Hyperkalaemia and Hypokalaemia ECG

[jsmith613]

Why does Hyperkalaemia cause:

• tall peaked T-wave
• loss of P-wave
• widening of QRS

and why does Hypokalaemia cause:

• ST depression
• flattened T-waves
• appearance of U wave

on an ECG? thank you

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[Rendar5]

will wait on someone else for the answers because I haven't remembered that stuff since medical school. but to complicate things futher, hyperkalemia can also cause asystole, bradycardia, and bradyarrhythmias even without the above. So if any cards folks show up, maybe they can explain that one to me, lol.

 

[Kaustikos]

Well... Higher K causes a depolarization of the resting membrane. Which would make you think it'd make it easier to conduct sodium currents but no. It leads to less sodium channels activated which means the Vmax is decreased. Less influx = weaker conduction. This is why you see weak/absent P waves and why QRS complexes take longer initially (wider). But the higher K outside drives a faster/stronger current for repolarization due to the Ik. This is why the QT is short and why you have peaked T waves (strong K conduction out of cell).

The more K outside = higher resting = less sodium channels to conduct AP. It gets worse and worse leading to asystole/bradycardia. That's why we use it for bypass/transplants

 

[addme]

Espresso, espresso, espresso. (Except during surgery - you can't necessarily go to the bathroom whenever you feel like it, so fluid restriction and no caffeine is really important.)