Anti-arrhythmic question

[Phloston]

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Why does hyperkalaemia cause toxicity with the class-I anti-arrhythmics? (p. 310 of FA).

 

[loveoforganic2]

Hyperkalemia prolongs depolarization and class I's are Na channel blockers.

During depolarization, the Na channels are (physiologically) switched off and slowly return during repolarization. Prolonged depolarization due to hyperkalemia along with Na channel blockers exacerbates that physiologic Na channel "off switching"

Haven't taken pharm yet, just my understanding from previous miscellaneous interest reading, so caveat emptor on that explanation

 

[Phloston]

I honestly must be on crack (been up all night here in Australia).

Thanks for the help/reminder.