Examination: cardiac ultrasound
Parameters:
(1) heart rate in beats per minute
(2) body surface area (BSA) in square meters
(3) left ventricular outflow tract (LVOT) diameter in cm
(4) velocity time interval (VTI) in cm of left ventricular outflow
LVOT is measured from a horizontally lined image of the anterior and posterior limits of the left ventricular outflow tract.
VTI is calculated as the area under the curve of the left ventricular outflow made with a clear apical 5-chamber view, which is obtained with an apical 4-chamber view and then angulating the probe slightly towards the patient’s head until the left ventricular outflow tract can be visualized. The pulsed-wave Doppler cursor is placed near the aortic valve annulus. There should be alignment of the pulse Doppler sample volume parallel to the aortic flow with minimal spectral broadening.
stroke volume in mL =
= PI() / 4 * ((LVOT diameter)^2) * (VTI)
stroke volume index = SVI =
= (stroke volume in mL) / (body surface area)
cardiac index in liters =
= (stroke volume index) * (heart rate) /1000
Interpretation:
• The normal cardiac index is 2.5 to 4.0 liters per square meter.
