Methods

Study Subjects

Local Ethical Committee approval was obtained prior to this prospective study (2014/07-07). A total of 34 patients (17 of each gender, mean age 9.9±4.9 years) who were being followed at the Dokuz Eylül University Medical School Allergy Outpatient Clinics were included in the study. Patients eligible for the study group had a positive sweat test and/or gene mutation assay and a stable clinical course with no concomitant cardiac disease. Exclusion criteria included having experienced an acute lower respiratory tract infection in the last three months, being on a waiting list for lung transplantation, and poor quality of the echocardiographic image.
The selected control group consisted of 37 healthy subjects with a comparable age and sex distribution (18 girls and 19 boys with a mean age of 9.8±4.3) and normal physical, laboratory, electrocardiography (ECG) and TTE results.

Echocardiographic studies

Echocardiography examinations were performed with an ultrasound device (model iE33, Philips Medical Systems, Netherlands) with an S5-1 MHz transducer by the same observer, who had been blinded to the clinical condition of the patients. Two researchers who were similarly blinded as to the clinical condition and grouping of the patients performed the data analysis off-line.
Two-dimensional echocardiographic images were obtained in standard parasternal, apical and subcostal views. The following end-diastolic and end-systolic parameters were measured in M-mode echocardiography in a parasternal long-axis view: interventricular septal thickness (IVSd and IVSs, respectively), LV dimensions (LVDd and LVDs), and LV posterior wall thickness (LVPWd and LVPWs). LV systolic function was assessed from an apical four-chamber view by measuring the left ventricular ejection fraction (LVEF) using the modified monoplane Simpson’s rule. Mitral valve inflow Doppler flow was measured in an apical four-chamber image, E-wave (early filling), A-wave (late filling) and the E/A ratio were derived to evaluate LV diastolic function. Pulmonary artery systolic pressure (PAPs) was determined using the Bernoulli equation on the Doppler continuous wave measurement of tricuspid valve insufficiency flow. Right atrial pressure was evaluated using the inferior vena cava inspiratory collapsibility.
Color TDI images were obtained in the apical view. At least four consecutive cardiac cycles were recorded for each parameter. A Doppler frame scanning rate of 100-140 Hz with 40-80 frames/sec was used. Early diastolic myocardial wave (e’), atrial diastolic myocardial wave (a’), systolic myocardial wave (s’), total systolic time (TST), ejection time (ET), isovolumetric relaxation time (IVRT) and isovolumetric contraction time (IVCT) were measured during the baseline pulse-wave color TDI examination of the LV free wall and of the interventricular septum. The myocardial performance index (MPI) was calculated using the following formula: MPI=IVCT+IVRT/ET. Diastolic function was assessed by calculating the E/e’ ratio.
For the STE evaluation with simultaneous ECG at frame rates of 70-100 frames/s, apical four-chamber (A4C), apical three-chamber (A3C) and apical two-chamber (A2C) images were recorded in the apical view and in the parasternal short axis view the parasternal apical (SAXA), parasternal medial (SAXM) and parasternal basal (SAXB) images. At least four consecutive cardiac cycles were recorded for each parameter. The recorded images were transferred onto DVD and analyzed on a computer using the QLAP software (Philips Medical Systems). The mitral annulus lateral and septal and the LV apical endocardial planes were marked for each three apical chambers, providing for automated generation of the LV wall by the program. The LV endocardial-myocardial border was adjusted manually on the systolic frames. Peak systolic strain, peak systolic strain rate and global strain values were calculated automatically by the software for six segments (apical, middle, basal) based on septum and LV lateral wall motion values. In all three parasternal views, the endocardial-myocardial border was adjusted manually after the program had automatically generated the ventricular wall. Patients whose results were abnormal due to poor image quality were excluded from the study.

Statistical Analysis

Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) software, version 22.0 (SPSS Inc.; Chicago, IL, USA). Continuous data were described as mean ± standard deviation while categorical data were presented as numbers of patients. The Chi-squared test was used for comparison of categorical variables, while parametric continuous variables were compared by Student’s t-test. Data were checked for normal distribution by the Kolmogorov–Smirnov test. A value of p<0.05 was considered statistically significant. Evaluations were repeated by a second, independent observer, to assess interobserver variability. Interobserver variability was calculated as the absolute difference divided by the average of the two observations for all parameters.