The following clips and video tutorial will outline step-by-step performance of stroke volume and cardiac output by spectral Doppler. We would like to thank Dr. Deschamps from the Universite De Montreal for collaborating in producing this video.
The assessment of stroke volume and cardiac output is a helpful tactic to objectively assess left ventricular performance in critically ill patients. The indications are many but among these the assessment of LV function in shock and sepsis is likely the most common.
Obtain high-quality acoustic window with left ventricular outflow tract (LVOT).
In trans-thoracic echo, this is often the apical 5- or 3-chamber.
In trans-esophageal echocardiography (TEE), this may be the trans-gastric long axis or distal trans-gastric.
Ensure blood flow in the left ventricular outflow tract is parrallell to the Doppler angle of insonation Place sample volume gate (pulse wave Doppler) within 1 cm of aortic valve or at aortic valve annulus. Trans-thoracic echocardiography is often more favourable for trans-LVOT/aortic blood flow, but TEE can be used in the majority of patients as well with the above views.
Press “Doppler (PW)” on most machine will yield this distinct below baseline spectral waveform. This normal waveform (“stroke distance”) as a distinct Doppler “envelope” whereby the outer edges are white and distinct and the inside is dark, reflecting the unique flow acceleration through the LVOT in a well-placed PW Doppler signal (i.e. range specificity). The scale should be increased to ensure the entire waveform can be seen.
Manually “trace” the spectral waveform from the baseline to the apex and back down to baseline. This will yield a velocity-time integral (i.e. VTI). A normal VTI for a person in sinus rhythm with a HR between ~50-120 is approximately 18-22, independent of body surface area.
**VTI may be inaccurate (i.e. not reflective of true stroke volume) at the upper extreme of age, heart rate, and body size/BMI.
Measure the LVOT diameter in the parasternal long axis view in systole. The measurement can be within 1 cm of aortic valve or at the aortic valve leaflet insertion point; this depends on where the Doppler signal was taken.
The cross sectional area (as shown here) multiplied by the VTI will give the stroke volume. This is then multiplied by the HR to give the non-indexed cardiac output.
Angle of Doppler insonation (< 20 to 30 degrees)
Atrial fibrillation (Must average minimum 5 beats)
Annulus measurement, area
Aortic regurgitation
Marked tachycardia (Hr >120-130)
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