Discussion
Coronavirus disease 19 (COVID- 19) pandemic has affected the medical
practice in general and the cardiology practice in particular.
It has been shown that prone ventilation can improve oxygenation in
patients with acute respiratory distress (ARDS) secondary to COVID-19.1
The use of TTE to assess the cardiovascular complications of COVID-19 is
very challenging on patients kept in the prone position.2
A recently published study by Marvaki et al.8 has showed the feasibility
of an innovative use of a TEE probe to perform TTE on patients with
COVID-19 who were invasively ventilated in the prone position. They have
concluded that the innovative use of a TEE probe to perform TTE in the
prone positioned and invasively ventilated ICU patients, was feasible
and of diagnostic quality in most cases, and could be an alternative to
conventional TTE on prone patients.
The findings of our study confirmed that the unconventional use of TEE
probe to perform TTE with patients kept in the prone position was
feasible and reproducible. There was generally good agreement between
the linear 2D measurements of the left ventricle by this innovative
technique and the corresponding measurements obtained by the standard
supine TTE. In this study we recruited apparently healthy adult
individuals who were examined by both techniques in the same sitting by
the same echocardiography machine thus it is considered as a proof of
concept that was previously proposed by Marvaki et
al. 8
Small, yet statistically significant differences, were noticed in the LV
EF and LA anteroposterior diameter between the two techniques, being
lower in the prone position. This could be explained by the effect of
changing the direction of the transverse gravitational stress on
cardiovascular variables. Also, foreshortened views in the prone
position may explain the smaller left atrial dimensions in this
position.
Bettina Pump et al.10 studied the physiological effects of the supine,
prone, and lateral positions on cardiovascular and renal variables in
humans. They concluded that the prone position reduced the stroke volume
by 16%, and increased the sympathetic nervous system activity as
evidenced by: increased heart rate, total peripheral vascular resistance
and plasma concentration of norepinephrine. These effects may have been
caused by some compression of the thorax leading to impediment of the
arterial filling and thus inhibition of the arterial baroreflexes. But
no significant difference in the left atrial diameter was noted on
comparing the effects of the supine with the prone positions.
Also on performing agreement analysis, the LVEDD in the prone position
was the farthest from its corresponding measurement in the supine
position (as it showed the largest mean difference). This was concordant
with the observations noted by Wolfgang M. Schaefer et al,11 who
investigated the effect on LV volumes, EF, and heart rate in the prone
versus the supine positions during gated 99mTc-Sestamibi single photon
emission computer tomography (SPECT). They found that the end-diastolic
volume and stroke volume were significantly lower in the prone
acquisitions than in the corresponding supine measurements; however, the
end-systolic volume and LV EF did not differ significantly.
In the prone position, we were able to acquire parasternal views (either
long axis or short axis) in most of our patients (29/30 patients)
compared to the original study, that reported diagnostic image quality
in 17 out of 21 patients. In the majority of patients, the image quality
was fair in the prone position, with significantly longer scan time than
in the supine position. Most studies required an assistant to handle the
echocardiography machine while the main operator was controlling the
probe.
However, this novel technique allowed, in less than a quarter of an
hour, an informative assessment of global LV systolic function, right
ventricular out flow tract, pulmonary artery, and also rapid screening
of the valvular morphology and function with exclusion of any
valve-related masses, intracardiac thrombi or pericardial effusion. This
technique was not only reproducible, but also offered a relatively
comfortable and safe transthoracic examination for the patients in this
challenging prone position.