Potassium exists as a charged mineral, called an electrolyte, in the body. It is important for electrical conduction in cells, including nerve, muscle, heart and other types of cells. Changes in the level of potassium can effect electrical conduction in the cells, including those of the heart. The electrical conduction of the heart can be measured by external electrodes -- a test called an EKG.
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Heart cells conduct an electrical current that spreads through the heart and tells the cells to contract in a regulated manner. The heart conducts electrical currents using electrolytes. The potassium level in heart cells is higher inside the cells than outside of them. In contrast, the sodium and calcium levels are higher outside the cells. Signals generated by pacemaker cells in the heart cause sodium to enter the cells, causing them to go from a negative charge to a positive charge, which has two effects. First, it causes the muscle to contract. Second, it causes sodium to enter the cells nearby and also contract. Cells become negative and relax when potassium leaves the cells. A special pump restores the normal balance of electrolytes, and the cycle begins again, causing the heart to beat.
An EKG -- also referred to as an ECG, or electrocardiogram -- is a painless procedure that uses 12 electrodes placed across the skin to measure the electrical conduction of the heart. Electrolytes entering and exiting the cells form the electrical current that is passed through the heart from top to bottom, causing it to contract, and creating waves on the EKG reading.
Effect of Low Potassium
When the electrical current passes through the top of the heart, called the atria, it causes the first wave on the EKG, called the P wave. The bottom chambers of the heart, called the ventricles, contract to form the next wave, called the QRS complex. Finally when the heart returns to resting electrical activity as potassium flows out of the cells, the third wave is formed, called the T wave. When the potassium levels in the blood are low, more rushes out of the cells. This can cause the T wave to become flatter or invert, and form another wave after the T wave, called a U wave. It can also increase the interval between some of the other waves.
The EKG reflects changes to the electrical activity of the heart brought about by low potassium, and these changes result in problems for the beating of the heart. The timing of he heartbeat may become too fast, too slow or uncoordinated, leading to problems pumping the blood. Since this can be a serious medical issue, disorders of the heart or mineral balance should be diagnosed and treated in concert with the consultation of a physician.