Recent advances in the understanding of the mechanisms underlying postural tachycardia syndrome in children: practical implications for treatment

Comorbidity of Neurally Mediated Syncope and Allergic Disease in Children

Neurally mediated syncope (NMS) is the most common underlying disease of pediatric syncope, which generally includes vasovagal syncope (VVS), postural tachycardia syndrome (POTS), and situational syncope. Allergic diseases involving the respiratory system, digestive system, skin, and other systems are prevalent in children. In recent years, increasing attention has been paid to children with the comorbidity of NMS and allergic diseases. This article reviews the featured clinical manifestations and pathogenesis of the comorbidity according to the progress of related studies. Clinical studies have shown that the comorbidity rate of pediatric VVS and/or POTS with allergic diseases amounts to ~30-40%, referring to the whole population of children with VVS and/or POTS. Additionally, children with the comorbidity present some relatively special clinical characteristics. A series of mechanisms or regulatory factors relating to allergies, such as the imbalance of vasoactive elements, dysfunction of the autonomic nervous system (ANS), and autoimmunity may play a role in the development of the comorbidity. Moreover, 90% of children with cough syncope, a type of situational syncope, have a history of asthma, indicating a potential relationship between asthma and NMS. Further studies exploring the clinical characteristics and pathogenesis of the comorbidity are still needed to aid in the diagnosis and treatment of children with NMS.

Postural Tachycardia Syndrome in Children and Adolescents: Pathophysiology and Clinical Management

Postural tachycardia syndrome (POTS), characterized by chronic (≥6 months) orthostatic intolerance symptoms with a sustained and excessive heart rate increase while standing without postural hypotension, is common in children and adolescents. Despite the unclear pathogenesis of POTS, the present opinion is that POTS is a heterogeneous and multifactorial disorder that includes altered central blood volume, abnormal autonomic reflexes, "hyperadrenergic" status, damaged skeletal muscle pump activity, abnormal local vascular tension and vasoactive factor release, mast cell activation, iron insufficiency, and autoimmune dysfunction. A number of pediatric POTS patients are affected by more than one of these pathophysiological mechanisms. Therefore, individualized treatment strategies are initiated in the management of POTS, including basal non-pharmacological approaches (e.g., health education, the avoidance of triggers, exercise, or supplementation with water and salt) and special pharmacological therapies (e.g., oral rehydration salts, midodrine hydrochloride, and metoprolol). As such, the recent progress in the pathogenesis, management strategies, and therapeutic response predictors of pediatric POTS are reviewed here.

Efficacy of β-Blockers on Postural Tachycardia Syndrome in Children and Adolescents: A Systematic Review and Meta-Analysis

Background: Postural tachycardia syndrome (POTS) is a severe health problem in children. Short-term β-blockers are recommended for pharmaceutical treatment. However, there have been contradictory data about its efficacy among pediatric patients. Methods and Results: Eight studies comparing β-blockers to conventional treatments for children with POTS were selected, where 497 cases of pediatric POTS were included. The efficacy of β-blockers was evaluated using the effective rate, the change of symptom score, the change of heart rate difference and adverse events. The results were stated as relative ratio (RR) and mean difference (MD) with a 95% confidence interval (95% CI). A random-effects meta-analysis for the effective rate indicated that β-blockers were more effective in treating pediatric POTS than controlled treatment (79.5 vs. 57.3%, RR = 1.50, 95%CI: 1.15-1.96, P < 0.05). A fixed-effects model analysis showed that β-blockers were more effective in lowering the symptom score and the heart rate increment during standing test than controlled treatment with a mean difference of 0.81 (95% CI: 0.44-1.18, P < 0.05) and 3.78 (95% CI: 2.10-5.46, P < 0.05), respectively. There were no reported severe adverse events in included studies. Conclusion: β-blockers are effective in treating POTS in children and adolescents, alleviating orthostatic intolerance, and improving hemodynamic abnormalities.

[Hemodynamic changes in standing-up test of children and adolescents with postural tachycardia syndrome]

OBJECTIVE

To explore the hemodynamic changes in standing-up test of children and adolescents with postural tachycardia syndrome (POTS) and to compare hemodynamic parameters of POTS patients with decreased cardiac index (CI) and those with not-decreased CI.

METHODS

A retrospective study was conducted to show the trends of CI, total peripheral vascular resistance index (TPVRI), heart rate and blood pressure in standing-up test of 26 POTS patients and 12 healthy controls, and to compare them between the two groups. The POTS patients were divided into two groups based on CI decreasing or not in standing-up test, namely decreased CI group (14 cases) and not-decreased CI group (12 cases). The trends of the above mentioned hemodynamic parameters in standing-up test were observed and compared between decreased CI group and not-decreased CI group.

RESULTS

In standing-up test for all the POTS patients, CI (F=6.936, P=0.001) and systolic blood pressure (F=6.049, P<0.001) both decreased significantly, and heart rate increased obviously (F=113.926, P<0.001). However, TPVRI (F=2.031, P=0.138) and diastolic blood pressure (F=2.018, P=0.113) had no significant changes. For healthy controls, CI (F=3.646, P=0.016), heart rate (F=43.970, P<0.001), systolic blood pressure (F=4.043, P=0.020) and diastolic blood pressure (F=8.627, P<0.001) all increased significantly in standing-up test. TPVRI (F=1.688, P=0.190) did not change obviously. The changing trends of CI (F=6.221, P=0.001), heart rate (F=6.203, P<0.001) and systolic blood pressure (F=7.946, P<0.001) over time were significantly different between the patients and healthy controls, however, no difference was found in TPVRI and diastolic blood pressure (P > 0.05). Among the POTS patients, CI was significantly different between decreased CI group and not-decreased CI group (F=14.723, P<0.001). Systolic blood pressure of the former decreased obviously (F=8.010, P<0.001), but it did not change obviously in the latter (F=0.612, P=0.639). Furthermore, none of the changes of TPVRI, heart rate and diastolic blood pressure in standing-up test were significantly different between the two groups (P > 0.05). Age was an independent factor for decreased CI patients (P=0.013, OR=2.233; 95% CI, 1.183 to 4.216).

CONCLUSION

POTS patients experience vital hemodynamic changes in standing-up test, part of them suffering from decreased CI, but others from not-decreased CI. Age is an independent factor for patients suffering from decreased CI.

Autonomic dysfunction and chronic disease

INTRODUCTION

The majority of chronic diseases are accompanied by symptoms of more or less pronounced dysautonomia, which frequently and noticeably deteriorate the quality of patients' life.

SOURCES OF DATA

Pubmed.

AREAS OF AGREEMENT

Functional disorders in the autonomic nervous system (ANS) require very precise diagnostics; frequently involving several specialists and a number of diagnostic tests.

AREAS OF CONTROVERSY

Dysautonomia symptoms are of a very discrete nature and may develop much earlier than symptoms specific for a given chronic disease, significantly influencing the treatment process itself.

GROWING POINTS

ANS dysfunctions should be considered at each stage of the diagnostic and treatment processes, as a predictor for the patient's clinical condition.

AREAS TIMELY FOR DEVELOPING RESEARCH

Many researchers indicate that a decrease in dysautonomia intensity has a direct effect on the progress of the underlying disease and undoubtedly contributes to the improvement of the general health condition or to symptoms remission.

Plasma Homocysteine Level in Children With Postural Tachycardia Syndrome

The study was designed to evaluate the changes of plasma homocysteine (Hcy) level in children with postural tachycardia syndrome (POTS) and explore its significance. A total of 65 subjects were recruited in our study, of whom 35 children were in the POTS group and 30 healthy children were in the control group. Plasma Hcy levels were determined in all subjects. The relationship between the plasma Hcy level and the symptom score was analyzed in the 35 POTS patients. The relationship between the plasma Hcy level and the change in heart rate from the supine to upright position (ΔHR) and between the plasma Hcy level and the rate of increase in heart rate from the supine to upright position (ΔHR/sHR × 100%) were analyzed in all subjects. The plasma Hcy levels were significantly higher in the children with POTS than those in the control group (9.78 [7.68, 15.31] μmol/L vs. 7.79 [7.46, 9.63] μmol/L, P < 0.05). The plasma Hcy levels were positively correlated with symptom scores in the POTS patients (n = 35, r = 0.522, P < 0.01). The plasma Hcy levels were also positively correlated with ΔHR (n = 65, r = 0.332, P < 0.01) and ΔHR/sHR × 100% (n = 65, r = 0.341, P < 0.01) in all the subjects. In conclusion, the plasma Hcy levels were elevated in the children with POTS positively correlated with the severity of POTS, suggesting that Hcy might be involved in the pathogenesis of POTS.