CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
400
AFRICA
The effect of the metabolic syndrome on the risk and
outcome of coronary artery bypass graft surgery
MARIUS J SWART, WIHAN H DE JAGER, JOHANN T KEMP, PAUL J NEL, SAREL L VAN STADEN,
GINA JOUBERT
Abstract
Background:
The individual components of the metabolic
syndrome are risk factors for coronary artery disease.
The underlying pathophysiology of a low-grade inflamma-
tory process postulates that the metabolic syndrome could
compromise a procedure such as coronary artery bypass
graft surgery (CABG) done on cardiopulmonary bypass
(CPB).
Methods:
From a single institution, 370 patients with the
metabolic syndrome (IDF and ATP III criteria) and 503
patients without the metabolic syndrome were identified. The
influence of the metabolic syndrome on the pre-operative
core risk factors for CABG mortality as well as its effect on
the mortality and major morbidity post surgery were inves-
tigated.
Results:
Patients with the metabolic syndrome were operated
on less urgently than those without the metabolic syndrome.
The EuroSCORE was also lower in those with the metabolic
syndrome. Patients with the metabolic syndrome required
fewer units of homologous red blood cells, but stayed statisti-
cally longer in hospital.
Conclusions:
In this surgical population the metabolic
syndrome had no detrimental clinical effect on either the
pre-operative risk factors or the outcome after CABG.
Keywords:
CABG, metabolic syndrome
Submitted 14/6/11, accepted 4/7/12
Cardiovasc J Afr
2012;
23
: 400–404
DOI: 10.5830/CVJA-2012-055
Major surgery such as coronary artery bypass graft surgery
(CABG) has the risk of mortality and morbidity. Co-morbidities
will contribute to this potential risk of complications. In the well-
known Parsonnet risk model for mortality from the late eighties,
obesity, hypertension and diabetes mellitus were all risk factors
for mortality.
1
Opposed to that, none of these risk factors were
considered important in the EuroSCORE, which was developed
a decade later, from 19 000 patients in Europe who had had a
CABG.
2
In a recent study of 10 000 patients, obesity was not a risk
factor for immediate mortality after CABG.
3
Large studies are
required to have the power to reach statistical significance and
to demonstrate the influence of such co-morbidities. Combining
146 000 patients from various hospitals showed a mortality of
3.7% for patients with diabetes mellitus and 2.7% for those
without diabetes mellitus.
4
According to the Society of Thoracic Surgeons’ database, the
odds ratio for mortality for patients with diabetes mellitus and
hypertension is 1.3 and 1.2, respectively, compared to a redo
CABG with an odds ratio of 3.1.
5
A combination of these risk
factors could strengthen their individual statistical power.
A triad of obesity (in particular central obesity), hypertension
and diabetes mellitus fulfils the criteria for the metabolic
syndrome. Dyslipidaemia is the fourth factor for diagnosing the
metabolic syndrome.
In 1988 Gerald Reaven attributed the irregularities associated
with the metabolic syndrome to insulin resistance.
6
Abdominal fat
functions as an endocrine organ that secretes pro-inflammatory
adipokines, which could be the underlying pathophysiology
for insulin resistance.
7
C-reactive protein (CRP) is a marker of
subclinical inflammation and a predictor of coronary incidents.
8
Furthermore, central obesity leads to an increase in CRP. In fact,
as the various components of the metabolic syndrome are added,
the CRP increasingly rises.
9
If a patient has an underlying inflammatory condition, as
with the metabolic syndrome, and is subjected to a further
inflammatory insult during cardiopulmonary bypass, it is
postulated that the risk for mortality and morbidity could be
higher. This was confirmed by a study in 2007. The prevalence
of the metabolic syndrome among these 5 300 patients was 46%.
The relative risk for mortality for patients with the metabolic
syndrome was 3.04 (95% CI: 1.73–5.32;
p
=
0.0001). Obesity
and diabetes mellitus, as single risk factors, could not be
established as independent hazards for mortality.
10
Morbidity
was also more prominent among patients with the metabolic
syndrome.
A year later another study came to a different conclusion. The
metabolic syndrome had no impact on survival after treatment.
These patients were treated with medication (
n
=
516), by
percutaneous coronary intervention (
n
=
1 274), and CABG
(
n
=
1 096).
11
The prevalence of the metabolic syndrome is high. Among
United States adults older than 20 years it is 24%, increasing
with age to 40% among 60-year-olds.
12
But it is not only a
problem of the West. China experiences an epidemic of obesity,
with the metabolic syndrome present in 13% of adults.
13
In South
Africa the prevalence is unknown, but from a study done in the
Free State province among blacks, it could be as high as 31%,
using the WHO criteria.
14
Mediclinic Bloemfontein, South Africa
MARIUS J SWART, MB ChB, FCS (SA),
School of Medicine, University of the Free State,
Bloemfontein, South Africa
WIHAN H DE JAGER
JOHANN T KEMP
PAUL J NEL
SAREL L VAN STADEN
Department of Biostatistics, Faculty of Health Sciences,
University of the Free State, Bloemfontein, South Africa
GINA JOUBERT, MSc
