Arrhythmia therapy Flashcards
What protein is mainly responsible for creating the resting membrane potential
Sodium-potassium ATPase
Give an example of a Class 1A antiarrhythmic and describe how it works
QUINIDINE
Procainamide
Dyspyrimide
(Moderate) sodium-channel blockade, thus reducing amplitude of AP and conduction velocity
Give an example of a Class 1B drug and describe how it works
LIDOCAINE
Mexiletine
Tocainide
(Weak) sodium-channel blockade, thus reducing amplitude of AP and conduction velocity
Reduce the effective refractory period
Give an example of a Class 1C drug and describe its mechanism of action
FLECAINIDE
propafenone
(Strong) sodium-channel blockade, thus reducing amplitude of AP and conduction velocity
Increase the effective refractory period
What is the alternative name for Class 2 antiarrhythmics?
Beta blockers
Eg Bisoprolol, atenolol
Describe the mechanism of Class 2 antiarrhythmic drugs
Block Beta 1 adrenergic receptors at the SA node
Slows SA discharge & AV conduction
Also reduces contractility
Give an example of a Class III antiarrhythmic and describe its mechanism of action
Amiadarone
Bretylium
Sotalol
Prolong refractory period by slowing K+ outflow from cells
This increases the duration of the action potential
Give an example of a class IV antiarrhythmic and explain its mechanism of action
Class IV = Rate limiting Calcium channel blockers
Eg Diltiazem, Verapamil
Decrease automaticity & slows AV conduction ∴ reduces heart rate
Give an example of a class V antiarrhythmic and explain how it works
Digoxin
Blocks Na-K ATPase
Slows SA & AV conduction
(another is adenosine)
A patient has Atrial fibrillation
What drug would you first prescribe to treat AF and why?
Bisoprolol
Inhibits B1 receptors at the SA node to block sympathetic stimulation of the heart.
This slows SA discharge and AV conduction.
Your first choice treatment for Atrial fibrillation is not working. What is used now?
Amiadarone
Prolongs the refractory period by slowing K+ outflow from cells
What would you use to treat Ventricular tachycardia?
Amiadarone
What precautions would you take before prescribing amiadarone?
Avoid giving it alongside Digoxin
What are the possible side effects of amiadarone?
Hyper or hypothyroidism
Pulmonary fibrosis
Slate-grey pigmentation of skin
Corneal deposits of keratin
Liver function impairment
What is digoxin used to treat?
Atrial fibrillation (if bisoprolol isn’t working)
Atrial flutter
Supraventricular tachycardia
Heart failure
What precautions must be taken when prescribing Digoxin?
Check renal function
Monitor potassium and digoxin levels in the blood to avoid toxicity
Monitor heart rate
Monitor heart rhythm
Check patients vision
What are the effects of Digoxin toxicity?
Nausea / vomiting
Xanthopsia (patient sees yellow)
Bradycardia
Tachycardia
Arrhythmias (VT & VF)
Why is it important to check a patient’s heart rate and rhythm when giving them digoxin?
Digoxin toxicity can cause Bradycardia, tachycardia, VT or VFib
‘Reverse tick’ appearance of ST segment in lateral leads of ECG
When could you use Class IV antiarrhythmics?
Paroxysmal SVT
Rate control for AFib and Atrial flutter
What is used to treat Digoxin toxicity?
Digibind
This Digoxin immune antibody will bind to digoxin and be excreted in urine
What is the use and mechanism of adenosine?
IV adenosine
Slows/blocks conduction through the AV node
Used to convert paroxysmal SVT to sinus rhythm (may cause asystole for a short time)
What factors increase the risk of a stroke for a patient with AFib?
Smoking Diabetes Previous CVD Previous AF Hypertension
Give examples of oral anticoagulants
Warfarin
Dabigatran
Rivaroxaban, Apixaban
Describe the mechanism of warfarin
Vitamin K epoxide reductase antagonist
Vitamin K used to convert precursor molecules to clotting factors
∴ reduced clotting factors ∴ less thrombin ∴ less fibrin
How does dabigatran work?
Directly inhibits thrombin from converting fibrinogen to fibrin ∴ stops clot formation
How do anticoagulants like rivaroxaban or apixaban work?
Directly inhibit Xa ∴ stops conversion of prothrombin to thrombin
Stops fibrin production ∴ stops clot formation
What is the INR?
International normalised ratio (for monitoring warfarin)
Normal is 1
Therapeutic INR is 2.5 - 4.0
What are the contraindications for Warfarin usage?
Previous haemorrhagic stroke
Brain trauma / surgery within the past 6 months
Known bleeding disorder / active bleeding
If they are on one of the million drugs that interacts with warfarin badly
Pregnancy
Why is pregnancy a contraindication for warfarin?
Teratogenic (chondrodysplasia)
Increased risk of retroplacental bleeding and foetal intracerebral bleeding
Avoid in 1st and 3rd trimesters
How would Aspirin or sulfonamides affect the activity of warfarin?
Decrease the binding of Warfarin to albumin
∴ increase Warfarins activity
What is the effect of Cimetidine, Erythromycin or Clarithromycin on warfarin?
These inhibit the degradation of warfarin through the Cytochrome P450 pathway
This means that giving them together increases the activity of warfarin
How would Oral antibiotics affect warfarin?
Increase it’s activity through decreasing the synthesis of clotting factors
What is the effect of giving both warfarin and aspirin together?
Inhibition of platelets promotes bleeding
What is the effect of giving warfarin alongside Heparin or antimetabolites?
Inhibits clotting factors
∴ promotes bleeding
What is the effect of barbiturates or Phenytoin on warfarin’s activity?
Decrease Warfarins activity
They do this through the induction of cytochrome P450 enzymes
Warfarin is metabolised by the Cytochrome P450 pathway
What is the effect of Vitamin K on warfarin’s activity?
Decrease warfarin’s activity
Vitamin K promotes clotting factor synthesis
What is the effect of cholestyramine on the activity of Warfarin?
Decrease the activity of Warfarin by reducing it’s absorption
