Antiarrythmics Flashcards
Conduction pathway
SA, atria
AV, bundle of his, bundle branches, purkinje, ventricles
Where is SA node located
Right atria, posterior wall, by SVC
Where is AV node
Septal wall near coronary sinuses
Phase 0
Phase 1
Rapid depolarization
Partial repolarization
Phase 2
Phase 3
Plateau
Repolarization
Phase 4
Refractory period
Pacemaker potential
Phases 1-3
What occurs in phase 0
Rapid depolarization, fast na channels open, inward Na movement
What happens phase 1
Begin repolarization, na channels close
What happens phase 2
Plateau, slow ca ch open, slow inward ca
What happens phase 3
Repolarization, ca channels close, k channels open, slow outward k
What happens phase 4
Pacemaker potential. Return to RMP
SA node rate controlled by
ANS
SNS stim
Receptors
What happens
B1.
Inc: catecholamines, hr (chronotropy), automaticity
Facilitation of conduction of AV node
PNS ___
Receptors
What they do
Predominates
M2 muscarinic
Decreases HR, inhibits AV conduction, reduced automaticity
Arrhythmias classified by
Site of origin (atrial, junctional, ventricular)
Wide or narrow ecg
Rhythm
HR inc or dec
4 mechanisms of arrhythmia production
Altered automaticity
Delayed after depolarization
Re entry
Conduction block
Altered automaticity
Latent pacemaker cells take over SA node role, escape beats
Delayed after depolarization
Normal action potential of cardiac cell triggers abn depolarizations
Re entry
Refractory tissue reactivated repeatedly and rapidly d/t unidirectional block, continuous circuit
Conduction block
Impulse fail to propagate in nonconducting tissue
Factors underlying cardiac arrhythmias
8
Arterial hypoxemia, electrolyte abn, acid base abn, myo ischemia, alt SNS activity, bradycardia, drugs, enlargement/failing ventricle
When arrhythmias require tx
Can’t be corrected by removing cause
Hemodynamic compromise
Predisposes to more serious arrhythmias
Non pharm prophylaxis
Radio frequency catheter ablation
Implantable defibrillator
Class and phase they tx
Class I drugs
Class II
Na channel blockers, phase 0
BB, phase 4
Class and phase tx
Class III
Class IV
K ch blockers, phase 1 and 2
Ca ch blockers, phase 2
Class and phase tx
V
Unclassified drugs
Effects of class I agents
Phase 0 depresses vmax velocity, dec in AP propagation, slows conduction velocity
IA agents
Dissociation
4 effects
Intermediate
Decrease: depolarization rate phase 0, decrease conduction velocity. Prolong repolarization phase 3. Inc AP duration
IA drugs 3
Quinidine (prototype)
Procainamide
Disopyramide
Disopuramide
Indic
Route
SE
Suppresses vent tachyarrythmias. PO. Myocardial depressant, potentiates HF/hypotension. Atropine like effects.
IB agents
Dissociation
How they work
Fast na channel block. Alt AP by inhibit na influx, bind to na ch. little effect on max velocity, shortens ap duration and refractory period. Dec automaticity.
IB agents
4
Lidocaine (prototype)
Mexiletine
Tocainide
Phenytoin
Lidocaine
Class
Action
IB antiarrythmic
Na fast ch blocker
Lidocaine
Indic
Acute tx and prevention of v dysrhythmias, immeadiate aftermath of MI. V tach, v fib, pvcs
Lidocaine
Dose
Protein binding
1-1.5 mg/kg IV, then 1-4 mg/min gtt, max 3 mg/kg
50% binding
Lidocaine
Metabolism
Slowed by
Active metabolite prolongs 1/2t. Impaired by drugs: cimetidine, propranolol, or CHF, MI, liver dysfunc, GA.
Lidocaine
Metab induced by
Elim
Barbs, phenytoin, rifampin
10% renal elim
Lidocaine
E 1/2t
Therapeutic plasma level
2 hrs
1-5 mcg/ml
Lidocaine
AE
Low bp and hr, seizure, drowsy, dizzy, lightheaded, tinnitus, confusion, apnea, myo, cns, and vent depression, sinus arrest, heart block, cv arrest, augment Nm blockade
Phenytoin
Class
Indic
IB agent
Suppression of ventricular arrhythmias, assoc w dig toxicity (torsades)
Phenytoin
Give how
What happens in PIV
IV, ppt in D5W mix in NS
Pain or thrombosis
IC agents
What they do
Slow na ch blocker. Doesnt vary in cv cycle. Potent dec depolarization rate phase 0 and conduc rate w inc AP. Inhib thru his/purkinje.
IC agents 2
Flecainide prototype
Propafenone
Flecainide
Indic
Sf
Duration
Tachyarrythmias w abn conduction pathways, WPW
Proarrythmic SE
Long acting
Propafenone Indic Properties Route SE
Vent and atrial tachyarrythmias.
Weak BB and ca block. PO.
Proarrythmic SE
Class II agents
What they are, phase
How they act
BB. Depress phase 4 depolarization, dec SA node discharge. Slows HR and dec myo 02 reqs, good for CAD. Slows AV conduc, prolongs PR. Dec automaticity.
Class II
Indications
Tx SVT, atrial, and vent arrhythmias (esp post MI and reperfusion). Tx tachyarrythmias assoc w dig toxicity and SVT (afib or flutter)
Class II
Prevents binding of what
Catecholamines to beta receptors
Class II agents
4
Propranolol- prototype
Metoprolol
Esmolol
Labetolol- off label use
Propranolol
Class
Indic
Beta adrenergic agonist, nonselective.
Prevents reoccurrence of supra and ventricular tachyarrythmias ppt by SNS stim
Propranolol
Dose
1 mg/min (total 3-6 mg) IV or 10-80 mg po
Propranolol Onset Peak Duration E 1/2
2-5 min
10-15 min
3-4 hrs
2-4 hrs
Propranolol
Protein binging
Metabolism
Therapeutic level
90-95%
Hepatic, weak metabolite
10-30 Ng/ml
Propranolol
Cv effects
Caution with
Bradycardia and myocardial depression
Reactive a/w disease, hypovolemia, CHF, AV block
Metoprolol
Class
Dose
B adrenergic antag, selec B1
5 mg IV over 5 min, max dose 15 mg over 20 min
Metoprolol Onset 1/2 life Metab Can be used in
2.5 min
1/2 life 3-4 hrs
Liver
Mild CHF
Esmolol
Class
Dose
Beta adrenergic Antag, b1 selec
0.5 mg/kg iv over 1 min, then 50-300 mcg/kg/min
Esmolol
Duration
Effects what w/o effecting what
<15 min. Hr w/o dec bp significantly in small doses
Esmolol
Metab
No effect on
Hydrolyzed by plasma esterases
Not same esterases as cholinesterase, so no effect on sux
Class III
Action
Prolongs cv depolarization and inc AP duration, lengthens repolarization. Dec proportion of cycle when myo cells excitable, susceptible to triggering event
Class iii
Indications
Suppressing supra and ventricular arrhythmias. Prophylaxis cv surgery for afib. Preventative for pts posT CV death not candidate for ICD. Controls rhyth afib.
Class iii drugs 3
Amio- prototype
Dronedarone
Sotalol
Amio
Which class
III. But has I, II, and IV properties
Amio
Blocks what
K, na, ca channels. Alpha and beta adrenergic antagonist
Amio
Indic
Prophylaxis or tx atrial and vent arrhythmias (refractory SVT/VT/VF/AF), 1st line w VT/VF resistant to defibrillation
Amio
Dose
150-300 mg iv over 2-5 min. Up to 5 mg/kg. Then 1 mg/min x.6 hrs, 0.5 mg/min 18 hrs
Amio
E 1/2 t
Metabolism and excretion
10-100 days (long)
Hepatic, active metabolite
Biliary and intestinal excretion
Amio
Therapeutic level
Protein binding
Vd
1-3.5 mcg/ml
Extensive. 96%
Large
Amio
AE
Pulm toxicity/fibrosis/edema. ARDS. Photosensitive rash, grey/blue skin. Thyroid abn. Corneal deposits. CNS/GI disturb. Can cause torsades. Heart block. Low bp. Nightmares. Abn LFT. Inhibits -450
Sotalol
Class
Class II and III. Nonselective beta adrenergic antag.
Sotalol
Indic
Severe sustained vtach and vfib, prevents reoccurrence of tachyarrythmias, esp aflutter and Afib
Sotalol
SE
Cation
Excretion
Prolongs QTi, bradycardia, myoc depression, fatigue, dyspnea, AV block
Asthma pts
Urine
Ibutilide
Class
Indic
Pure class III Conversion afib/flutter, control rate. Prolongs AP duration and increases refractory period.
Dofetilide
Class
Route
Indic
Class III. Oral. Maintenance NSR after afib or conversion.
Dofetilide
SE
Ok in who
Proarrythmic
Post MI pts
Class IV agents
Primary site/action
Blocks slow ca ch. primary site at AV node. Dec conduction thru AV, shortens phase 2 (plateau), of AP in ventricular myocytes. Contractility dec.
Class iv
Indications
Not used in
SVT, ventricular rate control in afib/aflutter.
Prevents reoccurrence SVT
Not used in ventricular arrhythmias
Class IV agents
Ex
Ca ch blockers
Verapamil- prototype
Diltiazem
Verapamil
Dose
2.5-10 mg iv over 1-3 min. Max dose 20 mg.
Continuous gtt 5 mcg/kg/min
Verapamil
Dont use iv w/what
1/2 life
B blocker, heart block
6-8 hrs
Verapamil
Highly what
Metab
Excretion
Protein bound
Hepatic w active metabolite
Urine and bile
Verapamil
SE
Myocardial depression, hypotension, constipation, bradycardia, nausea, prolongs NMB
Verapamil
Caution
Myo dep and vasodil w inhalational drugs. Pot NMB. LA toxicity inc risk. Hyperkalemia w dantrolene. Dec dig clearance. Contraindication in WPW. Caution w BB
Dilt
Class
Dose
IV, Ca ch blocker
5-20 mg iv (0.25-0.35 mg/kg) over 2 min
Gtt 10 mg/hr
Dilt 1/2 life Highly what Metab Excretion
4-6 hrs
Protein bound
Hepatic
Urine
Dilt
SE
Myocardial depression, hypotension, constipation, bradycardia, nausea, prolongs NMB
Class V drugs 3
Adenosine, digoxin, atropine
Adenosine
Action
Binds to A1 purine nucleotide receptors, opens K channels. Slows AV nodal conduction
Adenosine
Indic `
Acute rx, terminated SVT or dx of VT
Adenosine
Dose
Duration
Elim
6 mg IV fast bolus. Repeat in 3 min, 6-12 mg iv
20-30 secs
Vascular endothelial enzymes
Adenosine
SE
Contraindicated in
AV/SA node inhib, flushing, HA, dizzy, SOB, CP, nausea, bronchospasm
Contra: asthma and heart block
Digoxin
What it is
Action
Cardiac glycoside
Inc vagal activity, dec SA node activity and prolongs conduction thru AV node. Dec HR, preload, and afterload. Inc contractility in CHF
Dig
Indication
Manage afib or flutter, controls ventricular rate, esp w imp heart func
Digoxin
Dose
Onset
t 1/2
0.5-1 mg divided doses over 12-24 hrs
Onset 30-60 min
36 hrs
Digoxin
Therapeutic index
Weak what
Excretion
Narrow, 0.5-1.2 ng/ml
Protein binding
90% kidneys, reduce in elderly and renal impaired
Digoxin
AE
Arrhythmias, heart block, anorexia, nausea, diarrhea, confusion, agitation
Digoxin
Potentiated by
Toxicity tx
Hypokalemia and hypomagnesemia
Phenytoin (vent arrhythmias), pacing, atropine, antidote: immune fab
Atropine
Class
Indic
Muscarinic receptor antag
Unstable bradyarrythmias
Atropine
Dose
Onset
Duration
0.4-1 mg IV
1 min
30-60 min
Atropine
Metab by
Cation dosing less than what, why
Liver.
0.4 mg, paradoxical response, penetrates BBB and CNS fx