= Left ventricular outflow tract
The \b[left ventricular outflow tract], LVOT, is the passage within the <left ventricle> leading to the <aortic valve>. It links the ventricular cavity with the <aortic root>; the neighboring anterior <mitral valve> leaflet and ventricular septal structures help define this outflow region.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Left Ventricle and internal heart anatomy]{ref}<Surgical anatomy of the aortic valve and root—implications for valve repair by Ruggero De Paulis and Andrea Salica>[General considerations; The VAJ and the VBR]{ref}
Its measurement is useful in <Doppler echocardiography>. In a fixed-area model, a cross-sectional area $A$ and area-mean axial <velocity> $\overline u(t)$ give the forward transported volume
$$
V=A\int_{\rm ejection}\overline u(t)\,dt=A\,\mathrm{VTI},
$$
where the <velocity-time integral> has dimensions of length. It is not a peak <velocity> or a volume by itself. The primary technical report uses paired diameter and Doppler measurements at a consistent outflow site.<Recommendations for Noninvasive Evaluation of Native Valvular Regurgitation by William A. Zoghbi and others>[Section II.B.6.a, quantitative pulsed Doppler; Table 7, SV method]{ref}
For a stipulated circular diameter $D=2.0$ cm and <velocity-time integral> 20 cm,
$$
A=\frac{\pi D^2}{4}=\pi\ \mathrm{cm}^2,\qquad V=20\pi\simeq62.8\ \mathrm{mL}.
$$
If the measured diameter is instead 2.2 cm with the same integral, the estimated area and volume both increase by $(2.2/2.0)^2=1.21$, or $21\%$. A $10\%$ diameter change therefore does not produce only a $10\%$ volume change.
The approximation requires consistent geometry and velocity sampling. A noncircular outline, changing area, nonuniform flow or an angled ultrasound beam can alter the relation between a measured signal and area-mean <velocity>. The <left ventricular outflow tract> also names anatomy, while <aortic stenosis> names a pathological narrowing at the valve: a passage's location alone does not establish whether it is obstructed.
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