CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 4, May 2012
AFRICA
187
severity classification system, the Acute Physiology and Chronic
Health Evaluation II (APACHE II) score, was also evaluated.
Methods
In this cohort study, all 135 patients admitted to the medical
ICU (10 beds) from January to July 2008 were enrolled
consecutively. The patients mostly suffered from sepsis (
n
=
21,
15.5%), stroke (
n
=
11, 8.1%) and pulmonary disease, including
chronic obstructive pulmonary disease (COPD) and pneumonia
(
n
=
11, 8.1%). This investigation was approved by the ethics
committee of the Iran University of Medical Sciences. Verbal
consent was obtained from all patients (or from their next of kin)
after detailed explanations and a letter of explanation was given.
On admission to the medical ICU, demographic and baseline
clinical characteristics, including age, gender and APACHE
II score and the diagnoses of all patients were recorded. The
APACHE II system incorporates acute physiological variables
and chronic health evaluation into a measurement of the risk
of in-hospital mortality.
23
Levels of cardiac biomarkers such as
creatine kinase (CK) and creatine kinase isoenzyme (CK-MB),
and history of cardiovascular disease were included. All patients
in the ICU had electrocardiography (ECG) within 24 hours of
admission. The length of stay in the ICU was also recorded. The
clinical endpoint was death or discharge from the ICU at any
time during hospitalisation.
Troponin measurements were collected within the first 24
hours of ICU admission and on the fourth, seventh and 10th
day after admission. This was suggested by the ICU team and
was based on their clinical judgment. Troponin T was measured
using a radio-immunoassay. The analytical sensitivity (lower
detection limit) of this assay is 0.01
µ
g/l. Troponin concentration
of 0.1
µ
g/l was considered normal. Because of a laboratory
mistake, 16 patients did not have troponin T levels measured on
admission, but troponins were measured on days four, seven and
10; these data were included in the analysis. Of all patients, 74
patients had the first two, 47 had the first three, and 25 had four
serial measurements for cTnT concentrations. Patients did not
have cTnT levels measured on discharge or on death.
Statistical analysis
Baseline characteristics of the negative (normal levels) and
positive (elevated levels) cTnT groups were compared using the
Pearson’s chi-square test. Continuous variables were compared
using the Student’s
t-
test for normally distributed variables, and
the Mann–Whitney
U
test if either of these conditions were
not met. Linear regression analysis was done to evaluate the
independent association betweenAPACHE score and cTnT levels.
For evaluation of the changes in cTnT levels during ICU
stay, repeat-measurement ANOVA analysis was carried out.
The Breslow method was used to compare patient survival in
the Kaplan–Meier analysis. Data are presented as mean
±
SD.
A
p
-value less than 0.05 was considered significant. Receiver
operating characteristics (ROC) were used for the detection of
cut-off points for APACHE to predict elevated cTnT levels.
Results
The study population consisted of 135 patients admitted to the
ICU over a period of seven months. There were 73 (54%) men
and 62 (46%) women, with a mean age of 60.9
±
21.5 years,
ranging from 15 to 100 years old.
The most common diagnosis was infectious disease, including
sepsis (
n
=
21, 15.5%), stroke (
n
=
11, 8.1%), and pulmonary
disease, including chronic obstructive pulmonary disease and
pneumonia (
n
=
11, 8.1%). There was no significant difference in
measured cTnT levels on the first, fourth, seventh and 10th days
of ICU stay between patients with different diseases (
p
>
0.05).
History of cardiovascular disease, including MI, hypertension
and heart failure was positive in 51 (37%) patients. The
frequency of patients with elevated cTnT levels was not
significantly different in patients with and without a history of
cardiac disease.
On admission, 83 patients (70.3%) had normal cTnT levels,
whereas 35 (29.7%) had elevated levels
>
0.01 ng/ml, mean
=
0.28
±
0.5 ng/ml (range 0.03–2.00 ng/ml). The clinical and
laboratory characteristics of the two groups are shown in
Table 1. There was no significant difference between the two
groups with normal and elevated cTnT levels in some baseline
characteristics, including Glasgow coma score (GCS) (
p
=
0.223) and partial arterial oxygen tension (PaO
2
;
p
=
0.607) on
admission. A significant difference was found in the APACHE II
score (
p
=
0.003) and serum creatinine levels (
p
=
0.003) between
the two groups with different troponin results.
Patients with negative baseline troponin T levels had a
significantly lower APACHE II score (17.75
±
7.76 vs 24.3
±
8.8,
p
=
0.003). The APACHE II score on the fourth day after
ICU admission was significantly higher in patients with positive
TABLE 1. BASELINE LABORATORY PARAMETERS OF
118 CRITICALLY ILL PATIENTS ONADMISSION TO ICU
Baseline parameters
Negative
cTnT level
(
n
=
83)
Positive
cTnT level
(
n
=
35)
p
-value
Age (years)
59.8
±
21.63 61.3
±
20 0.732
APACHE II score
17.75
±
7.76 24.3
±
8.8 0.003
Mean arterial pressure (mmHg) 93.47
±
13.43 95.17
±
16.24 0.569
Heart rate (beats/min)
91.56
±
19 94.74
±
22.69 0.446
Respiratory rate (per min)
21.41
±
4.52 20.48
±
5.7 0.363
PaO
2
(mmHg)
97.5
±
56.6 91.2
±
46.7 0.607
FiO
2
(%)
61.9
±
27.5 61
±
26.4 0.887
HCO
3
(mmol/l)
25.1
±
8.34 25.11
±
12.67 0.995
Sodium (mmol/l)
141
±
7.05 140.5
±
6.69 0.713
Potassium (mmol/l)
4.11
±
0.6 4.11
±
0.7 0.998
Creatinine (mg/dl)
1.19
±
0.96 2.58
±
2.53 0.003
Haematocrit (%)
35.55
±
9.33 32.5
±
8.33 0.114
White blood cell count (per ml)
12.22
±
6.49 12.22
±
4.97 0.999
pH
7.36
±
0.09 7.34
±
0.1 0.422
Systolic blood pressure (mmHg) 127.4
±
18.6 129.7
±
18.7 0.545
Diastolic blood pressure (mmHg) 76.49
±
12.58 77
±
17.8 0.854
GCS (median)
9
10
0.223
CK (U/l)
236.12
±
255 420
±
735 0.262
CK-MB (ng/ml)
28.63
±
21 128.3
±
190 0.72
Male/female (ratio)
45/38
17/18
0.531
History of cardiac disease
(yes/no)
29/54
12/23
0.959
ST change on ECG (yes/no)
36/47
18/15
0.29
PaO
2
: arterial O
2
tension, FiO
2
: fraction of inspired oxygen, HCO
3
-
: bicar-
bonate, GCS: Glasgow coma scale, CK: creatine kinase, CK-MB: creatine
kinase-MB.
