Potassium and your heart rhythm: when a deficiency becomes dangerous

What does potassium do in your heart?

Every heartbeat is caused by an electrical signal that runs through your heart muscle cells. Potassium is indispensable in this process: it flows in and out of the cell, thereby determining how quickly a cell is ready for the next electrical stimulus. That process happens continuously, with every heartbeat.

If there is too little potassium available, the electrical charge in and around the heart muscle cell changes. The cells become more sensitive to stimuli that shouldn't be there, and the heart can go out of sync: too fast, too slow, or irregular. That is the core of why a potassium deficiency is not just a matter of fatigue or muscle complaints, but can directly affect your heart rhythm.

Hypokalemia: how does a potassium deficiency occur?

A potassium deficiency has a medical name: hypokalemia. This simply means that the amount of potassium in your blood drops below the normal value. At most laboratories, the reference value for potassium is around 3.5 to 5.0 mmol/l, although this may vary slightly from lab to lab. A deficiency rarely arises from insufficient potassium intake through diet: potassium is present in so many products that a purely dietary deficiency is unusual with a healthy diet. More often, the cause lies in the loss of potassium through the body: Diuretics (water pills), such as furosemide or hydrochlorothiazide, used for conditions such as high blood pressure or fluid retention, increase the excretion of potassium through the kidneys. This is one of the most common causes of a potassium deficiency.

• Prolonged vomiting or diarrhea, during which the body loses potassium through the digestive tract.
• Excessive use of laxatives, for the same reason.
• Excessive sweating during intense exertion or heat, although this is usually a smaller factor than the other causes.

Often it is not a single cause, but a combination: someone who is already using diuretics and is also going through a period of diarrhea is at greater risk of a genuine deficiency than with each factor individually.

What are the symptoms of a potassium deficiency?

A mild potassium deficiency often causes few or no symptoms. As the deficiency increases, you may notice:

• Fatigue that does not go away with rest
• Muscle weakness or cramps, especially in the legs
• Heart palpitations or an irregular sensation in your heartbeat
• Dizziness, even leading to fainting in the case of a severe deficiency
• The tricky part is that each of these symptoms is associated with dozens of other, much more innocent causes. That is precisely why blood tests are necessary to definitively diagnose a potassium deficiency: it cannot be recognized by symptoms alone.
  

  When does a potassium deficiency become dangerous for your heart?

  Not every potassium deficiency is an emergency. A slightly low value generally does not pose immediate heart risks and is often only discovered by chance during a blood test for something else. As potassium levels continue to drop, the risk of a disturbed heart rhythm increases, and at a severely reduced level, this can result in a serious cardiac arrhythmia. Important to remember: this is not an issue you should try to correct yourself with a supplement. Both too little and too much potassium can disrupt the heart rhythm, and the correct treatment depends entirely on how low the level actually is and what the underlying cause is. This can only be determined by a blood test. Do you have palpitations accompanied by chest pain or pressure that does not go away, shortness of breath, the feeling that you are going to faint, or do you suddenly feel restless, nauseous, and sweaty? Then call your GP or the out-of-hours GP service immediately, and do not wait for a scheduled blood draw. This is the same checklist that GPs generally use for palpitations, and therefore applies just as well if the underlying cause may lie with your potassium.
  

  Who is at increased risk?

  A number of groups have a higher chance of hypokalemia:

• People who use diuretics, particularly with long-term use without monitoring of blood levels
• People with impaired kidney function, where potassium balance is already more unstable
• People with persistent gastrointestinal complaints, such as chronic diarrhea
• Athletes who sweat intensely and for long periods, although this is usually a smaller risk factor

If you fall into one of these groups and recognize the symptoms listed above, that is a good reason to have your potassium measured, even without acute alarm symptoms.