Aortic dissection is the formation of a wall dissection in the aorta, which used to be called dissection aortic aneurysm. It refers to the rupture of the intima of the aortic wall caused by various reasons, and the blood flow enters the aortic wall, resulting in the delamination of the vessel wall and the formation of a “double-lumen aorta” by the separation of the peeled intima. However, Coady reported that in 8% to 15% of cases, there is no intimal tear, which may be due to bleeding in the middle layer of the aortic wall, also known as intermural hematoma.
1. Sudden and severe pain
This is the most common symptom at the onset, seen in more than 90% of patients, and has the following characteristics.
(1) The intensity of pain is more characteristic than its location: the pain is extremely intense and unbearable from the beginning; the nature of pain is pulsating, tearing or cutting, and is often accompanied by vaso-vagal excitation manifestations, such as profuse sweating, nausea and vomiting, and syncope.
(2) The site of pain helps to suggest the starting site of separation: severe pain in the anterior chest mostly occurs in the proximal entrapment, while the most severe pain in the interscapular region is more often seen in the starting distal entrapment; although the proximal and distal entrapments can feel pain in the anterior chest and back at the same time, if there is no pain in the interscapular region behind, the distal entrapment can be excluded because more than 90% of the patients with distal entrapment have back pain; pain in the neck, pharynx, frontal The pain in the neck, pharynx, forehead, or teeth often suggests that the entrapment involves the ascending aorta or the aortic arch.
(3) Wandering pain sites suggest an expanding aortic entrapment: pain can move from the starting site to other sites, often following a detached path and direction, causing head and neck, abdominal, lumbar, or lower extremity pain, a feature that is present in approximately 70% of patients. It also causes dysfunction of the adjacent organs of each branch of the aorta due to the expansion of the extent of the entrapped hematoma.
(4) Pain is often persistent: in some patients, pain persists from the onset until death and is difficult to be relieved by analgesics such as morphine; in some cases, the pain disappears due to the rupture of the distal endothelium of the entrapment so that the blood in the entrapment hematoma returns to the aortic lumen; if the pain disappears and then recurs, one should be alert to the risk of the aortic entrapment continuing to expand and rupture outward again; in a few patients without pain, there is a tendency for the early onset of A few painless patients have painful symptoms masked by syncope or coma in the early stage of the disease.
2. Hypertension
Patients have the appearance of shock due to severe pain, anxiety, profuse sweating, pale face and accelerated heart rate, but blood pressure is often not low or increased. Many patients with pre-existing hypertension have higher blood pressure due to pain after the onset of the disease. Hypotension, often as a result of pericardial filling, pleural cavity or peritoneal cavity rupture due to the separation of the sandwich, and when the sandwich involves the head and arm vessels so that the limb arteries are damaged or occluded, the blood pressure cannot be accurately measured and pseudo hypotension occurs.
3.Symptoms of entrapment rupture or compression
The clinical manifestations of multi-system damage occur due to the compression of the surrounding soft tissues by the entrapment hematoma, which spreads to the large branches of the aorta or breaks into the adjacent organs causing damage to the corresponding organ systems.
(1) Cardiovascular system.
(1) Aortic regurgitation: Aortic regurgitation is one of the important features of proximal aortic coarctation, which can appear as a diastolic murmur in the aortic valve area, often music-like, more clearly along the left edge of the sternum, and can vary in intensity with high and low blood pressure. Depending on the degree of regurgitation, other peripheral vascular signs of aortic valve insufficiency may also be present, such as widened pulse pressure or watery veins, and heart failure may occur in acute severe aortic valve insufficiency. The mechanism of aortic valve closure insufficiency due to proximal coarctation has four aspects.
A, entrapment causes dilatation of the aortic root, enlargement of the annulus, and failure of the aortic valve leaflets to close during diastole.
B, in asymmetric coarctation, the coarctation hematoma compresses one valve leaflet below the closing line of the other valve leaflets, resulting in incomplete closure.
C, a tear in the valve leaflet or annular stent that leaves one valve leaflet free or in a shackle, resulting in incomplete valve closure.
D, entrapment hematoma tearing the endothelial sheet free below the aortic valve leaflet, affecting aortic valve closure.
②Pulse abnormalities: half of the proximal entrapment may involve the head and arm vessels, and a few distal entrapments may involve the left subclavian artery and femoral artery, resulting in signs of vascular obstruction such as a weakened or absent pulse, or unequal strength on both sides, or a marked difference in blood pressure between the two arms, or a reduced blood pressure gap between the upper and lower extremities. The reason for this is either due to direct compression of the arterial lumen by the extension of the entrapment
(2) The obstruction of blood flow is either due to direct compression of the arterial lumen or due to the torn endothelial sheet covering the vessel opening (Figure 3).
(3) Other cardiovascular damage manifestations: angina pectoris or myocardial infarction may occur when the entrapment involves the coronary artery; superior vena cava syndrome may occur when the hematoma compresses the superior vena cava; when the entrapment hematoma ruptures into the pericardial cavity, it may rapidly cause pericardial blood accumulation, leading to acute pericardial tamponade and death.
(2) Nervous system.
If the clotted hematoma extends upward along the innominate artery or common carotid artery or involves the intercostal artery or vertebral artery, dizziness, confusion, limb numbness, hemiparesis, paraplegia and coma may occur; compression of the recurrent laryngeal nerve may lead to hoarseness; compression of the cervical sympathetic ganglion may lead to Horner’s syndrome, etc.
(3) Digestive system.
If the entrapment involves the abdominal aorta and its branches, the patient may experience severe abdominal pain, nausea, vomiting and other manifestations similar to acute abdomen; if the entrapment hematoma compresses the esophagus, swallowing may be impaired, and if it breaks into the esophagus, it may cause hematemesis; if the hematoma compresses the superior mesenteric artery, it may cause ischemic necrosis of the small intestine and blood in the stool.
(4) Urinary system.
The entrapment involves the renal artery, which may cause back pain and hematuria. Acute ischemia of the kidney may cause acute renal failure or renal hypertension, etc.
(5) Respiratory system.
Intercalated hematoma breaking into the thoracic cavity may cause accumulation of blood in the thoracic cavity, chest pain, dyspnea or hemoptysis, etc., sometimes accompanied by hemorrhagic shock.
The main treatment of aortic coarctation is to prevent the extension of the aortic coarctation, because its fatal complication is not the coarctation extension itself, but the consequences caused by the coarctation extension. In the early 1980s, Wheat summarized previous experience and proposed a generally accepted “standard” treatment protocol, namely Drug therapy or concomitant surgical treatment. In recent years, there have been significant advances in both pharmacological and surgical treatment.
Internal pharmacological treatment focuses on two main areas: (i) lowering systolic blood pressure; and (ii) lowering left ventricular ejection velocity (dp/dt). The latter is thought to be an important factor in the formation and extension of aortic coarctation in the aortic wall. Initially, medical drug therapy was only used for patients with severe disease that could not tolerate surgery, but today, medical therapy is the basis of early treatment for all patients with aortic coarctation until a clear diagnosis is made on imaging, and can also be used as a long-term treatment for some patients.
1.Early emergency treatment
All patients with high suspicion of aortic coarctation should be admitted to the emergency care unit immediately and monitored for blood pressure, heart rate, central venous pressure, urine output and, if necessary, small pulmonary artery wedge pressure and cardiac output. The goal of early treatment is to reduce pain and promptly lower systolic blood pressure to 100-110 mmHg or to a low level sufficient to maintain perfusion of vital organs such as the heart, brain, and kidneys. At the same time, β-blockers should be given regardless of systolic hypertension or pain to control the heart rate at 60-75 bpm to reduce arterial dp/dt, so that the continued expansion of aortic coarctation can be effectively stabilized or aborted. To this end, guanethidine and lisdexamfetamine were used in the 1970s, and camphor sulfamethoxazole (Alfannate) was commonly used in the early 1980s, but these drugs have large side effects and are prone to drug resistance.
In recent years, foreign countries generally believe that the propranolol (insulin) intravenous intermittent administration and sodium nitroprusside intravenous combination is a more ideal program, the former to reduce dp / dt, the latter to reduce blood pressure. Sodium nitroprusside can be 50-100mg added to 5% glucose 500ml, start with 20μg/min speed drip, according to the blood pressure response to adjust the dose, the maximum dose up to 800μg/min, generally use time not more than 48h, high dose or long-term use can cause nausea, irritability, drowsiness, hypotension and cyanide-like or thiocyanate-like toxic effects. The first maximum dose of propranolol (insulin) should not exceed 0, 15mg/kg (also recommended to be given intravenously at a test dose of 0, 5mg), and propranolol (insulin) should be given intravenously again every 4-6 hours to maintain the appropriate beta-blocker effect, usually slightly lower than the first dosage, i.e. 2-6mg. in patients with chronic stable aortic coarctation, oral propranolol (insulin) can be given The contraindications are bradycardia, conduction block, heart failure, or asthma. Other beta-blockers are equally effective, especially those that act selectively on the heart, such as atenolol (Atenolol) and metoprolol (Metoprolol). The disadvantages of the above-mentioned regimens are that they require continuous blood pressure monitoring and also require infusion pumps to regulate medication administration, etc., which is even less conducive to transporting patients.
Pathogenesis
1. Cystic degeneration of the middle layer of the aorta
Degenerative changes in the middle layer of the aorta, i.e. degenerative degeneration of collagen and elastic tissue, often with cystic changes, are considered to be a prerequisite for aortic coarctation. Cystic midlayer degeneration is an intrinsic feature of genetic defects in connective tissue and is particularly seen in Marfan syndrome and Ehler-Danlos syndrome. Aortic coarctation, especially proximal coarctation, is often a serious and common complication of Marfan syndrome, which has been reported in 6-9% of patients with aortic coarctation. More recently, aortic coarctation has also been reported in patients with Noonan and Turner syndromes, where cystic mid-layer degeneration may be a common problem. There is an unexplained relationship between pregnancy and aortic coarctation. about half of the aortic coarctations in women under 40 years of age occur during pregnancy and tend to occur within the second trimester or early in the puerperium, and women with Marfan syndrome and aortic root dilatation have an increased risk of acute aortic coarctation during pregnancy. Increased blood volume, cardiac output and blood pressure may also be risk factors during pregnancy, but have not been proven.
2. Hypertension
Hypertension is an important factor contributing to clamping. About half of those with proximal and almost all of those with distal aortic coarctation have hypertension, and all have elevated blood pressure during acute attacks, sometimes accompanied by an aortic atheromatous plaque ulcerated surface. Because long-term hypertension can cause smooth muscle cell hypertrophy, degeneration and mid-layer necrosis.
3.Trauma
Direct trauma can cause aortic coarctation, and blunt contusion can cause aortic coarctation due to local laceration and hematoma in the aorta. Intra-aortic cannulation or intra-aortic balloon counterpulsation cannulation can cause aortic coarctation. Cardiac surgery, such as aortic-coronary artery bypass grafting, can occasionally cause aortic coarctation.