why is atropine not effective in treating a sinoventricular rhythm in hyperkalemia?

There are four main types of antiarrhythmia drugs: 1) Na channel
blocker, 2) beta blockers, 3) action potential elongation (usually K
channel blocker), 4) Ca channel blockers. Atropine is a muscarinic
antagonist, and so it blocks the sympathetic nervous system. It is
mainly used for increasing heart rate, such as with poisoning with
agents that slow the heart. It can be used to shorten the refractory
period of the AV node, thus increasing ventricular rate in patients
with atrial fibrillation. But in general, it is rarely used to treat
any type of arrhythmia. I'll try to look up more on this if I get
time, but that should help.

I meant to say atropine blocks the PARAsympathetic system.