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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 1, January/February 2017
AFRICA
49
after cardiovascular interventions, and its association with early
and late mortality and morbidity following coronary artery
bypass graft (CABG) surgery has recently been reported,
10
several
studies failed to find such an association.
11-13
We hypothesised
that the MS could adversely affect the outcome in patients
undergoing CABG surgery and designed a prospective study to
determine the impact of the MS on postoperative morbidity and
mortality rates after CABG.
Methods
We prospectively enrolled 152 consecutive patients who underwent
elective CABG at Siyami Ersek Thoracic and Cardiovascular
Surgery Centre, Istanbul, Turkey, between January and September
2011. Diagnosis of the MS was made according to the NCEP
ATP III criteria. Patients were divided into two groups (with and
without the MS) depending on the MS diagnosis.
Pre-operative and operative data of all patients were
prospectively collected and transfered to a computerised database.
Demographic features, and clinical, laboratory and intensive care
unit (ICU) data of the patients were obtained by trained personnel
supervised by a nurse author, as well as data on risk factors,
medications and functional status. Postoperative complications
were recorded prospectively by an author, and all major adverse
events were simultaneously validated by an experienced cardiac
surgeon according to standardised definitions.
Patients undergoing emergency surgery, re-operative
surgery, CABG on a beating heart, additional valve repair
or replacement, having an ejection fraction of less than 45%,
requiring pre-operative pacemaker implantation, and those with
liver failure were excluded from the study. The study protocol
was approved by the institutional review board of the hospital.
Demographic and clinical features included age, gender, mean
blood pressure, body mass index (BMI), waist circumference,
smoking status and co-morbidities, including type 2 diabetes
mellitus, systemic hypertension and obesity. Weight was measured
in kilograms using a calibrated digital scale, height was measured
in centimetres using a calibrated stadiometer (Seca GmbH & Co,
Germany) and body mass index (BMI) was calculated. Waist
circumference was measured by a trained nurse, with a cloth tape
around the waist placed in a mid-axillary line at the midpoint
between the highest point of the iliac crest and the lowest part
of the costal margin. Diabetes mellitus was defined as the use of
diabetes medications or fasting plasma glucose concentration of
≥ 110 mg/dl (6.11 mmol/l).
The patients’ characteristics included the following: age,
gender, height, BMI, waist circumference, duration of diabetes,
alcohol consumption, use of insulin or anti-diabetic drugs,
low-density lipoprotein (LDL-C) and high-density lipoprotein
cholesterol (HDL-C), triglyceride and fasting blood glucose
levels, smoking status, levels of postprandial blood glucose
(PPBG), blood urea nitrogen (BUN), creatinine, aspartate
aminotransferase (AST), alanine aminotransferase (ALT),
HbA
1c
, haematocrit, haemoglobin, thyroid stimulating hormone
(TSH) and free T
4
, number of grafts used during CABG, left
ventricular ejection fraction, and percentage of carotid artery
stenosis on Doppler ultrasonography.
Blood pressure (BP) measurements were made pre-operatively
using a mercury sphygmomanometer with the patient in a
sitting position following at least a 10-minute rest. The average
of three measurements taken at two-minute intervals was
defined as clinical BP. Hypertension was defined as BP being
≥ 140/90 mmHg from at least two measurements or the use of
antihypertensive therapy. A total cholesterol level of
>
200 mg/
dl (5.18 mmol/l) or a history of elevated serum total cholesterol
during the past six months resulting in lipid-lowering drug use
was defined as hyperlipidaemia. Current smokers and former
smokers who had stopped smoking within the past three years
were considered smokers.
Peri-operative variables included the number of CABG
surgeries, number of grafts, cardiopulmonary bypass time
(min) and aortic cross-clamp time. Postoperative variables
were all-cause mortality, death within one month after the
operation, renal failure, postoperative creatinine level
>
2.5 mg/dl (221 mmol/l), need for haemodialysis, the use of
prolonged pulmonary ventilator
>
24 hours, acute myocardial
infarction, ST-segment changes, prolonged ventilation (more
than 72 hours), re-intubation, wound infection, stroke and
regional neurological dysfunctions that resolved within 24 hours
with no sequela. Additional data included the length of ICU and
hospital stay.
Under local anaesthesia, radial and pulmonary arterial
catheters were introduced. In all patients, anaesthesia induction
was obtained before tracheal intubation using midazolam 0.05–
0.1 mg/kg, fentanyl 4–8 µg/kg or sufentanil 0.6–0.8 µg/kg,
atracurium 0.5 mg/kg or pancuronium 0.1 mg/kg and thiopental
sodium 1–2 mg/kg. All operations were performed under CPB at
mild to moderate hypothermia (28–32°C). Myocardial protection
was ensured by intermittent antegrade or combined antegrade
and retrograde saline or blood cardioplegia. Operative outcomes
included the CPB time and aortic cross-clamp time.
Statistical analysis
Statistical analysis was done using the NCSS 2007 software
(Number Cruncher Statistical System, LCC Statistical Software,
Utah, USA). Data are expressed with descriptive statistics using
mean
±
standard deviation, median, frequency and percentage.
The Kolmogorov–Smirnov test was used to assess the compliance
of numerical variables with normal distribution. The two groups
were compared with regard to pre-operative demographic data,
operative data and early postoperative morbidity and mortality
rates. The Student’s
t
-test was used for intergroup comparisons
of normally distributed variables, including age, BMI, female
and male waist circumference, ejection fraction, number of
grafts, CPB, aortic cross-clamp time, PPBG, BUN, creatinine,
total cholesterol, LDL-C, HDL-C, haematocrit, haemoglobin,
free T
4
and HbA
1c
values.
Variables that did not show a normal distrubution
(EuroSCORE, fasting blood glucose, AST, ALT, triglycerides,
TSH, drainage, ICU stay, hospital stay, erethrocyte sedimentation
rate and fresh frozen plasma) were compared using the Mann–
Whitney
U
-test. For the comparison of categorical variables,
Pearson’s chi-squared test was used when expected and observed
counts were sufficient, Yates’ correction for continuity test was
used when observed counts were insufficient (
<
20), and Fisher’s
exact test was used when expected counts were insufficient (
<
5).
A
p
-value
<
0.05 was considered statistically significant. A
post
hoc
power analysis showed the adequacy of the sample size for
further analyses.