4.5 Assessment of narrowed LVOT using Doppler echocardiography
The assessment of LVOT narrowing using continuous wave Doppler is problematic because the measurement of the peak velocity or PG often has technical difficulties, including Doppler angulation and inaccuracy of the location of the smallest area.22 To mitigate these problems, instead of peak PG, we analyzed the change in PG from before to after procedure. The reason why LVOT gradient was increased even though the smallest area was not dramatically changed after TMVI may be due to the following: the valve implantation newly creates a narrowed LVOT surrounded by the valve and left ventricular septum, which potentially causes a tunnel effect increasing the blood flow velocity compared to the pre-procedural condition.23Thus, the change or increase of peak velocity and PG (∆PG) reflects the newly created LVOT geometry after TMVI, and, for that reason, an increase in LVOT gradient by more than 10 mm Hg was used to define LVOT obstruction.14 However, further study will be required to show whether this cut-off value is reasonable and clinically meaningful as definition.