Arrhythmias - Therapies Flashcards
What is an arrhythmia?
A deviation from the normal rhythm of the heart
What are some types of arrhythmias?
Sinus arrhythmia, bradycardias, tachycardias, supraventricular arrhythmia (AF and SVT) and ventricular arrhythmia (tachycardia and fibrillation)
What are the most important drugs used for treatment of arrhythmais?
Flecainide
Atenolol, bisoprolol
Amiodarone
Diltiazem, verapamil
Digoxin
How are the drugs for arrhythmias classified?
Class I-V
Vaughan-William’s classification - classified as which receptor they act upon
Explain Class I - Sodium Channel Blockers
Membrane-stabilizing agents which decrease size of action potential and reduce velocity of conduction/excitation
Act on fast sodium channels which are responsible for phase 0
Describe Class I drugs
Divided into IA, IB and IC agents - according to their effect on AP duration and the effective refractory period
They are more effective at higher HR
What is the most common Class I drug?
Class IC - flecainide
Strong Na+ channel blockage and keeps the same effective refractory period but slow depolarisation
Describe class II beta blockers
Act on B1 receptors to block sympathetic stimulation of the heart
This prolongs phase 4 depolarisation - slows SA discharge and AV conduction
This reduced excitability in non-nodal tissue
Also shortens phase 2 - negative effect on contractibility
What is Class II beta blockers used for treatment?
First line in atrial fibrillation - bisoprolol
Supresses VEs and some VT
What are some common beta blockers used?
Atenolol - BP control
Bisoprolol - more cardio specific
Propranolol
Describe Class III potassium channel blockers
Increase AP duration, prolong repolarisation in phase 3 and prolong the ERP
Ex. amiodarone, bretylium and sotalol
What is class III potassium channel blocker drugs used in treatment for?
Dysthymias that are difficult to treat
Life-threatening ventricular tachycardia or fibrillation, atrial fibrillation or flutter - resistant to other drugs
Sustained ventricular tachycardia
What is amiodarone used for?
Is a class III potassium channel blocker
Used for VT and occasionally in supraventricular tachycardia
What is the side effects of amiodarone?
Thyroid - hypo or hyperthyroidism
Pulmonary fibrosis, Slate (grey pigmentation), corneal deposits and LFT abnormalities
Describe Class IV calcium channel blockers
Bind to Lcard type voltage gated channels and depress phase 4 in SA and AV nodes
This slows heart rate
Also shortens phase 2 plateau phase - reduce contractibility
More effective at higher HR
What are class IV calcium channel blockers used in treatment for?
Verapamil and diltiazem
Used for paroxysmal supraventricular tachycardia and rate control for AF and flutter
What is an example of a class V drug and what are they?
Digoxin and Adenosine
Have properties of several classes and are not placed into one particular class
What is the mechanism of action for digoxin?
Cardiac glycoside and it inhibits the sodium-potassium ATPase pump
Increases vagal tone so slows conduction, reduced refractory period in myocardium and increases intracellular Ca so positive inotropic effect