Left Ventricular Function in Children and Adolescents With Type 1 Diabetes Mellitus

Study population

We studied 38 children and adolescents who participated in the 2007 Diabetes Summer Education Camp in Daegu and 9 pediatric patients who were attending the Diabetes Clinic for Children of the Keimyung University Dongsan Medical Center. All patients were diagnosed with type I DM and received insulin therapy only. The patients consisted of 16 boys and 31 girls, with a mean age of 12.8 years (range, 7.1-16.8 years). The mean duration of disease was 3.4 years (range, 0.3-7.7 years). None of the patients had definite DM-induced complications, including renal impairment, retinopathy, neuropathy, and clinical symptoms of cardiac dysfunction or cardiomyopathy. The conventional laboratory chemistry results were normal, except for the glycosylated hemoglobin (HbA1c) level. The control group consisted of 38 children (18 boys and 20 girls), with a mean age of 11 years (range, 6.9-17.1 years). They were referred to us with a chief complaint of heart murmurs or chest pain, and did not show abnormal findings on laboratory testing, electrocardiograms, or echocardiography.

Echocardiography

An echocardiography was performed using an Acuson Sequire 512 (Siemens Medical Solution, Mountain View, CA, USA) with a 4 or 8 MHz transducer. All of the tests which were performed were saved on a hard drive and magneto-optical (MO) disk of echocardiographic equipment. On the parasternal long axis view, with the use of M-mode and conventional echocardiography, several parameters, including fractional shortening (FS), ejection fraction (EF), LV dimension, and volume per surface area, were measured.

For diastolic functional analysis, the mitral inflow signal was acquired in an apical four-chamber view. The pulsed Doppler sample volume was 2 mm and it was placed at the mitral valve tip. The early peak flow velocity (E) and atrial filling velocity (A) were measured three times and averaged, and the E/A ratio was calculated. The time elapsed until the maximal E reached the baseline {the early filling deceleration time (DT)}, and the time from aortic valve closure to mitral valve opening {the isovolumic relaxation time (IVRT)}, were measured.

Tissue Doppler imaging (TDI) measurements were performed on the basal septum and mitral annulus. The maximal systolic myocardial velocity (S') and early and late diastolic myocardial velocity (E', A') were measured. In this study, the sample volume was set at 3 mm. The time between mitral valve closure and opening (a') and the systolic time (b') were measured. The value of (a'-b') was divided by b' and the modified myocardial performance index (modified Tei index) was obtained.

To analyze the vector velocity imaging (VVI), an ultrasound window of the images was controlled in such a manner that the number of frames should be >70 frames per single cardiac beat on an apical 4-chamber view and 2D images were acoustically captured. Secured images were saved on a MO disk for off-line analysis. The contour of the endocardium was manually traced before the analysis was performed on the saved images with the use of an offline analysis program {Syngo US Workplace 3.0 (Simens Medical Solution, Mountain View, CA, USA)}. The tracing was performed several times to achieve the most appropriate endocardial contour, which was confirmed by the visual display mode of the velocity images. In the septum and lateral wall of the LV, the basal and middle parts were subjected to the measurement of maximal velocity, strain, strain rate (SR), and displacement.

All of the echocardiographic parameters obtained for pulsed wave Doppler and TDI were measured by a single investigator from three cardiac cycles and averaged. The parameters which were obtained from the VVI were the average value of the measurement performed twice.

Statistical analysis

All of the results which were measured using echocardiography were expressed as the mean±SD. Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) for Windows, version 14.0 (SPSS Inc., Chicago, IL, USA). A comparison of echocardiographic measurements in the septum and lateral wall of the LV between the patient and control groups was made with the use of an independent t-test. The correlation between echocardiographic parameters and the duration of DM or the HbA1c level was assessed using correlation analysis. A p<0.05 was considered statistically significant.

Patients

The clinical data of the patients and controls are listed in Table 1. The age of patients was higher than the controls (p=0.014). The number of patients with a duration of disease <36 months was 19 and the number of patients with a duration of disease >48 months was 18.

Table 1
Clinical characteristics of patients with diabetes mellitus and controls in the study groups

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Analysis of the cardiac function using 2-dimensional and Doppler methods

The data derived from conventional echocardiographic analysis are listed in Table 2. The E velocity of the patients was significantly lower than that of controls (p=0.028). However, the other conventional echocardiographic parameters in the patient group, including mitral flow patterns, were not significantly different from the controls. Although the findings of pulsed wave TDI at the annular level showed a lower S', E', and E'/A', and a higher Tei index in the patient group, these differences were not significant (Table 3).

Table 2
Echocardiographic parameters derived from two-dimensional and Doppler imaging in the study groups

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Table 3
Tissue Doppler imaging findings in the study groups

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An analysis of the cardiac function using vector velocity imaging

The regional myocardial velocity, strain, systolic and diastolic SR, and displacement findings evaluated at the basal and mid-septal, and basal and mid-lateral wall levels are listed in Table 4. These parameters also did not show significant differences between the patient and control groups.

Table 4
Vector velocity imaging findings in the study groups

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Relationship between duration of diabetes mellitus and echocardiographic parameters

Characteristic and conventional echocardiographic data according to duration of DM are listed in Table 5. The group with a duration of DM >4 years had a higher HbA1c than the group with a duration of DM <3 years (p=0.01). The group with a duration of DM >4 years had a lower EF, FS, E velocity, and prolonged IVRT compared to the group with a duration of DM <3 years; however, these results were not significantly different between the two groups. The findings of pulsed wave TDI at the annular level did not show significant differences. The regional myocardial systolic and diastolic velocities evaluated at the basal septum using VVI were lower in the group with a duration of DM >4 years than the group with a duration of DM <3 years and the control group (Table 6). Also, the regional myocardial systolic and diastolic SRs evaluated at the basal and mid-septum were lower in the group with a duration of DM >4 years; however, none of the values were significantly different between the two groups.

Table 5
Baseline characteristics and echocardiographic parameters according to duration of DM

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Table 6
Echocardiographic parameters derived from vector velocity imaging according to duration of DM

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Based on the conventional and unconventional indices of systolic and diastolic function, no significant relationship existed between the duration of DM and echocardiographic parameters. DT and E'/A' had significant inverse correlations with HbA1c (Fig. 1) (p=0.042 and p=0.016, respectively). No significant relationship existed between the duration of DM or HbA1c and several parameters obtained from the VVI.

Fig. 1
Correlation between echocardiographic parameters and glycosylated hemoglobin (%). A: correlation between deceleration time (DT) and glycosylated hemoglobin (%). B: correlation between tissue Doppler imaging (TDI) E'/A' ratio and glycosylated hemoglobin (%).

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