CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
AFRICA
401
A study was therefore undertaken to investigate the
consequences of the metabolic syndrome on a local population
of CABG patients. This was done to establish its effect on the
pre-operative risk factors for mortality as well as on the outcome
after CABG.
Methods
The study was an analytical cohort study. The target population
was all patients who had had a CABG done by one surgeon (MJS)
at the Mediclinic Bloemfontein between November 2000 and
October 2010. The metabolic syndrome was defined according
to the criteria set by the International Diabetes Federation (IDF)
in 2005.
15
When the body mass index (BMI) was
<
30 kg/m
2
but hypertension, diabetes mellitus and dyslipidaemia were
present, the definition from the National Cholesterol Education
Programme Adult Treatment Panel (ATP III) in 2001 was used
16
(Table 1). Central obesity was assumed with a BMI
≥
30 kg/m
2
,
which is acceptable according to IDF criteria.
To ascertain the effect of the metabolic syndrome on the
pre-operative risk factors for mortality after CABG, the seven
core risk factors from a previous study were used and adapted.
17
These risk factors were older age, female gender, re-operation,
left ventricular ejection fraction
≤
40%, critical left main stem
disease, number of bypasses as an indication of disease severity,
and urgency of operation. In this study, urgency was assumed
when the operation was done from the coronary care unit
with or without an intra-aortic balloon pump (IABP). These
patients included those admitted with unstable angina and acute
myocardial infarction.
Further information that was gathered included the older
additive EuroSCORE for each patient and renal function
according to the shortened Modification of Diet in Renal Disease
formula (sMDRD).
18
Patients with chronic kidney disease grade
III were also documented.
Postoperative data that were evaluated were the Society of
Thoracic Surgeons’ major negative outcomes: re-exploration,
permanent stroke, renal impairment (new dialysis or 50% rise
in serum creatinine level from pre-operative value), mechanical
ventilation longer than 48 hours, and deep sternal infection,
but for this study rewiring of the sternum for dehiscence was
considered deep sternal infection.
19
Patients who were discharged,
but re-admitted within six weeks for sternal rewiring were
considered part of the study. Other information obtained from
patient records included the mediastinal drainage, homologous
red blood cell transfusion, in-hospital mortality, and length of
stay (LOS).
Patients were excluded from this study if it was not possible
to make a diagnosis of the metabolic syndrome. Those patients
who had a major procedure combined with the CABG, patients
who were on pre-operative dialysis, and those who died on the
operating table were also excluded. The study group was divided
between patients with the metabolic syndrome and those without
the metabolic syndrome. A group without central obesity,
hypertension or diabetes mellitus was also identified.
Statistical analysis
All the data were analysed by the Department of Biostatistics at
the University of the Free State. Numerical data are expressed
as means and ranges. Categorical variables are indicated in
percentages. Differences were assessed using chi-square tests,
Fisher exact tests,
t
-test or Kruskall-Wallis tests depending on
the data type. This study was approved by the Ethics Committee
of the Faculty of Health Sciences at the University of the Free
State, Bloemfontein. All data were treated anonymously.
Results
The initial study population was 1 475 patients. Unfortunately
495 patients had insufficient information to diagnose them with
the metabolic syndrome or definitely exclude the metabolic
syndrome. Ninety-three patients had another major cardiac
procedure with the CABG and were not considered for the study.
Three patients had an associated malignant resection at the time
of cardiac surgery. Seven patients who had been on renal dialysis
before the surgery were excluded, as were the four patients who
died in theatre and could not be evaluated postoperatively.
From the remaining patients, 370 had the metabolic syndrome
(322 according to the IDF criteria) and 503 patients did not meet
the criteria. The prevalence of the metabolic syndrome among
this study group was 42%. Of the group without the metabolic
syndrome, 319 had no central obesity, hypertension or diabetes
mellitus. On the other hand, 169 patients from the non-metabolic
syndrome group had at least one of these three criteria and 15
had two criteria of the metabolic syndrome. However, three
criteria are needed to diagnose the metabolic syndrome.
Table 2 summarises the results for the two groups, patients
with the metabolic syndrome and those without the metabolic
syndrome. The gender distribution was equal between the groups.
Although the metabolic syndrome patients were slightly younger
(median 59 years) than the non-metabolic syndrome group
(median 61 years), this did not reach statistical significance.
As far as the other risk factors for mortality after CABG are
concerned, there was no difference with regard to redo CABG,
poor ventricular function, main stem lesion and number of
bypasses. However, the metabolic syndrome group was operated
on less urgently, as 67.6% were operated from the coronary care
unit compared to 75.7% of the non-metabolic syndrome group
(
p
=
0.0076).
The mean EuroSCORE also differed statistically (
p
=
0.0494).
The metabolic syndrome group had a mean EuroSCORE of
3.26 (median 3) and the non-metabolic syndrome group 3.61
(median 3). The mean sMDRD was 76.2 and 76.1 ml/min for
TABLE 1. CRITERIA FOR THE METABOLIC SYNDROME
ATP III (2001)
IDF (2005)
Three or more:
1. Abdominal obesity:
waist circumference
≥
94–102 cm (males)
≥
80–88 cm (females)
2. Triglycerides:
≥
1.7 mmol/l
3. HDL-C:
<
1.03 mmol/l (males)
<
1.29 mmol/l (females)
4. Hypertension:
systolic
≥
130 mmHg
or diastolic
≥
85 mmHg
5. Fasting blood glucose:
≥
6.1 mmol/l
Central obesity
Waist circumference, ethnicity specific
plus any two:
1. Triglycerides:
≥
1.7 mmol/l or specific treatment
2. HDL-C:
<
1.03 mmol/l (males)
<
1.29 mmol/l (females)
or specific treatment
3. Hypertension:
systolic
≥
130 mmHg
or diastolic
≥
85 mmHg
or specific treatment
4. Fasting plasma glucose:
≥
5.6 mmol/l
or previously diagnosed type 2
diabetes
HDL-C: high-density lipoprotein cholesterol.
