Differential Transesophageal Echocardiographic Diagnosis Between Linear Artifacts and Intraluminal Flap of Aortic Dissection or Disruption: Origins of Linear Artifacts
Using in vitro experiments, Appelbe et al confirmed the origin of multiple-path linear artifact by imaging two water-filled latex balloons of varying size placed in series in a water tank. A linear artifact was only observed within the balloon representing the ascending aorta when its size exceeded that of the second balloon representing the left atrium. In addition, the distance between the transducer and balloon interface was equal to the distance separating this interface from the linear artifact. Using M-mode echocardiography, Evangelista et al recently described three distinct types of linear artifacts within the ascending aorta: type-A artifacts (53%), which were located twice as far from the transducer as the posterior aortic wall; type-B artifacts (40%), which were located at the same distance from the posterior aortic wall as the latter was from the right pulmonary posterior wall; and type-C artifacts (7%), which were located at the same distance from the posterior aortic wall as a reverberation from the right pulmonary artery posterior wall. All these artifacts exhibited a movement parallel to the posterior aortic wall, as in the current series. The reverberation images observed in the present study were type A (Fig 6, left, A) and type B (Fig 1, center, B; Fig 3, bottom right, D; Fig 4, top left, A) artifacts. Type-A artifacts are thought to be generated when the echo of the posterior aortic wall is partly reflected back by the transducer,’ while type-B artifacts correspond to ultrasound reverberations from a moving target (ie, the right pulmonary posterior wall) and a moving mirror (ie, the posterior aortic wall). canadian health care mall
The origin of type-A and type-B artifacts was confirmed in vivo in the present study. In patients with intraluminal linear artifacts, the diameter of the ascending aorta consistently exceeded that of the adjacent posterior anatomic structure (diameters ratio > 1), and was significantly greater than that seen in patients without intra-aortic linear images. As a result, reverberation images were more commonly observed when relative aortic dilatation was present (Fig 6, left, A), a finding commonly associated with aortic dissection. These results are in keeping with those recently reported by Losi et al, who showed that a diameter of the ascending aorta (> 5 cm) that exceeds the diameter of the left atrium (with a ratio < 0.6), was predictive of the presence of an underlying linear artifact. In addition, in our patients with intra-aortic linear artifacts, the mean distance between the transducer (type-A artifacts), or the posterior wall of the right pulmonary artery (type-B artifacts), and the posterior wall of the ascending aorta was similar to that separating the latter wall from the leading edge of the intraluminal image (28.8 ± 6.1 mm vs 28.6 ± 5.7 mm; p = 0.9; Fig 1, center, B; Fig 3, bottom right, D; Fig 4, top left, A; Fig 6, left, A). Similarly, Losi et al reported that linear artifacts were consistently located in the aortic lumen twice as far from the transducer as the posterior aortic wall, such as type-A artifacts.
In patients with linear artifacts within the descending thoracic aorta, the mean diameter of this vessel was similar to that of patients without reverberation images. However, in the presence of misleading linear artifacts, the descending thoracic aorta was consistently shifted anteriorly. This explains probably the higher incidence of linear artifacts within the descending thoracic aorta in patients with severe blunt chest trauma in whom a traumatic hemomediastinum, which usually results in an increased distance between the esophageal probe and the anteromedial aortic wall, was frequently observed (Fig 5, top left, A; Fig 6, right, B). Because hemomediastinum is frequently associated with TDA, accurate diagnosis of linear artifacts within the aortic isthmus in this clinical setting is critical to avoid false-positive TEE results.