What are the EKG (electrocardiogram) findings in hypokalemia (low potassium levels)?

EKG Findings of Hypokalemia

Hypokalemia produces a progressive series of EKG changes including T-wave flattening, ST-segment depression, prominent U waves, and in severe cases, can lead to life-threatening arrhythmias. 1

Characteristic ECG Changes in Hypokalemia

Hypokalemia causes several distinct electrocardiographic abnormalities that correlate with the severity of potassium depletion:

• Early/Mild Hypokalemia:

  • T-wave flattening and decreased amplitude
  • ST-segment depression (can mimic myocardial ischemia)
  • Prominent U waves (best seen in leads V2-V4)
  • Prolonged PR interval
  • Increased P wave amplitude 1, 2

• Moderate to Severe Hypokalemia:

  • More pronounced U waves (may exceed T-wave amplitude)
  • Progressive ST-segment depression
  • T-U wave fusion
  • QT interval prolongation (when measured to the end of the U wave) 1, 3

Arrhythmias Associated with Hypokalemia

Hypokalemia creates an arrhythmogenic substrate through multiple electrophysiologic mechanisms:

• Supraventricular arrhythmias:

  • Atrial fibrillation
  • Premature atrial contractions
  • Paroxysmal atrial tachycardia 1

• Ventricular arrhythmias:

  • Premature ventricular contractions
  • Ventricular tachycardia
  • Torsades de pointes (particularly concerning in patients on digoxin) 3, 1

• Advanced cases:

  • Progression to PEA (pulseless electrical activity)
  • Asystole 3

Electrophysiologic Mechanisms

Hypokalemia affects cardiac conduction and excitability through several mechanisms:

• Increases resting membrane potential
• Prolongs action potential duration
• Extends refractory period (to a greater degree than action potential duration)
• Increases threshold potential and automaticity
• Decreases conductivity 4

These combined effects create conditions favorable for both reentrant and automatic arrhythmias.

Clinical Implications and Monitoring

• Continuous cardiac monitoring is recommended for:

  • Patients with moderate to severe hypokalemia (<3.0 mEq/L)
  • Those with underlying cardiac disease
  • Patients taking digoxin (increased risk of digitalis toxicity) 1

• Always check magnesium levels, as hypomagnesemia frequently coexists with hypokalemia and can exacerbate ECG abnormalities 1

• Patients with heart failure should maintain potassium levels of at least 4 mEq/L to reduce arrhythmia risk 1

Common Pitfalls and Caveats

1. Misdiagnosis: Hypokalemia-induced ST-segment depression can be misinterpreted as myocardial ischemia 1, 5

2. Overlooking U waves: U waves may be subtle and mistaken for part of the T wave, especially when they fuse with T waves 2

3. Pseudonormalization: During potassium replacement, ECG changes may normalize before serum potassium levels fully correct, creating a false sense of security 1

4. Rebound hypokalemia: Rapid shifts in potassium can occur, especially in patients with transcellular shifts (e.g., insulin administration, β-agonist use) 6

5. Underestimating severity: Serum potassium levels may not accurately reflect total body potassium deficit; mild hypokalemia can be associated with significant total body depletion 7

By recognizing these characteristic ECG patterns, clinicians can promptly identify hypokalemia, assess its severity, and initiate appropriate treatment to prevent potentially life-threatening complications.