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.
Why & whenThe 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.
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LV function assessment
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Step-by-step
Step 1. Acquire windowObtain 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. |
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Step 2. Place PW Doppler gateEnsure 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.
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Step 3. Spectral DopplerPress "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.
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Step 4. Trace the VTIManually "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. |
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Step 5. Convert VTI into cardiac outputMeasure 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. |
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Step 6. Consider limitationsLimitations |
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) |
Video tutorial on cardiac output by Spectral dOppler
References
Anavekar NS, Oh JK (2009) Doppler echocardiography: A contemporary review. Journal of Cardiology 54:347–358.
Bakhru RN, Schweickert WD (2013) I. Physics, equipment, and image quality. Annals of the American Thoracic Society 10:540–548.
Blanco P (2020). Rationale for using the velocity–time integral and the minute distance for assessing the stroke volume and cardiac output in point-of-care settings. Ultrasound Journal 12.
Edelman S. Understanding Ultrasound physics.
Goldman JH, Schiller NB, Lim DC, Redberg RF, Foster E. Usefulness of stroke distance by echocardiography as a surrogate marker of cardiac output that is independent of gender and size in a normal population. American Journal of Cardiology. 2001;87(4):499-502.
Huntsman LL, Stewart DK, Barnes SR. Noninvasive Doppler determination of cardiac output in man. Clinical validation. Circulation. 1983;67(3):593-602.
Le HT, Hangiandreou N, Timmerman R, et al (2016) Imaging Artifacts in Echocardiography. Anesthesia and Analgesia 122:633–646.
Zhang Y, Wang Y, Shi J, Hua Z, Xu J. Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis. PLoS ONE. 2019;14(10):1-17.
Bakhru RN, Schweickert WD (2013) I. Physics, equipment, and image quality. Annals of the American Thoracic Society 10:540–548.
Blanco P (2020). Rationale for using the velocity–time integral and the minute distance for assessing the stroke volume and cardiac output in point-of-care settings. Ultrasound Journal 12.
Edelman S. Understanding Ultrasound physics.
Goldman JH, Schiller NB, Lim DC, Redberg RF, Foster E. Usefulness of stroke distance by echocardiography as a surrogate marker of cardiac output that is independent of gender and size in a normal population. American Journal of Cardiology. 2001;87(4):499-502.
Huntsman LL, Stewart DK, Barnes SR. Noninvasive Doppler determination of cardiac output in man. Clinical validation. Circulation. 1983;67(3):593-602.
Le HT, Hangiandreou N, Timmerman R, et al (2016) Imaging Artifacts in Echocardiography. Anesthesia and Analgesia 122:633–646.
Zhang Y, Wang Y, Shi J, Hua Z, Xu J. Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis. PLoS ONE. 2019;14(10):1-17.