Aortic dissection (AD) is a rare and catastrophic disease of the cardiovascular system in which blood from the aortic lumen enters the aortic wall through a tear in the aortic intima, causing an entrapment hematoma to form in the middle layer of the aortic wall and expand along the longitudinal axis of the aorta. If left untreated, the early mortality rate is as high as 1% per hour; with timely and appropriate drug and surgical treatment, the survival rate can be greatly improved and the mortality rate reduced to 18%-27%. Therefore, rapid clinical recognition and characteristic diagnostic tests are essential for the management of such patients.
1. Epidemiology.
The incidence of AD has been increasing year by year, and the exact incidence is not known. Early autopsy data from developed countries indicate an average annual incidence of 5/10 million to 10/10 million people, with at least 2,000 new cases per year in the United States. The ratio of male to female incidence is 2:1 to 5:1, most often occurring in men aged 50 to 70 years, and younger patients often have unique risk factors, and the mortality rate is not lower than that of the elderly. It is often misdiagnosed and underdiagnosed due to lack of awareness, especially in primary care hospitals. The number of reports in China is increasing year by year.
2. Etiology
2. 1 Degeneration of the middle layer of the aorta Degeneration of the middle layer of the aorta is considered to be the primary predisposing factor. It manifests as degeneration of collagen and fibrous tissue with cystic changes, and causes separation of the coarctation when the aortic wall is chronically irritated. Marfan and Enler2Danlos syndromes, which have inherited connective tissue defects, are seen in young and middle-aged people and often result in proximal entrapment. Marfan syndrome accounts for 6-9% of AD.
2. 2 Hypertension can cause hemodynamic disorders and promote the development of atherosclerosis, which is the most important predisposing factor for AD. Elevated blood pressure is present in 70% to 90% of AD patients. About half of the proximal and almost all of the distal AD patients have hypertension.
2. 3 Pregnancy There is no clear causal relationship between pregnancy and aortic dissection; half of the dissections in women under 40 years of age occur during pregnancy, typically in the second third of pregnancy, and occasionally in the early postpartum period. Elevated blood volume, cardiac output, and blood pressure in late pregnancy are at risk for entrapment separation.
2. 4 Other congenital vascular malformations such as bilobed aortic valve, aortic constriction; medical trauma such as arterial catheterization, intra-aortic balloon pump, coronary artery bypass and valve replacement; and trauma or cocaine abuse, cellular arteritis triggers are rare.
3.Pathogenesis
Any disease process or other condition that destroys the integrity of the elastic or muscular components of the middle layer can cause the aortic intima to tear and blood to enter the middle layer to form an interstitial layer, or the rupture of the trophoblastic vessels in the arterial wall can lead to an intramural hematoma that gradually develops into an aortic coarctation. The ascending aorta and descending aorta are the most impacted by the blood flow, which causes more damage to the elastic fibers in this part of the middle membrane. Most of the endothelial tears are broken in one place, but they can also be multiple, forming multiple false lumens. It has been found that the downward motion of the aortic root during the cardiac cycle may be related to the formation of aortic coarctation. Recently, it has been found that matrix metalloproteinase activity plays an important role in the development of AD.
4. Clinical typing
4.1DeBakey method
Type I: The fissure is located in the ascending aorta and extends distally across the aortic arch to the descending aorta and beyond. It is the most common, accounting for 60% to 70%.
Type II: The fissure starts and is limited to the ascending aorta, and the lesion is limited in extent.
Type III: The fissure starts in the descending aorta and the lesion extends distally, rarely extending retrogradely to the aortic arch and ascending aorta. This type accounts for 20%-30%.
4.2tanford method
Type A: all lesions involving ascending aortic coarctation.
②Type B: all lesions not involving ascending aortic coarctation.
4.3 The clinical manifestations of AD are varied and variable, and those within 2 weeks are defined as “acute”, accounting for 2/3; those 2 weeks or more are defined as “chronic”, accounting for 1/3.
4. 2 Clinical symptoms
4. 2. 1 Chest pain was the most common first symptom, accounting for 74-90%. Unbearable tearing pain with sweating, nausea, vomiting and syncope, which cannot be relieved by morphine. Severe pain in the anterior chest is mostly proximal AD; severe pain in the scapular region is more often seen in distal AD; pain in the neck and pharynx is often indicative of entrapment involving the ascending aorta or the aortic arch.
Painful site shifts, often along the path of the dissection, are a feature of approximately 70% of patients. The pain disappears when the blood from the false lumen reenters the aortic lumen distally, but if the pain recurs, the patient should be alerted for continued AD extension. Chronic entrapment is mostly painless and is only detected incidentally on imaging. It should be differentiated from acute myocardial infarction and pulmonary embolism. If AD involves the coronary artery, it can cause acute myocardial infarction, mostly with gradually increasing pain, and affects the right coronary artery more than the left coronary artery, then thrombolytic treatment is catastrophic and should be paid great attention.
4. 2. 2 The main cause of early death in sudden death is AD rupture or obstruction of arteries supplying blood to vital organs, such as coronary arteries, cephalobrachial arteries or visceral arteries. Sudden death usually results from acute pericardial tamponade or massive bleeding into the mediastinum or pleural cavity.
4. 2. 3 Neurological symptoms Clinical syncope (9%), cerebrovascular accidents such as hemiparesis, impaired consciousness (5%), and paraplegia can be detected and easily misdiagnosed as cerebrovascular accidents. In cases of syncope without focal neurological localization, the proximal entrapment into the pericardial cavity often leads to cardiac tamponade, or occasionally the descending aorta may rupture into the pleural cavity.
4. 2. 4 Gastrointestinal symptoms are common in DeBakey type III AD, and the causes of gastrointestinal symptoms are as follows: extension of AD lesions to large branches of the abdominal aorta, causing abdominal pain, nausea and vomiting; liver function impairment and jaundice when the hepatic artery opening is involved; rupture of the entrapment hematoma into the esophagus, causing dysphagia and vomiting of blood; ischemia of the small intestine due to ischemic necrosis of the superior mesenteric artery, which is seen in 3% to 5% of AD patients and can cause It can cause acute abdomen, mesenteric ischemia and necrosis, and the morbidity and mortality rate is very high.
4. 2. 5 Renal failure Commonly seen in DeBakey type III AD, about 3-8% of AD patients have unilateral or bilateral renal artery involvement, which can lead to severe renal vascular hypertension and even acute renal failure. 4. 2. 6 Respiratory symptoms
4. 2. 6 Respiratory symptoms Unilateral or bilateral pleural effusions, most often on the left side, are often exudative inflammatory reactions surrounding the involved aorta, but in some cases they are the result of transient leakage or rupture of the entrapment. Rarely, there is upper airway obstruction, hoarseness, even respiratory failure, hemoptysis produced by the rupture of the outer membrane of the entrapment into the tracheobronchial tree, etc., which can be easily misdiagnosed as bronchiectasis, pulmonary tuberculosis and lung tumor, etc.
4. 2. 7 Chronic entrapment Some studies have reported that chronic entrapment may present with a long course of unexplained low to moderate fever, night sweats, decreased body mass, pleural effusion, and occasionally recurrent arterial embolism (due to dislodgment of thrombus in the pseudolumen), which should be differentiated from connective tissue diseases and tumors. A small number of patients with AD may be asymptomatic and only incidentally detected on imaging.
4. 2. 8 Other rare clinical manifestations include superior vena cava syndrome, sternoclavicular pulsation syndrome, neck mass pulsation, Horner’s syndrome, and, more rarely, a continuous heart murmur with rupture of the entrapment into the right atrium, right ventricle, or left atrium resulting in congestive heart failure.
4. 3 Physical signs
(1) Weakness or shortage of pulse. Patients with acute chest pain with pulse shortage or inconsistent blood pressure in the extremities strongly suggest AD. proximal AD has pulse shortage in about 50% of cases, while distal AD only accounts for 15%, usually involving the femoral or left subclavian artery. The shortage of pulses in AD may be transient due to decompression caused by the reentry of the distal end of the false lumen into the true lumen or the departure of the endothelial piece from the occluded vessel opening.
De2Bakey type I and II AD (25 %) are significantly more frequent than DeBakey type III AD (4 %), which is caused by cardiac compression, severe aortic valve insufficiency, and bleeding from the coarctation into the pleural or pericardial cavity; it should be differentiated from pseudohypotension caused by a cephalobrachial vascular lesion involving the brachial artery.
(iii) Aortic valve insufficiency. It occurs in more than 50% of patients, commonly in DeBakey type I and II AD, with a sudden diastolic murmur in the aortic valve area, increased pulse pressure, and in severe cases, congestive heart failure. It is easily misdiagnosed as aortic valve insufficiency due to other causes.
(6) Pleural effusion. The intercalated layer may break into the thoracic cavity and cause accumulation of blood in the chest cavity, resulting in chest pain, dyspnea or hemoptysis, etc. It may also be accompanied by hemorrhagic shock. Some of the effusion can be caused by the inflammatory exudative reaction of the diseased aorta.
(7) Pericardial tamponade. It is the most serious complication of proximal AD and is commonly seen in type I and II AD. Most of the proximal clips break into the pericardial cavity and produce pericardial effusion. Patients become unconscious, extremely agitated, dyspnea, jugular venous anger, and hypotension, which often leads to sudden death.