Sodium, Potassium & the Heart Rate

Sodium, potassium and other nutrients are required to maintain the body’s normal health. These elements, along with several others, are absolute requirements for human life. They are so basic to the function of every cell that any imbalance between them can cause serious problems. The heart is an organ that is particularly vulnerable to changes in the ratios of these elements in the blood.

A woman is checking her exercise monitor or pulse monitor. (Image: DGLimages/iStock/Getty Images)

Sodium and Potassium

Sodium and potassium are elements found in nature. In plants and animals, they can exist bound to other atoms or large molecules, such as occurs in the salt or chelated forms, respectively of these elements. When these forms are ingested, the body processes them and releases the sodium and potassium atoms from their bound counterparts. Sodium and potassium are known as electrolytes because once released from a bound state, they become ions in a water environment. Electrolytes are able to conduct electricity. This basic physical property is why sodium and potassium ions, among other ions, are used to carry on fundamental processes in the body.

Fundamental Need

Sodium, potassium and other ions are crucial components of life and necessary in every cell of the body. They are used in a wide variety of cell processes such as maintaining cell membrane integrity, regulating water balance between cells and their extracellular space, and transporting nutrients or waste across cell membranes. "The Textbook of Medical Physiology" says that since so many vital functions are based on these elements, their balance is tightly regulated by the body. Any imbalance of sodium, potassium or other electrolytes can offset the normal function of various tissues and organs, such as the heart. Knowing the blood levels of sodium, potassium and other electrolytes through laboratory testing gives doctors a window into the body’s health and can help diagnose a number of pathologies based on the relative ratios of electrolytes.

Sodium and Potassium Imbalance

According to the "Encyclopedia of Surgery," the normal blood sodium level is 135 to 145 mEq per liter. The normal blood potassium level is 3.5 to 5.0 mEq per liter. If sodium or potassium exceeds these levels in the blood, the conditions are called hypernatremia or hyperkalemia, respectively. If sodium or potassium falls below these levels in the blood the conditions are called hyponatremia or hypokalemia, respectively. The organs most responsible for regulating the blood levels of these electrolytes are the kidneys. If the kidneys do not effectively retain or excrete these electrolytes according to the body’s needs, an electrolyte imbalance can result. Such occurs with kidney disease or while taking certain medications.

Heart Function

The heart is one of the organs most immediately affected by the levels of sodium and potassium in the blood. For the heart to function properly, electrolyte balance in the blood must be kept within the normal range. Otherwise, heart irregularities will quickly manifest. These irregularities relate to physiological properties such as the heart’s force of contraction and its rate or rhythm. There is a complex association between electrolytes and heart function. However, generally speaking, higher blood levels of potassium can cause a slowed heart rate and irregular heartbeat or arrhythmia, while lower levels produce a rapid heartbeat. Excessive blood levels of sodium can also depress heart function, whereas higher sodium levels can produce cardiac fibrillation, a type of irregular heart rhythm. A doctor must assess the relative ratios of electrolytes to determine whether heart function is affected by the imbalance.

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