Evaluation of P-Wave Dispersion, Diastolic Function, and Atrial Electromechanical Conduction in Pediatric Patients with Subclinical Hypothyroidism

P-Wave Changes Associated with Chiari Network in the Right Atrium

The Chiari network (CN) is a mobile, net-like structure occasionally present in the right atrium, near the opening of the inferior vena cava and coronary sinus. While typically asymptomatic, it may contribute to thromboembolism or right atrial pathologies. Here, we hypothesized that existing differences in P-wave morphology on electrocardiograms (ECG) may be associated with atrial conduction changes. Seventy-one children with a CN were recruited and matched to 60 healthy controls. P-wave duration, P-wave amplitude, P dispersion (Pd), QRS, PR, QT, and QTc (calculated with Bazett formula) intervals were measured and compared. Between the control and the patient groups, the mean P-wave duration was 78.1 ms and 88.7 ms, P amplitude was 1.3 mm and 1.1 mm, and Pd was 18.9 and 35.5 ms, respectively. These differences were statistically significant across all measurements (p < 0.05). Atrial conduction may be affected in patients with CN, and these patients may then develop atrial arrhythmia.

Left and right ventricular functions may be impaired in children diagnosed with subclinical hypothyroidism

Subclinical hypothyroidism (SH) may influence both ventricular functions. The aim of this study was to evaluation the findings of Tissue Doppler Imaging (TDI) and other echocardiography modalities in children with SH. We compared left ventricular mass index (LVMI) and TDI parameters of patients with SH and children with euthyroidism. Subclinical hypothyroidism was diagnosed when thyroid stimulating hormone level was higher than the reference value of the laboratory (> 4.2 mIU/L) and free thyroxine level was in normal range. The study included a group of 35 patients with SH and a control group of 38 children with euthyroidism (mean age was 7.6 ± 3.5 years and 9.0 ± 2.4 years, respectively). LVMI was significantly higher in the patient group (p = 0.005). TDI parameters including mitral septal ejection time was lower (p = 0.003) and mitral septal myocardial performance index was higher (p = 0.009) in the patient group. Right ventricular TDI revealed that tricuspid lateral E/Ea and tricuspid septal E/Ea were higher (p = 0.015 and p = 0.024, respectively) and tricuspid septal Ea/Aa and ejection time were lower (p = 0.018 and p = 0.017, respectively) in the patient group. SH may lead to increase LVMI. Left ventricular systolic and diastolic TDI parameters (lower mitral septal ejection time, higher mitral septal myocardial performance index) as well as right ventricular systolic (lower tricuspid septal ejection time) and diastolic (higher tricuspid septal and lateral E/Ea, lower tricuspid septal Ea/Ea) functions may be also impaired in children with subclinical hypothyroidism. TDI is a useful method used for the assessment of the effect of SH on cardiac functions.

Evaluation of cardiovascular risk by growth-differentiation factor-15 and tissue Doppler imaging in children with subclinical hypothyroidism

OBJECTIVE

Subclinical hypothyroidism, defined as increased TSH serum levels and normal serum free T4 concentrations, has been associated with an increased risk of heart disease in adults. But, data in children and adolescents are scanty and treatment of subclinical hypothyroidism is controversial. Growth differentiation factor-15 (GDF-15) is a promising biomarker of cardiac remodeling. This study aimed to evaluate the cardiovascular risk factors in children with subclinical hypothyroidism, measured with tissue Doppler echocardiography (TDE), and conventional echocardiography and GDF-15 level.

METHODS

The study comprised a total of 41 pediatric patients with subclinical hypothyroidism (SH) (mean age 9.6 ± 4.7 years) and 31 healthy children (mean age 11.2 ± 3.4 years) as the control group. Subclinical hypothyroidism was defined as a thyroid-stimulating hormone level higher than 4 mIU/l and a normal free-thyroxine level (0.6-1.8 ng/dl). Tissue Doppler echocardiography was performed to all individuals in the control group and patient group at the beginning of the study. Global systolic function as assessed by left ventricular ejection fraction was compared between groups. The serum GDF-15 level was measured.

RESULTS

There were no significant differences in demographic parameters between the SH and control groups. The left ventricular internal diameter end systole, interventricular septal end diastole, left ventricular posterior wall end diastole, and tricuspid annular plane systolic excursion values were significantly different between the SH and control groups (p = 0.038, 0.028, 0.005, and 0.000, respectively). The mean mitral isovolumic relaxation time value of the SH group was 57.2 ± 9.3 ms, compared to 44.5 ± 5.6 ms for the control group (p = 0.000). The mean tricuspid isovolumic contraction time value of the SH group was 58.7 ± 9.4 ms, and that of the control group was 45.1 ± 5.3 ms (p = 0.000). The mean tricuspid isovolumic relaxation time value of the SH group was 58.03 ± 9.5 ms, and that of the control group was 45.1 ± 5.3 ms (p = 0.000). There were no significant differences in the other m-mode or pulse Doppler echocardiography values between two groups. The GDF-15 value of the SH group was 382.6 ± 268.2 pg/mL, and that of the control group was 473.6 ± 337.9 pg/mL; this difference was not significant.

CONCLUSION

Patients with subclinical hypothyroidism versus healthy individuals had some changes in echocardiographic parameters that indicate involvement of diastolic function of the left ventricle. They were significantly different when compared SH group and the control group. This study demonstrated ventricle diastolic dysfunction in pediatric patients with hypothyroidism. The results of our study suggest that cardiac follow-up may be useful in patients with subclinical hypothyroidism and clinical trials are needed to explore therapeutic effects of T4 and T3 administration in this patients.

P-wave dispersion: an update

P-wave dispersion (PWD, Pd or Pdis) is a noninvasive electrocardiographic (ECG) marker for atrial remodeling and predictor for atrial fibrillation (AF). PWD is defined as the difference between the widest and the narrowest P-wave duration recorded from the 12 ECG leads. Increased P-wave duration and PWD reflect prolongation of intraatrial and interatrial conduction time with lack of a well-coordinated conduction system within the atrial muscles, with inhomogeneous, asynchronic, pro-inflammatory and anti-inflammatory effect mediated by interleukin-6 (IL-6) in patients with the CG + GG genotype IL-6 -634C/G polymorphism [1] and discontinuous propagation of sinus impulses mainly between the left and right atria, interstitial/extracellular fibroblast activation and collagen deposition with fibrosis (via TGF-β) in atrial tissue, insufficient blood supply, significant not isotropic myoelectric activity, and thin wall thickness and consequent expansion tendency all well-known electrophysiological characteristics in patients with atrial arrhythmias and especially paroxysmal atrial fibrillation (PAF) [2].