Discussion
Tracheal sweep offers a reliable, easy, and reproducible method in patients of various sizes and levels of acuity to define aortic arch sidedness and may aid in ruling out double aortic arch, complementing the existing American Society of Echocardiography (ASE) protocol as a potentially helpful adjunct in challenging cases.
The importance of accurate diagnosis of aortic arch sidedness and other aortic anomalies has been well established, and current ASE protocol for diagnosis with echocardiography is known to be a reliable and consistent method.11 Despite this long history of experience, however, it has been reported that additional advanced imaging is often needed for correct diagnosis in up to 28% of patients with aortic arch anomalies.8 Madry et al demonstrated that echocardiographic diagnosis was particularly challenging in patients with left aortic arch and aberrant right subclavian artery, and in patients with double aortic arch. Clinical experience has also shown that determining arch anatomy with echocardiography can also be difficult in low-birthweight neonates and other patients who are critically unstable with limited ability for neck extension. The tracheal sweep method utilized in this study provides a complimentary technique that is easy to attain and can reliably establish arch anatomy without the need for advanced imaging. This technique is also able to diagnose arch anatomy in cases of aberrant subclavian arteries as it does not depend on a normal aortic arch branching pattern and may also improve the sensitivity of diagnosing double aortic arch.
Specific use of imaging the trachea with echocardiography has been described in limited fashion but is often considered to be difficult and has very limited evidence of its use as a reliable diagnostic method for aortic arch sidedness or presence of double aortic arch.6,7,12 This cohort demonstrated that, despite being air-filled, the trachea can be recognized by the classic echogenic appearance of the tracheal rings in a suprasternal (or high parasternal) parasagittal view. The trachea was seen in patients of all ages, sizes, and clinical conditions ranging from newborns with a BSA of 0.2 m2 to 17.9-year-old adolescents with BSA well above 2.0 m2. While a majority of the patients were imaged in the outpatient setting, the tracheal sweep method was shown to be successful in critically ill patients who were intubated in the neonatal and pediatric intensive care units with the endotracheal tube creating excellent contrast and serving as a surrogate for the trachea. This study was also able to demonstrate the feasibility of imaging the trachea in a wide variety of complex cardiac and non-cardiac pathologies. Visualization of the relationship between the trachea and aortic arch was even able to successfully diagnose arch sidedness in a patient without a right-SVC. With successful imaging of the trachea in 97% of time, the diagnosis of aortic arch sidedness was accurate every time the trachea was seen and there were no missed diagnoses of aortic arch anomalies. Excluding patients who had previous surgical intervention on their PAs, tracheal imaging was also able to successfully rule-out PA sling in nearly all patients.
The relative ease of this method is supported by the high rate of success achieved by an imager with very limited experience, in that nearly 90% of scans were completed by a cardiology fellow in their first year of fellowship with no prior echocardiographic experience. These images were also obtained without other standard echocardiographic views that can help orient an inexperienced sonographer, and nearly all studies were completed without the assistance of sedation or anesthesia. The notable limitations of tracheal imaging with echocardiography were in patients with particularly challenging acoustic windows that would have also limited standard echocardiographic methods.
It should be noted that this study primarily focused on the ability to reliably image the trachea and its relationship to the aortic arch and pulmonary artery bifurcation with echocardiography. This study was adequately powered to show significant success with this technique, and was not meant to compare superiority or non-inferiority to current methods in standard echo protocols as recommended by the ASE. In otherwise challenging cases, however, the tracheal sweep can be a helpful adjunct method to aid in making the correct diagnosis without needing to expose the patient to additional radiation via CT or sedation/anesthesia as is often needed for MRI. The percentage of patients with right aortic arch in this study is similar to previously reports population rates and all arch variants in this patient cohort were correctly diagnosed by tracheal sweep. Further study is needed to assess the success of the tracheal sweep method in diagnosing arch anomalies in cohorts with larger numbers of patients who have anomalous aortic arch anatomy or pulmonary artery sling. These techniques were also successfully utilized in many critically ill patients. However, it would also be beneficial to demonstrate this technique in larger numbers of critically ill patients.