An essential positively charged ion, potassium is intimately connected with the electrical conduction system of the heart, according to "Rapid Interpretation of EKG's." Imbalances in potassium, an electrolyte, can produce dangerous heart conduction abnormalities, which sometimes manifest as palpitations. The state of high levels of potassium is referred to as hyperkalemia, while low levels are called hypokalemia. Both conditions result in deadly arrhythmias and cardiac arrest.
Electrical Conduction and Potassium
The relaxation phase of cardiac cells known as myocytes is directed by the movement of potassium ions out of the intercellular environment, or ICF. This passive outflux is the reason why myocytes are able to prepare for the next wave of electrical contraction, according to "Harrison's Principles of Internal Medicine."
Electrocardiograms, or EKGs, record the electrical impulses conducted by myocytes as a pattern of waves. The P wave on an EKG is the first small blip, representing the contraction of the top two chambers of the heart called the atria. The large spike that follows the P wave is collectively termed the QRS complex, which represents the contraction of the ventricles, according to "Rapid Interpretation of EKG's." Abnormal potassium levels can alter any of these waves, depicting serious conduction problems.
Hyperkalemia
"Rapid Interpretation of EKG's" states that high potassium levels appear on the EKG as tall peaked T waves. The T waves represent the relaxation phase of the lower chambers of the heart. The narrowed waves let practitioners know that the length of the ventricles' relaxation time has substantially decreased. Smaller relaxation time leads to less time the ventricles have to fill with blood. Thus, the ability of the heart to pump adequate amounts of blood to the body is hindered.
"Rapid Interpretation of EKG's" explains that hyperkalemia depresses the sinoatrial node action as well. The pacemaker of the heart, the SA node is responsible first for the electrical conduction of the atria. If the electrical current produced by the SA node is lowered, then atrial contraction is affected. The atria are where the blood first collects in the heart. In addition, the P waves eventually disappear and the patient begins to experience the characteristic heart palpitations that lead to heart attack and death.
Hypokalemia
According to "Harrison's Principles of Internal Medicine," hypokalemia produces symptoms of heart palpitations as well. With low levels of potassium, the ventricles become irritable and fire spontaneous impulses, which are represented by premature beats on the EKG. Thus, the patient experiences the heart-fluttering sensation. Other conduction abnormalities caused by low potassium levels include paroxysmal atrial tachycardia associated with heart block and torsades de pointes, which is a very rapid but brief burst of heart palpitations.
Other Signs and Symptoms
"Current Consult Medicine 2007" provides a list of additional systemic signs and symptoms associated with hyperkalemia. The authors, Maxine Papadakis, M.D., and Stephen McPhee, M.D., note the key features of this condition as muscle weakness, diarrhea and abdominal distention. A limp muscle paralysis can also occur in rare situations.
In the case of hypokalemia, Dr. Papadakis and Dr. McPhee indicate that muscle cramps, fatigue and constipation are common. Decreased deep tendon reflexes, destruction of muscle fibers and tetany also occur.
Treatments
"The Johns Hopkins Hospital: The Harriet Lane Handbook" describes effective treatment for both hypokalemic and hyperkalemic states. In cases of hyperkalemia, it is important to neutralize potassium's effect on the resting membrane potential of cells; therefore, intravenous calcium is given. Glucose and insulin are also administered. The safest treatment for hypokalemia is giving oral potassium chloride. In severe cases, intravenous potassium can be administered.
References
- "Harrison's Principles of Internal Medicine" 17th ed.; Anthony Fauci, M.D., et al., eds.; 2008
- "The Johns Hopkins Hospital: The Harriet Lane Handbook" 17th ed.; Jason Robertson, M.D., and Nicole Shilkofski, M.D.; 2005
- "2007 Current Consult Medicine"; Maxine Papadakis, M.D., and Stephen McPhee, M.D.; 2007
- "Step-Up to Medicine" 2nd ed.; Steven Agabegi, M.D., and Elizabeth Agabegi, M.D.; 2008
- "Rapid Interpretation of EKG's"; Dale Dubin, M.D.; 2000
