From the Guidelines
Hypokalemia is associated with several characteristic EKG findings, 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, including premature ventricular contractions, ventricular tachycardia, and potentially ventricular fibrillation, as reported in the most recent study by Sandau et al 1.
EKG Findings in Hypokalemia
The EKG changes associated with hypokalemia are due to the crucial role of potassium in cardiac cell membrane potential and repolarization. Low potassium levels alter the electrical properties of cardiac cells, affecting the heart's conduction system and making it more susceptible to arrhythmias.
- The severity of EKG changes generally correlates with the degree of hypokalemia, with more pronounced abnormalities appearing as potassium levels decrease.
- Prompt recognition of these EKG patterns is essential as they may precede life-threatening arrhythmias and indicate the need for immediate potassium replacement.
Clinical Implications
It is essential to note that hypokalemia can be asymptomatic until potassium levels are significantly low, and patients with heart failure may require higher potassium levels to prevent arrhythmias, as suggested by recent studies 1.
- The classification of hypokalemia as mild (3.0–3.5 mEq/L), moderate (2.5–2.9 mEq/L), or severe (<2.5 mEq/L) can help guide treatment and management decisions.
- The American Heart Association has updated practice standards for electrocardiographic monitoring in hospital settings, emphasizing the importance of recognizing electrolyte abnormalities, including hypokalemia, and their potential impact on cardiac function 1.
From the FDA Drug Label
Potassium depletion may produce weakness, fatigue, disturbances or cardiac rhythm (primarily ectopic beats), prominent U-waves in the electrocardiogram, and in advanced cases, flaccid paralysis and/or impaired ability to concentrate urine. The EKG findings associated with hypokalemia are:
- Disturbances of cardiac rhythm (primarily ectopic beats)
- Prominent U-waves in the electrocardiogram 2
From the Research
EKG Findings in Hypokalemia
The electrocardiogram (EKG) findings associated with hypokalemia include:
- Dynamic changes in T-wave morphology, ST-segment depression, and U waves, which are often best seen in the mid-precordial leads (V2–V4) 3
- Prolonged PR interval along with an increase in the amplitude of the P wave 3
- Presence of U waves greater than 1 mm and U waves larger than the T wave in the same lead (with associated ST-segment depression) 4
- T:U ratio of 1 or less and a U wave greater than 0.5 mm in electrocardiographic lead II or greater than 1.0 mm in lead V3 4
- T-wave flattening, ST-segment depression, and QTc prolongation 5
Relationship Between Potassium Levels and ECG Abnormalities
Studies have shown that decreasing potassium levels are associated with a concentration-dependent increase in ECG variables such as heart rate, QRS duration, corrected QT (QTc) interval, ST-segment depressions, T-wave flattening, and T-wave inversion 5 ECG abnormalities are present in 40% of hypokalemic patients, with T-wave flattening, ST-segment depression, and QTc prolongation occurring in 27%, 16%, and 14% of patients, respectively 5
Clinical Implications
Hypokalemia can increase the risk of life-threatening arrhythmias, and ECG abnormalities can be used to monitor and manage patients with hypokalemia 3, 6, 4 However, ECG abnormalities are poor prognostic markers for short-term adverse events under the current standard of care 5