From the Guidelines
In a patient with hypokalemia, you would expect to find characteristic ECG changes including broadening of the T waves, ST-segment depression, and prominent U waves, as well as various arrhythmias such as first or second-degree atrioventricular block, atrial fibrillation, and ventricular arrhythmias 1. These changes occur because potassium plays a crucial role in maintaining normal cardiac electrical activity. When serum potassium levels fall below 3.5 mEq/L, the resting membrane potential of cardiac cells becomes more negative, leading to hyperpolarization.
- The prominent U wave is particularly characteristic of hypokalemia and represents delayed repolarization of the Purkinje fibers.
- As potassium levels decrease further (below 2.5 mEq/L), more severe ECG changes may develop, including PR interval prolongation and increased risk of ventricular arrhythmias such as torsades de pointes. The ECG changes associated with hypokalemia can be classified based on the severity of the condition, with mild hypokalemia (3.0–3.5 mEq/L) typically showing minimal changes, moderate hypokalemia (2.5–2.9 mEq/L) showing more pronounced changes, and severe hypokalemia (<2.5 mEq/L) showing the most severe changes, including life-threatening arrhythmias 1. It is essential to promptly initiate potassium repletion, especially in symptomatic patients or those with severe hypokalemia (K+ < 2.5 mEq/L), to reverse these ECG changes and prevent potentially fatal complications.
From the Research
ECG Changes in Hypokalemia
On an electrocardiogram (ECG) of a hypokalemia patient, several changes can be expected, including:
- Dynamic changes in T-wave morphology 2
- ST-segment depression 2, 3
- U waves, often best seen in the mid-precordial leads (V2–V4) 2, 3, 4
- Prolonged PR interval 2
- Increased amplitude of the P wave 2
- Prolonged QTc interval 3
Mechanisms and Clinical Significance
These ECG changes are a result of the altered cardiac ionic currents kinetics caused by hypokalemia 4. Hypokalemia can increase the risk of life-threatening arrhythmias, making it essential to recognize these ECG changes and manage the condition promptly 2, 4. The presence of these changes can guide clinicians in diagnosing and treating hypokalemia, especially in patients with cardiovascular disease 5.