Potassium is a major mineral and an electrolyte, which means that it carries an electrical charge. Most of the potassium in your body is found inside your cell membranes. The remaining potassium circulates in the fluid outside your cells. This balance of potassium in your body is ensures proper muscle contraction, which is crucial to a normal heart beat, defined as 60 to 100 beats per minute.
Physiology
Your heart consists of four main chambers: the right atrium, the left atrium, the right ventricle and the left ventricle. The muscles of these chambers contract and relax in a certain succession to properly pump blood throughout your body. The proper muscle contraction depends on the heart's electrical system, which begins in a structure called the sinoatrial, or SA, node, located in the right atrium. The electrical impulse then continues to the atrioventricular, or AV, node, which is between the atria and the ventricles. The electrical system of the heart relies heavily on the right balance of electrolytes, including potassium, in the blood. When potassium levels fall or rise, it disrupts nerve impulses that send messages to the heart muscles to either contract or relax. As a result, heart beat becomes irregular.
Hypokalemia
Hypokalemia is a medical condition characterized by a decreased amount of potassium in the blood. When your potassium levels drop, it actually increases your heart rate, leading to a type of heart arrhythmia called tachycardia, which is defined as more than 100 heart beats per minute. If your heart is beating too quickly, it does not allow sufficient time for the heart chambers to fill with blood. As a result, your tissues do not receive enough blood, and over time, can become deprived of oxygen. Some people with an increased heart rate do not experience any symptoms, while others experience dizziness, shortness of breath, chest pain, lightheadedness and heart palpitations. If left untreated, tachycardias can lead to stroke or cardiac arrest.
Hyperkalemia
Hyperkalemia occurs when the amount of potassium in the blood increases beyond normal concentrations. When potassium levels increase, it decreases your heart rate, leading to an abnormal heart rhythm called bradycardia, which is defined as less than 60 beats per minute. As with tachycardia, a slow heart beat causes your tissues to become starved of oxygen. Some possible symptoms of bradycardia include dizziness, fatigue, weakness, chest pain, shortness of breath, confusion and loss of consciousness. If left untreated, bradycardia may lead to heart failure or sudden cardiac arrest.
Causes
The kidneys are responsible for maintaining the proper level of potassium in the blood. Because of this, most potassium imbalances are caused by kidney disease. Other possible causes of hypokalemia include diuretics, antibiotics, eating disorders, chronic diarrhea, excessive sweating and vomiting. Hyperkalemia may occur as a result severe burns, blood disorders, surgery, injury, Addison's disease and certain tumors.
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