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.