Hyperkalemia electrocardiogram


 * Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]

Overview
Hyperkalemia is an elevated blood level (above 5.0 mmol/L) of the electrolyte potassium. Extreme degrees of hyperkalemia are considered a medical emergency due to the risk of potentially fatal arrhythmias. EKG is an important tool in diagnosing hyperkalemia howeever, EKG changes do not always correlate with the degree of hyperkalemia. Some of the EKG changes that can be seen associated with hyperkalemia are Peaked T waves (T wave tenting), PR interval prolongation, QRS complex widening, absent P wave, sine wave pattern and sinus arrest.

Electrocardiogram
Electrocardiography (ECG) is generally done early to identify any influences on the heart, as hyperkalemia may cause fatal arrhythmias. With moderate hyperkalemia, there is reduction of the size of the P wave and development of tent-shaped T waves. Further hyperkalemia will lead to widening of the QRS complex, that ultimately may become sinusoidal in shape. There appears to be a direct effect of elevated potassium on some of the potassium channels that increases their activity and speeds membrane repolarization. Also, (as noted above), hyperkalemia causes an overall membrane depolarization that inactivates many sodium channels. The faster repolarization of the cardiac action potential causes the tenting of the T waves, and the inactivation of sodium channels causes a sluggish conduction of the electrical wave around the heart, which leads to smaller P waves and widening of the QRS complex.

Spcific findings include the following:

Tall, narrow, and peaked T waves

 * Earliest sign of hyperkalemia
 * Occurs with K > 5.5 meq/li
 * Differential diagnosis of this EKG change includes the T wave changes of bradycardia or stroke.
 * Prominent U waves and QTc prolongation are more consistent with stroke than hyperkalemia.

Intraventricular conduction defect

 * Observed when K > 6.5 meq/li
 * There is a modest correlation of the QRS duration with serum K
 * As the K rises, the QRS complexes may resemble sine waves
 * Generally the widening is diffuse and usually there is no resemblance of the morphology to that of either LBBB or RBBB

Decrease of the amplitude of the P wave or an absent P wave

 * Decreased P wave amplitude occurs when the K is > 7.0 meq/li
 * P waves may be absent when the K is > 8.8 meq/li
 * The impulses are still being generated in the SA node and are conducted to the ventricles through specialized atrial fibers without depolarizing the atrial muscle
 * Moderate or sever hyperkalemia can cause sinus arrest

ST segment changes simulating current of injury

 * Have been labeled the dialyzable current of injury

Cardiac arrhythmias: bradyarrhythmias, tachyarrhythmias, atrioventricular conduction defects

 * Occurs with severe hyperkalemia, not mild to moderate hyperkalemia