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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 1, January/February 2017
52
AFRICA
has yet to be demonstrated in the generation of AF. Therefore,
further research is needed to clarify whether, like other factors,
free fatty acid burden associated with hyperlipolytic visceral fat
storage contributes to the generation of postoperative AF.
27
It is believed that MS patients are more prone to postoperative
AF through a potential pathway.
28
Atrial remodelling involves
two substrates: atrial architecture acting as an anatomical
substrate (involved in atrial dilatation, fibrosis), and electrical
inhomogeneity acting as a functional substrate (involved
in shortness of effective refractory period, dispersion of
refractoriness and conduction, abnormal automaticity, and
anisotropic conduction).
29
These latter processes have been
shown to be potential substrates for postoperative AF.
30
Bell andO’Keefe reported that postoperative AFwas observed
in 25% of patients undergoing CABG, and was associated with
elevated rates of mortality and postoperative stroke, prolonged
hospital stay and increased cost of hospitalisation.
31
Kara
et al
.
32
found that the incidence of AF was high (19.2%) after CABG,
and they defined some independent clinical predictors.
Echahidi
et al
.
2
reported that the MS had a significant
effect on clinical outcomes after cardiac surgery and was an
independent predictor of postoperative AF. Girerd
et al
.
33
showed a significant correlation between postoperative AF
and increased waist circumference and/or increased C-reactive
protein levels. The authors also reported that the MS was an
independent risk factor for AF occurring after CABG.
32
In our
study, the rate of AF was significantly higher (20.9%) in MS
patients compared to those without the MS (
p
<
0.01).
Gharipour
et al
.
34
found no significant difference in the
incidence of postoperative stroke between CABG patients with
and without the MS. In our study, although the rate of stroke
was higher in MS patients (6.3 vs 1.1%), it was not associated
with a significant difference (
p
=
0.162). This may be attributed
to the absence of atherosclerotic plaque in the carotid arteries.
In our patients, carotid Doppler ultrasound showed moderate
stenosis (50–70%), which was considered insufficient to lead
to haemodynamically significant conditions. Carotid stenosis
is an important risk factor for stroke during CABG surgery,
but neurological events may develop from other causes as well,
including aortic and carotid atherosclerosis (62%), intracardiac
thrombi (1%), haemorrhage (1%), hypoperfusion (11%), and
other factors of unknown origin (25%).
35
The severity of carotid
stenoses detected in patients undergoing CABG has been reported
as greater than 70% in 10% of the cases, 50–70% in 9–22% of
the cases, and less than 50% in 80–91% of cases.
35,36
Of interest,
50–75% of patients who suffered a stroke did not have carotid
stenosis.
37
Lee
et al
.
38
reported that intracranial atherosclerosis was
the main determinant of stroke, while extracranial atherosclerotic
processes played a relatively smaller role.
Of note, pre-operative critical risk factors for mortality after
CABG were not affected by the MS. By contrast, patients without
the MS required urgent operations more frequently than did
those with the MS. This is not surprising because patients with
the MS are normally on strict follow up to control hypertension,
diabetes mellitus and dyslipidaemia, all of which are known to
be underlying risk factors for coronary artery disease. Therefore,
patients without the MS and with poorly controlled coronary risk
factors are more likely to have urgent, non-elective interventions.
The presence of factors known to increase mortality rates in
MS patients may itself be a limitation to the study. These factors
include male gender, widespread coronary artery involvement,
and increased cross-clamping time. Therefore, the effect of the
MS on mortality rate itself may be considered a limitation. The
biggest limitation was that the study was underpowered to draw
conclusions on some of the outcomes, for example, mortality.
Components of the MS cannot be completely minimised
by conventional pharmacological treatment modalities. It
is well known that statins, angiotensin converting enzyme
inhibitors, and beta-blockers have little or no effect in metabolic
disturbances observed in MS cases.
28
Conclusion
Since MS patients already present with many cardiovascular risk
factors, the MS was associated with increased morbidity rates in
the early postoperative period after CABG; however, its effect on
early mortality rate was similar to that seen in patients without
the MS. Considering the increased postoperative morbidity rate,
the MS should be taken into consideration in pre-operative
assessment of CABG patients.
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