Advantages Of Tee In Aortic Dissection

The major advantage of TEE as the optimal screening test is its ease of application at the bedside, which allows immediate and accurate diagnosis for the potential emergent surgical intervention. A TEE can generally be done within 10-15 minutes with very little preparation compared with angiography, computed tomographic scanning, and magnetic imaging, which may require 30 minutes to one hour to organize and perform, time that may be life threatening. Aortography and coronary arteriography can then be performed if there is a need to delineate the blood supply of vital organs or the coronary arteries or if the TEE is inconclusive especially if a penetrating ulcer is a consideration.

TEE has been used very successfully because of the high-quality imaging of the thoracic aorta. It provides a dynamic assessment of the intimal flap and of the presence and extent of luminal thrombus and an assessment of sites of communications. Erbel and the European Cooperative Study Group for Echocardiography4 published a multicenter study showing the diagnostic accuracy in 164 consecutive patients with suspected aortic dissection. The sensitivity and specificity were 99% and 98%, respectively, for TEE compared with 83% and 100%, respectively, for computed tomographic scanning, and 88% and 94%, respectively, for aortic angiography. Experienced operators in this study used only the monoplane TEE probe.

Hashimoto et al.33 have utilized the next generation biplane transesophageal probe and demonstrated that the intimal flap and entry site can be recognized in 100% of cases. Ballal et al.5 have shown the superior diagnostic yield with TEE for the diagnosis of the aortic dissection. However, their study was limited because of the use of aortography to exclude the diagnosis of dissection. Bansal et al.30 have shown the limitations of aortography and the improved diagnosis of dissection by TEE. A thrombosed false lumen, noncommunicat-ing dissection and equal flow in both the true and false lumen and intramural hematoma were all missed by aortography and correctly diagnosed by TEE. Keren et al.34 have shown that biplane and multiplane imaging provided better visualization of the arch and ascending aorta permitting highly reliable diagnosis of dissection with a sensitivity and specificity of 98% and 95%, respectively. The specificity for type A and type B dissection was 97% and 99%, respectively. However, it did not improve on the high degree of sensitivity, specificity, and accuracy reported by other investigators using monoplane

TEE4,5,30,32,33

Nienaber at al.35 and Moore et al.36 have demonstrated a lower specificity for the diagnosis of dissection by TEE. The sensitivity for the diagnosis of dissection was 97.7% and specificity was 76.9% in Nienaber's study. The authors, however, conceded that there is a learning curve for differentiating artifacts, and this can adversely affect the specificity of the TEE37. Moore et al.36 have also shown that overall specificity for the diagnosis of dissection by TEE was 88% and was slightly better for type A, compared with type B dissection (90% versus 80%). That study too may suffer from learning curve errors. It is important to know the technical limitations of TEE and their impact on diagnosis. Svenson et al.11 demonstrated that in 5% of their patients the dissection was not recognized despite multiple noninvasive imaging modalities and required aortography. These missed diagnoses were due to an inability to completely image an eccentric aortic aneurysm with a small intimal tear (but no flap) which was located in the far field.

Movsowitz et al.38 have demonstrated the additional benefit of using TEE to identify who might require aortic valve replacement or repair by assessing the mechanism of aortic regurgitation prior to surgery. They demonstrated that 16 of 22 patients with moderate to severe regurgitation had normal valve leaflets and the valve could be repaired in 15 patients.

TEE also has an important role in the follow-up of patients with aortic dissection. Mohr-Kahaly et al.39 followed 18 patients with aortic dissection by serial TEE performed in the outpatient setting. The TEE study showed the structure of the dissection, the surgical repair, and blood flow dynamics in the true and false lumen. It showed the evolution of the dissection in many patients; 25% having complications of either extension of the dissection (5%), dilatation of the aorta (11%), or aortic regurgitation (17%). In addition, in two patients, TEE documented healing of the dissection and obliteration of the false lumen with time. This study shows the potential application of TEE to follow up these patients for disease progression, healing, or the need for surgical intervention as an alternative to the more often used CT scan.

Thus, in a patient suspected of dissection both TTE and TEE provide reliable complementary information essential for clinical decision making. This information can be obtained within 10 to 15 minutes either at the bedside or in the emergency room. However, one should be aware of the pitfalls. When the diagnosis is elusive one should not hesitate to use other equally sensitive and specific diagnostic modalities such as spiral computed tomography or even MRI if the clinical condition permits.

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