LVOT VTI

Velocity Time Integral (VTI) is the area under the curve on a Pulse Wave Doppler tracing. It represents the distance blood travels during one heartbeat. In the LVOT (Left Ventricular Outflow Tract), the Doppler tracing shows velocity on the Y-axis and time on the X-axis. By calculating the area under this curve (VTI), and multiplying it by the cross-sectional area of the LVOT, you can estimate stroke volume.

Stroke Volume = LVOT area × VTI
LVOT area = π × (LVOT radius)²
Normal VTI ranges from 18-22cm.

LVOT VTI can be particularly useful to assess if an intervention (ie inotropes) is improving overall cardiac output or having minimal benefit to the patient.

Pitfalls: poor doppler beam alignment, not measuring LVOT diameter, misinterpreting waveforms, not averaging multiple cycles.

Image Acquisition

Parasternal Long Assessment of LVOT

Place cardiac probe at nipple line near the left side of sternum. Slide on anterior chest until obtain view.
Center the heart on screen.
Rotate = length the LV/open the LVOT.
Sweep/fan to widen the LV. Freeze image and zoom into LVOT.
Click 'calcs' then LV function then LVOT VTI.
Measure the LVOT diameter in cm during systole with aortic valve open (use cineloop for this).
Click camera to save.

VTI Determination

Obtain apical 4 chamber view (see prior slides for details).
Fan/sweep probe + obtain apical 5 chamber view.
Place pulse wave doppler place at the LVOT. initiate doppler then freeze image.
Click back into calcs, LV function. Now click VTI and trace the LVOT VTI doppler tracing. Machine will calculate VTI.
Click camera to save image.

Cardiac Output Calculation

Determine heart rate.
Math Calculation:
- Use the LVOT diameter to find LVOT area: Area = pi * radius ^2.
- Cardiac output (ml/min) = LVOT area * LVOT VTI * heart rate.
- Note: the machine will do this entirely in the calcs section.

Assess for improvements in your cardiac output following intervention (ie fluid bolus, starting inotropes).