Determining Stroke Volume (SV) with Explanation – Velocity Time Integral (VTI) Video Clip (1:01)

Example: This patient is in atrial fibrillation – averaging of the VTIs would be recommended in this case.

• This video starts with an apical 5 chamber view.
• The 5 chamber view of the Left Ventricular Outflow Tract (LVOT) is obtained by angling anterior from the conventional apical 4 chamber view.
• Switch to Pulse Wave (PW) Doppler.
• Place the PW gate in the LVOT, trying to be as parallel as possible.
• Then, engage the spectral Doppler trace.
• Choose the best represented envelope and trace it.
• The ultrasound system will generate the VTI.
  • Note, in this case, the patient has an irregular rhythm so averaging of the VTI’s would be the most accurate approach.

Reminder: The area of the LVOT for this example was 3.49 cm2

• Strove Volume (SV) = area of the LVOT (πr2) x VTI (h)
• 3.49 cm2 x 13.2 cm = 46.1 cc
• SV = 46.1 cc
• Note, an average SV is around 60 cc.
• Cardiac Output (CO) = SV x Heart Rate (HR)
• In this example, the HR was 85.
• CO = 46.1 cc x 85 = 3918.5 cc or 3.9 L/min
• CO = 3.9 L/min (this is low)
• We now have a number to aid us in the clinical decisions ahead and to compare to and monitor after potential interventions.
• An average SV is 60 cc; an average HR is 60-70, so the average CO is 4.5-5.5 L/min.

Reminder: SV is influenced by:

• Preload
• Systemic Afterload
• Contractility of the Heart

In this case, the contractility is insufficient to meet CO needs. If this patient had oliguria, rising lactate, or other evidence of organ failure related to poor oxygen delivery, initiating inotrope would probably be the most appropriate next step.