Heart Drugs Flashcards
What is the mode of action of Lidocaine?
Inactivates Na gated channels in both nerves AND cardiac muscle
Therefore decreases conduction.
What are the side effects of lidocaine?
CNS activation / depression
Hypotension
How is lidocaine administered?
Is not orally active so has to be given by injection
Metabolised by liver
1/2 life = 90-120 mins
Describe the 4 phases of the cardiac cycle
Phase 0 – rapid depolarisation due to voltage-gated Na+ channels opening – Na+ flows into myocyte.
Phase 1 – initial repolarisation – Na+ channels close, DRKC open – K+ leaves myocyte
Phase 2 – plateau – Ca2+ channels opened (time and voltage dependent) – Ca2+ in = K+ leaving. Ca channels stay open until end of plateau phase when they start to close.
Phase 3 – rapid repolarisation – Ca2+ channels closed, DRKC open, K+ leaves – myocyte repolarises.
Phase 4 – resting potential – K+ leaves myocyte through IRKC
K+ channels – are 2 types = inward rectifier K+ channels and delayed rectifier K+ channels.
- Inward rectifier K+ channels (IRKC) = maintain resting Vm until AP. Open when Vm <-60mV. Function – to clamp the Vm at rest by letting K+ out of cell, repolarising it.
- Delayed rectifier K+ channels (DRKC) = part of AP – open when membrane depolarises and closes after time delay = is both voltage and time dependent.
How do β blockers affect the nodes?
They slow spontaneous depolarisation of cardiac tissue
Which drugs are considered Class I in the VW classification?
Class I = Fast channel blockers
Disopyramide
Lidocaine
Flecanide
Which drugs are considered Class II in the VW classification?
Class II = Β blockers
Bisoprolol
Atenolol
Which drugs are considered Class III in the VW classification?
K+ channel blockers
Amiodarone
Which drugs are considered Class IV in the VW classification?
Ca Channel Blockers
Verapamil
Diltiazem
How do Class 1 agents selectively inhibit tachycardias?
They bind strongly when the channel is open or inactive (not resting).
Therefore the more frequently the channel is open (e.g. in tachycardia) - the greater the block.
Thus they inhibit tachycardia but allow normal HR
What is the difference between class 1 drugs?
What is flecanide used for?
Paroxysmal AF
AVRT
WPW
Slows condition in accessory pathways
Stabilises atria
DONT USE FOR VENTRICULAR ARRHYTHMIAS
What are the SEs of flecanide?
Can be pro-arrhythmic - do Echo prior to starting to check for abnormalities
Increases pacing thresholds - do pacemaker check before prescribing
Dizziness
Blurred vision
(Because it acts on neurological tissue as well as heart tissue)
Do ECG before starting and changing dose
Is amiodarone lipo-phillic or lipo-phobic?
Lipiophillic - highly - concentrates in the fat in the body
Means it has a LONG half life!
What is the loading dose of amiodarone?
200mg TDS - 1 week
200 mg BD - 1 week
200mg OD
Which molecule does amiodarone contain?
Iodine
How does amiodarone work?
Blocks ion channels inc delayed rectifier K+ channels = prolonged action potential (delays Phase III depolarisation)
Stabilises atrial and ventricular myocytes
Slows AV node conduction
Blocks accessory pathways
What are the side effects of amiodarone?
Lots!
Inc blue grey skin
Initially it causes pneumonitis which can progress to fibrosis
Iodine - important in thyroid hormone - can cause hyper and hypo thyroid
Secreted in tears - can become deposited on the cornea and cause keratitis. Can cause visual problems at night
How often should Ps on amiodarone be monitored?
What can amiodarone be used for?
AF - when other medication has failed to control
Malignant ventricular arrhythmias
Apart from amiodarone, which other Class III agent can be used for arrhythmias?
Dronedarone
Not used very often - used as an alternative to amiodarone when they can’t tolerate it - much less effective than amiodarone
What are the following receptors in the adrenergic system responsible for?
- α 1
- α 2
- β 1
- β 2
Which drug is first line for most tachyarrhythmias?
β blockers