Discussion
Cardiovascular complications have a serious impact on the survival and
quality of life of uremic patients, and left ventricular diastolic
dysfunction is its most prominent feature. Echocardiography needs to
find subclinical damage of left ventricular function early. 2D-STI is a
new echocardiography technique, which can provide objective
quantification of cardiac function on the basis of analyzing myocardial
deformation.
Previous studies have confirmed [1, 13] that left
ventricular global longitudinal strain (LVGLS) can accurately evaluate
left ventricular systolic function, while GLS is affected by volume load[14]. Recently, experts recommended[15-17] to add left atrial strain to the
evaluation of left ventricular diastolic function. Therefore, speckle
tracking imaging was used to evaluate left atrial strain function before
and after dialysis in ESRD patients, and to explore the influence of
volume load on left atrial function.
During the cardiac cycle, LA has three main functions: the reservoir
function when blood fills LA in systole, constrit function corresponding
to passive LV filling in early diastole, and the active contractile
function in late diastole.
Reservoir function is the ability of left atrium to receive blood flow
from pulmonary vein during ventricular systole and mitral valve closure.
It is determined by atrial stiffness and compliance, and is also
affected by left ventricular contractile force. After hemodialysis, the
strain value of LASr decreased, which proved that the blood entering the
left atrium from pulmonary vein corresponding to the decreased volume.
Conduit function is the difference between reservoir function and
contractile function. In the early
stage of ventricular diastole, blood flows directly into left ventricle
through left atrium, which is mainly determined by left atrial
compliance, and is also closely related to left ventricular diastolic
tension and stiffness. After hemodialysis, the strain value of LAScd
also decreased, indicating that the blood flowing through left atrium
and entering left ventricle decreased in early diastole.
The contractile function is the plateau strain value in the late
diastolic period of the ventricle, which reflects the active pump
function of the left atrium. In the late diastole, the left atrium plays
an autonomous booster pump function, and the atrial muscle actively
contracts, pumping out the remaining blood and increasing the left
ventricular filling [18]. It plays a vital role in
maintaining the best cardiac circulation. Once the left ventricular
myocardium is damaged and the compliance is decreased, in order to
maintain sufficient cardiac output, the left atrium will do compensatory
work to supplement the left ventricular filling[15]. In this study, after hemodialysis, while
blood volume decreased, the cardiac output was still in the normal
range, the passive function of atrium (LASr, LAScd) decreased, but the
pump function of atrium itself (LASct) did not change significantly.
Furthermore, uremic patients are in a state of volume overload for a
long time, and the cardiac output after hemodialysis is more in line
with their physiological needs, so there is no need for extra work of
the left atrium.
Consistent with Frank-Starling law: in a certain range, when the volume
load increases, the myocardial fiber adjusts its initial length, which
improves the myocardial deformation ability, that is, the myocardial
contractility increases. In this study, the volume was overloaded before
hemodialysis, and the LVGLS parameters (subendocardium, midmyocardium
and subepicardium) were close to those of the normal control group.
After the excess fluid was removed, the heart cavity became smaller, the
myocardium returned to physiological length, and the LVGLS decreased.
Consistent with Breetveld N-M et al. [19], under
the condition of normal myocardial contractility, left ventricular
myocardial fibers reshape with the change of volume load, and the
absolute value of myocardial strain decreases with the decrease of
volume load after hemodialysis. However, Sun MM et al.[20] put forward different viewpoints. The
incidence of myocardial damage in patients with renal insufficiency is
higher, and the compensatory ability of myocardium is weaker than that
of normal people. A large amount of fluid is removed, and myocardial
blood perfusion is reduced, which can cause myocardial cell injury and
stunning, resulting in a decrease in left ventricular strain.
It may be possible to detect subclinical cardiac changes in patients
early by strain of left atrium. The thickness of atrial muscle is
thinner than that of ventricular, and atrial myocardium is more
vulnerable to damage due to long-term deposition of uremic toxins and
metabolites and retention of water and sodium. In this study, the atrial
strain parameters (LASr, LAScd, LASct) before hemodialysis were lower
than those in the control group. It can be found that ESRD patients are
overloaded with volume, and the damaged left ventricular myocardial
fibers are passively stretched. At this time, the left ventricular
strain value has not decreased, and the atrial strain parameters have
already decreased. After hemodialysis, the pump function of atrium
itself has no obvious change, which further indicates that the passive
function of atrium (LASr, LAScd) is greatly affected by volume load,
while the active deformation (LASct) is less affected.
Consistent with previous studies, traditional Doppler parameters of
diastolic function and left ventricular globe strain parameters depend
on volume load [21]. When these parameters are
still normal, LA strain parameters evaluated by STE can find subclinical
LA dysfunction in ERSD patients early, provide more quantitative
indicators for cardiac function evaluation and prognosis evaluation of
such patients, and find subclinical myocardial damage in time, so as to
obtain more timely treatment and improve clinical results.
Limitations : 1. She is a study of left atrial function with
single center; 2. The patients with end-stage renal disease in this
study had left ventricular wall hypertrophy and left atrial strain had
decreased. It is necessary to to expand the size to study the changes of
left atrial function in the early stage of renal insufficiency.
Author contributions
Z B-Y and L Y-P contributed the study conception and design. Y Y
contacted with the patients for the echocardiography. M Y-X and W L
wrote the manuscript. M Y-X and W L performed the statistical analysis.
M Y-X and W L were responsible for image off-line analysis. Z B-Y and L
Y-P reviewed and edited the manuscript before submission. All authors
read and approved the final manuscript.