Transesophageal echo (TEE) in COVID-19: a new outlook
TEE offers multiple advantages including better imaging windows by
virtue of the TEE probe being close to the cardiac chambers and great
vessels compared with conventional TTE probes. In addition, TEE is not
hampered by other factors such as high PEEP positive ventilation, prone
position, body habitus, and emphysematous lungs that constitute a
limiting factor for obtaining good images by TTE [55,56]. Studies
demonstrated that superior vena caval (SVC) collapsibility index is
superior to IVC distensibility index in predicting fluid
responsiveness[57,58]. As TEE is generally required to measure SVC
collapsibility, it is inherently able to predict volume status much
better than TTE among critically ill patients. Given the fact that ECHO
is the modality of choice in investigating cardiogenic shock[59],
TEE could help in providing real time information regarding LV function,
trends of quantitative indices under acute therapy and whether or not
cardiac dysfunction is acute and reversible (as in septic
cardiomyopathy) [60]. With the challenges of volume resuscitation
among COVID-19 patient with ARDS, TEE may prove to be an important tool
in fluid management.
TEE is also essential in identification of acute cor pulmonale (ACP) as
it provides the necessary short axis view of the heart required to
identify ACP[56]. With regards to assessing RV systolic function,
the RV fractional area change (FAC) measured by TEE is still considered
the best parameter for measurement [61]. However, the measurement of
an accurate RV FAC requires the entire endocardium to be clearly
visible, which is sometimes difficult in patients who develop ACP and
are on mechanical ventilation. In this subset of patients, measurement
of the tricuspid longitudinal annular displacement (TMAD), a
bi-dimensional strain parameter that tracks the tricuspid annular tissue
motion toward the RV apex, thereby allowing an objective quantitative
assessment of RV systolic function may be helpful[62]. TMAD is also
angle independent and is unaffected by endocardial definition, which
further adds to its ability to identify and quantify RV systolic
dysfunction in patients in whom a traditional FAC measurement would be
difficult. In a study by Beyls et al, a TMAD at the RV free wall
(TMADlat) cutoff value of 18.5 mm was found to be statistically
significant in identifying RV systolic dysfunction as compared with RV
GLS. The sensitivity and specificity of TMADlat in identifying RV
systolic dysfunction were 80% and 70%, respectively and the
intraobserver reproducibility of TMADlat was excellent (intraclass
correlation coefficient = 0.98 [0.93 to 0.99]), thereby, adding
support for the use of this measurement in COVID-19 patients to identify
RV systolic dysfunction[63].
Recent international guidelines recommend the use of ECMO therapy in
patients with severe ARDS due to COVID-19 who have failed mechanical
ventilation[64,65]. Pre-procedure TEE plays a fundamental role in
ECMO initiation as it can identify unexpected and reversible findings
while ruling out severe valvular abnormalities that may affect the
success of venovenous(VV) or venoarterial(VA) ECMO therapy. In addition,
the presence of severe LV dysfunction identified by TEE before placement
of ECMO prompts consideration of VA ECMO instead of VV ECMO[66,67].
Embryologic remnants of right heart structures or other congenital
abnormalities may affect the safe and appropriate placement of venous
cannulas during ECMO initiation. A persistent left SVC leading to a
dilated coronary sinus may be accidentally cannulated, leading to
compromised oxygenation on ECMO. Similarly, a prominent Chiari network
may impede cannula positioning and may increase the risk of subsequent
thrombosis. TEE guidance can help confirm the course of a guidewire
during insertion and help in excluding coiling of the guidewire in the
right atrium, crossing of the guidewire across the interatrial septum or
its entrance in the coronary sinus. It can also ensure that the return
cannula is positioned clear of the interatrial septum and the tricuspid
valve, thereby reducing the risk for recannulation [67–71]. TEE can
also help identify the cause for worsening hypoxemia during ECMO which
includes scenarios where the cannula tips are too close to each other
causing recirculation, hypovolemia causing inadequate ECMO flow and
thrombus formation in the cannula which may be impeding adequate
flow[66].
Despite the numerous advantages TEE has over TTE, its performance is
difficult as there is a decreased availability of health care providers
who have adequate training and expertise in performing the procedure.
There is also an increased risk of aerosol exposure to healthcare
providers during a TEE when compared with a conventional TTE. Although,
obtaining expertise in TEE requires a lot of hands-on training,
competence in performing TEE for assessing central hemodynamics can be
achieved in a short span of time after approximately 35 examinations.
This number is based on the international consensus statement on
training standards for advanced critical care ECHO citing evidence from
a prospective, multicentric trial that validated the number of TEEs
required to be performed to gain competence in monitoring central
hemodynamics[72,73]. Adoption of adequate personal protective
measures as per current guidelines should lead to a decreased risk of
acquiring transmissible diseases while performing TEE[15].