Discussion
As a subtype of CHD, TVD is more serious than single-vessel and
double-vessel disease, which has a higher incidence of cardiovascular
events and
mortality[10]. At
present, we need a technique to evaluate the changes of LV function
early and accurately. Conventional echocardiography considers the LVEF
is the most common parameter to evaluate myocardial systolic
function[11], but
relevant studies have shown that the sensitivity of it is poor in
detecting mild myocardial dysfunction[12]. Speckle
tracking is a new echocardiographic technique developed in recent years.
At present, 2D-STE has been widely used in clinical and experimental
research[13,14].
But the limitation of 2D-STE is that the tracking of myocardial acoustic
spots is limited to the two-dimensional section, which makes it
untraceable when some of the spots move completely outside the
two-dimensional section. The
3D-STE overcomes
the‘out-of-plane’phenomenon of 2D-STE in
scanning[15,16].
It can quantitatively evaluate the deformation of regional myocardium in
multiple directions, and reflect motion and function of myocardium in
three-dimensional space more realistically and
accurately[17,18].
Crosby et al.[19]study on local myocardial function using speckle tracking technology
shows that 3D-STE can accurately identify the myocardium with local
dysfunction.
In our study, the LV structure of the group B was no obvious difference,
and LVEF was also within the normal range compared with group A.
However, the group C had larger LV volume and lower LVEF than those in
other two groups. The LV structure and LVEF can remain normal in group
B, because the motion of myocardium in the ischemic region may be
compensated by adjacent normal myocardium. With the aggravation of the
degree of stenosis, the range of affected myocardium expands, and the LV
function is gradually decompensated, resulting in cardiac enlargement
and heart failure.
The myocardium of the LV is divided into three layers: the inner layer
of the right hand spiral, the middle layer of the ring spiral and the
outer layer of the left hand
spiral[20,21].
Due to the orientations of myocardial fibers are different, its movement
directions are also different. When the inner layer and outer layer
myocardial fibers contract, there is movement in the direction of the
long axis, and when the middle layer myocardium contracts, there is
movement in the direction of the short axis. GLS, GCS and GRS
respectively represent the myocardial deformation in the longitudinal,
circumferential and perpendicular directions of endocardium. In
addition, GAS is a new
parameter[22,23],
which is the integration of GLS and GCS, and it represents the area
change rate of endocardium. Longitudinal motion of myocardium is mainly
determined by the myocardium fibers in the inner layer, and
circumferential are determined by the myocardium fibers in the middle
layer[24,25].
Our study found that the GLS in groups B and C were obviously reduced
compared to control group, and the changes were statistically
significant. Blood supply to the endocardium comes from the vessels at
the end of the coronary artery and studies have shown that change of GLS
is dominated by the endocardial
myocardium[26]. So
the endocardium is more sensitive to ischemia and hypoxia when the
patients with TVD have myocardial ischemia, which means that GLS has
changed under normal conditions of
LVEF[27]. If
stenosis rate of TVD further aggravates leading to the overload of
cardiac and the enlargement of cardiac, the decrease of GLS is more
significant. In our study, it was found that the GCS in groups B and C
were obviously lower than that in control group(P<0.05). The
circumferential contraction of the short axis of the cardiac is mainly
caused by the movement of the middle layer. Generally, myocardial
ischemia gradually expands from the endocardium to the
epicardium[28], so
when myocardial ischemia and hypoxia occur, the middle layer of
myocardial segments are affected, resulting in reduction of GCS. As a
specific indicator of 3D-STE, GAS is the integration of GLS of the
ventricular long axis and GCS of the ventricular short axis, so the
significant reduction of GAS can better assess the cardiac systolic
dysfunction in patients with TVD.
GRS represents the thickness of the ventricular wall and the change of
the LV volume from the LV short axis
view[29]. In our
study, the reduction of GRS in groups B were not statistically
significant compared with group A. It might be because the radial
thickening of ventricular wall is the result of the interaction of cross
fibers between different myocardial layers and the inner and outer of
fibers perpendicular to fiber orientation. Under normal physiological
conditions, the systolic thickening ability of ventricular wall mainly
depends on the myocardial fibers in the intimal layer. When the
contractility of endocardial myocardium is reduced due to ischemia, the
outer subepicardial layer contributes to thickening and short-axis
function through cross-fiber shortening. In the group C, GRS was
obviously decreased compared with the other two groups. It showed that
the further development of the disease had affected the middle layer,
which was consistent with the research results of Winter et
al[30]. In
addition, the research of Chan et
al[24]. showed that
when the degree of coronary stenosis is severe or even myocardial
infarction occurs, the peak value of radial strain can show a
significant decrease. Therefore, GRS is less sensitive to early
identification of myocardial ischemia of TVD.
Diastolic movement of the heart is an active energy consuming process,
and the threshold of diastolic function reduction is lower than systolic
function[31].
Therefore, the reduction of diastolic function is earlier than systolic
function during myocardial ischemia. Our study evaluated LV diastolic
function in line with the guideline issued by the American society of
echocardiography in
2016[32], which
proved that the LV diastolic function was decreased in groups B and C,
and group C was lower than group B. This is consistent with the results
of Rydberg et
al.[33], indicating
that LV diastolic function is closely related to the degree of coronary
artery stenosis. LVEDP measured by left cardiac catheterization is the
gold standard for the diagnosis of LV diastolic
dysfunction[34].
This study found that LVEDP in groups B and C increased, and that in
group C was higher than in group B, the difference was statistically
significant. At present, there are few studies on the correlation
between 3D-STE and LVEDP, and only shin et
al.[35] research
confirmed that GLS and GAS were closely related to LVEDP. We results
also suggest that the GLS and GAS had significant correlations with
LVEDP in group B and group C. In addition, this study found that GCS and
GRS also had high correlations with LVEDP in group B and group C.
Therefore, 3D-STE has a certain reference value for evaluating LV
diastolic function in the patients with TVD.
NT-proBNP is produced by the hydrolysis of proBNP which can produce BNP
at the time, and NT-proBNP may be more specific to cardiac activity than
BNP[36]. Studies
have confirmed BNP may be actively degraded in peripheral blood, so the
test of NT-proBNP is more
reliable[37].
NT-proBNP, as a polypeptide neurohormone, is mainly synthesized and
secreted by ventricular
myocytes[38]. In
recent years, more and more attention has been paid to the diagnostic
and prognostic of BNP in patients with different clinical types of
CHD[39-41]. Some
studies have showed the change of serum NT-proBNP closely related to
myocardial ischemia and hypoxia. When the systolic function of cardiac
is abnormal, the ventricular volume load increases and the ventricular
wall is pulled, causing the synthesis and release of
NT-proBNP[42]. Our
results showed the level of NT-proBNP was distinctly difference among
the three groups. NT-proBNP of group C was highest among of three
groups. It was due to the severe stenosis of the TVD result in ischemia
of cardiomyocytes and LV systolic dysfunction, which stimulates the
synthesized and secreted of NT-proBNP by ventricular myocytes. In group
C, the study demonstrated each 3D-STE strain parameter were negatively
correlated with NT-proBNP. And the correlation analysis also
demonstrated GLS was negatively correlated with NT-proBNP in group B.
Therefore, the level of serum NT-proBNP is consistent with the 3D-STE in
the evaluation of LV systolic function in patients with TVD.