Aortic Dissection

Decision Points

Aortic dissection is a tear in the wall of the aorta that causes blood to flow between the layers of the wall of the aorta and force the layers apart. Aortic dissection is a medical emergency and can quickly lead to death, even with optimal treatment. If the dissection tears the aorta completely open (through all three layers), massive and rapid blood loss occurs. Aortic dissections resulting in rupture have an 80% mortality rate, and 50% of patients die before they even reach the hospital. If the dissection reaches 6 cm, the patient must be taken for emergency surgery.

 As with all other arteries, the aorta is made up of three layers, the intima, the media, and the adventitia. The layer that is in direct contact with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. The next layer is known as the tunica media, or the muscular layer. It is composed of a mixture of smooth muscle cells and elastic fibers. The outermost layer is the tunica adventitia or the adventitia. This layer is composed of connective tissue.

In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure rips the tissue of the media apart along the laminated plane splitting the inner 2/3 and the outer 1/3 of the media apart. This can propagate along the length of the aorta for a variable distance forward or backwards. Dissections that propagate towards the iliac bifurcation (with the flow of blood) are called anterograde dissections and those that propagate towards the aortic root (opposite of the flow of blood) are called retrograde dissections. The initial tear is usually within 100 mm of the aortic valve so a retrograde dissection can easily compromise the pericardium leading to a hemocardium. Anterograde dissections may propagate all the way to the iliac bifurcation of the aorta, rupture the aortic wall, or recanalize into the intravascular lumen leading to a double barrel aorta. The double barrel aorta relieves the pressure of blood flow and reduces the risk of rupture. Rupture leads to hemorrhaging into a body cavity and prognosis depends on the area of rupture. Retroperitoneal and pericardial ruptures are both possible.

About 96% of individuals with aortic dissection present with severe pain that had a sudden onset. It may be described as tearing in nature, or stabbing or sharp in character. 17% of individuals will feel the pain migrate as the dissection extends down the aorta. The location of pain is associated with the location of the dissection. Anterior chest pain is associated with dissections involving the ascending aorta, while interscapular (back) pain is associated with descending aortic dissections. If the pain is pleuritic in nature, it may suggest acute pericarditis caused by hemorrhage into the pericardial sac. This is a particularly dangerous eventuality, suggesting that acute pericardial tamponade may be imminent.

While the pain may be confused with the pain of a myocardial infarction (heart attack), aortic dissection is usually not associated with the other signs that suggest myocardial infarction, including heart failure, and ECG changes. Also, individuals suffering from an aortic dissection usually do not present with diaphoresis (profuse sweating).

Individuals with aortic dissection who do not present with pain have chronic dissection.

Less common symptoms that may be seen in the setting of aortic dissection include congestive heart failure (7%), syncope (9%), cerebrovascular accident (3-6%), ischemic peripheral neuropathy, paraplegia, cardiac arrest, and sudden death. If the individual had a syncopal episode, about half the time it is due to hemorrhage into the pericardium leading to pericardial tamponade.

Neurologic complications of aortic dissection (i.e., cerebrovascular accident (CVA) and paralysis) are due to involvement of one or more arteries supplying portions of the central nervous system.

If the aortic dissection involves the abdominal aorta, compromise of the branches of the abdominal aorta is possible. In abdominal aortic dissections, compromise of one or both renal arteries occurs in 5–8% of cases, while mesenteric ischemia (ischemia of the large intestines) occurs 3–5% of the time.

Source:wikipedia