What are the ECG changes associated with hypokalemia and how are they managed?

From the Guidelines

Hypokalemia causes characteristic ECG changes including flattened or inverted T waves, prominent U waves, ST-segment depression, and prolonged QT intervals, and management focuses on potassium replacement, with the route and rate determined by severity and symptoms, as recommended by the American Heart Association 1.

ECG Changes Associated with Hypokalemia

The ECG changes associated with hypokalemia are broadening of the T waves, ST-segment depression, and prominent U waves, which can progress to ventricular arrhythmias, including torsades de pointes, if left untreated 1.

• Flattened or inverted T waves
• Prominent U waves
• ST-segment depression
• Prolonged QT intervals

Management of Hypokalemia

Management of hypokalemia involves potassium replacement, with the route and rate determined by severity and symptoms.

• For mild hypokalemia (3.0-3.5 mEq/L) without ECG changes, oral potassium chloride 40-80 mEq/day divided into multiple doses is appropriate.
• For moderate hypokalemia (2.5-3.0 mEq/L) or mild hypokalemia with ECG changes, higher oral doses or slow IV replacement may be needed.
• Severe hypokalemia (<2.5 mEq/L) or cases with significant ECG changes or symptoms require IV potassium chloride, typically at 10-20 mEq/hour (not exceeding 20 mEq/hour) with continuous cardiac monitoring.

Important Considerations

• The maximum concentration for peripheral IV administration is 40 mEq/L, while central lines can tolerate up to 60-80 mEq/L.
• Concurrent magnesium deficiency should be corrected as it can impair potassium repletion.
• The underlying cause of hypokalemia must also be identified and addressed, whether it's medication-induced (diuretics, insulin), gastrointestinal losses, or other causes.
• Frequent serum potassium monitoring is essential during replacement therapy to guide dosing and prevent overcorrection, as recommended by the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines 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 ECG changes associated with hypokalemia include:

• Disturbances of cardiac rhythm, primarily ectopic beats
• Prominent U-waves in the electrocardiogram These changes are managed by restoring normal potassium levels, which can be achieved by:
• Correcting the fundamental cause of the deficiency
• Supplemental potassium in the form of high-potassium food or potassium chloride 2

From the Research

ECG Changes Associated with Hypokalemia

• Hypokalemia can cause various ECG changes, including 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.
• The PR interval can also be prolonged along with an increase in the amplitude of the P wave 3.
• Decreasing potassium levels are associated with a concentration-dependent increase in heart rate, QRS duration, corrected QT (QTc) interval, ST-segment depressions, T-wave flattening, and T-wave inversion 4.
• 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%, respectively 4.

Management of ECG Changes Associated with Hypokalemia

• Reducing diuretic dose and potassium supplementation are the most direct and effective therapies for hypokalemia 5.
• Combining with a potassium-sparing diuretic or blocker of the renin-angiotensin system also reduces the risk of hypokalemia 5.
• Lowering salt intake and increasing intake of vegetables and fruits help to reduce blood pressure as well as prevent hypokalemia 5.
• Recognition and treatment of life-threatening dysrhythmias in hypokalemia are key to managing these potassium abnormalities 6.
• Electrocardiogram (ECG) findings and treatment algorithms are crucial in managing hypokalemia, with recommendations on criteria for disposition 6.

Prognostic Value of ECG Abnormalities in Hypokalemia

• ECG abnormalities are poor prognostic markers for short-term adverse events under the current standard of care 4.
• In patients with mild hypokalemia, a heart rate >100 bpm, ST-depressions, and T-wave inversion are associated with increased hazard ratios for 7-day mortality and ICU admission 4.
• However, the low number of events with ventricular arrhythmia limited evaluation for this outcome 4.