| disease | Aortic Dissection |
| alias | Aortic Dissection Aneurysm, Aortic Dissection, Aortic Dissection Hematoma, Aortic Dissection, Aortic Dissecting Hematoma, Aortic Dissecting Aneurysm |
Aortic dissection refers to the formation of a hematoma when blood in the aortic cavity enters the middle layer of the aortic wall through a tear in the inner membrane, rather than the dilation of the aortic wall. This condition differs from an aortic aneurysm. Previously, it was referred to as an aortic dissecting aneurysm, but it is now more commonly called an aortic dissecting hematoma or aortic dissection, often abbreviated as aortic dissection.
bubble_chart Etiology
The cause of the disease remains unclear to this day. Over 80% of patients with aortic dissection have hypertension, and many also exhibit cystic medial necrosis. Hypertension is not the direct cause of cystic medial necrosis but can accelerate its progression. Clinical and animal studies have shown that it is not the absolute level of blood pressure but rather the amplitude of blood pressure fluctuations that correlates with aortic dissection. In animal experiments, feeding pigs with lathyrus peas can induce aortic dissection, as the β-aminopropionitrile in lathyrus peas affects the aortic matrix, medial muscle, and elastic tissues, rendering the aorta fragile. Similarly, feeding mice with aminoacetonitrile and deoxycorticosterone can also lead to aortic dissection. A copper-deficient diet in animals impairs the synthesis of elastin, producing similar outcomes. In the genetic disorder Marfan syndrome, cystic medial necrosis of the aorta is quite common, increasing the likelihood of aortic dissection. Other genetic conditions, such as Turner syndrome and Ehlers-Danlos syndrome, also predispose individuals to aortic dissection. Aortic dissection is also more likely to occur during pregnancy, though the reason is unknown. It is speculated that endocrine changes during pregnancy alter the aortic structure, making it more prone to tearing.
The aortic wall in normal adults can withstand significant pressure, requiring over 66.7 kPa (500 mmHg) to cause an intramural tear. Therefore, a prerequisite for dissection is a defect in the aortic wall, particularly in the medial layer. In older individuals, degenerative changes in the medial muscle are the primary issue, while in younger individuals, the lack of elastic fibers is more prominent. In rare cases of aortic dissection without an intimal tear, the cause may be intramural hemorrhage due to rupture of vasa vasorum within areas of medial degeneration. The coexistence of atherosclerosis can also contribute to the occurrence of aortic dissection.bubble_chart Pathological Changes
The basic lesion is cystic medial necrosis. In the stirred pulse, there is localized fragmentation or necrosis of the medial elastic fibers, with mucoid and cystic changes in the matrix. Dissection often occurs in the ascending stirred pulse, where the impact of blood flow is greatest, while the distal portion of the stirred pulse arch shows fewer and milder lesions. The stirred pulse wall splits into two layers, with blood and clots accumulating between them, causing the stirred pulse to expand significantly, taking on a spindle or sac-like shape. If the lesion involves the stirred pulse valve ring, the ring expands, leading to stirred pulse valve insufficiency. The lesion can extend from the root of the stirred pulse to distant areas, reaching as far as the iliac stirred pulse and femoral stirred pulse, and may also affect various branches of the stirred pulse, such as the innominate stirred pulse, common carotid stirred pulse, subclavian stirred pulse, and renal stirred pulse. The coronary stirred pulse is generally unaffected, but the dissecting hematoma at the root of the stirred pulse may compress the coronary stirred pulse orifice. Most dissections originate from a transverse tear in the inner membrane, often located above the stirred pulse valve. There may also be two tears, connecting the dissection to the stirred pulse lumen. In a few cases, the inner membrane remains intact without tears. In some cases, rupture of the outer membrane causes massive hemorrhage, with ruptures typically occurring in the ascending stirred pulse. Bleeding can easily enter the pericardial cavity, while ruptures at lower sites may enter the mediastinum, pleural cavity, or retroperitoneal space. Chronic dissections may form a double-lumen stirred pulse, with one channel nested inside another, commonly seen in the thoracic stirred pulse or the descending branch of the stirred pulse arch. DeBakey classified stirred pulse dissections into three types: Type I originates in the ascending stirred pulse and extends to the descending stirred pulse, Type II is confined to the ascending stirred pulse, and Type III starts in the descending stirred pulse and extends distally.
bubble_chart Clinical Manifestations
The manifestations vary depending on the location of the lesion, with the main symptoms as follows:
(1) Pain When the dissection occurs suddenly, most patients experience abrupt chest pain that radiates to the front of the chest and back. As the dissection extends, the pain may spread to the abdomen, lower limbs, arms, and neck. The pain is severe and unbearable, reaching its peak immediately after onset, often described as knife-like or tearing. In rare cases with a slow onset, the pain may be mild.
(2) Hypertension Patients may exhibit signs of shock due to severe pain, such as anxiety, profuse sweating, pale complexion, and rapid heart rate. However, blood pressure is often not low or may even be elevated. If the outer membrane ruptures and bleeds, blood pressure may drop. Many patients have pre-existing hypertension, and the severe pain upon onset can further elevate blood pressure.
(3) Cardiovascular symptoms ① Aortic valve insufficiency. This occurs when the dissecting hematoma involves the aortic valve ring or affects the support of the heart valve leaflets, leading to the sudden appearance of a diastolic blowing murmur in the aortic valve area, widened pulse pressure, and acute aortic regurgitation, which can cause heart failure. ② Pulse changes, typically observed in the carotid, brachial, or femoral arteries, where the pulse on one side weakens or disappears, indicating compression of the aortic branch or obstruction by an intimal flap. ③ Pulsation may appear at the sternoclavicular joint or a pulsatile mass may be palpable in the suprasternal fossa. ④ A pericardial friction rub may be present; rupture of the dissection into the pericardial cavity can cause cardiac tamponade. ⑤ Pleural effusion may occur if the dissection ruptures into the pleural cavity.
(5) Compression symptoms Compression of the abdominal artery or mesenteric artery by the aortic dissection can cause nausea, vomiting, abdominal distension, diarrhea, melena, and other symptoms. Compression of the cervical sympathetic ganglion may result in Horner's syndrome; compression of the recurrent laryngeal nerve can cause hoarseness; compression of the superior vena cava may lead to superior vena cava syndrome. Involvement of the renal artery can cause hematuria, anuria, and elevated blood pressure due to renal ischemia.
bubble_chart Auxiliary Examination
(1) Electrocardiogram (ECG) may show left ventricular hypertrophy and nonspecific ST-T changes. When the coronary artery is involved, acute myocardial ischemia or even acute myocardial infarction changes may appear. In cases of pericardial effusion, ECG changes consistent with acute pericarditis may be observed.
(2) X-ray Chest radiographs may reveal an enlarged superior mediastinum or aortic arch, with irregular aortic contours and localized bulging. If calcification of the aortic intima is visible, the thickness of the aortic wall can be accurately measured. Normally, it ranges from 2–3 mm; if it increases to 10 mm, aortic dissection is likely, and if it exceeds 10 mm, the diagnosis is confirmed. Aortography can identify the location of the tear, clarify branch involvement and aortic valve status, and assess the severity of aortic regurgitation. However, it is an invasive procedure with associated risks. CT can demonstrate aortic dilation and detect intimal calcification more effectively than plain X-rays. If calcified intima shifts inward, it suggests aortic dissection; if it shifts outward, it indicates a simple aortic aneurysm. CT can also reveal an intimal flap caused by aortic intimal tearing, dividing the aorta into true and false lumens. CT is highly accurate for diagnosing descending aortic dissection, but due to aortic tortuosity in the ascending and arch segments, false positives or negatives may occur. However, CT struggles to determine the tear location and branch vessel involvement and cannot assess aortic regurgitation.
(3) Echocardiography This is crucial for diagnosing ascending aortic dissection and easily identifies complications (e.g., pericardial effusion, aortic regurgitation, and hemothorax). M-mode echocardiography may show aortic root dilation, with the dissected aortic wall appearing as two separated echo bands instead of one. Two-dimensional echocardiography can visualize the oscillating intimal flap and the true and false lumens of the dissection. Pericardial or pleural effusion may also be detected. Doppler echocardiography not only identifies abnormal blood flow between the dual echoes of the dissected aortic wall but also provides valuable diagnostic information on dissection classification, tear location, and quantification of aortic regurgitation. Transesophageal echocardiography combined with real-time color flow imaging is reliable for evaluating ascending aortic dissection and also has high specificity and sensitivity for descending aortic dissection.
(4) Magnetic Resonance Imaging (MRI) MRI directly visualizes the true and false lumens of aortic dissection, clearly displaying the intimal tear location, dissected intimal flap, or thrombus. It determines the dissection extent, classification, and relationship with aortic branches. However, its limitations include high cost, inability to directly assess aortic regurgitation, and contraindication in patients with pacemakers or metallic implants (e.g., artificial joints or metal pins).
(5) Digital Subtraction Angiography (DSA) Noninvasive DSA is accurate for diagnosing type B aortic dissection, identifying the dissection location and extent, and sometimes visualizing the torn intimal flap. However, its diagnostic value is limited for type A dissections. DSA also reveals aortic hemodynamics and branch perfusion and can detect calcifications not visible on conventional angiography.
(6) Blood and Urine Tests White blood cell count often rises rapidly. Hemolytic anemia and jaundice may occur. Red blood cells may appear in the urine, even gross hematuria.
Sudden onset of severe chest pain, hypertension, sudden aortic regurgitation, unequal pulses in both limbs, or presence of a pulsatile mass should raise suspicion of this condition. Chest pain is often considered as acute myocardial infarction, but in myocardial infarction, the chest pain usually starts mildly and gradually worsens, or subsides before intensifying again. It does not radiate below the chest and can be relieved with analgesics, accompanied by characteristic ECG changes. If shock is present, blood pressure is typically low, and unequal pulses are not observed. These points are sufficient for differentiation.
In recent years, various diagnostic methods have greatly aided in confirming aortic dissection. Echocardiography, CT scans, and magnetic resonance imaging can all be used for diagnosis. However, aortography remains essential for those being considered for surgery.
bubble_chart Treatment Measures
Once suspected or diagnosed with this disease, the patient should be immediately hospitalized for monitoring and treatment. The goals of therapy are to reduce myocardial contractility, slow the left ventricular contraction velocity (dv/dt), and lower the peripheral arterial pulse pressure. The treatment targets are to maintain systolic blood pressure between 13.3–16.0 kPa (100–120 mmHg) and heart rate between 60–75 beats/min. This effectively stabilizes or halts the continued dissection of the aortic dissection, alleviates symptoms, and eliminates pain. Treatment is divided into two stages: emergency treatment and consolidation therapy.
(1) Emergency Treatment: ① Pain relief: Administer morphine and sedatives. ② Volume replenishment: Transfuse blood if there is bleeding into the pericardium, pleural cavity, or aortic rupture. ③ Blood pressure reduction: For hypertensive patients, propranolol 5 mg can be administered intravenously intermittently along with sodium nitroprusside infusion at 25–50 µg/min, adjusting the infusion rate to lower blood pressure to the clinical target. A significant reduction or disappearance of pain after blood pressure reduction is a clinical indicator that the dissection has stopped expanding. Other medications such as verapamil, nifedipine, captopril, and prazosin may also be used. Reserpine 0.5–2 mg intramuscularly every 4–6 hours is also effective. Additionally, labetalol, which has dual α- and β-blocking effects and can be administered intravenously or orally, may be used. Important considerations: Hypertensive patients with obstruction of major aortic branches should not undergo blood pressure reduction as it may worsen ischemia. For patients without hypertension, blood pressure-lowering drugs should not be used, but propranolol can be administered to reduce myocardial contractility.
(2) Consolidation Therapy: Surgical intervention is indicated for proximal aortic dissection, ruptured or impending rupture of aortic dissection, or patients with aortic valve insufficiency. For slowly progressing or distal aortic dissection, medical therapy may be continued. Maintain systolic blood pressure at 13.3–16.0 kPa (100–120 mmHg). If the aforementioned medications are ineffective, captopril 25–50 mg orally three times daily may be added.
Most cases die within hours to days after onset, with an hourly mortality rate of 1-2% in the first 24 hours, depending on the location, extent, and severity of the lesion. The prognosis is better for lesions that are more distal, smaller in extent, and involve less bleeding.
