
There are several other associated radiographic findings:
The “calcium sign”: describes an apparent separation of intimal calcification from the outer aortic margin by more than 10 mm.
Pleural effusions: most commonly in descending aortic dissections and typically on the left side.
Others: the obliteration of the aortic button, depression of the left main bronchus, loss of the paratracheal band, and tracheal deviation.
Notably, about 12-20% of aortic dissections are not detectable by chest radiography; therefore, a “normal” chest radiograph does not rule out aortic dissection.
If there is high clinical suspicion, a more sensitive imaging test (computed tomography angiography, magnetic resonance angiography, or transesophageal echo) may be warranted.
Computed tomography
Computed tomography angiography is a rapid, non-invasive test that provides an accurate three-dimensional view of the aorta.
These images are produced by taking quick thin slices of the chest and abdomen and combining them on the computer to create cross-sections.
An iodinated contrast material is injected into a peripheral vein to delineate the aorta with the accuracy necessary to make a proper diagnosis. Contrast is injected, and the scan is done with a bolus tracking method.
This scan is synchronized with an injection to capture the contrast as it enters the aorta. The scan follows the difference as it flows through the vessel.
It has a 96 to 100% sensitivity 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.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) is also used to detect and evaluate 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, which allows the physician to determine the location of the intimal rupture and involvement of the branch vessels and to locate secondary tears.
It is a non-invasive test, does not require iodinated contrast material, and can detect and quantify the degree of aortic regurgitation.
The downside of an MRI scan versus aortic dissection is that it has limited availability and is often found only in larger hospitals. The scan is relatively slow, which can be dangerous in people who are already very sick.
Due to the high-intensity magnetic fields used during MRI, it is contraindicated in individuals with metal implants. Also, many people experience claustrophobia while in the MRI scan tube.
Ultrasound
The transesophageal echocardiogram (TEE) is a relatively good test for diagnosing aortic dissection, with a sensitivity of up to 98% and a specificity of up to 97%.
It has become the preferred imaging modality for suspected aortic dissection. It is a relatively non-invasive test, which requires the individual to swallow the echocardiography probe.
It is perfect for evaluating aortic regurgitation in the context of ascending aortic dissection and in determining whether the Ostia (origins) of the coronary arteries are involved.
While many institutions provide sedation during transesophageal echocardiography for patient comfort, it can be performed in cooperative individuals without sedation.
Disadvantages of the transesophageal echocardiogram 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 transesophageal echocardiogram can be technically challenging to perform in individuals with esophageal strictures or varices.
Aortograma
An aortogram involves placing a catheter into the aorta and injecting contrast material while X-rays are taken.
The procedure is known as an aortography. It was previously thought to be the gold standard for diagnosis and supplanted by other less invasive imaging modalities.
Classification
Several different classification systems have been used to describe aortic dissections. One of these classifications is based on chronicity and labels aortic dissections as hyperacute (<24 hours in duration), acute (2-7 days), subacute (8-30 days), and chronic (> 30 days).
Commonly used systems are based on the anatomy of the dissection or the duration of onset of symptoms before the presentation. The Stanford system is more widely used now as it is more in tune with patient management.
DeBakey
The DeBakey system, named for cardiothoracic surgeon Michael E. DeBakey, is an anatomical description of aortic dissection.
It categorizes the dissection based on where the original intimal tear is located and the extent of the dissection (found in either the ascending or descending aorta or involves both the ascending and descending aorta).
Type I: Originates in the ascending aorta and spreads to at least the aortic arch and often beyond it distally. It is often seen in patients under 65 years of age and is the deadliest form of the disease.
Type II: originates in and is confined to the ascending aorta.
Type III: Originates in the descending aorta and rarely extends proximally but will extend distally. It occurs more frequently in elderly patients with atherosclerosis and hypertension.
Stanford
The Stanford classification is divided into A and B groups, depending on whether the ascending aorta is involved.
A: affects the ascending aorta and the aortic arch, and possibly the descending aorta. The tear can originate in the ascending aorta, the aortic arch, or, more rarely, the descending aorta. Includes DeBakey types I and II.
B: involves the descending aorta or arch (distal to the left subclavian artery) without affecting the ascending aorta. Includes DeBakey type III.
The Stanford classification is helpful because it follows clinical practice, as type A ascending aortic dissections require primary surgical treatment. In contrast, type B dissections are generally treated medically as initial treatment, with surgery reserved for any complications.
The reason for surgical repair of type A dissections is that ascending aortic dissections often involve the aortic valve, which, having lost its suspensory support, is displaced towards the aortic root, resulting in aortic incompetence.
The valve must be resuspended to re-close and repair or prevent a coronary artery injury. Additionally, the dissection area is removed and replaced with a Dacron graft to prevent further dissection.
However, type B dissections are not alleviated, from the standpoint of mortality, by the operation unless they are leaked, ruptured, or compromised by other organs, e.g., kidneys.
Prevention
Among the recognized risk factors for aortic dissection, hypertension, abnormally high levels of lipids (such as cholesterol) in the blood, and tobacco use are considered preventable risk factors.
Repair of an enlarged ascending aorta from an aneurysm or unrecognized and untreated aortic dissections is recommended when the size is greater than 6 cm (2.4 inches) to decrease dissection risk.
A repair may be recommended when the size is more significant than 4.5 cm (1.8 inches) if the person has one of several connective tissue disorders or a family history of aortic rupture.
Treatment
In an acute dissection, the choice of treatment depends on its location. Surgical treatment is superior to medical therapy for Stanford type A dissection (ascending aortic dissection).
Medical treatment is preferred over surgical therapy for uncomplicated Stanford type B (distal aorta) dissections (including abdominal aortic dissections).
The risk of death from aortic dissection is highest in the first few hours after dissection begins and decreases afterward. Because of this, therapeutic strategies differ for treating acute versus 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, their prognosis improves.
About 66% of all dissections occur in the acute phase. People who present two weeks after the start of the dissection are said to have chronic aortic dissections.
These people have been self-selected as survivors of the acute episode and can be treated with medical therapy as long as they are stable.
Medication
Aortic dissection generally presents as a hypertensive emergency, and the primary consideration in medical management is strict control of blood pressure.
The target blood pressure should be a mean arterial pressure (MAP) of 60 to 75 mmHg or the lowest tolerated blood pressure. Initial decreases should be around 20%.
Another factor is to reduce the sheer force of dP / dt (blood ejection force from the left ventricle). Long-term physical, emotional, and psychological efforts are essential in controlling blood pressure.
Beta-blockers are the first-line treatment for patients with acute and chronic aortic dissection.
In acute dissection, fast-acting agents that can be administered intravenously are preferred and have doses that are easier to adjust (such as esmolol, propranolol, or labetalol).
Vasodilators such as sodium nitroprusside can be considered for people with ongoing high blood pressure. Still, they should never be used alone, as they often stimulate a reflective increase in heart rate.
Calcium channel blockers can be used to treat aortic dissection, mainly if there is a contraindication to the use of beta-blockers.
Due to their combined vasodilator and adverse inotropic effects, verapamil and diltiazem commonly use calcium channel blockers.
If the individual has refractory hypertension (persistent hypertension with the maximum doses of three different classes of antihypertensive agents), renal artery involvement in the plane of aortic dissection should be considered.
Surgical
Indications for surgical treatment of aortic dissection include an acute proximal aortic dissection and an acute distal aortic dissection with one or more complications.
Complications include:
- Vital organ involvement.
- Impending rupture of the aorta.
- Retrograde dissection in the ascending aorta.
- History of Marfan syndrome or Ehlers-Danlos syndrome.
The surgical treatment of aortic dissection is to resect (remove) the most severely damaged segments of the aorta and nullify the entry of blood into the false lumen (both in the initial intimal tear and in secondary tears along the vessel ).
Although excision of the intimal tear can be performed, it does not significantly change mortality. The particular treatment used depends on the segments of the aorta involved. Some treatments are:
Open aortic surgery: replace the damaged section of the aorta with a tubular graft (often made from Dacron) when no damage to the aortic valve is seen.
Bentall procedure: replacement of the damaged section of the aorta and replacement of the aortic valve.
David’s procedure: replacement of the damaged section of the aorta and reimplantation of the aortic valve.
Thoracic Endovascular Aortic Repair – A minimally invasive surgical procedure usually combined with ongoing medical management.
Replacement of the damaged section of the aorta: with a Dacron graft reinforced with a sutureless vascular ring connector. The Vascular Ring Connector is a titanic ring used as a stent in the vascular graft to achieve a rapid, blood-sealed, sutureless anastomosis.
Two grooves on the surface of the ring are for the fixation of the vascular graft and the aorta. The tapes used to tie against the crew provide a larger contact surface area than traditional stitches, providing a stronger anastomosis and better surgical results.
Several comorbid conditions increase the surgical risk of aortic dissection repair. These conditions include the following:
- Prolonged preoperative evaluation (increased time before surgery).
- Advanced age.
- Comorbid conditions (such as coronary artery disease).
- Aneurysm leaks.
- Cardiac tamponade.
- Shock (shock).
- History of myocardial infarction.
- History of kidney failure (acute or chronic kidney failure).
Follow-up
Long-term follow-up in individuals who survive aortic dissection involves close blood pressure monitoring.
The relative risk of late rupture of an aortic aneurysm is ten 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 people should be followed closely during this period. About 29% of late deaths after surgery are due to the rupture of a dissecting aneurysm or another aneurysm.
In addition, there is a 17% to 25% incidence of new aneurysm formation, typically due to dilation of the residual false lumen. These new aneurysms are more prone to rupture due to their thinner walls. Serial imaging of the aorta is suggested, with magnetic resonance imaging the preferred technique.
epidemiology
Establishing the incidence of aortic dissection has been difficult because many cases are only diagnosed after death (which may have been attributed to another cause) and are often initially misdiagnosed.
Aortic dissection affects an estimated 2.0-3.5 people per 100,000 each year. Studies from Sweden suggest that the incidence of aortic dissection may be increasing.
Men are more commonly affected than women: 65% of all people with aortic dissection are men. The mean age at diagnosis is 63 years.
Half of the aortic dissections in women before age 40 occur during pregnancy (usually in the third trimester or early postpartum). Dissection occurs in approximately 0.6% of pregnancies.
Forecast
Of all people with aortic dissection, 40% die immediately and do not get to a hospital in time. Of the rest, 1% die every hour, making diagnosis and treatment a priority.
Even after diagnosis, 5-20% die during surgery or in the immediate postoperative period. In ascending aortic dissection, if it is decided that surgery is not appropriate, 75% fail within two weeks.
The 30-day survival for chest dissections can be as high as 90% with aggressive treatment.
History
The first fully documented case of aortic dissection is attributed to Frank Nicholls in his autopsy report on King George II of Great Britain, who had been found dead on October 25, 1760; the report describes the dissection of the aortic arch and within the pericardium.
The term “aortic dissection” was introduced by the French physician JP Maunoir in 1802, and René Laennec labeled the condition “aneurysm dissection.”
London cardiologist Thomas Bevill Peacock contributed to understanding the condition by publishing two case series described in the literature so far: 19 cases in a review from 1843 and 80 in 1863.
The characteristic symptom of chest pain was recognized in 1855 when a case was diagnosed in life. Surgery for aortic dissection was introduced and developed by Michael E. DeBakey, Denton Cooley, and Oscar Creech, cardiac surgeons associated with the Baylor College of Medicine, Houston, Texas, in 1954.
DeBakey developed aortic dissection at the age of 97 in 2005 and underwent surgery in 2006. Endovascular treatment of aortic dissection was developed in the 1990s.
Society and Culture
Ritter Rules
Ritter’s rules are a compilation of reminders, symptoms, and risk factors designed to prevent misdiagnosis of thoracic aortic dissection.
The rules were named after actor John Ritter, who died of a thoracic aortic dissection on September 11, 2003. Ritter was initially misdiagnosed and later treated for a heart attack.
