CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 2, March 2012
AFRICA
65
erative period. RV ejection fractions before and after the opera-
tion were not different.
Postoperative RV diastolic parameters are presented in Table
2. In the sequential graft group (A), RV mean E-wave peak
amplitude and E/A ratio were observed to significantly increase
(9.5
±
1.6 vs 7.6
±
2.7 cm/s,
p
=
0.009 and 1.4
±
0.2 vs 0.9
±
0.2,
p
=
0.01, respectively), while RV mean A-wave peak amplitude
and isovolumic relaxation times were found to be significantly
decreased (6.8 ± 2.1 vs 8.3
±
3.4 cm/s,
p
<
0.0001 and 55.2
±
11.9 vs 87.2
±
16.2 ms,
p
<
0.0001, respectively). Although the
right ventricular S-wave peak amplitude decreased in group A, it
did not reach statistical significance (9.1
±
1.3 vs 9.3
±
1.2 cm/s;
p
>
0.05). These findings have suggested that RV diastolic func-
tion improved in the sequential CABG group of patients.
Discussion
Although the echocardiographic assessment of left ventricular
function is simple and well established, there is no gold standard
for assessing right ventricular function by standard echocar-
diography since the evaluation is complicated by the complex
anatomy of the chamber. In general practice, physicians rely
largely on non-invasive imaging methods for assessment of right
ventricular function and two-dimensional echocardiography is
still the mainstay for its analysis. Recently, alternative techniques
have been proposed such as tissue Doppler imaging techniques,
three-dimensional echocardiography, magnetic resonance imag-
ing, and even invasive assessment of pressure–volume loops.
12
RV systole comprises a complex pattern of contractions of the
RV myocardium along its long and short axes as well as rotation
along its longitudinal axis. Despite these caveats, decreased RV
function after CABG has clearly been demonstrated using the
amplitude of tricuspid annular motion assessed by conventional
M-mode or two-dimensional echocardiography immediately
and six months after the operation.
7,8
Subsequently, systolic and
diastolic tricuspid annular velocities recorded by tissue Doppler
imaging were shown to represent the respective systolic and
diastolic functions of the right ventricle.
13,14
However, possible
beneficial effects of sequential venous grafting of the RCA
on right ventricular diastolic function, which the present study
sought to examine, have not been assessed.
The findings of our study showed that RV diastolic function
significantly improved in the patients who underwent saphen-
ous bypass grafting of the RCA using the sequential technique,
whereas the systolic function did not improve. To our knowledge,
this issue has not been studied before. Decreased RV function is
known to occur after CABG operation; both RV filling and RV
contraction are impaired after CABG.
15-17
Cardiac surgery with
cardiopulmonary bypass, cardioplegia, peri-operative myocar-
dial ischaemia, aortic clamping and pericardial disruption/adhe-
sions have all been proposed as the underlying reasons for this
phenomenon.
While the E wave reflects RV relaxation in tissue Doppler
examinations, the A wave is associated with atrial activity. The
E/A ratio shows the passive elongatory ability of RV myocardial
fibres, and a ratio
<
1.0 refers to abnormal compliance.
On the other hand, the isovolumic relaxation time (IVRT)
corresponds to the energy-dependent phase of the cardiac cycle.
It was found to be significantly higher in the sequential graft
group of patients, which may translate into improved compli-
ance. These improvements may be due to haemodynamic
advantages of sequential grafting of the RCA, as O’Neill
et al
.
9
demonstrated higher flow velocity in the proximal segment of a
sequential bypass graft than in individual grafts. The higher the
flow velocity, the better preserved the perfusion and diastolic
function of the right atrium and ventricle may be. This hypoth-
esis could also be supported by the fact that sequential grafting
enables the operation to be completed more quickly, thereby
diminishing the period of total circulatory bypass and the level
of oxidative stress on the right ventricle.
It has been demonstrated that peak systolic velocity (S
wave)
<
11.5 cm/s identifies the presence of RV dysfunction
with a sensitivity and specificity of 90 and 85%, respectively.
18
Tricuspid annulus velocities also decrease in the early and late
(one-year) postoperative period.
16,17
Therefore, similar decreases
in S-wave peak velocities after CABG in both groups (both
<
11.5 cm/s) may initially suggest that the sequential technique
had no positive effect on RV systolic function. On the other hand,
observation of similar decreases in S-wave velocities in both
groups may probably be due to the non-specific harmful effects
of surgery.
TABLE 1. BASAL DEMOGRAPHICAND
ECHOCARDIOGRAPHIC FINDINGS
Demographic characteristics
Group A
(
n
=
20)
Group B
(
n
=
15)
p
-value
Age (years)
62.3
±
4.0 64.7
±
6.2 NS
Male gender,
n
(%)
12 (60)
8 (53)
NS
Hypertension,
n
(%)
14 (70)
9 (60)
NS
Diabetes mellitus,
n
(%)
7 (35)
5 (33)
NS
Smoking,
n
(%)
9 (45)
8 (53)
NS
Hyperlipidaemia,
n
(%)
5 (25)
5 (33)
NS
Family history,
n
(%)
7 (35)
4 (27)
NS
Previous MI,
n
(%)
2 (10)
2 (13)
NS
Basal echocardiographic findings
Left atrial diameter (cm)
4.3
±
0.5 4.4
±
0.7 NS
PASP (mmHg)
34.3
±
13.3 32.9
±
10.8 NS
LVEDD (cm)
4.41
±
0.9 4.39
±
1.1 NS
LVESD (cm)
2.9
±
0.4 2.8
±
0.6 NS
RV S-wave peak velocity (cm/s)
12.7
±
1.8 12.1
±
2.5 NS
RV E-wave velocity (cm/s)
8.1
±
2.0 7.9
±
2.2 NS
RV A-wave velocity (cm/s)
7.2
±
2.4 7.0
±
1.7 NS
RV E/A
1.2
±
0.3 1.1
±
0.4 NS
RV IVRT (ms)
69.2
±
14.6 72.1
±
11.8 NS
PASP: pulmonary artery systolic pressure, LVEDD: left ventricular end-
diastolic diameter, LVESD: left ventricular end-systolic diameter, RV:
right ventricular, IVRT: isovolumic relaxation time, NS: non-significant.
TABLE 2. POSTOPERATIVE FINDINGS OF RIGHT
VENTRICULAR TISSUE DOPPLER EXAMINATION
Group A
(
n
=
20)
Group B
(
n
=
15)
p
-value
RV S-wave peak velocity (cm/s) 9.1
±
1.3 9.3
±
1.2 NS
RV E-wave velocity (cm/s)
9.5
±
1.6 7.6
±
2.7 0.009
RV A-wave velocity (cm/s)
6.8
±
2.1 8.3
±
3.4 0.03
RV E/A
1.4
±
0.2 0.9
±
0.2 0.01
RV IVRT (m)
55.2
±
11.9 87.2
±
16.2
<
0.0001
RV: right ventricular, IVRT: isovolumic relaxation time, NS: non-
significant.
