32 / 84
CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 2, March/April 2018
94
AFRICA
The study population was composed of 819 patients. Their
clinical features and laboratory findings were collected using
electronic medical records.
The study was approved by the local institutional review
board and was conducted according to the Declaration of
Helsinki. The institutional review board exempted written
informed patient consent (MJH 2015-01-068).
Carotid artery examination was performed using a Vivid
E9 ultrasound system (GE Healthcare, Little Chalfont, UK)
and an 11L linear probe. Mean CIMT measurements were
performed by an experienced ultrasonographer on the far wall of
both common carotid arteries at end-diastole along an arterial
segment of 10 mm in length located 10 mm proximal to the
carotid bulb, using semi-automated border detection software.
Carotid plaques were defined as focal and isolated areas of
abnormal intima protruding into the lumen, greater than 15
mm or 50% of the surrounding IMT value.
16
Carotid plaque-free
segments were evaluated for CIMT analysis.
The mean CIMT value was calculated by averaging the CIMT
measurements of the left and right common carotid arteries. For
evaluating carotid plaque, the common carotid arteries, carotid
bifurcations and external and internal carotid arteries were
scanned. We also evaluated the incidence of a composite of a
CIMT value higher than the 75th percentile plus the presence
of carotid plaque. We defined this composite as subclinical
atherosclerosis. The 75th percentile values of the mean CIMT
value were estimated according to gender.
Abdominal ultrasound is the most commonly used imaging
tool for diagnosing fatty liver disease.
17
Abdominal ultrasound
examination was performed by an experienced ultrasonographer
using an Acuson Sequoia 512 ultrasound system (Siemens
Medical Solutions, USA) and a 4C1 curved probe. Normal
liver echogenicity was equal to the echogenicity of the cortex of
the right kidney.
18
Fatty liver disease was diagnosed if the liver
echogenicity was diffusely increased compared to the cortex
echogenicity of the right kidney.
19,20
Calcium score CT was performed to evaluate for coronary
artery calcifications (GE LightSpeed VCT, USA). CT images
were obtained with a 2.5-mm slice thickness from the carina to
the bottom of the heart. The CACS from all calcified plaques
in the coronary tree was calculated by an automated program
according to the Agatston method.
21
We also evaluated the
incidence of a CACS over 100, which was a threshold in a
previous study, known to increase the risk of atherosclerotic
cardiovascular disease.
22
Statistical analysis
All data were summarised as frequencies and percentages or
means and standard deviations. The laboratory findings of
liver function and lipid profiles were summarised as median
and interquartile range. The Pearson chi-square test was used
to compare categorical variables. The Student’s
t
-test was used
to compare continuous variables and the Mann-Whitney
U-
test
was used when the sample size of at least one group was less
than 30. The mean CIMT value, CACS value and the presence
of carotid plaques were stratified by age.
Univariate followed bymultivariate logistic regression analyses
were performed to evaluate the association between subclinical
atherosclerosis and fatty liver disease, with adjustments for
individuals following traditional risk factors for atherosclerosis:
age, hypertension, diabetes and dyslipidaemia. A
p
-value of less
than 0.05 was considered statistically significant. All analyses
were performed using SPSS 18.0 (SPSS Inc, Chicago, IL).
Results
Among a total of 819 patients (mean age: 53.3
±
11.2 years
old) who met the inclusion criteria for this study, 330 (40.3%)
patients had fatty liver disease. Patients’ baseline characteristics
are presented in Table 1. Patients with fatty liver disease had
significantly larger waist and hip circumferences and body mass
indices than patients without fatty liver disease. In addition,
patients with fatty liver disease had a higher incidence of
medical co-morbidities, including hypertension, diabetes and
dyslipidaemia and had worse clinical laboratory findings,
including haemoglobin A
1c
, homocysteine, total cholesterol,
triglycerides, low-density lipoprotein cholesterol, aspartate
aminotransferase, alanine aminotransferase, gamma-glutamyl
transpeptidase and alkaline phosphatase levels than patients
without fatty liver disease.
Of the 819 patients, the mean CIMT was 0.77
±
0.17 mm;
194 (23.7%) patients had carotid plaques (Table 2). The CIMT
was significantly higher in patients with fatty liver disease than
among patients with normal livers (0.79
±
0.17 vs 0.76
±
0.17
mm,
p
=
0.012). Carotid plaques were identified more commonly
in patients with fatty liver disease, but did not reach statistical
significance (27.0 vs 21.7%,
p
=
0.094). The incidence of a
composite of larger CIMT (
≥
75th percentile) plus the presence
of carotid plaque was significantly higher in patients with fatty
liver disease (43.3 vs 36.0%,
p
=
0.041). The 75th percentile
CIMT value of male patients was 0.92 mm and that of female
patients was 0.88 mm.
Among 819 patients, 561 (68.5%) had a CACS of zero. The
mean CACS was 53.07
±
250.14 (Table 2). Conversely, there were
no significant differences in the mean CACS and in the incidence
of a CACS greater than 100 between patients with fatty liver
disease and those with normal livers.
Table 3 shows the mean CIMT values, the presence of carotid
plaques, and the CACS according to the age groups. Interestingly,
among patients under 50 years old (
n
=
310), the CIMT value
was significantly higher in the group with fatty livers than among
those with normal livers. These young patients with fatty liver
disease had increased risk of subclinical atherosclerosis [odds
ratios (OR) 1.92, 95% confidence interval (CI): 1.05–3.49,
p
=
0.034]. After adjustment for age, hypertension, diabetes and
dyslipidaemia, fatty liver disease also increased the risk of
subclinical atherosclerosis in young patients (OR 1.90, 95% CI:
1.01–3.59,
p
=
0.047].
However, there were no significant differences in CACS
and carotid plaque presence among patients with fatty liver
disease compared to those with normal livers according to age
group. Young patients with fatty liver disease did not have a
significantly increased incidence of CACS
>
100 (OR 0.79, 95%
CI: 0.14–4.37,
p
=
0.785) or incidence of carotid plaque presence
(OR 1.65, 95% CI: 0.74–3.70,
p
=
0.221).
Of the patients with a CACS of zero (
n
=
561), the patients
with fatty liver disease (
n
=
212) had a significantly higher mean
CIMT value than the patients with normal livers (
n
=
349) (0.77
±
0.15 vs 0.72
±
0.16 mm,
p
=
0.002) (Fig. 1). In addition, among