21 / 80
CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 3, May/June 2017
AFRICA
155
chronic kidney disease, chronic obstructive pulmonary disease,
bundle brunch block, atrioventricular block and malignancy.
The patients were evaluated with echocardiography and 12-lead
ECG at least 10 days after an attack. Levels of haemoglobin and
C-reactive protein (CRP), and erythrocyte sedimentation rate
(ESR) and white blood cell count (WBC) were obtained from
laboratory records.
The study protocol was approved by the institutional ethics
committee. Informed written consent was obtained from each
patient.
Twelve-lead ECGs (10 mm/mV, 25 mm/s, Cardiofax V; Nihon
Kohden Corp, Tokyo, Japan) were obtained with the subject
at rest in the supine position. All ECGs were transferred to a
computer via a scanner and then used at 400% magnification via
Adobe Photoshop software. Measurements of Tp-Te and QT
intervals were performed on the computer by two experienced
cardiologists, who were blinded to the clinical data of each
patient and control subject.
QT and R-R intervals were measured in all derivations. The
QT interval was defined as the time from the start of the QRS
to the point at which the T wave returns to the isoelectric line.
The R-R interval, which was measured as the average of three
complexes, was used to calculate heart rate, and the QTc was
calculated with Bazett’s formula.
13
The QTd was defined as the
difference between the maximum and minimum QT interval in
different leads. Excluded from the study were subjects with U
waves and low-amplitude T waves on their ECGs.
Although tail and tangent methods can be used in the
measurement of Tp-Te interval, the tail method is a better
predictor of mortality than the tangent method,
14
and was
therefore used in this study. In this method, the Tp-Te interval
was defined as the interval from the peak to the end of the T
wave to the point where the wave reached the isoelectric line.
15
Measurement of the Tp-Te interval was obtained from leads V2
and V5, corrected for heart rate (cTp-Te).
11
The Tp-Te/QT and
cTp-Te/QT ratios were calculated from these measurements.
Measurements were made by two independent cardiologists
taking the average of three consecutive beats. Intra-observer
variability for Tp-Te interval obtained from leads V2 and V5
were 3.4 and 3.8%, respectively. Furthermore, inter-observer
variability for the Tp-Te interval obtained from leads V2 and V5
were 2.5 and 2.9%, respectively.
All echocardiographic examinations (General Electric Vivid
S5, Milwaukee, WI, USA) were performed in all subjects
using a 2.5–3.5-MHz transducer in the left decubitus
position. Two-dimensional and pulsed Doppler measurements
were obtained using the criteria of the American Society
of Echocardiography.
16
Left ventricular ejection fraction
(LVEF) was assessed using Simpson’s method. Left ventricular
end-diastolic and end-systolic volumes (LVEDV and LVESV)
were performed using Simpson’s method in the apical four- and
two-chamber views at end-diastole and end-systole.
Statistical analysis
Statistical analyses were performed using SPSS software (SPSS
18.0 for windows, Inc, Chicago, IL, USA). Categorical variables
are expressed as
n
(%) and continuous variables are expressed as
mean
±
standard deviation. Mean values of continuous variables
were compared between the groups using the Student’s
t
-test.
The chi-squared test was used to assess differences between
categorical variables. The relationship between parameters
was determined using Pearson’s coefficient of correlation.
Multivariate linear regression analysis was used to identify
the independent predictors of prolonged cTp-Te interval and
independent variables that differed significantly in the bivariate
analyses (
p
<
0.1). A
p
-value
<
0.05 was considered significant.
Results
Baseline demographic, clinical and echocardiographic
characteristics of all subjects are shown in Table 1. Age, gender,
body mass index, and glucose and cholesterol levels were similar in
both groups. All subjects had similar heart rates, and no significant
differences were observed in blood pressure between the groups.
The standard echocardiographic values were within normal limits
for both groups. Additionally, erythrocyte sedimentation rate
(ESR) and and C-reactive protein (CRP) levels were significantly
higher in FMF patients compared with the controls.
Table 2 shows ECG measurements of the two groups. Heart
rate, QT interval, QTd, QTc interval and QTc dispersion were
similar between the groups. The Tp-Te and cTp-Te intervals
(Fig.1), and Tp-Te/QT and cTp–Te/QT ratios were significantly
prolonged in FMF patients compared to the controls.
Correlations and regression analyses between the cTp-Te
interval in the V5 lead and the study parameters were performed.
There were significant correlations between the cTp-Te interval
and ESR (
r
=
0.418,
p
<
0.001) and CRP levels (
r
=
0.382,
p
<
0.001) and neutrophil–lymphocyte ratio (NLR) (
r
=
0.192,
p
=
0.033) and mitral E/A ratio (
r
=
–0.190,
p
=
0.034) (Fig. 2A, B).
Table 1. Demographic, echocardiographic and biochemical
characteristics in patients with FMF and controls
FMF patients
(
n
=
66)
Controls
(
n
=
58)
p
-value
Age (years)
26.0
±
5.0
26.5
±
5.5
0.616
Female,
n
(%)
39 (59.1)
35 (60.3)
0.887
BMI (kg/m
2
)
24.1
±
4.3
22.7
±
4.3
0.079
BSA (m
2
)
1.96
±
0.17
1.63
±
0.18 0.051
E/A ratio
1.58
±
0.5
1.46
±
0.44 0.182
LVEDV (ml)
92.6
±
6.5
91.3
±
6.4
0.253
LVESV (ml)
77.4
±
12.8
79.6
±
12.4 0.830
LVEF (%)
55.5
±
3.7
54.9
±
3.4
0.352
Glucose (mg/dl)
91.5
±
9.1
89.6
±
7.6
0.223
(mmol/l)
(5.05
±
0.51)
(4.97
±
0.42)
Total cholesterol (mg/dl)
163.9
±
28.6 162.1
±
32.5 0.750
(mmol/l)
(4.25
±
0.74)
(4.20
±
0.84)
LDL cholesterol (mg/dl)
103.3
±
26.3
96.4
±
29.1 0.164
(mmol/l)
(2.68
±
0.68)
(2.5
±
0.75)
Haemoglobin (mg/dl)
14.3
±
1.5
14.8
±
1.2
0.099
CRP (mg/l)
6.0
±
4.8
3.8
±
0.9
<
0.001
ESR (mm/h)
11.4
±
12.5
6.4
±
5.7
0.006
NLR
2.09
±
1.05
2.0
±
0.68 0.577
WBC count (×10
9
/l)
7.37
±
1.82
7.76
±
1.93 0.244
BMI
=
body mass index; BSA
=
body surface area; LVEDV
=
left
ventricular end-diastolic volume; LVESV
=
left ventricular end-
systolic volume; LVEF
=
left ventricular ejection fraction; LDL
=
low-density lipoprotein; CRP
=
C-reactive protein; ESR
=
erythrocyte
sedimentation rate; NLR
=
neutrophil–lymphocyte ratio; WBC
=
white blood cell. Data are presented as mean
±
SD.