ECG: Electrolyte Imbalance

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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
Ca	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)
K	Early to late findings: T wave: decr. amplitude T wave: flat or inverted ST depression U wave QTc prolonged	Early to late findings: T wave: tall, then "peaked", symmetrical P wave flattening PR prolonged QRS widening Nodal blocks, escape beats 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

References

• 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