the vaughan williams system drugs

mechanism of class i drugs

• block sodium channels in phase 0 of cardiac muscle action potential

• influx of sodium, reduce speed of conduction in the heart

what drugs can be used if patient has atrial fibrillation/ flutter and no history of myocardial infarction, coronary heart disease

• beta blockers -lol (type ii)

• calcium channel blockers (type iv)

• flecainide (type 1c sodium)

• amiodarone (type iii potassium)

what drugs given if patient has atrial fib/flutter and has had myocardial infarction, chd

• beta blockers

• calcium channel blockers

• amiodarone

what drugs given if patient has acute afib/flutter

• potassium channel blockers

• (amiodarone)

what drugs given for supraventricular tachycardia SVT

• adenosine for acute treatment

• beta blockers

• verapamil

• amiodarone

examples of class i drugs

• lidocaine (1b)

• flecainide (1c)

mechanism of class ii

• inhibit sympathetic nervous system effects

  • slows down av node conduction

• block calcium channels in phase 0 - prolonged refractory period

• reduce slope of pacemaker potential (phase 4)

• neg chronotropic

when are class ii drugs used

• sinus tachycardia

• ectopic pacemakers

• atrial fibrillation

• atrial flutter

side effects of class ii drugs

• worsen heart block

• cause bradycardia

• precipitate heart failure

• inc likelihood of diabetes

examples of class ii drugs

• beta 1 adrenoreceptor antagonists, end in -lol

• atenolol

• bisprolol

class iii mechanism

• potassium channel blockers

• prolong phase 3 of cardiac action potential by inhibiting efflux, delays repolarisation

example of class iii drug

amiodarone (but also fits into many other classes)

class iv mechanism

• calcium channel blcokers

• effect on sa and av nodes in phase 0 depolarisation

• slow firing rate of the SA node and delay conduction through the AV node

class iv example

• verapamil

• main example of cardio selective calcium channel blocker

when is lidocaine used

• in emergency settings for ventricular dysrhythmias

  • intravenous administration IV

• local anaesthetic

lidocaine action

• rapid action

• short duration

• selectively targets inactivated channels - found in ischaemic tissues

side effects of lidocaine

• seizures

• coma

• death at higher doses

when is flecainide used

• supraventricular tachycardia

• eg atrial fibrillation

• not used in structural heart damage patients - can cause tachycardia/fibrillation

flecainide mechanism

• binds to open state sodium channels

• longer duration of action

• used as tablet

• fewer side effects than lidocaine

irony of antidysrhythmic drugs

can cause dysrhythmias

mechanism of amiodarone

• potassium channel blocker

• inhibits beta adrenoreceptors (Class ii)

• blocks calcium channels (iv)

• inhibits sodium channels (!a)

• delays repolarisation - prolongs ap, refractory period

• dec av node conduction

• dec re entry circuit development

use of amiodarone

• atrial fibrillation and flutter

• ventricular and supraventricular tachycardias

• cardioversion of ventricular fibrillation

• limited by side effects and pharmacokinetics

pharmacokinetics of amiodarone

• orally or iv administration

• fat soluble so diff to establish stable plasma conc

• 100 days half life

• metabolised by CYP3A4

side effects of amiodarone

• lung fibrosis

• visual problems

• liver toxicity

• skin discolouration

• thyroid function interference due to iodine

• bradycardia or av node block worsening

verapamil mechanism

• acts on sa node, av node conduction is slowed

• dec slope of phase 0 depolarisation

• metabolised by CYP3A4

verapamil use

• paroxsymal supraventricular tachycardia

• av node re-entry tachycardia

• NOT IN WOLFF PARKINSON WHITE WITH AFIB

side effects of verapamil

• bradycardia

• worsening of heart block

• vasodilation - flush, hypotension, odeoma, headahce

• constipation

• dangerous if wolf parkinsons patient has atrial fibrillation

adenosine mechanism

• short acting

• gi protein - gabba subunit stimulates potassium channels, K+ efflux, hyperpolarisation

• dec slope of phase 4

which drugs increase action potential duration

• potassium channel blockers

drugs used to treat ventricular tachycardia, DAD, re-entry

• primarily amiodarone

• beta blockers

• lidocaine

best drugs post myocardial infarction

lidocaine