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.