Discussion
Aim of our study was to determine the parameters that will predict the
improvement of mitral regurgitation after implatation of CRT in patinets
with HFrRF with moderate or severe functional mitral regurgitation by
measuring the geometric parameters of mitral valve with 3D TEE by 4D MVQ
program automatically. Our results have shown that in patients with
lower posterior leaflet angle, CRT resulted in the marked improvement of
mitral regurgitation.
As it is known, functional mitral regurgitation arises as a consequance
of the imbalance between closing and tethering forces responsible for
valve competence. (4) Systolic dysfunction,ventricular remodelling,
mitral annulus dysfunction, alteration in LV geometry and size and
dyssnchrony are supposed to be the main causes of MR. (6)
Several echocardiogrphic parameters were found to be related to the
significance of functional mitral regurgitation in patients with low EF
heart failure. Posterior leaflet angle has been investigated many times
as in our study. In a study echocardiography and cardiac MR were used in
order to evaluate anterior and posterior leaflet angles, in the groups
with severe MR; along with asymmetrical tethering, mean posterior
leaflet angle was found to be a 38.37° and significant relation was
demonstrated between RV and posterior leaflet angle. (r = 0,90 p =
0,037) (7)
Likewise, in the study of Kwan et al, in the evaluation of geomteric
parameter measurements in ischemic cardiomyopathy, it was demonstrated
that posteior leaflet angle of 47 degree was major predictor of severe
MR with sensitivity of 96% and specifity of 84%. (positive predictive
value 92%, negative predictive value 100%) (8)
CRT is a treatment option which can interrupt the vicious circle that
deteriorates heart failure caused by MR.In acute period,
resynchronization of papillary muscle enables the MR duration to be
shortened and MR onset to be delayed , resulting in increase in
transmitral pressure gradient and modification of mitral annulus
contraction via increased con tractility. (6) Moreover, in chronic
period, resynchronization associated with remodelling brings about
increase in closing forces within weeks to months and restores more
coordinated movements of mitral valve components. (9) Beside this, there
is an improvement in ejection fraction in the long term after CRT and it
provides improvement in MR. However in our study we have evaluated the
short term improvent at the end of three month and there was no change
in LVEF and LV sizes and the improvement is only related to the CRT
treatment. Although long term studies would be more valuable, results of
our study shows solely effect of CRT on mitral regurgitaion is related
to posterior mitral valve angle.
In the study of Kanzaki et al investigating the impact of CRT on early
MR, it was revelaed through longitudinal strain measurements that after
CRT implantation, mechnical activation of papillary muscles retension
zone, became more coordinated and temporal delay between papillary
muscles was decreased and improvement in dysynchrony was linked to
improvement in MR.(10)
Three dimensional TEE, which has recently become popular in clinical
practice, yields quite objective data in the evaluation of mitral valve.
In a study including 112 patients with mitral valve prolapsus and severe
MR, 2D and 3D TEE were compared and it was stated that measurements made
with 3D TEE were superior in the determination of pathology. (11)
In addition to 3D TEE, full automated mitral analysis softwares enabling
detailed evaluation of mitral valve has become more common in clinical
practice. In the study of Nobuyuki et al comparing manual screening
software with fully automated software in the three dimensional
evaluation of mitral valve, it was stated that automated software had
comparable accuracy to manual software as well as being time saving.
(12)
Many measurements of the mitral valve can be made with these full
automated mitral analysis softwares. And these reveal the effects of CRT
on the mitral valve. Previous studies have demonstrated that the tenting
hight and tenting area are related to both severity of mitral
regurgitaiton and the response, by reason of tenting hight and the
tenting area are the final results of the all the geometrical changes
seen in dilated ventricle and accused for the development of mitral
regurgitaiton annulus also has an adjuctive role by seperating the
mitral leafleats.(13) However we had few number of the patients we could
not included all the parameters that we would be measured with 3D TEE,
we have included the parameters that are related to functional mitral
regurgitaiton such as annulus size and diameters, anterior leaflet angle
and as our results clinically important posterior leaflet angles.
Posterior leaflet angle is an indicator of posterior tethering. In
dilated ventricle, the displacement of posterior papilary muscle will
lead to increase in posterior tethering forces and in posterior leaflet
angle and the resulting imbalance between tethering and closing forces
will give rise to mitral regurgitation. Hence, in mitral valve complex
with higher posterior leaflet angle, the response to treatment with CRT
will be at a lower degree.
In conclusion, in heart failure patients with low ejection fraction, the
accompanying moderate or severe mitral regurgitation portends poor
prognosis and it is reduced after after CRT implantataion in about two
thirds of the patients, which yields clinical benefit with decrease in
mortality. Mitral valve measurments that will be made with 3D TEE prior
to implantation may help to predict the response of MR to CRT. Hence, in
the present study, we have tried to find out the parameters that will
predict reponse to treatment of MR by evaluating mitral valve anatomy
with 3D TEE and concluded that posterior leaflet angle may be an
important parameter influencing the improvement in mitral regurgitation
following CRT. (28,93 ± 8,41 vs. 41,25 ± 10,90, p = 0,006). Three
dimensional TEE and is a highly valuable method for the both visual
evaluation and quantitative analysis of mitral valve and further studies
would be done with larger number of the patients to predict the mitral
regurgitaiton responce to CRT implantation.