Thoracic aortic aneurysm

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Thoracic aortic aneurysm
Other namesAneurysm - thoracic aortic [1]
Thoracic Aortic Aneurysm.png
Specialty Cardiology   OOjs UI icon edit-ltr-progressive.svg

A thoracic aortic aneurysm is an aortic aneurysm that presents primarily in the thorax.

Aortic aneurysm orta to greater than 1.5 times normal size.

An aortic aneurysm is an enlargement (dilatation) of the aorta to greater than 1.5 times normal size. They usually cause no symptoms except when ruptured. Occasionally, there may be abdominal, back, or leg pain.

Contents

A thoracic aortic aneurysm is the "ballooning" of the upper aspect of the aorta, above the diaphragm. Untreated or unrecognized they can be fatal due to dissection or "popping" of the aneurysm leading to nearly instant death. Thoracic aneurysms are less common than an abdominal aortic aneurysm. [2] However, a syphilitic aneurysm is more likely to be a thoracic aortic aneurysm than an abdominal aortic aneurysm. This condition is commonly treated via a specialized multidisciplinary approach with both vascular surgeons and cardiac surgeons.

Abdominal aortic aneurysm aortic aneurysm that is located in the abdominal aorta

Abdominal aortic aneurysm is a localized enlargement of the abdominal aorta such that the diameter is greater than 3 cm or more than 50% larger than normal. They usually cause no symptoms, except during rupture. Occasionally, abdominal, back, or leg pain may occur. Large aneurysms can sometimes be felt by pushing on the abdomen. Rupture may result in pain in the abdomen or back, low blood pressure, or loss of consciousness, and often results in death.

Vascular surgery medical specialty

Vascular surgery is a surgical subspecialty in which diseases of the vascular system, or arteries, veins and lymphatic circulation, are managed by medical therapy, minimally-invasive catheter procedures, and surgical reconstruction. The specialty evolved from general and cardiac surgery as well as minimally invasive techniques pioneered by interventional radiology. The vascular surgeon is trained in the diagnosis and management of diseases affecting all parts of the vascular system except those of the heart and brain. Cardiothoracic surgeons and interventional cardiologists treat diseases of the heart vessels. Vascular surgeons treat extracranial cerebrovascular disease while Neurosurgeons and interventional neuroradiologists treat diseases of the vessels in the brain.

Cardiac surgery surgery on the heart or great vessels

Cardiac surgery, or cardiovascular surgery, is surgery on the heart or great vessels performed by cardiac surgeons. It is often used to treat complications of ischemic heart disease ; to correct congenital heart disease; or to treat valvular heart disease from various causes, including endocarditis, rheumatic heart disease, and atherosclerosis. It also includes heart transplantation.

When an artery abnormally enlarges locally, the disease is typically identified as an aneurysm. A thoracic aortic aneurysm is an aneurysm at the ascending part of the thoracic aorta, which is the largest artery bridging the heart and the rest of the body. The current clinical ATAA managements rely mostly on aneurysm diameter, blood pressure, and lifestyle; however, other mechanical and biological factors can also contribute to aneurysm progression. To investigate the biomechanical influence on ATAAs, computer models were built to simulate blood flow through ATAA and a mechanical heart valve. It was found that the aneurysm's geometrical characteristic, hypertension, and hematocrit can all affect the mechanical load and fluid-induced stress on ATAA and heart valve.

Cardiovascular mortality accounts for a major proportion of total deaths in industrialized societies. In the US alone, it accounted for approximately 31% of the total mortality in 2014 with approximately ten thousand people dying because of aortic aneurysm and dissection. An aortic aneurysm occurs when an aorta enlarges abnormally at a localized region. When the enlargement occurs around the thoracic aorta, it is classified as thoracic aortic aneurysm (TAA). By the same token, when the enlargement occurs around the abdominal aorta, it is classified as abdominal aortic aneurysm(AAA).   The complications of aortic aneurysm are significant and are of considerable concern as the prevalence of the condition is increasing.

Presentation

Thoracic aortic aneurysm with arrow marking the lateral border of the aorta. AneurysmT.PNG
Thoracic aortic aneurysm with arrow marking the lateral border of the aorta.

Complications

A contrast enhanced CT demonstrating a large thoracic aneurysm of about 7 cm which has ruptured. CTRupturedTA.PNG
A contrast enhanced CT demonstrating a large thoracic aneurysm of about 7 cm which has ruptured.

The principal causes of death due to thoracic aneurysmal disease are dissection and rupture. Once rupture occurs, the mortality rate is 50–80%. Most deaths in patients with Marfan syndrome are the result of aortic disease.

Aortic dissection injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart

Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or back pain, often described as "tearing" in character. Also, 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 from not enough blood flow to the heart or complete rupture of the aorta.

Aortic rupture is the rupture or breakage of the aorta, the largest artery in the body. Aortic rupture is a rare, extremely dangerous condition. The most common cause is an abdominal aortic aneurysm that has ruptured spontaneously. Aortic rupture is distinct from aortic dissection, which is a tear through the inner wall of the aorta that can block the flow of blood through the aorta to the heart or abdominal organs.

Marfan syndrome genetic disorder of the connective tissue

Marfan syndrome (MFS) is a genetic disorder of the connective tissue. The degree to which people are affected varies. People with Marfan tend to be tall and thin, with long arms, legs, fingers and toes. They also typically have flexible joints and scoliosis. The most serious complications involve the heart and aorta, with an increased risk of mitral valve prolapse and aortic aneurysm. Other commonly affected areas include the lungs, eyes, bones and the covering of the spinal cord.

Causes

There are a number of causes, [3] Aneurysms in patients younger than 40 usually involve the ascending aorta due to a weakening of the aortic wall associated with connective tissue disorders like the Marfan and Ehler-Danlos syndromes or congenital bicuspid aortic valve. Younger patients may develop aortic aneurysms of the thoracoabdominal aorta after an aortic dissection. It can also be caused by blunt injury.

Atherosclerosis is the principal cause of descending aortic aneurysms, while aneurysms of the aortic arch may be due to dissection, atherosclerosis or inflammation.

Age

The diagnosis of thoracic aortic aneurysm usually involves patients in their 60s and 70s.

Risk factors

Blood pressure is a critical parameter that predicts aortic enlargements in conjunction with other factors such as the imbalance between protein synthesis and degradation of matrix proteins. While several other well known risk factors, such as age, gender, smoking and genetics, may lead to the development of TAA formation, the precise causes, physical or biochemical, of aneurysm formations is unknown in most cases. Approximately 10% of patients may have other family members who have aortic aneurysms. It is also important to note that individuals with a history of aneurysms in other parts of the body have a higher chance of developing a thoracic aortic aneurysm. [4]

Diagnosis

Aorta segments, with thoracic aorta in area marked in green. Aorta segments.jpg
Aorta segments, with thoracic aorta in area marked in green.

Thoracic abdominal aneurysm is defined as a diameter exceeding the following cutoff:

A diameter of 3.5 cm is generally considered dilated. [5] However, average values vary with age and size of the reference population, as well as different segments of the aorta.

Upper limits of the standard reference range of the thoracic aorta in a United States population: [7]
Small and youngLarge and elderly
Ascending aorta 3.3 cm4.3 cm
Descending aorta 2.3 cm3.2 cm

Screening

Ruptured thoracic aortic aneurysm as seen on ultrasound [8]

Guidelines were issued in March 2010 for early detection of thoracic aortic disease, by the American College of Cardiology, the American Heart Association, and other groups. Among the recommendations:

Treatment

A stent graft placed in the thoracic aorta to treat a thoracic aortic aneurysm. TAstent.PNG
A stent graft placed in the thoracic aorta to treat a thoracic aortic aneurysm.

The size cut off for aortic aneurysm is crucial to its treatment. A thoracic aorta greater than 4.5 cm is generally defined as aneurysmal, while a size greater than 6 cm is the distinction for treatment, which can be either endovascular or surgical, with the former reserved for pathology at the descending aorta. [10]

Indication for surgery may depend upon the size of the aneurysm. Aneurysms in the ascending aorta may require surgery at a smaller size than aneurysms in the descending aorta. [11]

Treatment may be via open or via endovascular means.

The current standard practices for patients, who have aortic aneurysms and dissections, are primarily managed by evaluating the size of the dilated blood vessels as well as patients' blood pressures. More specifically, the assessments and managements of TAA, ascending thoracic aortic aneurysm (ATAA), and AAA relies heavily on the diameter of an aneurysm and blood pressure rather than biomechanical and hemodynamic parameters such as arterial wall deformation or wall shear stress. However, in some circumstances, the patients with smaller vessel diameter may develop an aortic dissection before blood vessel diameter reaches the recommended threshold for surgery. Once a surgical option is deemed to be suitable, an open procedure remains the gold standard for a treatment. Given an approximately 30% of the patient population are not suitable for open procedures due to potential complications, the risk of surgery is preferred over the risk of further developments of aneurysms and dissections. One of the potential alternative treatment option of aortic aneurysm would be endovascular aortic repair (EVAR), which avoid the need of introducing open surgical procedures with the increased risk. However, EVAR is not risk-free as the stent graft relies on the outward expansion force generated from the stent frame, the imperfections from the repair would introduce further series complications including endovascular leakages and retrograde dissections.

Pathology

While the exact disease pathway for the progression of an aneurysm is still unclear, there are several key factors identified that prompt the aneurysm developments. As proposed by Shimizu et al. for the progression of aneurysms, there should be a two-step process where the normal healthy   blood   vessel   undergoes   initial   aortic  wall  damage  after  the  first  trigger   due to environmental or genetic events.

A second trigger, which is caused by environmental factors, would be followed such that the progression of an aneurysm is continued. Although their work is limited to the investigation of AAA, the same process for TAA and ATAA may apply . The primary cause of ATAA progression is the degradation of the media layer, which has decreased elastin concentration and reduced smooth muscle cells. Since the environmental factors are the second trigger, it can be argued that biochemical or biomechanical factors are the main factors in ATAA progression. As ascending thoracic aorta receives the highest amount of the blood flow from the heart, the investigation of ATAA progression from the biomechanics point of view could provide further clinical insights for the patients.

It is known that fluid shear stress would initiate the remodeling of blood vessels as well as create damage to blood cell; however, to physically measure fluid shear stress without influencing fluid flow in real-time can be very challenging. Due to the shear stress generated under pulsatile blood flow, it was shown that the endothelial cells and the adhesion of the neutrophils to endothelial cells responded to the gradients of WSS and potentially influenced the stability of the atherosclerotic plaque. Given the main components of blood are red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), and plasma, the biomechanical factors should have majority effects on these four components. Combining the evidence of blood damage under high shear stress and the thrombus generation under shear flow, one can argue that platelets initiate thrombus formation due to abnormal hemodynamics under pathological conditions.

A further investigation reveals that there is a close biophysical connection between the interaction of platelets and fluid shear stress. Briefly, the increase in blood shear stress would cause platelets to release and upregulate tissue growth factors. Specifically, human aortic smooth muscle cell (SMC) apoptosis has been observed with the overexpression of connective tissue growth factor (CTGF), which is released by platelets or other mechanical stimuli. Additionally, CTGF has been shown to increase the risk of a cardiovascular event and proposed as an independent risk predictor for the atherosclerotic disease. 4D magnetic resonance imaging (MRI) study has revealed a potential linkage by concluding that the bicuspid aortic valve (BAV) patients with aortic dilation are experiencing higher shear stress than the patients with tricuspid aortic valve (TAV).


Epidemiology

Each year in the United States, some 45,000 people die from diseases of the aorta and its branches. Acute aortic dissection, a life-threatening event due to a tear in the aortic wall, affects 5 to 10 patients per million population each year, most often men between the ages of 50 and 70; of those that occur in women younger than 40, nearly half arise during pregnancy. The majority of these deaths occur as a result of complications of thoracic aneurysmal disease


Biomechanical Modelling and of Thoracic Aortic

Cardiovascular diseases account for the most cause of death over the globe annually, summarized by the World Health Organization. An aortic aneurysm is one of the cardiovascular diseases with localized abnormal growth of a blood vessel with the primary risk of aneurysm rupturing or aortic wall dissecting. The precise pathological pathway for disease progression in aneurysm formation is not completely understood; however, biomechanically, disrupted blood flow from a diseased heart valve and thrombus formation potential in the dissection could contribute to the increased risk. The current ascending thoracic aortic aneurysm (ATAA) management rely heavily on ATAA diameter and blood pressure rather than biomechanical and hemodynamical parameters including arterial wall deformation or wall shear stress (WSS).

Ascending aortic curvature, aortic stiffness, peak wall stress (PWS), as well as wall shear stress (WSS) are biomechanical factors that may provide information for the disease predictions. Unfortunately, besides the aortic geometries, most of these factors cannot easily be directly measured in vivo . A method for calculation of arterial wall stress, blood flow velocity, and WSS would be of considerable value for disease assessments.

Although the size of the aorta has been studied in TAA; the impact of increasing aortic arch curvature has received less attention. The curvature might dramatically increase the force experience by ascending aorta even if under the conditions of lower systole pressure and smaller vessel diameter. Data suggest that the aorta and aortic aneurysm might be influenced considerably by its geometrical configuration but this has not been studied in detail. It is reasonable to begin an investigation on aortic aneurysm from a biomechanical perspective and to consider blood vessel displacement under pulsatile blood pressure. Since arterial wall stiffness increase with aging especially in patient with hypertension, investigation of aortic wall stress should provide important insights on how the stress is distributed.

In addition, evaluation of PWS, or overall arterial wall stress, should assist in identifying regions of the aorta that are subject to high stress rendering them at high risk for aneurysm rupture and/or dissection.

Related Research Articles

Aorta largest artery in the body

The aorta is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries. The aorta distributes oxygenated blood to all parts of the body through the systemic circulation.

Artery blood vessels that carry blood away from the heart

An artery is a blood vessel that takes blood away from the heart to all parts of the body. Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical arteries, which carry deoxygenated blood to the organs that oxygenate it. The effective arterial blood volume is that extracellular fluid which fills the arterial system.

Aneurysm bulge in the wall of a blood vessel

An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms are a result of a weakened blood vessel wall, and may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus for clot formation (thrombosis) and embolization. The word is from Greek: ἀνεύρυσμα, aneurysma, "dilation", from ἀνευρύνειν, aneurynein, "to dilate". As an aneurysm increases in size, the risk of rupture increases, leading to uncontrolled bleeding. Although they may occur in any blood vessel, particularly lethal examples include aneurysms of the Circle of Willis in the brain, aortic aneurysms affecting the thoracic aorta, and abdominal aortic aneurysms. Aneurysms can arise in the heart itself following a heart attack, including both ventricular and atrial septal aneurysms.

Bicuspid aortic valve human disease

Bicuspid aortic valve (BAV) is an inherited form of heart disease in which two of the leaflets of the aortic valve fuse during development in the womb resulting in a two-leaflet valve instead of the normal three-leaflet valve (tricuspid). BAV is the most common cause of heart disease present at birth and affects approximately 1.3% of adults. Normally, the mitral valve is the only bicuspid valve and this is situated between the heart's left atrium and left ventricle. Heart valves play a crucial role in ensuring the unidirectional flow of blood from the atrium to the ventricles, or from the ventricle to the aorta or pulmonary trunk.

Aortic valve repair

Aortic valve repair or aortic valve reconstruction is the reconstruction of both form and function of the native and dysfunctioning aortic valve. Most frequently it is applied for the treatment of aortic regurgitation. It can also become necessary for the treatment of aortic aneurysm, less frequently for congenital aortic stenosis.

Ascending aorta Part of the heart

The ascending aorta (AAo) is a portion of the aorta commencing at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum.

Loeys–Dietz syndrome Human disease

Loeys–Dietz syndrome (LDS) is an autosomal dominant genetic connective tissue disorder. It has features similar to Marfan syndrome and Ehlers–Danlos syndrome. The disorder is marked by aneurysms in the aorta, often in children, and the aorta may also undergo sudden dissection in the weakened layers of the wall of the aorta. Aneurysms and dissections also can occur in arteries other than the aorta. Because aneurysms in children tend to rupture early, children are at greater risk for dying if the syndrome is not identified. Surgery to repair aortic aneurysms is essential for treatment.

The Bentall procedure is a type of cardiac surgery involving composite graft replacement of the aortic valve, aortic root, and ascending aorta, with re-implantation of the coronary arteries into the graft. This operation is used to treat combined disease of the aortic valve and ascending aorta, including lesions associated with Marfan syndrome. The Bentall procedure was first described in 1968 by Hugh Bentall and Antony De Bono.

Traumatic aortic rupture life-threatening injury to the aorta

Traumatic aortic rupture, also called traumatic aortic disruption or transection, is a condition in which the aorta, the largest artery in the body, is torn or ruptured as a result of trauma to the body. The condition is frequently fatal due to the profuse bleeding that results from the rupture. Since the aorta branches directly from the heart to supply blood to the rest of the body, the pressure within it is very great, and blood may be pumped out of a tear in the blood vessel very rapidly. This can quickly result in shock and death. Thus traumatic aortic rupture is a common killer in automotive accidents and other traumas, with up to 18% of deaths that occur in automobile collisions being related to the injury. In fact, aortic disruption due to blunt chest trauma is the second leading cause of injury death behind traumatic brain injury.

Endovascular aneurysm repair Norwegian Bokmål

Endovascular aneurysm repair, is a type of endovascular surgery used to treat pathology of the aorta, most commonly an abdominal aortic aneurysm (AAA). When used to treat thoracic aortic disease, the procedure is then specifically termed TEVAR for "thoracic endovascular aortic/aneurysm repair." The procedure involves the placement of an expandable stent graft within the aorta to treat aortic disease without operating directly on the aorta. In 2003, EVAR surpassed open aortic surgery as the most common technique for repair of AAA, and in 2010, EVAR accounted for 78% of all intact AAA repair in the United States.

The following outline is provided as an overview of and topical guide to cardiology, the branch of medicine dealing with disorders of the human heart. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in cardiology are called cardiologists.

Familial aortic dissection

Familial aortic dissection or FAD refers to the splitting of the wall of the aorta in either the arch, ascending or descending portions. FAD is thought to be passed down as an autosomal dominant disease and once inherited will result in dissection of the aorta, and dissecting aneurysm of the aorta, or rarely aortic or arterial dilation at a young age. Dissection refers to the actual tearing open of the aorta. However, the exact gene(s) involved has not yet been identified. It can occur in the absence of clinical features of Marfan syndrome and of systemic hypertension. Over time this weakness, along with systolic pressure, results in a tear in the aortic intima layer thus allowing blood to enter between the layers of tissue and cause further tearing. Eventually complete rupture of the aorta occurs and the pleural cavity fills with blood. Warning signs include chest pain, ischemia, and hemorrhaging in the chest cavity. This condition, unless found and treated early, usually results in death. Immediate surgery is the best treatment in most cases. FAD is not to be confused with PAU and IMH, both of which present in ways similar to that of familial aortic dissection.

Open aortic surgery surgical technique

Open aortic surgery (OAS), also known as open aortic repair (OAR), describes a technique whereby an abdominal or retroperitoneal surgical incision is used to visualize and control the aorta for purposes of treatment. OAS is used to treat aneurysms of the abdominal and thoracic aorta, aortic dissection, acute aortic syndrome, and aortic ruptures. Aortobifemoral bypass is also used to treat atherosclerotic disease of the abdominal aorta below the level of the renal arteries. In 2003, OAS was surpassed by endovascular aneurysm repair (EVAR) as the most common technique for repairing abdominal aortic aneurysms in the United States. In OAS for abdominal aortic aneurysm, the aneurysmal portion of the aorta is replaced with a graft, usually made of dacron or PTFE.

Inflammatory aortic aneurysm

Inflammatory aortic aneurysm (IAA), also known as Inflammatory abdominal aortic aneurysm (IAAA), is a type of abdominal aortic aneurysm (AAA) where the walls of the aneurysm become thick and inflamed. Similar to AAA, IAA occurs in the abdominal region. IAA is closely associated and believed to be a response to and extensive peri-anuerysmal fibrosis, which is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process IAA accounts for 5-10% of aortic aneurysms. IAA occurs mainly in a population that is on average younger by 10 years than most AAA patients. Some common symptoms of IAA may include back pain, abdominal tenderness, fevers, weight loss or elevated Erythrocyte sedimentation rate (ESR) levels. Corticosteroids and other immunosuppressive drugs have been found to decrease symptoms and the degree of peri-aortic inflammation and fibrosis

Hemodynamics of the aorta Study of the flow patterns and forces in the thoracic aorta

The hemodynamics of the aorta is an ongoing field of research in which the goal is to identify what flow patterns and subsequent forces occur within the thoracic aorta. These patterns and forces are used to identify the presence and severity of cardiovascular diseases such as aortic aneurysm and atherosclerosis. Some of the methods used to study the hemodynamics of aortic flow are patient scans, computational fluid dynamics models, and particle tracking velocimetry (PTV). The information gathered through these studies can be used for surgery planning and the development of implants. Greater understanding of this topic reduces mortality rates associated with cardiovascular disease.

References

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