The Postural Tachycardia Syndrome from the Pediatrics point of view
POTS is believed to be a procured sickness, and the beginning of orthostatic bigotry manifestations frequently follows an irresistible disease. Changing situation from recumbent to upstanding requires fast and viable circulatory and neurologic changes to keep up pulse and consciousness.
An upright posture is a distinctive trait of human beings. Rapid and synthetic coordination between circulatory and neurologic changes is required when changing from a supine to an upright position. This is due to the need to maintain an adequate level of blood pressure and hence consciousness in humans. However, this balance or coordination could get disturbed and is medically termed as orthostatic tachycardia syndrome. This disabling syndrome was first described in the 1940s and is the most common reason to be attributed to chronic orthostatic intolerance. The feelings of fainting, dizziness, nausea, fatigue, heat, palpitations are experienced by a human body when changing from a supine to an upright position. In addition to this, an increase in heart rate and transient hypotension is also noticed. Schondorf and Low operationally defined the Postural tachycardia syndrome (POTS) as an increase in heart rate from >30 beats per minute or to a heart rate of >120 beats per minute within 10 minutes of head-up tilt (HUT). POTS is not uncommon as it is reported to affect millions of patients that are aged between 12 to 50 years, 80% of them being women. Other symptoms of POTS include viral infections or other inflammatory conditions.
POTS is known to be a disease that is not present since birth but actually begins at some point during one’s lifetime. The start of the symptoms of orthostatic intolerance is followed by an infectious disease. After patients are initially infected with the illness, they do see an improvement in condition but only to become ill again or having an intercurrent infection. In some POTS patients, autonomic dysfunction, such as gastrointestinal symptoms and sudomotor abnormalities is often reported. POTS is increasingly becoming prevalent in children and adolescents. But, a complete and thorough understanding of the pathophysiology of POTS is absent.
POTS is not a single, distinctive disease but rather a category of disease. What is the common factor in all the variants in this category is the final physiological pathway which involves an excessive reduced venous return to the heart when standing up. There is no, one unifying case that is likely to be found due to the range of symptoms in this syndrome being so wide and involving an interplay of numerous organ systems. However, studies to date agree with the reasoning that POTS is most likely caused by either dysfunction or dysregulation of the autonomic nervous system. The related symptoms in all POTS patients are believed to be a result of excessive central hypovolemia, as deduced from current evidence. Due to this, the signature tachycardia may be the outcome of related reflex parasympathetic withdrawal and sympathetic activation. Studies conducted of heart rate and variability in blood pressure reflect vagal withdrawal and at least relative cardiac sympathetic excess. Additional information about orthostasis-induced alterations in cerebral blood flow in POTS has been ascertained by the recent studies conducted in the laboratory. These studies also propound that the differences in vascular function may be the answer to explain some findings in POTS.
This issue of The Journal carries two studies, each being retrospective, of a POTS population which is adolescent pediatric. POTS, which affects millions of patients, was initially related to being an adult entity but is greatly seen in the pediatric demographic, especially adolescents. The two reports bring an increased and clearer understanding of the functional capabilities and findings related to this non-adult POTS arena. Furthermore, both the reports explain the wide array of symptoms and signs seen in POTS-affected children and adolescents.
Burkhardt et al. conducted studies and described the findings reported in more than 200 adolescents who have symptoms that indicate autonomic dysfunction (fatigue, dizziness, abdominal discomfort, and physical pain) and who underwent autonomic testing, including the HUT-test and exercise tolerance test. Determination of the existence of POTS in these patients was carried out and the researchers concluded that low stroke volume and slower heart rate recovery after exercise in POTS patients, although consistent with both deconditioning and reduced cardiac preload, does not necessarily signify the existence of POTS. That is to say that changes in the heart rate in POTS are not solely attributed to inactivity resulting in deconditioning. This conclusion is on the similar lines of a study conducted by Hurwitz in adult patients experiencing chronic fatigue syndrome. These adults reflected similar symptoms to those affected with POTS and also witnessed a reduction in cardiac output and a decrease in blood volume. The researchers deduced that such findings were not a consequence of physical deconditioning or diminished cardiac contractility, but actually an outcome of co-morbid hypovolemia. This conclusion is contradictory to a recent report of adults by Levine wherein the authors claim that POTS is not a co-morbidity, or deconditioning (i.e, cardiac atrophy and hypovolemia) but is a consequence. Moreover, they state that an increase in cardiac size and mass and expansion in blood volume brought about by physical exercise improves or cures POTS. Therefore, aerobic exercise programs are recommended for POTS patients but the usefulness of such exercise may be restricted for patients who undergo fatigue.
Another study by Ojha et al. does not discuss functional capabilities, but the co-morbidities noticed in a group of POTS pediatric patients. The study goes on to explain the usefulness of deriving pertinent clinical information from questionnaires. This signifies a peculiar insight into the range and scope of symptoms reported in these pediatric POTS patients. Also, it describes in detail the individual organ systems that are affected when diagnosed with POTS. The researchers suggest that POTS does not make one isolated organ system dysfunctional with accompanying co-morbidities but rather that multiple organ systems are involved and affected. In another recent study, this pediatric group showed that POTS-affected children who otherwise show significant gastrointestinal symptoms now exhibited gastric motility abnormalities. These abnormalities were brought forth by HUT, and are maybe an outcome of regional autonomic dysfunction, either of the gastric pacing mechanism, the splanchnic vasculature, or both.
The research in the pediatric realm of POTS remains scarce due to the fact that this syndrome is considered a novelty in the medical fraternity. It was only in 1999 that the first report of POTS in the pediatric segment was published. Hence, these two reports become substantially important and welcomed as they aid in defining the scope and range of findings associated with POTS in children. Furthermore, the reports also propose suggestions of potential therapies to help reverse many findings related to POTS, like hypovolemia, support the argument of the benefits of classified and directed exercise, and aim towards the treatment of individual symptom sets. Controlled clinical trials of treatment modalities directed toward specific symptoms, maybe with the treatment of the POTS tachycardia are needed to delve deeper into this. Another important facet discovered in these studies is that each study made use of the same criteria for the POTS diagnosis: elicitation of a defined tachycardia within 10 minutes of HUT with the explanation of symptoms of orthostasis like dizziness, nausea, and palpitations. Such standardized testing for all segments of POTS patients should be aspired by all autonomic testing laboratories.