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.