Week 4 Flashcards
class III antiarrythmetic drugs general
K+ channel blockers slows repolarization increases refractory period Lengthens QT interval Ex. Amiodarone
amiodarone
class III antiarrythmetic drug (K+ channel blocker, slows repolarization)
SE: MOST IMPORTANT: Dose related pulmonary toxicity.
because of its Class IV effects, it ca produce bradycardia and heart block in patient with preexisting SA or AV node disease.
Other SEs:
Hypersensitivity hepatitis
skin deposits -> photodermatitis, gray-blue skin discoloration in sun exposed areas
corneal microdeposits in nearly all patients
hypo and hyperparathyroidism
Drug accumulates in tissues (heart, lung, liver, skin, and tears) Blocks peripheral conversion of thyroxine (T4) to triiodothyronine (T3) and source of inorganic iodine
Dofetilide
class III antiarrhythmic (K+ channel blocker, slows repolarization)
contraindicated in long QT, bradycardia, hypokalemia
Ibutilide
Class III antiarrhythmic (K+ channel blocker, slows repolarization)
also slows inward Na+ channels
Common side effects of all class III antiarrhythmic drugs
prolonging QT interval can produce torsades de pointes
class IV antiarrhythmic drugs general
binds to and blocks L-type Ca channels (some do T-type) located on the vascular smooth muscle, cardiac myocytes, and SA/AV nodes
In smooth muscle:
- decreases vascular resistance by relaxation, lowers BP
in cardiac myocytes:
- reduces contractility
- shortens refractory period
in nodal tissues:
- slows the rate of depolarization, slowing HR
- slows conduction velocity (mostly in AV node)
*can be used to treat re-entry circuits (ectopic foci) because they decrease pacemaker depolarization rate.
can be used to treat angina and hypertension too - vasodilation and decreased HR, decreases O2 demand
Class IV drug Dihydropyridines
vascular specific calcium channel blocker.
used for hypertension. (not used for angina because the decreased TPR can cause reflex tachycardia and contractility) Longer lasting Dihydropyridines have less reflex responses.
names all end in “pine”
SE: flushing, headace, excessive hypotension, edema, reflex tachycardia
how are ectopic foci usually generated?
the cells loose the ability to use sodium as the thing that depolarizes them , so they use calcium instead
Class IV drugs non-dihydropyridines
verapamil - myocardium specific calcium channel blocker. Tx for angina, arrythmias. Blocks both activated and inactivated L-type Ca channels. greater effect on tissues that fire frequently, are less polarized, or are nodal tissue.
Diltiazem - intermediate specificity for vascular and myocyte calcium channels. reduces arterial pressure without as much reflex tachycardia that is seen in dihydropyridines.
SE: excessive bradycardia, impaired electrical conduction (AV block), depressed contractility
can you give a class IV antiarrythmic to someone on a beta blocker?
NO
Verapamil
Class IV non-dihydropyridine
myocardium specific calcium channel blocker. Tx for angina, arrhythmias. Blocks both activated and inactivated L-type Ca channels. greater effect on tissues that fire frequently, are less polarized, or are nodal tissue.
contraindicated in Wolf-Parkinson-White
SE: excessive bradycardia, impaired electrical conduction (AV block), depressed contractility
Diltiazem
Class IV non-dihydropyridine
Diltiazem - intermediate specificity for vascular and myocyte calcium channels. reduces arterial pressure without as much reflex tachycardia that is seen in dihydropyridines.
SE: excessive bradycardia, impaired electrical conduction (AV block), depressed contractility
adenosine: usage as antiarrhythmic
activation of K channels and inhibition of L-type Ca channels
results in hyperpolarization and s uppression of Ca dependent action potential (nodal tissue)
DOC for prompt conversion of paroxysmal supraventricular tachycardia
not effective in atrial flutter or fibrillation.
SE: Related to vasodilatory properties. Flushing and headache. Arterial hypotension (reversed shortly after stopping infusion). AV block. (Contraindicated in patients with second and third degree AV blocks.)
caffeine can competitevely antagonize the binding of this antiarrhythmic
adenosine
what antiarrhythmic is contraindicated in patients with second and third degree AV blocks? Why
adenosine
because it can cause AV blocks, you don’t want to exacerbate the blocks
