ECG Electrolyte Imbalance

Author: Steve Field, MD
Updated: 9/21/2012

ECG: Electrolyte Imbalance

Normal ECG with overlay showing all the measurable intervals

Image courtesy of Life in the Fast Lane

PR Interval

Short Prolonged
Pre-excitation, e.g. Wolff-Parkinson-White High K, Low Ca

QRS Duration

Narrow Wide
Low K, Low Ca, Normal High K, High Ca

QTc Interval

Short Prolonged
High Ca Low K, Low Ca

ST Segment

Depressed Elevated
Low K, High Ca High K

T Wave

Peak/Tall Flattened
High K Low K

U Wave

Absent Present
Normal Low K, Low Ca

Heart Rate

Slow Fast
High K, High Ca Low K, Low Ca

Electrolyte Imbalances

Low High

  • QTc prolonged
  • U wave
  • Heart blocks
  • Dysrhythmias (heart block, torsades, ventricular)
  • QTc shortened
  • ST depression and shortening
  • QRS widening
  • Dysrhythmias (bradydysrhthmias, bundle branch block, high degree AV block)

Early to late findings:
  1. T wave: decr. amplitude
  2. T wave: flat or inverted
  3. ST depression
  4. U wave
  5. QTc prolonged
Early to late findings:
  1. T wave: tall, then "peaked", symmetrical
  2. P wave flattening
  3. PR prolonged
  4. QRS widening
  5. Nodal blocks, escape beats
  6. Sine wave → VF or asystole

Magnesium Derangements:

  • Nonspecific ECG findings
  • Often co-exists with Ca derangements
  • Classic teaching: Low Mg level → QTc prolongation → Torsades de pointes


  • Goldberger A., Clinical Electrocardiography: A Simplified Approach, 8th Edition, 2006
  • Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. Electrocardiographic manifestations: electrolyte abnormalities. J Emerg Med. 2004 Aug;27(2):153-60. [PubMed]
  • Marx J, Hockberger R., Walls R., Rosen’s Emergency Medicine: Concepts and Clinical Practice, 7th ed, 2010