Antiarrythmics Flashcards
Drugs that decrease phase 4 slope
Beta Blockers (Class2)
Drugs that increase threshold potential
Na+ Channel blockers (Class 1) - Procaineamide (1a) and Flecanie (1c)
Drugs that increase diastolic potential (hyper polarization)
Na+ channel blockers - Lidocaine (ventricular cells only)
Drugs that increase action potential duration
K+ channel blocker (class 3) - Sotalol (3,2) and Amidarone (3,2,4)
Na+ channel blocker binding
bind only to activated and inactivated phases, cannot bind to resting channel because binding site is within channel.
MOA for Class 1
decrease rate of rise of phase 0 depolarization resulting in slower conduction of impulses through reentrant circuits; increase effective refractory period (ERP)
Class 1A
intermediate dissociation rate; prolongs action potential duration due to K+ Channel blocking properties - Procaineamide, Quinidine, Disopyramide.
Class 1B
Rapid dissociation, effective anti-tachycardia drug, narrows AP duration - Lidocaine
Procainamide
suppresses ectopic pacemaker activity in partially depolarized cells, reduces conduction velocity (reduced phase 0), prolongs AP duration
Used for Atrial and Ventricular arrhythmias; primarily acute atrial arrhythmias
Side effects: drug induced lupus, Torsades de Pointes
Quinidine
Class 1A MOA; dose dependent QT prolongation/Torsades de Pointes and V. Tach/Fib
S.E. diarrhea, autoimmune thrombocytopenia
Rarely used due to pro arrhythmia likelihood
Disopyramide
prominent vagolytic effect
Leads to urinary retention, dry mouth, blurred vision, negative inotropic effect leading to HF
Rarely used due to SE
Lidocaine
Class 1B - rapid kinetics; preferentially binds to Na+ channels in partially depolarized cells to suppress abnormal automaticity; no effect on conduction with normal heat rate
Highly effective for suppressing Ventricular arrhythmias
Extensive first pass metabolism so must be given IV (rapidly goes to fat tissues so must be given in two phases)
Tox: CNS, agitation, confusion, seizures
Mexilitine can be used orally, but GI distress limits use
Flecainide
Class 1C - long lasting Na channel blocker that suppresses automaticity and increases ERP in atria and ventricles
Increased mortality in post MI patients - do not use in patients with structural heart disease
Used for Supraventricular arrhythmias with no structural issues
Only used for life-threatening issues due to high risk of pro-arrhythmic effects
Propafenone
Class 1C MOA with Beta adrenoreceptor blocking properties; only used in Afib and Aflutter without structural heart disease
Treatments for V. Tach/Fib
Class 1 (not Flecanide) and 3 - treatment is aimed at interrupting reentry
MOA of Class 3 Potassium channel blockers
increase AP duration and ERP by blocking K+ channels, prolonging phase 3 of the AP thus prolonging ERP - shown on EKG as prolongation of QT
Prolonging ERP in the slow conducting limb of a reentrant circuit interrupts reentry
Amiodarone
MOA: K+ channel blockade, Na/Ca channel blockades and Beta adrenergic blocking properties as well; prolongs AP, inhibits abnormal automaticity, decreases conduction velocity, prolongs ERP
EKG: prolongation of PR, QRS, QT and sinus bradycardia
Uses: atrial and ventricular arrhythmias; IV for V. Tach/Fib
Drug of choice for cardiac resuscitation
slow elimination, highly lipophilic; metabolized by CYP3A4 (inhibits)
S.E.: pulmonary fibrosis, photo dermatitis, corneal microdeposits, optic neuritis, hypo/hyper thyroidism, hepatitis, prox. muscle weaknes
Interacts with digoxin and warfarin
Dronedarone
non-iodinated form of Amiodarone (no thyroid issues) used for paroxysmal AFib or maintenance of sinus rhythm
Contraindicated: patients with decompensated congestive heart failure due to increased risk of death, stroke, and worsened heart failure
Sotalol
nonselective beta blocker with AP prolonging characteristics
MOA: K+ channel blocker with 1/3 beta blocking effect of propranolol
Uses: atrial, ventricular, AV nodeal reentrant arrythmias including V tach
Effective (not as much as Amiodarone) with less toxicity
Metabolism: kidneys
Contra: extended QT interval, renal issues, asthma/COPD, CHF, brady, acute MI
SE: Torsade de Pointes
Dofetilide
pure class 3 drug; used for Afib
Rhythm control
SE: Torsades de Pointes
Contra: patients with long QT
initial therapy inpatient with EKG
Ibutilide
IV only; used for acute termination of A Fib/Flutter
Rhythm control
SE: Transient asystole and Torsades de Pointes
Drugs that cause Torsade de Pointes
Class 3, Class 1 (Quinidine, Procaineamide), non-sedating antihistamines
Optimal treatment for V Tach
Implantable Cardiac Defibrillator (ICD); followed by Amiodarone
Optimal treatment strategy for A Fib
Rate control: digoxin, B-blocker, Diltiazem, Verapamil and Warfarin
