Antiarrhythmics Flashcards
what is cardiac arrhythmia
loss of cardiac rhythm
what are the two types of cardiac action potentials
- those characteristic of atrial and ventricular muscle such as purkinje fibers are called fast response action potentials
- those observed in the sinoatrial (SA) node and atrioventricular (AV) node are called slow response action potentials
resting potential in most myocardial cells
80 - 95 mV
how are arrhythmias classified
supraventricular (atrial or AV junctional)
ventricular
what are all arrhythmias a result of
- disturbances in impulse formation
- disturbances in impulse conduction
- or both
what are the different types of arrhythmias
- premature atrial contractions
- premature ventricular contractions (PVCs)
- atrial fibrillation
- atrial flutter
- paroxysmal supraventricular tachycardia (PSVTs)
- ventricular tachycardia (V-Tach)
- ventricular fibrillation (V-fib)
- sinus node dysfunction
describe premature atrial contraction, premature ventricular contractions, and atrial fibrillation
- premature atrial contraction is an early extra beat that originates in the atria and is harmless
- premature ventricular contraction is most common arrhythmias. it is a skipped beat caused by stress, exercise, nicotine, heart disease and etc and does not require treatment
- atrial fibrillation is irregular heart rhythm causing the atria to contract abnormally
describe atrial flutter, paroxysmal supraventricular tachycardia, ventricular tachycardia
- atrial flutter is caused by one or more rapid circuits in the atrium. it is more regular than a-fib
- paroxysmal supraventricular tachycardia is a rapid heart rate with regular rhythm originating from above the ventricles
- v-tach is a rapid heart rhythm originating in ventricles and requires treatment immediately
describe v-fib and sinus node dysfunction
- v fib is erratic disorganized firing of impulses from ventricle that prevents it from contracting and pumping out blood to the body and requires immediate response
- sinus node dysfunction is a slow heart rhythm due to abnormal SA node and requires treatment with a pace maker
what is an electrical cardioversion
if drugs not controlling irregular heart rhythm, this is used to deliver electrical shock that synchronizes the heart and allows normal rhythms to restart
why are the class I drugs classified into different subgroup and how does each subgroup differ?
classified based on their rate of drug binding and dissociation from the channel receptor
- class IA: intermediate in speed of binding and dissociation from receptor
- class IB: most rapid for both
- class IC: slowest for both
mechanism of class I drugs
- blocks Na channels –> automaticity (ability to generate action potential) is decreased by shifting threshold to more positive potentials and decreasing slope of phase 4 depolarization
- basically it raises the threshold for action potential and slows the rate of depolarization
what types of cells are not affects by class I drugs
nodal tissues because they do not rely on Na channels for depolarization
what is the class IA drug and what do they do
QUinidine, PROCainamide, DISOPYRAMIDe
the QUeen PROClaims DISO’s PYRAMID
- they are sodium channel blockers thereby inhibiting phase 0 depolarization hence increased action potential duration
- they also block K channels in phase 3 (rectifying K channels) resulting in prolongation of the refractory period (unable to initiate another action potential) in atria and ventricles —-> increased QT interval
- antimuscarinic properties
what is a big difference between the class IA drugs
quinidine and procainamide decrease vascular resistance while disopyramide increases vascular resistance
what is the effect of a metabolite of procainamide called NAPA (n-acetyl procainamide)
it has little effect on sodium channels but still blocks the K channels so acts more like a class III drug
clinical uses of class IA drugs
atrial fibrillation, supraventricular and ventricular arrhythmias
adverse effects of quinidine
- precipitate arrhythmias
- increases toxicity of digoxin by decreasing its renal clearance
- Cinchonism (blurred vision, tinnitus, headache, tinnitus)
- thrombocytopenia purpura
- hemolytic anemia
adverse effects of procainamide
- reversible lupus like syndrome
- aggravation of underlying HF
- induction of ventricular arrhythmias
adverse effects of disopyramide
- heart failure
- hypotension
- severe antimuscarinic effects
contraindications for quinidine
- complete heart block
- watch those with increased QT interval, history of torsades de pointes, incomplete heart block, uncompensated heart failure, myocarditis, severe myocardial damage
contraindication for procainamide
- hypersensitivity
- complete heart block
- 2nd degree block
- SLE
- torsades de pointes
- heart failure and hypertension
contraindication for disopyramide
-uncompensated heart failure
what are the class IB drugs
Lidocaine
Mexiletine
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mechanism of class IB drugs
- slows phase 0
- shortens phase 3 repolarization
- decrease slope of phase 4
clinical applications of class IB drugs
ventricular tachyarrhythmias
mexiletine used with v-tachy and lidocaine in digitalis induced arrhythmias
adverse effects of class IB drugs
lidocaine - convulsions/seizures and coma if in toxic range
mexiletine - CNS and GI effects
what are the class IC drugs
Flecainide
Propafenone
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mechanism of class IC drugs
-blocks sodium channels and due to its slow kinetics has a much higher increase in QRS
propafenone also has beta blocking activity
clinical applications of class IC drugs
- life threatening supraventricular tachyarrhythmias
- ventricular tachyarrhythmias
- prevention of paraoxysmal a-fib
- maintenance of normal sinus rhythm
- used exclusively for atrial arrhythmias
adverse effects of flecainide and propafenone
- negative inotropic effects
- CNS effects (headaches etc)
- life threatening arrhythmias and ventricular tachycardia
propafenone also has beta blocking activity so bronchospasm and aggravation of underlying heart failure
what are class II drugs and name them
they are beta blockers
metoprolol, propanolol, and esmolol
mechanism of class II drugs
- inhibit sympathetic tone which affects slow response tissues
- slows conduction of impulses
- reduce rate of spontaneous depolarization in cells with pacemaker activity
clinical uses of class II drugs
- supraventricular arrhythmias (a-fib, a-flutter, AV nodal re-entrant tachycardia)
- ventricular tachyarrhythmias
- reduce incidence of sudden arrhythmic death after MI
useful in tx of acute arrhythmias occuring during surgery or in emergency situations
esmolol
adverse effects of beta blockers
sleep disturbances
GI upset
bradycardia
hypotension
contraindications of beta blockers
acute CHF
severe bradycardia
heart block
severe hyperactive airway disease
