CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
AFRICA
403
without diabetes mellitus were found to have diabetes one month
after surgery.
25
A pure non-metabolic syndrome group of patients
is therefore hard to identify in sufficient numbers among patients
with coronary artery disease.
In our study, the prevalence of 42% of patients with the
metabolic syndrome correlates with others studies where the
metabolic syndrome and CABG were investigated (46, 47,
51%).
10,
29,30
However, in an overview of the metabolic syndrome
in young SouthAfricanAsian patients with myocardial infarction,
the prevalence of the metabolic syndrome, depending on the
definition, was as high as 69%.
26
The perception was that patients with the metabolic syndrome
might be younger. The median age difference was in fact two
years, but this did not reach statistical significance. However
the difference in the EuroSCORE was important. Age older than
60 years adds one percentage point to the EuroSCORE and this
age difference below and above the age of 60 years probably
contributed to the difference in EuroSCORE.
The metabolic syndrome made no impact on the pre-operative
critical core risk factors for mortality after CABG; in fact it was
patients without the metabolic syndrome who were operated on
more urgently than patients with the metabolic syndrome. A
possible explanation for this observation might be that patients
with the metabolic syndrome have underlying risk factors
for coronary artery disease such as hypertension, diabetes
mellitus and dyslipidaemia and therefore are better followed
up and intervention occurs sooner on a more elective basis.
The lack of effect of the metabolic syndrome on renal function
pre-operatively was surprising.
The postoperative outcome demonstrated hardly any difference
between the two groups. The percentage of explorations for
excessive mediastinal drainage was more than double in the
non-metabolic syndrome group (3.0 vs 1.4%), but this did not
reach statistical significance. In a study on the effect of obesity
on the outcome after CABG, the rate of re-operation because of
bleeding was double (
p
<
0.001) in the non-obese patients.
27
The
difference in actual volume of drainage was also not important.
A significant difference between the two groups was indeed
observed in the number of units of homologous red blood cells
transfused. Patients with the metabolic syndrome have higher
BMI and therefore a higher blood volume and better reserves
for loss of blood. It is also postulated that patients with the
metabolic syndrome have less fibrinolytic activity and are more
prone to hypercoagulability.
28
This study could not demonstrate
a difference between the two groups in the percentage of patients
with stroke and renal impairment after CABG.
A Japanese study showed that on multivariate analysis,
the metabolic syndrome had odds ratios of 2.47 (95% CI:
1.22–4.99;
p
=
0.012) for postoperative stroke and 3.81 (95%
CI: 1.42–10.3;
p
=
0.008) for postoperative renal failure.
29
The
group of 319 patients without central obesity, hypertension or
diabetes mellitus had less acute renal impairment after CABG
(5.3 vs 11.4% with the metabolic syndrome;
p
=
0.0035). If
the metabolic syndrome group was compared with this ‘clean’
group, the occurrence of mortality plus major morbidity was
significantly different (15.7 vs 9.1 %;
p
=
0.0095), but it is
probably the renal outcome that drove this finding. As far as the
metabolic syndrome and non-metabolic syndrome per definition
is concerned, this study could not show an effect of the metabolic
syndrome on mortality and major morbidity.
The length of hospital stay was statistically longer in patients
with the metabolic syndrome although the median stay was
similar. This is explained by the fact that the group without
the metabolic syndrome had more patients staying four days or
less, than the group with the metabolic syndrome (41 vs 27%).
Although statistically important, the clinical effect of 0.1 day
(difference in mean) longer or shorter stay is negligible.
In another smaller study (657 patients) than this one, the
hospital stay was also longer for patients with the metabolic
syndrome (8.3 vs 6.6 days;
p
=
0.003). In addition, this smaller
study also found no difference for morbidity, although female
patients with the metabolic syndrome had a higher mortality
rate.
30
Conclusions
This study confirmed the high prevalence of the metabolic
syndrome among patients who undergo CABG. It failed
to demonstrate an effect of the metabolic syndrome on the
pre-operative risk factors for CABG mortality. In fact, patients
with the metabolic syndrome were operated on more electively
than those without the metabolic syndrome. The only negative
outcome in patients with the metabolic syndrome was their
longer stay, although not clinically important. The ‘benefit’
of having the metabolic syndrome was the lower risk for
homologous blood transfusion after surgery.
This study can contribute numbers for future analysis of the
influence of the metabolic syndrome in patients undergoing
CABG. Until then, Simons
et al.
might be correct that the
metabolic syndrome as they see it should only been regarded as
an educational tool and has limited practical value for diagnosis
or management.
31
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