what is the biggest warning sign for Bad Stuff on the EKG in an arrhythmia associated with hyperkalemia?

Hyperkalemia triggers a progression of electrocardiographic changes, beginning with peaked T waves and PR prolongation.

Widening QRS is the single most dangerous sign in K-induced arrhythmias and usually occurs with a K around 8-9. It is a warning that you should treat the patient immediately with calcium gluconate, and be prepared to dialyze them if need be. (Insulin + glucose is a second-line treatment since it doesn’t work as quickly.)

With the widening QRS, you can see loss of P waves and in severe cases, you might see a classic sine-wave rhythm (usually a K around 10):

from nejm.org
from nejm.org

This can degenerate into ventricular fibrillation if it goes untreated.

However, don’t freak out with every patient who comes in with “hyperkalemia.” In a study at University of Pittsburgh Medical Center, only 46% of patients with potassium levels greater than 6.0 mEq/L had electro-cardiographic changes, and only 55% of patients with potassium levels greater than 6.8 mEq/L had changes consistent with hyperkalemia.

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