Hyperkalemia electrocardiogram

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]

Overview

Extreme degrees of hyperkalemia are considered a medical emergency due to the risk of potentially fatal arrhythmias. The EKG is an important tool in diagnosing hyperkalemia. However, EKG changes do not always correlate with the degree of hyperkalemia. Some of the EKG changes that can be seen associated with hyperkalemia include peaked T waves (T wave tenting), PR interval prolongation, QRS complex widening, absent P waves, a sine wave pattern and sinus arrest.

Pathophysiology

There appears to be a direct effect of elevated potassium on some of the potassium channels that increases their activity and speeds membrane repolarization. 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.

Moderate Hyperkalemia

With moderate hyperkalemia, there is reduction of the size of the P wave and development of tent-shaped T waves.

Severe Hyperkalemia

Further hyperkalemia will lead to widening of the QRS complex, and the QRS complex may ultimately become sinusoidal in shape (sine wave pattern).

EKG FIndings

Specific findings include the following:

Peaked T waves

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.

Peaked T waves

Tall, symmetric, narrow based T waves in a hyperkalemic patient.

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

Intraventricular Conduction Defect on EKG Before and After Treatment for Hyperkalemia

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