Assessment of Agreement Between Two Measurement Methods of Left Ventricular Outflow Tract (LVOT) Velocity Time Integral (VTI)

Acute circulatory failure (ACF) is a common cause of admission in intensive care unit (ICU). Echocardiography is a widespread tool nowadays for the initial assessment and the hemodynamic monitoring. An interesting data from this exam is the Left ventricular outflow tract (LVOT) velocity time integral (VTI), reflecting stroke volume, and therefore cardiac output. A new tool for automated recording has been developped on the VENUE GE echograph. This study aims at assessing this automated measurement of LVOT VTI compared with the classic manual method.

Acute circulatory failure is a dramatically common issue in critical care, affecting nearly 1/3 of the patients admitted in ICU, and associated with a high morbi-mortality. Echocardiography enables a quick point of care assessment of the hemodynamic status of the patient. One key parameter is stroke volume, which can be estimated by LVOT VTI. In practice, the guidelines recommend measuring LVOT VTI in a 5 chambers cavity window with pulsed wave doppler, trying to get an angle between aortic flow and the doppler signal as cloth as possible to 0°. Than VTI must be calculated from an average of 3 to 5 cycles in sinus rhythm, or 5 to 10 cycles in arrythmia such as atrial fibrillation. The main issue is that this approach is time consuming and tedious, and most of the practitioners choose to measure only the most representative beat (" Best VTI "), likely to be source of a loss of reproducibility. In order to make it easier, some companies have developed softwares to help the intensivist. Thereby, General Electric has equiped the VENUE echograph with a system that helps first selecting the proper place for sampling, and then automatically acquire, trace, and calculate the average LVOT VTI based on a 4 seconds sample. Finally, this tool gives a VTI trending when several measures are repeated along the patient' stay. This program has already been tested on a swine model in hemorrhagic shock with encouraging results (better agreement with cardiac output by thermodilution with the automated method than with the manual one). However, feasibility was only 60%. This human study aims at assessing the interest of automated LVOT VTI measurement compared to the manual standard one when performing a cardiac echography for hemodynamic assessment of patients hospitalised in ICU. Otherwise, a measure of the " Best-VTI " will be done at the same time in accordance with the current practice, in order to assess this approach. Finally, when a fluid resuscitation will be indicated, a second exam will be done, and agreement of VTI variation between automated and manual method studied.