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A 68-year-old female has AF, which is treated with an antiarrhythmic agent that blocks Na+ channels. On a recent office visit, she complained of recurrent attacks of feeling faint and of experiencing an episode of loss of consciousness. An EKG showed marked prolongation of the QT interval. Plasma concentration of the drug was in the therapeutic range. Which of the following drugs is most likely to have caused the adverse effect?
A.
Adenosine
B.
Amiodarone
C.
Bretylium
D.
Flecainide
E.
Procainamide
F.
Propafenone
G.
Quinidine
H.
Sotalol
I.
Tocainide
J.
Verapamil

Quinidine

b, amiodarone

The answer is: G

Quinidine causes prolongation of the QT interval at therapeutic doses, possibly because of its antimuscarinic actions. In some patients, this is associated with recurrent lightheadedness and fainting (known as quinidine syncope). The symptoms result from torsades de pointes. They typically terminate but may become fatal by degeneration into ventricular fibrillation.

not clear.all antiarrythmatics are proarrythmetics at therapeutic dosing.answer could be amoidarone or even sotalol.and it do not degenerate in to VF but degenrates in to TDP (TOrsade De POINTES) which is a polymorpihc v tach not vf.

what is the treatment? Mg??