Pharmacology: Cardiac Arrhythmia Drugs Flashcards
What is the generalised action of class 1 drugs?
They block Na channels. This slows conduction of phase 0 but has minor effects on the action potential duration. 1A has moderate affects on phase 0 1B has no change in phase 0 1C has marked effects on phase 0
What is the action of class 2 drugs?
Beta-blockers prevent entry of calcium during phase 2 of the action potential.
This diminishes the phase 4 depolarisation
What is the action of class 3 drugs?
Block K channels.
Therefore the depolarisation occurs more slowly - the refractory period is prolonged so the cell cant be excited for long. Increases the overall action potential duration.
What is the action of class 4 drugs?
Block calcium channels
There is a decrease in the phase 4 spontaneous depolarisation. There is no change in the duration of the action potential.
What is the action of class 4 drugs on the slow action potential?
Calcium channels blockers
Decrease the gradient of the slope 0 which lengthens the refractory period
Describe the ways in which abnormal impulse generation can arise
Automatic rhythms:
Enhance normal - sinus tachycardia where there is increase APs from the SA node.
Ectopic focus - APs arise from sites other than the SA node.
Triggered rhythms: (abnormal depolarisation)
Delayed afterdepolarisation - arises from the resting potential
Early afterdepolarisation - arises from the plateau eg before the repolarisation is complete
Describe the abnormal conduction patterns
Conduction block: the impulse is not conducted from the atria to the ventricles. Can be 1st 2nd or 3rd degree.
Re-entry rhythms:
There is a unidirectional block where the impulse can travel retrograde
Abnormal anatomy:
Accessory pathway called the bundle of Kent, leads to WPW
What is the principle action of drugs used to treat arrhythmias caused by abnormal generation?
Decrease the phase 4 slow in the pacemaker cells. This slows conduction and increases the threshold.
What is the principle action of drugs used to treat arrhythmias caused by abnormal conduction?
- decrease the conduction velocity by decreasing slope of phase 0
- increase the effective refractory period so the cell wont be excited again
Name the class 1A agents
Procainamide
Quinidine
Disopyramide
What are the specific actions of class 1A agents?
- decrease conduction by decreasing phase 0 of AP
- increase refractory period by enhancing Na inactivation
- decrease automaticity by decreasing slpe of phase 4
- increasing threshold
What are the effects of 1A agents on ECG?
Increased QRS
Prolonged PR interval
Prolong QT interval
What are the uses of class 1A agents?
Not commonly used.
Quinidine - maintain sinus rhythm in AF and atrial flutter and prevent recurrence
Procainamide - IV treatment of supraventricular and ventricular rhythms
What are the side effects of class 1A agents?
hypotension reduced CO dizziness confusion insomnia seizure (high doses) GI effects common Lupus-like syndrome esp procainamide Can actually be pro-arrhythmic
Name the class 1B agents
Lidocaine - IV only
Mexiletine - oral
What are the specific actions of 1B agents?
AP duration slightly decreased
Increased threshold of APs
Decrease phase 0 in fast beating or ischaemic tissue but not normal tissue
What is the effect of 1B agents on ECG?
None in normal.
In fast or ischaemic tissue - increased QRS
What are 1B agents used for?
ventricular tachycardia esp during ischaemia
What are the side effects of 1B agents?
Safer than 1A due to less risk of pro-arrhythmia
CNS - drowsiness, dizziness
Gi upset common
Name the class 1C agents
Flecainide
Propafenone
Can be used orally or IV
What are the effects of 1C agents?
- substantial decrease of phase 0
- decreased automaticity by increasing threshold
- increase AP duration and refractory period esp in rapidly depolarising atrial tissue (AF)
What are the effects of 1C agents on ECG?
Increased PR interval
Increased QRS
Increased QT
What are class 1C agents used for?
Wide spectrum:
- AF and atrial flutter
- premature ventricular contractions
- WPW
What are the side effects of 1C agents?
Flecainide - chronic use can cause pro-arrhythmias and sudden cardiac death (contraindicated if previous MI)
CNS and GI upsets
Name the class 2 agents? What are the routes of administration?
Propanolol - oral or IV
Bisoprolol - long acting oral
Metoprolol - Oral or IV
Esmolol - IV only, half life 9 mins
What are the effects of class 2 agents?
Increased AP duration and refractory period in AV node to slow AV node conduction velocity
Decrease phase 4 depolarisation
What are the effects of class 2 agents on the ECG?
Increased PR interval
Decreased heart rate
What are the uses of class 2 agents?
- sinus tachycardia
- catecholamine tachycardia
- protecting the ventricles from high atrial rates such as AF
What are the side effects of class 2 agents?
Bronchospasm - need to be careful in asthma
Hypotension
Name the class 3 agents
Amiodarone - oral or IV, half life 3 months
Sotalol
What are the cardiac effects of amiodarone?
Affect all phases of the cardiac AP
- increase refractory period
- decrease phase 0
- increase threshold
- decrease phase 4
- decrease speed of AV conduction
What are the effects of amiodarone on the ECG?
Increased PR interval
Increased QRS
Increased QT
Decreased HR
What is amiodarone used for?
Very wide spectrum - effective for most arrhythmias
What are the side effects of amiodarone?
Side effects can be serious and the risks increase with chronic use ~3years
- pulmonary fibrosis
- hepatic injury (monitor warfarin)
- increased LDL
- thyroid disease (contains iodine)
- photosensitivity (need to wear factor 50)
- optic neuritis which can cause transient blindness
What are the effects of sotalol?
Increased AP duration and refractory period
Slows phase 4
Slows AV conduction
What are the ECG effects of sotalol?
Increased QT
Decreased HR
What are the uses of sotalol?
A step down from amiodarone
Wide spectrum - supraventricular and ventricular tachycardia
What are the side effects of sotalol?
Can be pro-arrhythmic
Fatigue
Insomnia
Prolonged QT
Name the class 4 agents
Verapamil - oral or IV
Diltiazem - oral
What are the effects of class 4 agents?
Slow conduction through the AV node
Increase refractory period in AV node
Increase slope of phase 4 in SAN to slow HR
What are the effects of class 4 agents on ECG?
Increased PR interval
HR can increase or decrease depending on the BP and baroreflex
What are the uses of class 4 agents?
Control the ventricles during supraventricular tachycardia
What are the side effects of class 4 agents?
Constipation
Need to be cautious in partial AV block, can get asystole if there is also a beta blocker taken
What is the mechanism of action of adenosine?
IV bolus with a half life of seconds
Binds to A1 receptors and activates K+ currents in AV and SAN.
Causes hyperpolarisation which decreases HR and increases refractory period. Get decreased calcium currents
What is adenosine used for?
To slow AV conduction
- convert re-entrant supraventricular arrhythmias
- hypotension during surgery
What is the action and effects of vernakalant?
Given as an IV bolus over 10 mins to block atrial specific K channels.
Slows atrial conduction (increased potency with higher HR) which can convert recent onset AF to normal sinus rhythm.
What is the action and use of ivabradine?
Given orally.
Blocks funny current in SA node so slows the node but doesnt affect BP (unlike beta blockers)
Used tor reduce sinus tachy and reduce HR in heart failure and angina - avoiding BP drops
How does digoxin work? What is it used for?
Enhances vagal activity, slows AV conduction and slows HR.
Used to reduce ventricular rates in AF and atrial flutter
What is the action and use of atropine?
Its a selective muscarinic antagonist which blocks vagal activity to speed Av conduction and increase HR
Used to treat vagal bardycardia
Which drugs can be used to treat AF?
Rate control (act at AV node) Bisoprolol or verapamil for asthmatics, diltiazem. Digoxin can be an add on therapy.
Rhythm control
Sotalol, if acute give IV flecainide with bisoprolol or amiodarone
What IV drugs can be used for VT?
Metoprolol
Lignocaine
Amiodarone but need to inform of risks and side effects
Choice of above 3 depends on drugs already prescribed
Should flecainide be used alone in atrial flutter?
No - need to also give an AV node blocker
If the conduction of the atria is reduced the AV node may take the new rate leading to faster ventricular rate
What is the best treatment for WPW?
Ablation can cure.
Flecainide is 1st line, oral or IV
Amiodarone can be used but inform of risks and side effects
List the drugs that can be used in re-entrant supraventricular tachycardia
Acute (IV):
Adenosine (dont use in asthma)
Verapamil
Flecainide
Chronic (oral): In order of line: - bisoprolol, verapamil - sotalol - flecainide, procainamide - amiodarone
What drugs can be used for ectopic beats?
1st line is bisoprolol
If fails can use flecainide, sotalol or amiodarone
NB flecainide should never be used in previous MI, ischaemia or structural heart disease
What drugs can treat sinus tachycardia?
Ivabradine - v specific, no drop in BP but do not use in pregnancy, teratogenicity unknown
Bisoprolol, verapamil - safer but drops BP
