The primary reason for TEE in critically ill patients in our institution is hemodynamic instability, which may result from hypotension, pulmonary edema, acute myocardial infarction, endocarditis, tamponade, trauma, or cardiogenic shock. Patients frequently present with shock syndrome that requires prompt intervention. Several reports show favorable results from the use of TEE in such patients. For example, of 44 patients with shock syndrome, only 48% were partially diagnosed by transthoracic echocardiography (TTE), whereas 100% were diagnosed with TEE. Critical information was obtained in 68%, with 30% undergoing urgent cardiac surgery (including mitral valve replacement, tamponade relief, correction of postinfarction ventricular septal rupture and aortic rupture, and closure of patent foramen ovale). Of the 4 patients with normal TEEs, all had a noncardiovascular cause of hemodynamic compromise, as established by other investigations. Pearson et al.11 reported similar success with different indications (aortic dissection, 29%; source of emboli, 26%; postinfarction complications, 10%); critically important clinical information, not seen on TTE, was obtained in 44%.
What is the best diagnostic procedure when aortic dissection is suspected?
Although magnetic resonance imaging (MRI) permits visualization of the thoracic aorta in multiple planes with high sensitivity, delay and transport of patients often pose problems. Moreover, multiple support systems, such as intravenous pumps, respirators, and monitors, make transport impossible or involve an unacceptably high risk. Newer generation computed tomography also has 95% accuracy but involves similar problems of transport and time for acquisition. TEE, on the other hand, is portable and quick, providing on-line interpretation. Transthoracic echocardiography has a sensitivity of 75-85%; sensitivity is lower for distal dissection. TEE has both a sensitivity and a specifity of 98%. TEE is also useful for detecting extracardiac complications of dissection, such as pericardial effusion (seen in -25%) and coronary artery dissection, as well as conditions that mimic dissection. Traumatic rupture of the aorta, as well as contained intimal disruption with thrombus, is also diagnosed by TEE, especially with multiplane imaging, with high sensitivity and specificity. Furthermore, TEE has the advantage of providing added diagnostic information, particularly in patients with chest trauma (e.g., from automobile accidents) that may result in pericardial effusions or hematomas, contusion, and infarction. Intravascular ultrasound also has gained popularity in diagnosing aortic dissection, especially in victims of trauma, but requires an invasive test as well as specialized training and equipment; it also lacks the advantage of additional echocardiographic data. More studies are needed to make direct comparisons.
TEE of proximal aortic dissection.