Lidocaine for digoxin toxicity?

[MudPhud20XX]

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1. So Kaplan pharm says lidocaine will decrease action potential duration (APD), so won't that increase the HR though?

For example, class III such as amiodarone does increase APD, which slowers HR as an antiarrhythmic drug (which slowers HR) right?

Or does APD have nothing to do with HR?

2. Can anyone explain the rationale using lidocaine for digoxin toxicity?
Lidocaine basically blocks the inactivated sodium channel and digoxin inhibits Na/K ATPAase which seems to be irrelevant to how lidocaine works, can anyone enlighten me?

Many thanks in advance.

 

[thehundredthone]

Lidocaine is useful for unstable PVCs or VTach due to digoxin toxicity especially when Fab is not avaliable. It suppresses automaticity without blocking the AV node. Phenytoin is a better choice than lidocaine for this.

Although lidocaine reduces APD, its main actions are to prolong the refractory period and depress phase 4 depolarization. Appartently lidocaine shortens the APD in fibres where it was previously longest, first, hence making APD more uniform.

Old paper, I know: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC481198/?page=1