A clinically high potassium level in the heart is called hyperkalemia. Potassium is one of the most crucial positively-charged ions for the cells of the heart. The resting membrane potential of cardiac cells is determined in part by the flow of potassium ions from the interior of the cells, called the intracellular fluid, or ICF, to the extracellular fluid, or ECF. According to Dr. Dale Dubin in his book "Rapid Interpretation of EKGs," this movement of potassium ions causes the heart muscle cells, also known as myocytes, to relax after contraction. Clinicians carefully watch potassium levels in patients because of the potentially fatal nature of hyperkalemic conditions. An imbalance in this mineral can lead to dangerous arrhythmias, which are abnormalities in the electrical conduction of the heart, and cardiac arrest.
Potassium and Electrical Conduction
To understand potassium's effects on the electrical conduction of the heart, it is important to understand electrocardiograms, or EKGs. Electrical impulses of the heart are manifested on EKGs in a characteristic wave pattern. "Rapid Interpretation of EKGs" explains that the P waves, which are the first little bump on the EKG, represent the contraction of the two upper chambers of the heart, known as the atria. The next largest spike is called the QRS complex, which records the contraction of the two lower chambers of the heart, called the ventricles. Potassium affects the repolarization, or the electrical recovery of both the atria and the ventricles. Potassium's action on the ventricles is represented by the interval between the S and T waves, called the ST segment, the T wave being the final bump on the EKG strip after the QRS spike.
Hyperkalemia and the Heart
An increase in the levels of potassium in the ECF affect the repolarization phase of the heart and can depress the action of the sinoatrial, or SA, node of the heart. The SA node is the main pacemaker of the heart, responsible for its contraction. Excess potassium can cause the P wave to disappear and lengthen ventricular contraction, demonstrated by a widened QRS complex on an EKG, according to "Rapid Interpretation of EKGs." Remember the P waves represent the contraction of the atria, so the disappearance of the P wave on an EKG indicates a severe decrease in the SA node's electrical conduction. Thus, if the SA node decreases in function, so does the heart's overall pumping capability. Another manifestation of hyperkalemia lies in the T wave. High levels of potassium cause characteristically high T waves, representing a decrease in the relaxation phase of the ventricles.
Causes of Hyperkalemia
According to the book "Step-Up to Medicine" by Drs. Steven Agabegi and Elizabeth Agabegi, the main causes of hyperkalemia are not dietary, but instead are due to conditions that cause acidosis and the destruction of cells. These conditions include kidney failure; trauma; hypoaldosteronism; sickle cell disease and a decrease in insulin, causing high blood sugar; Addison's disease; and the use of medications such as spironolactone, ACE inhibitors and trimethoprim.
Signs and Symptoms
Many cases of less-severe hyperkalemia are without symptoms. Moderate to severe cases manifest with generalized apathy, weakness, tingling or prickling of the extremities, heart palpitations and tetany. Hperkalemic signs include excessive sweating, abdominal distention and EKG abnormalities.
According to "The Johns Hopkins Hospital: The Harriet Lane Handbook," treatment is aimed at stopping potassium's positive-charge effect on the membrane potential. This includes intravenous calcium, which stabilizes the membrane potential. In more severe cases, IV glucose and insulin are added to the regimen. Lastly, kayexalate is given, which is an exchange resin that promotes bowel excretion of potassium.
- 2007 Current Consult Medicine; Dr. Maxine Papadakis and Dr. Stephen McPhee
- Rapid Interpretation of EKGs; Dr. Dale Dubin
- Step-Up to Medicine (2nd edition); Dr. Steven Agabegi and Dr. Elizabeth Agabegi
- Harrison's Principles of Internal Medicine (17th edition); Dr. Anthony Fauci et al
- The Johns Hopkins Hospital: The Harriet Lane Handbook (17th edition); Dr. Jason Roberston and Dr. Nicole Shilkofski
- doctor desk image by dinostock from Fotolia.com
This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.