Differential Transesophageal Echocardiographic Diagnosis Between Linear Artifacts and Intraluminal Flap of Aortic Dissection or Disruption: Discussion

In this study, we describe comprehensive TEE criteria that allow accurate differentiation between intra-aortic linear artifacts and true aortic flaps, resulting in improved diagnostic specificity. This may have a relevant clinical impact when considering the high prevalence of multiple-path artifacts noted in our cohort of patients undergoing a TEE to rule out an acute aortic condition. Because these artifacts are mostly observed in the ascending aorta, the routine use of these criteria could potentially avoid additional diagnostic workup and unnecessary surgery. Finally, the origin of these multiple-path artifacts recently demonstrated in vitro was confirmed in the present study using in vivo TEE measurements.

Incidence of Intra-aortic Linear Artifacts
The incidence of linear artifacts within the ascending aorta has been reported to be as high as 44 to 55% in patients undergoing a TEE study to rule out an acute aortic abnormality. In the present series, the incidence of linear artifacts was lower (81 of 351 patients; 23%). This difference is conceivably due to the larger size of our study population and to our use of strict criteria to select artifacts that needed to be differentiated from true intimal or medial flaps. As a result, easily identifiable pitfalls, such as reverberations of aortic wall calcifications or comet tail artifacts, were not recorded. As previously reported, linear artifacts were less commonly present in the descending thoracic aorta, being identified in only 24 of 351 of our patients (7%) studied for an AD or TDA. Interestingly, these linear artifacts were more frequently observed in victims of severe blunt chest trauma at high risk for TDA (13 of 90 patients vs 11 of 261 patients; p < 0.001). This finding is of particular relevance because linear artifacts appear to be more frequent in the vicinity of the aortic isthmus, where TDA predominantly occur.
TEE Identification of Linear Artifacts
The presence of a thick linear image (> 2.5 mm) and similar blood flow velocities on both sides of the image were strong individual predictors of an underlying ultrasound reverberation artifact within the ascending aorta. Nevertheless, these TEE findings may be present in certain patients suffering from type-A AD. Indeed, when involving a substantial part of the media, aortic intimal flaps may at times appear as thick linear images, similar to multiple paths artifacts. In addition, blood flow velocities may be similar on both sides of the intimal flap, particularly when a large entry tear located in the proximal ascending aorta results in a circulating false channel. In these cases, the use of the remaining TEE diagnostic criteria associated with linear artifacts (ie, angle > 85°, and parallel displacement to the aortic walls) remains useful, because in the current series linear artifacts were consistently found to be nearly horizontal within the ascending aorta. In contrast, aortic flaps had various orientations across the vascular lumen. As previously described, intra-aortic artifacts did not display the oscillatory movement frequently seen in intraluminal flaps, but rather exhibited a regular displacement that was parallel to aortic walls. Using M-mode echocardiography, Evangelista et al demonstrated the clinical value of this sign to improve the diagnostic accuracy of TEE for the identification of ascending AD. Finally, the presence of oppositely directed blood flow in the two lumina delimited by the intra-aortic linear image is suggestive of an underlying AD.
In the current study, displacement of the intra-aortic linear image parallel to the aortic walls in conjunction with overimposition of blood flow with similar velocities on both sides of the suspect image were individually predictive of the presence of a linear artifact within the descending thoracic aorta. Importantly, these TEE criteria may not be as valid in patients with suspected TDA, in whom multiple paths linear artifacts were more frequently encountered. In this condition, medial flaps are usually thicker than the intimal flaps associated with AD because they commonly involve the entire depth of the medial layer of the aorta. Although the medial flap fails to delimit two distinct channels with different blood velocities, high-velocity blood flow turbulence is usually observed in the surroundings of the disrupted aortic wall. In contrast, a near-normal laminar descending aortic flow pattern is consistently noted in the presence of linear artifacts.- Finally, subadventitial TDA is frequently associated with false aneurysm formation, whereas the aortic contour usually remains normal in the presence of intraluminal linear artifacts.

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