For patients with postural tachycardia syndrome (POTS), dietary sodium intake can be increased more confidently, suggests the first study to yield solid evidence to support this treatment strategy.
The results showed that high dietary sodium intake can lower plasma norepinephrine levels and ameliorate standing and orthostatic tachycardia for patients with POTS.
“These results suggest that increasing dietary salt is a good rationale for treatment of this condition, and this study gives reassurance we are doing the right thing for POTS patients by increasing their sodium intake,” senior author Satish R. Raj, MD, said in an interview.
The study, with lead author Emily M. Garland, PhD, was published online April 26, 2021, in the Journal of the American College of Cardiology.
Dr. Raj, who is professor of cardiac science at the University of Calgary (Alta.), explained that POTS includes a spectrum of disorders that affect the automatic nervous system, which regulates heart rate and blood pressure.
“It is a disorder of orthostatic intolerance – patients feel better when they lie down. It differs from orthostatic hypotension in that, when a POTS patient stands up, the blood pressure does not necessarily drop, but the heart rate increases excessively.”
Although it is normal for the heart rate to increase somewhat on standing, among patients with POTS, the heart rate increases excessively. The condition is defined as an orthostatic heart rate increase of at least 30 beats/min (or 40 beats/min among individuals aged 12-19 years ) in the absence of orthostatic hypotension.
The disorder is characterized by a range of symptoms, including lightheadedness, shortness of breath, palpitations, and exertional intolerance, that are worse when in an upright position. Patients also experience chronic fatigue and perceived cognitive impairment, Dr. Raj noted.
The typical demographic for POTS is young women; the condition often starts during the teenage years.
Patients often have low blood volume, so one approach to treatment is to increase the intake of salt and water so as to increase blood volume.
“This is one of the mainstays of treatment, but it has never really been properly studied,” Dr. Raj commented. Increasing salt intake “is an unusual message from a cardiologist, and there have been concerns that we are making recommendations against traditional advice, so we urgently need evidence to support this recommendation.”
The current crossover study enrolled 14 patients with POTS and 13 healthy control persons who, over a period of 6 days, underwent treatment with a low-sodium diet (10 mEq sodium per day) or a high-sodium diet (300 mEq sodium per day).
Supine and standing heart rate, blood pressure, serum aldosterone level, plasma renin activity, blood volume, and plasma norepinephrine and epinephrine levels were measured.
Results showed that, among the POTS patients, the high-sodium diet reduced upright heart rate and the change in heart rate on standing, compared with the low-sodium diet.
Heart rate increased by 46 beats/min with the high-sodium diet versus 60 beats/min with the low-sodium diet.
Total blood volume and plasma volume increased, and standing norepinephrine levels decreased with the high-sodium diet, compared with the low-sodium diet.
However, upright heart rate, change in heart rate, and upright norepinephrine levels remained higher among POTS patients than among control persons receiving the high-sodium diet.
There was a nonsignificant trend for a lower symptom burden score among the POTS patients who received the high-sodium diet in comparison with those taking the low-sodium diet. Scores for mental confusion, palpitations, lightheadedness, and headache trending downward on the high-sodium diet.
“We found that high levels of dietary salt did what we hoped, with increased blood volume and reduced norepinephrine levels on standing and reduced excessive increase in heart rate. While it didn’t completely normalize heart rate, this was reduced significantly,” Dr. Raj said.
Another observation from the study was that the increased salt intake seemed to be beneficial across the whole spectrum of patients.
“There are some patients who have very high levels of sympathetic activation, and there have been anecdotal reports that increasing salt may not work so well in this group,” he said. “In this study, we didn’t differentiate, but average norepinephrine levels were very high, and many patients would be considered to be hyperadrenergic. Our results suggest this treatment will help these patients too.”
He noted that sodium intake was increased in this study just through diet. “We had a special metabolic kitchen. In clinical practice, we advise patients to add regular table salt to their food, and we only use salt tablets when they cannot tolerate so much salt in their diet.”
Recognizing that there may be concerns about hypertension with long-term use of such a treatment, Dr. Raj said there were no signs of an increase in blood pressure in this study. “But this should be considered a short-term therapy for the time being, and patients need to be reassessed every few years as their physiology changes.”
The authors estimated that POTS affects up to 1% of the population. Because there is no diagnostic code for the condition at present, all incidence data are estimates.
Dr. Raj pointed out that potentially a lot of people are affected, but there is little recognition of the condition among patients and physicians.
“Many family doctors are unaware of POTS,” he noted. “Patients often have to research their symptoms themselves and inform their doctor of the condition. Many patients wait years and often see many different doctors before getting a correct diagnosis.”
He explained that patients with POTS are often diagnosed as having a psychiatric illness. “They are mainly young women with palpitations, heart pounding, shakiness, which is often labeled as anxiety.”
Dr. Raj urged clinicians to consider POTS if patients have symptoms that are worse when standing up. The diagnosis is confirmed if their blood pressure doesn’t fall when standing up but their heart rate increases by at least 30 beats/min.
He noted that not enough specialists treat this condition, so family doctors need to be able to diagnose and initiate treatment. If more aggressive treatment is required, patients can be referred to a specialist.
“One of the problems is that this condition pans across different medical specialties. No one field owns it, so it tends to get ignored. But there are clinicians who are interested in POTS, and the key is finding one of these,” he said.
“We have finally established that this high-sodium diet works as treatment for POTS,” he concluded. “We have been using it for some time, but now we have evidence for its use across the whole spectrum of patients.”
In an accompanying editorial (J Am Coll Cardiol. 2021 May 4;77[17]:2185-2186), Blair P. Grubb, MD, University of Toledo (Ohio) Medical Center, wrote that this “superb study by Garland et al. helps better establish our understanding of the pathophysiologic process taking place in POTS while at the same time providing good evidence for the augmentation of dietary sodium as one of the cornerstones of treatment.”
He added that the field needs more such studies “in our quest to better understand POTS and to elaborate therapeutic modalities to help those suffering from this debilitating illness.”
The study was supported in part by the National Heart, Lung, and Blood Institute; the National Center for Advancing Translational Sciences; and the Vanderbilt Hormone and Analytical Services Core. Dr. Raj has served as a consultant for Lundbeck NA and Theravance; has served as chair of the data safety and monitoring board for Arena Pharmaceuticals and as Cardiac Arrhythmia Network of Canada network investigator; and has served on the medical advisory board of Dysautonomia International and PoTS UK, both without financial compensation.
A version of this article first appeared on Medscape.com.