Pharm: Antiarrhythmics Flashcards
What are the classes/MOA of antiarrhythmic drugs?
Type 1 - sodium channel blockers
Type 2 - Beta blocker
Type 3 - potassium channel blockers
Type 4 - cardioactive calcium channel blockers
Misc - atropine
What antiarrhythmics don’t target ion channels?
What are the different subclasses of class 1 anti-arrhythmics?
What differentiates them (effect and EKG)?
all slow conduction velocity making them useful in tachyarrhythmias
Class 1A:
- blocks Na channels and K channels
- prolongs QRS/reduces slope of phase 0 (moderate)
- prolongs QT interval/delays phase 3 (via K channel) -> Torsades risk
Class 1B:
- blocks Na channels only (weak)
- prolongs QRS/reduces slope of phase 0 (least)
- decreases QT/interval/earlier phase 3
-favors depolarized/damaged tissue -> minimal effect on healthy tissue
Class 1C:
- blocks Na channels
- prolongs QRS/reduces slope of phase 0 (most)
- does not effect QT interval
What drugs are class 1A antiarrhythmics?
- quinidine
- disopyramide
- procainamide
What types of arrhythmias are Class 1A antiarrhythmics used to treat?
both supraventricular and ventricular tachyarrhythmias
What adverse effects occur with quinidine?
Cinhonism:
- tinnitus
- vision changes
- confusion
What adverse effects occur with procainamide?
-drug-induced SLE
What adverse effects occur with disopyramide?
Exacerbates heart failure due to negative inotropic effect
strong anticholinergic activity:
- tachycardia
- dry mouth
- warm
- vision changes
- confusion
What adverse effect common to all class 1A antiarrhythmics leads to them not being commonly used?
QT prolongation with risk of Torsade de pointes
What drugs are class 1B antiarrhythmics?
- lidocaine
- mexiletine
What types of arrhythmias are Class 1B antiarrhythmics used to treat?
-ventricular arrhythmias in the setting of MI (preferential binding to Na channels in damaged tissue)
What adverse effects occur with lidocaine?
neurologic effects; it also works on nerves:
- dizziness
- nausea
- seizures
What adverse effects occur with mexiletine?
neurologic effects; it also works on nerves:
- dizziness
- nausea
- seizures
What drugs are class 1C antiarrhythmics?
- flecanide
- propafenone
What types of arrhythmias are Class 1C antiarrhythmics used to treat?
mostly supraventricular tachyarrhythmis, some ventricular arrhythmias
What is a common contraindication of class 1C antiarrhythmics?
structurally abnormal hearts (especially h/x of MI)
does not prolong effective refractory period of venticular tissue; this plus slowing of tachyarrhythmia results in possible ventricular re-entry arrhythmias
What difference in activity is there between flecanide and propafenone?
propafenone has mild β-blocking activity
otherwise the two are roughly identical
How does β-blocker activity cause an antiarrhythmic effect?
β-agonists increase expression of cAMP which causes increased expresion of If (funny channels) and L-/T-type Ca channels
β-blockers inhibit this:
- decreased If and T-type Ca channel negative chronotorpic effect by decreasing slope of phase 4
- decreased L-type Ca channels prolongs depolarization -> increased threshold potential/decreased slope of phase 0
- these combine to decrease HR and conduction velocity in the SA and AV, especially in the AV node
What ekg and action potential changes are seen in with β-blockers?
- prolonged PR interval/decreased slope of phase 0
- increased R-R interval/decreased slope of phase 4 (decrease HR)
What β-blockers are used as anti-arrhythmics?
- propanolol
- esmolol
What types of arrhythmias are Class 2 antiarrhythmics used to treat?
primarily supraventricular tachyarrhythmias, due to prolongation of AV condution and negative chronotropic effect
- a-fib/flutter
- SVT
- hyperthyroid related arrhythmias
What are common contraindications of class 2 antiarrhythmics?
- prolonged PR intervals/bradyarrhythmias
- decreased cardiac output (ie. HF)
- asthma (β2 bronchodilating inhibition)
- PVD/Raynaud’s (β2 vasodilating inhibition)
What are common adverse effects of class 2 antiarrhythmics?
- reduced cardiac output
- AV block
- hypoglycemia
- asthma/COPD exacerbation
- dyslipidemia
What is special about esmolol use as an antiarrhythmic?
cardioselective, given IV and has a short half-life -> fast on, fast off
- used in termination of SVT
- used perioperatively to prevent anesthesia related arrhythmias
