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
What are the indications for digoxin?
Atrial dysrhythmias - AF, atrial flutter and possibly SVT
Heart failure
These drugs are usually second line and used with BB or CCB
How would you treat atrial fibrillation?
BB or CCB
If not effective rate control, therapy limited or acute HF/ hypotension then consider putting on digoxin
Describe digoxin and renal impairment
Digoxin has long half life which can be increased in renal impairment. Excretion is proportional to GFR
Commonly used in elderly - cautious with does as common for elderly to have renal impairment
Monitor potassium levels for toxicity
What are symptoms of toxicity with digoxin?
Nausea and vomiting, dehydration, xanthopsia, bradycardia, tachycardia and arrhythmias - VT and VF
What are signs of toxicity of digoxin on an ECG?
Reversed rick appearance of ST segment in lateral leads
What is the treatment for digoxin toxicity?
Stop digoxin but long half life
Give Digibind if level and risks are high of significant arrhythmia
Digoxin toxicity is more serious if potassium levels are low
Explain the drug Digibind
Has digoxin immune antibody, binds with digoxin which forms complex molecules and excreted in the urine
What is the mechanism of action for adenosine?
Bind to adenosine receptors in the AV node - slows/blocks conduction through the AV node
What is adenosine used in treatment for?
Used to convert paroxysmal SVT to sinus rhythm
What is the effect of adenosine on SVT?
Very short half life, only administered as fast IV push
May cause asystole for a few seconds and other minimal side effects
Avoided in patients with asthma as can cause marked bronchospasm
What is a side effect of antiarrhythmics?
Can cause arrhythmias
How does AF lead to thrombus formation?
AF causes flutters where blood is not properly squeezed into ventricles and can lead to stasis in left atrial appendage - thrombosis as Virchow’s triad
What is the chadsvasc score classification?
Calculates score for risk of stroke and if patient should be put on anticoagulants
If stage 2 and above then anticoagulants are given
Explain the chadsvasc score risk factors
Congestive heart failure
Hypertension
Age > 75
Age 65-74
Diabetes melilitus
Stroke/TIA/thromboembolism
Vascular disease
Sex female
What are the characteristics of an ideal anticoagulant?
Oral, no need for monitoring, no interactions with food or drugs, given once or twice a day, as effective as warfarin and safer then warfarin
What are the different types of oral anticoagulants used in AF?
Vitamin K antagonists - warfarin
Direct thrombin inhibitor - dabigatran
Direct Xa inhibitors
Describe the mechanism of action of warfarin
Inhibits production of active clotting factors - II, VII, IX and X
Structurally related to vitamin K
How is warfarin therapy monitored?
International normalised ratio (INR)
Actual prothrombin time/ standard prothrombin time
Normal is 1
What are some adverse effects of warfarin?
Bleeding, interactions with other drugs - P450 mechanism, pregnancy (teratogenic and avoid where possible)
What is the Hasbled classification used for?
Assess risk of bleeding
What are the Hasbled clinical characteristics?
Hypertension, abnormal liver function, abnormal renal function, stroke, bleeding, labile INRs, elderly, drugs and alcohol
What are some drugs which increase warfarin activity?
Aspirin - decrease binding to albumin
Cimetidine, erythromycin - inhibits degradation
Antibiotics - decrease synthesis of clotting factors
What are some drugs which promote bleeding with warfarin?
Aspirin - inhibition of platelets
Heparin - inhibition of clotting factors
What are some of the drugs which decrease warfarin activity?
Brabiturates and phenytoin - induce metabolising enzymes
Vitamin K - promotes clotting factor synthesis
Cholestyramine - reduced absorption
What are some inhibitors of cytochrome p450?
Omeprazole, disulfiram, erythromycin, valproate, isoniazid, ciprofloxacin an cimetidine, ethanol acutely and sulphonamides
What are some inducers of cytochrome p450?
Alcohol chronic use, barbiturates, carbamazepine, phenytoin, rifampicin and sulphonylureas
What are some new anticoagulants which can help reduce risk of stroke with AF?
Dabigatran, Rivaroxaban and Apixaban - less bleeding risk
What are some other cardiovascular indications for anticoagulation?
Metallic Heart Valves
DVT/PE - treatment and prophylaxis
