EKG Compass
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Electrolyte Effects on ECG
Drag the slider to see how abnormal electrolyte levels distort ECG morphology in real time. Canvas shows stylised Lead II waveforms scaled to clinical severity.
K⁺
Potassium — Lead II
Live ECG morphology preview
Serum K⁺ 1.5 – 9.0 mEq/L
1.5 3.0 4.5 6.0 7.5 9.0
4.0
mEq/L
Normal
Resting membrane potential Phase 3 repolarisation Inward rectifier K⁺
ECG Findings
Normal Sinus Rhythm
  • Normal P wave morphology (80–120 ms duration)
  • PR interval 120–200 ms
  • QRS ≤100 ms, normal axis
  • Upright T wave, T/R ratio <0.8
  • No U wave or minimal (<1 mm)
Clinical note: Normal potassium range is 3.5–5.0 mEq/L. Values outside this range cause progressive ECG changes proportional to severity.
Ca²⁺
Calcium — Lead II
QTc / ST segment effects
Serum Ca²⁺ 5.0 – 14.0 mg/dL
5.0 7.0 9.2 11.0 12.5 14.0
9.2
mg/dL
Normal
Phase 2 plateau (ICa,L) ST segment duration QTc interval
ECG Findings
Normal QTc Interval
  • Normal QTc 360–440 ms
  • ST segment of normal duration (~80 ms)
  • T wave upright, normal amplitude
  • No Osborn (J) wave
Clinical note: Normal ionised calcium 8.5–10.5 mg/dL. Calcium affects plateau phase duration, altering ST length and QTc without changing QRS.
Mg²⁺
Magnesium — Lead II
PR/QRS/QTc modulation
Serum Mg²⁺ 0.5 – 5.0 mEq/L
0.5 1.3 2.0 3.0 4.0 5.0
2.0
mEq/L
Normal
NMDA / Na⁺-K⁺-ATPase IKr channel block AV nodal conduction
ECG Findings
Normal — No ECG Changes
  • Normal PR interval 120–200 ms
  • QRS ≤100 ms, normal axis
  • Normal QTc interval
  • No T wave or U wave abnormalities
Clinical note: Normal Mg²⁺ is 1.3–2.5 mEq/L. Hypomagnesaemia frequently coexists with hypokalaemia and potentiates arrhythmias.