From the Guidelines
Hypokalemia is characterized by several distinct ECG changes, including broadening of the T waves, ST-segment depression, and prominent U waves, as noted in a 2017 update to practice standards for electrocardiographic monitoring in hospital settings by the American Heart Association 1. These changes can occur at various levels of potassium deficiency, with more severe hypokalemia (potassium levels <2.5 mEq/L) leading to more pronounced ECG alterations. Key ECG findings associated with hypokalemia include:
- Broadening of the T waves
- ST-segment depression
- Prominent U waves
- Potential for various arrhythmias, such as first or second-degree atrioventricular block, atrial fibrillation, ventricular arrhythmias (including PVCs, VT, TdP, VF, and cardiac arrest) It is essential for clinicians to recognize these ECG patterns, especially in patients with conditions that may lead to potassium depletion, such as diuretic use, vomiting, diarrhea, or certain endocrine disorders, to promptly correct hypokalemia and prevent potentially life-threatening cardiac complications, as suggested by Sandau et al in their update to practice standards 1.
From the Research
ECG Changes Associated with Hypokalemia
The following ECG changes are associated with hypokalemia:
- Dynamic changes in T-wave morphology 2
- ST-segment depression 2
- U waves, often best seen in the mid-precordial leads (V2–V4) 2
- Prolonged PR interval 2
- Increased amplitude of the P wave 2
Clinical Significance of Hypokalemia
Hypokalemia can increase the risk of life-threatening arrhythmias 2, 3. In patients with acute coronary syndrome, hypokalemia is significantly associated with the occurrence of life-threatening ventricular arrhythmias 3.
Comparison with Hyperkalemia
While hyperkalemia is associated with peaked T wave, expanded QRS complex, and low P amplitude 4, hypokalemia has distinct ECG changes, as listed above.
Importance of Potassium Regulation
Tight potassium regulation is important in patients with cardiovascular disease, and elevation of potassium in asymptomatic patients with lower normal concentrations and concurrent cardiovascular disease may be beneficial 5.