Fig. 4.2. Mechanisms of aortic regurgitation in aortic dissection. A. Circumferential tear with widening of aortic root and separation of aortic cusps. B. Displacement of one aortic cusp substantially below the level of the others by the pressure of the dissecting hematoma. C. Actual disruption of the annular leaflet support leading to a flail cusp. (Reproduced with permission from Slater EE. Aortic dissection: presentation and diagnosis. In: Doroghazi RM, Slater EE, eds. Aortic Dissection. New York: McGraw-Hill, 1983: 61-70.)

Classically, acute dissection is associated with severe, lancinating chest or interscapular pain with craniad or cephalad migration. Although the patient appears shocky with poor peripheral perfusion, the blood pressure is frequently elevated. Other symptoms and signs relate largely to which distal aortic tributaries become involved. Potentially fatal complications are those related to aortic rupture and aortic branch compression by the dissecting hematoma, leading to compromised end-organ perfusion. A complete examination of all peripheral pulses is critical, and blood pressure in both arms and legs should be assessed. A full neurologic examination is performed. If the patient is hypotensive, aortic rupture should be suspected.

The best diagnostic test is that which can be performed accurately and expeditiously in a given hospital. A chest radiograph is usually nondiagnostic. The goal of the initial diagnostic modality is to confirm the diagnosis of dissection and determine whether the ascending aorta is involved. Involvement of the ascending aorta can be determined with a high degree of accuracy using TEE, contrast-enhanced CT, MRI and aortography. TEE has emerged as a critical diagnostic tool and can determine the type and extent of the aortic dissection (Fig. 4.3). TEE remains limited in its inability to visualize the distal ascending aorta or superior transverse arch. Also, there may be artifacts leading to a falsely positive result in patients with large ascending aortas. CT is also reasonably accurate in the diagnosis of aortic dissection and can provide anatomic information for classification; however, it cannot consistently define the intimal tear (Fig. 4.4). MRI is highly accurate in the diagnosis of aortic dissection and provides delineation of the pathoanatomy (Fig. 4.5). Its main disadvantage, however, is that it cannot be performed in patients who are hemody-namically unstable and are on ventilatory support. Aortography is highly accurate in

Fig. 4.3. Transesophageal echocardiographic image demonstrating a dissection flap separating the true and false lumens in a patient with acute type B dissection.
Fig. 4.4. Contrast-enhanced computed tomographic scan of a patient with an acute type B dissection.
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