Flashcards in K+ and Ca2+ Antiarrhythmics Deck (21):
Primary role of K+ in myocyte action potential?
repolarization (phase 3)
Common EKG effect of all class III drugs with prolonged repolarization?
Class III antiarrhythmic
also potent Na+ channel blocker
weak Beta and Ca2+ blocker
slows HR and AV node conduction
Extracardiac effects of Amiodarone
Toxicity of Amiodarone
Bradycardia and heart block in pts w/ preexisting SA or AV node disease
Drug accumulation in tissue (LONG half life)
Blocks peripheral conversion of thyroxine (T4) to triiodothyronine (T3)--source of inorganic iodine
PK if Amiodarone:
Major metabolite is bioactive --- long last effects
-abnormal liver function
-corneal microdeposits (halos, optic neuritis, blindness)
CYP3A4 drug interactions
inhibits several P450s --> icr. levels of other drugs (ie. warfarin, statins, digoxin)
Uses of Amiodarone:
Most important adverse effect of Amiodarone:
dose related Pulmonary Toxicity
Very selective K+ blocker
Maintenance and restoration of NSR in a fib
Class III (very selective K+ blockade)
Tox: life threatening ventricular arrhythmias
PK: 100% bioavailability, hepatic met. CYP3A4
Use: a fib
contraindications: long QT, bradycardia, hypokalemia
also slow inward Na+ ACTIVATOR --> delays repolarization (inhibits Na+ inactivation, increasing ERP)
Toxicity: long QT, torsades --> life threatening ventricular arrhythmias
Use: acute conversion of a fib/flutter in NSR
Target channel for Class IV drugs?
-decreased cardiac contractility (less Ca2+ available to bind troponin)
Class IV drugs effect on nodal cells?
-decreased conduction (especially AV node)
Therapeutic indications for Class IV?
HTN (arteriole SM relaxation)
Angina (decreased afterload--decreased O2 demand)
Arrhythmias (decreased depol rate, decreased conduction velocity)
What are the two subclasses of Class IV drugs?
How do they differ?
1. Dihydropyridines -- smooth muscle selective --> can cause reflex cardiac stimulation
2. Non-dihydropyridines -- more selective for myocardium
**Diltiazem does both -- able to reduce arterial pressure without same degree of reflex cardiac stimulation
Class IV drugs should not be used in conjunction with?
Non-DHP Class IV
more specific for myocardium
used in SVT, a fib/flutter
Contraindicated in WPW
Non-DHP Class IV
More equivalent selectivity for vascular and myocardial SM
inhibits Ca2+ L type
results in hyperpolarization and suppression of nodal tissue
used for SVT
not effective for a fib/flutter
***contraindicated in 2 and 3 deg AV block
Inhibits Na+/K+/ATPase pump
improves contractility (reverses NCX--> more Ca2+ in cell)
activates vagal efferents to heart
primarily used in HF (also a fib/flutter)