Abstract

Background: Transthoracic echocardiography (TTE) in prone position is challenging. Innovative use of transesophageal echocardiography (TEE) probe to perform TTE for such patients was described; but reproducibility and correlation of the TTE measurements by this technique with those obtained by the standard supine TTE study are still unknown.Methods: We enrolled 30 non-COVID-19 individuals, with a mean (SD) age 35 (10.9) years and 11 females, to study the agreement between the transthoracic measurements of the left ventricular (LV), left atrial (LA) and aortic dimensions obtained in prone position using an external TEE probe versus the standard supine position using the conventional TTE probe. Results: There were no significant differences between LV end-diastolic and end-systolic diameters, septal wall thickness, posterior wall thickness and aortic root dimensions in the prone versus the supine positions, while the mean ejection fraction (EF) (60.3% vs. 63.1%, P = 0.014) and mean LA dimensions (1.8 vs. 1.9 cm/m2, P < 0.001) were significantly lower in the prone position. The mean time of scans was significantly longer in the prone as compared to the supine position (12.5 vs 4.5 minutes, P < 0.001). All supine studies had good quality while in the prone position 4 studies were of poor quality, and one was non-diagnostic.Conclusions: Assessment of cardiac dimensions and systolic function in the prone position using transthoracic TEE probe was feasible. LV and aortic dimensions agreed well with the standard TTE in supine position, however, LA dimensions and EF were lower in the prone position.Keywords: COVID-19, transthoracic echocardiography, transesophageal, prone position, cardiac dimensions, systolic function.

Introduction

Preexisting cardiovascular diseases are linked to more severe COVID-19 infection. Additionally, cardiovascular complications can be a significant contributor to the mortality associated with this disease.1, 2 It has been shown that prone ventilation can improve oxygenation in patients with acute respiratory distress syndrome (ARDS) secondary to COVID-19.3 Echocardiography used to assess their cardio-circulatory status, may be very challenging in patients kept in the prone position using conventional transthoracic echocardiography (TTE). Transesophageal echocardiography (TEE) is a traditional solution that can be performed in the prone position and was reported to be a safe procedure in ARDS patients.4 However, TEE carries a heightened risk of spread of the COVID-19, as it can promote the aerosolization of a large amount of virus.5 Additionally, acute access to TEE study is a logistic problem particularly that it requires highly trained professionals on image acquisition and interpretation. Ugalde et al.6 and Giustiniano et al.7 had previously described techniques to obtain TTE using the conventional probe during prone position ventilation, but those techniques were demanding and required special positioning and preparations. Lately, Marvaki A et al.8 described an innovative use of the TEE probe to perform a transthoracic study on patients with COVID-19, who were invasively ventilated in the prone position. This was feasible and of acceptable diagnostic value. However, the reproducibility and correlation of the echocardiographic measurements obtained by this novel technique with those obtained by the standard transthoracic study are still unknown. The aim of this work was to compare the basic left ventricular (LV), left atrial (LA) and aortic (Ao) dimensions obtained by TTE imaging in the prone position using a TEE probe versus the standard supine position using the conventional TTE probe in apparently healthy adults.

Patients and methods

Thirty apparently healthy non-COVID-19 patients, referred for routine TTE at the outpatient clinic of cardiology department at Cairo University hospital, were prospectively enrolled in July 2020. Each participant was examined in the same sitting, both in the prone position using a TEE probe and in the standard supine position using the conventional TTE probe, by two independent operators. All scans were performed with a Philips Affiniti 50C machine using the S4-2 TTE probe and the X7-2t TEE probe (Philips Healthcare, Andover, MA). The basic LV internal dimensions, wall thickness, and ejection fraction (EF), in addition to left atrial (LA) and aortic root (AoR) dimensions were obtained carefully in either position from electrocardiographically (ECG) - gated two-dimensional (2D) images of parasternal long axis view with great attention to be perpendicular to LV/LA long axis.
The standard supine position studies were done according to the American Society of Echocardiography (ASE) and European Association of Cardiovascular Imaging (EACVI) recommendations.9 Regarding the prone study the same innovative technique recently described by Marvaki A et al.8 was adopted. In this technique, the operator was standing on the left side of the patient at the level of the head, facing the patient’s right side. The probe was anchored to patient’s chest wall against bed mattress. The tip of the probe lubricated by gel was placed in the standard left parasternal position in the third or fourth left intercostal space. The transducer was facing upwards and was supported underneath by operator’s left hand. The probe shaft was held with the right hand to allow rotation. Images of the long axis of the heart were obtained at zero angle as in the conventional TTE parasternal long-axis view (Figure 1), while images of the short axis view were obtained by increasing the angle to 60 -120 degrees , usually at the level of the mitral valve. By rotating the probe clockwise, the mid-papillary level was obtained (Figure 2), while great vessels level was obtained by anticlockwise rotation.
The scan time was measured, and the image quality was graded as poor, fair, good or non-diagnostic. The quality of the images acquired by the TEE probe in the prone position was compared to that of the images obtained by TTE probe in the supine position.