- Left ventricular SV is calculated by multiplying the left ventricular outflow tract (LVOT) area and LVOT time velocity integral measured from LVOT velocity.
- From the Apical 5-Chamber (A5C) view, the sample volume is placed in the LVOT within 5 mm of the aortic annulus to avoid the flow acceleration.
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- Caption from Figure 4-6 of Oh Textbook: Examples of LVOT PWD velocity recording in a patient with atrial fibrillation. The sample volume needs to be placed about 5 mm from the aortic annulus to avoid flow acceleration. The spectral broadening (interval between two arrows with turbulent flow) should be less than 40 cm/s (left). The sample volume is too close to the aortic valve or too large in the example shown (right). Of note, there is some variation of LVOT velocity in this example because of atrial fibrillation.
- Normal values for LVOT peak velocity: 0.9 to 1.1 m/s
- Normal values for TVI: 20 to 24 cm.
- Stroke volume is proportional to LVOT TVI.
- Echo
- Although guidelines suggest that the LVOT measurement should be made 0.5 to 1.0 cm from the annulus, studies indicate that calculating AV area using the LVOT measured at the annulus is more reproducible and accurate. 1
📝 It should be noted that LVOT area is usually slightly underestimated since it has an oval shape, but LVOT area by 2D echocardiography assumes its circular shape. However, since LVOT area remains fixed, LVOT TVI can be used to monitor the change in stroke volume. Normally, there is no variation in LVOT velocity. However, in patients with severe LV dysfunction, LVOT velocity alternates every other beat (pulsus alternans), and in patients with tamponade or constrictive pericarditis, LVOT velocity varies with respiration (pulsus paradoxus).
- Sources:
- Chapter 4 of Oh textbook