Can Changes in LVOT VTI Before and After Passive Leg Raising (PLR) Test Serve as a Sensitive Indicator for Changes in SV and CO and Hence Volume Responsiveness ?

Can changes in LVOT VTI before and after passive leg raising (PLR) test serve as a sensitive indicator for changes in SV and CO and hence volume responsiveness ?

What is Doppler LVOT VTI? Placing a Pulsed Wave Doppler gate on the LVOT immediately below the opening of the aortic valve while aligning the Doppler beam as parallel to the LVOT/aortic axis as possible with an angle of Doppler alignment <20˚, one may obtain Doppler flow velocity measurements which can help measure the LVOT VTI (Velocity Time Integral). If one integrates this velocity profile between two time points (i.e., calculates the area under the curve), the distance traversed of "a region of blood" flowing during this period may be estimated. Since flow velocity is not constant throughout a flow cycle, all of the flow velocities during the entire ejection period is integrated to measure "distance traversed" of this "region of blood." This integration of flow velocities in a given period of time is called the velocity-time integral (VTI)(1) and yields length or distance (measured in cm).

Goal: Whether VTI (LVOT) measured from the deep transgastric (deep TG) or transgastric long axis (TG LAX ) views reflect changes in stroke volume(SV) and hence cardiac output (CO) measured by the gold standard method (PA CCO by thermodilution) before and after passive leg raising test (PLR).

Hypothesis: A validated technique to measure cardiac output (CO) using echocardiography is to calculate stroke volume from the product of LVOT area and LVOT VTI and multiplying the product with heart rate ( CO = SV x H/R; SV = LVOT area x LVOT VTI ).

The LVOT diameter for an individual is more or less a constant measurement. Therefore using the formula mentioned above (SV = LVOT area x LVOT VTI), if the LVOT area is constant, then SV should be proportional to the VTI. This means if a PLR manoeuvre or fluid bolus helps to achieve a rise in SV, then it should be reflected in an increase in VTI as well. If this assumption is true, then an increase in the value of VTI from baseline after fluid challenge (10-15%), should identify a volume responsive patient.