Class 1A Na+ channel blockers
- Quinidine, procainamide, disopyramide.
- Increase threshold for AP firing.
- Decrease Vmax (lowers rate of upstroke).
- Increase ERP.
Indirect effects:
- Blocks K+ channels (potential for EADs).
- Vagolytic effect (can increase AV conduction - would need to give Digoxin).
Uses: atrial flutter; a fib; prevent v tach and v fib. Contraindicated in patients with LQTS.
Class 1A (quinidine, procainamide, disopyramide)
Lidocaine
- Class: 1B
- Blocks Na+ channels in a use-dependent manner.
- Increase AP threshold.
- Decreases AP duration and ERP.
Use: V tach; digitalis-induced arrhythmias, safe for patients with LQTS.
Class IB (lidocaine)
Flecainide
- Class: 1C
- Increase AP threshold.
- Reduce Vmax.
Side effects: pro-arrhythmic.
Approved for use in life-threatening situations. Really potent. LQTS3.CPVT.
Class 1C (flecainide)
B-blockers
Class II
Propranolol (long-acting), Esmolol (short-acting).
Slow the rate of diastolic depolarization (prolong PR interval). Do not prolong repolarization (safe for LQTS).
Used for all atrial arrhythmias, v tach and v fib.
Class II (b-blockers)
K+ channel blockers
Amiodarone, Sotalol, Dofetilide
Block K+ channels; prolong AP repolarization. Increased ERP. Reverse use-dependence.
Most common target is IKr (hERG channel).
Class III (K+ channel blockers)
Amiodarone
Class III (K+ channel blocker)
- Blocks both IKr, IKs.
- Modest Na+ channel blocker
- Modest Ca++ channel blocker
- Modest B-blocker
Effective against v tach and v fib. Prophylaxis of a fib or flutter.
Not associated with TdP, but yes with hypothyroidism. *Pulmonary toxicity.
Sotalol
Major action is blocking IKr. Also has B blocking actions.
Most serious SE: TdP.
Effective against V tach, v fib, A tach and A Fib.
Administer with caution in conjuction with drugs that prolong the QT interval.
Renal clearance.
Dofetilide
Blocks IKr.
SEs: triggered arrhythmias, TdP.
Most often used for Afib and atrial flutter.
Drugs that interfere with renal secretion system are contraindicated (increase chance of TdP).
Ca++ channel blockers
Class IV (non-dihydropyridines: benzothiazepines, phenylalkylamines)
Act primarily on SA & AV node to slow the rate of depolarization. Increase nodal cell refractory period; increase threshold for AP firing in nodal cells.
Used primarily for paroxysmal SVT.
SEs: bradycardia, negative inotropic effect, hypotension.
Renal excretion.
Class IV (Ca++ channel blockers)
Adenosine
Very rapidly activates K+ channels to slow phase 4 depolarization at AV node.
Slows AV conduction and heart rate.
Digoxin
Enhances vagal parasympathetic activity to slow conduction at the AV node.
Used for Afib and SVT to control ventricular response rate.