POTS: dizziness and pounding heart

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Last February, a 57-year-old firefighter came to my cardiology clinic after experiencing a strange series of symptoms. A few weeks earlier, he had contracted COVID-19. As expected, he lost his sense of smell, developed a mild fever and muscle pain. Within a week, his COVID-19 symptoms were gone, but he continued to feel unwell. And the new symptoms he described – sudden dizziness on standing up and an unusually fast heartbeat – made me suspect a condition called postural orthostatic tachycardia syndrome, or POTS.

Below I will explain what is known so far about the triggers and characteristic symptoms of POTS. In a future article, I’ll talk about diagnosis and treatment.

What is POTS?

POTS is a syndrome, which means it is a collection of symptoms and medical findings that often come together. The hallmark of POTS is the bothersome symptoms that occur when standing. The medical term for these symptoms is orthostatic intolerance.

Most often people report

  • dizziness or vertigo when standing (fainting may occur in more severe cases)
  • tired
  • tremor
  • difficulty concentrating (also called brain fog)
  • palpitations (feeling of fast, pounding, or irregular heartbeat).

People with POTS also often experience headaches, digestive issues like bloating and constipation, insomnia, heat intolerance, and difficulty exercising due to shortness of breath and fatigue.

Who gets POTS?

POTS most often affects women between 15 and 50 years old. However, it was recently diagnosed in other groups of people following infection with COVID-19. People with long-haul COVID (sometimes called long-haul) can develop several different types of symptoms affecting various organs, including the brain, lungs, and kidneys. A long COVID subtype is POTS.

What do we know about recovery?

Research suggests about half of people diagnosed with POTS will recover or improve over a period of a few years.

However, for others, a vicious cycle can develop if POTS is left untreated. The cycle begins because people start spending more time in bed, avoiding activities that cause symptoms. As people become much less active, muscle mass in the legs is lost, heart capacity decreases, and the volume of circulating blood is reduced. These changes make standing even more uncomfortable, resulting in even more time spent in bed.

Over time, some people stuck in this cycle can become disabled. They are unable to perform daily household chores without becoming dizzy and exhausted. Many miss school or work.

What causes POTS?

The underlying cause of POTS is not yet known. It often follows a period of bed rest after an injury such as a concussion, surgery, or a viral illness such as mononucleosis or the flu. More recently, POTS has been diagnosed in some people who have had COVID-19. Even after the acute infection resolves, these people may experience persistent fatigue, dizziness, and rapid heart rate when standing.

Many researchers suspect that POTS may be an autoimmune disease, caused by an overzealous immune system. When this happens, the immune system correctly targets the intrusive virus, but mistakenly targets the body’s own healthy tissue, causing unwanted damage. In the case of POTS, this damage is thought to affect the lining of the blood vessels, which lose their ability to constrict or contract in response to standing.

Three clues: dizziness, changes in heart rate, and the effects of gravity

Before our firefighter, whom I call David, got sick, he was tracking his heart rate on his smartwatch. It was typically around 60 to 70 beats per minute (bpm) at rest. Now, however, her resting heart rate was in the 80s and hit 130s after a flight of stairs. Just getting up caused dizziness and a rapid heartbeat. He couldn’t finish his usual spin class anymore. He stopped taking hot showers because they made him dizzy.

While most of us take the simple act of standing for granted, a person with POTS may find it extremely uncomfortable. Why does POTS cause orthostatic intolerance? This first helps to understand the normal response to standing:

  • Gravity causes about a third of the blood volume to instantly accumulate below the waist.
  • Less blood returns to the heart, so less blood is then pumped to the body.
  • This leads to a drop in blood pressure in the brain (have you ever felt a short-lived feeling of dizziness or “seeing stars” when jumping quickly after sitting for a long time?).
  • The drop in blood pressure is detected by sensors in the heart.
  • These sensors activate the sympathetic nervous system (SNS), instructing the adrenal glands to release an adrenaline-like substance called norepinephrine into the bloodstream to help resolve the problem.

How norepinephrine affects the body

Norepinephrine signals the heart to beat faster and forcefully, restoring normal blood flow to the brain. It also signals the blood vessels to constrict, causing blood to flow back to the heart instead of pooling in the lower half of the body. Within seconds of standing, blood pressure returns to normal.

However, for reasons that are not well understood, this signal is ineffective in POTS and the blood vessels do not constrict in response to norepinephrine. There is more blood left in the lower part of the body, so less returns to the heart, and therefore less is pumped to vital tissues and organs. To maintain normal blood pressure, the heart beats faster to compensate for the decrease in the volume of blood pumped with each contraction of the heart.

An overactive response to flight or combat?

Thousands of years ago, evolution favored those who responded to the stress of physical danger by producing high levels of norepinephrine, allowing them to fend off an attack or flee from evil. By releasing norepinephrine into the bloodstream, the nervous system prepares virtually every organ for physical activity and potential injury. The pupils dilate; digestion slows down; the heart is beating fast. This has been dubbed the fight or flight response.

Norepinephrine levels measured in the blood of people with POTS are significantly higher than in those without it, resulting in an excessively fast heart rate and often a strong, pounding heartbeat. In addition to these effects on the heart, high levels of norepinephrine can target other organs, including the digestive system, causing abdominal bloating and constipation.

If you often experience the symptoms described in this article, you may want to ask your doctor to check you for POTS. A later article will discuss diagnosis, treatment, and living with POTS.

Follow me on twitter @daraleelewismd

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