aarythymia Flashcards
what are the Vaughn-Williams classification
Divided in to 4 classes Class I - Sodium channel blockers Class II - Beta Blockers Class III - Amiodarone like drugs Class IV - Calcium channel blockers
1) sodium channel blocker
Block voltage gated sodium channels phase 0 of the cardiac action potential
Block is use-dependent (similar to local anaesthetics covered in detail in PM3B pain- Dr Stephens)
Class Ia e.g. Disopyramide
Intermediate kinetics
Class Ib e.g. Lidocaine
Fast kinetics- block open channel during phase 0 reducing max depolarization, dissociate before next beat
Class Ic Flecainide
Slow kinetics steady state of block
Block during whole cardiac cycle
class 2- beta blocker
Block action of adrenaline/noradrenaline on heart prevent tachyarrhythmias
supress actions of sympathetic nervous system, reducing depolarization in phase 4 of the pacemaker AP (some effect on phase 4 of cardiac)
slow HR and force of contraction
Main side effects –
Hypertension
class 3 - amiodarone- like
Originally based on action of amiordarone (now others inc. Sotalol)
Complex action involving more than one mechanism
Sotalol also has Class II properties
Prolong the cardiac AP increasing the refractory period
Inhibit potassium channels involved in phase 3
Serious potential adverse effects
Can lead to pro-arrhythmic effects such by prolonging Q-T interval
class 4 - calcium channel blocker
Block L-Type VGCC (see hypertension lecture 1)
slow conduction in SA and AV node where AP depends on calcium entry (arrhythmia 1 lecture) verapamil the main used (in some cases diltiazem)
Reduce duration of Plateau (phase 2) of AP
Reduce force of heart beat
Also reduce after-depolarization preventing ectopic beats
dihydropyridines pro-arrhythmic
reflex tachycardia esp. nifedipine
what is adenosine used for
Adenosine used in SupraVentricularTachycardia
Stops SVT if other measures fail, actions are short lived - safer than verapamil
what is digoxin used for?
Digoxin (see lectures on cardiac failure – Dr Vaiyapuri) used in AF as slows AV conduction
By blocking Na/K ATPase involved in resetting the pacemaker cell ion balances.
what are the non-pharmacological treatment of arrythmia?
DC cardioversion
Electronic paddles deliver shocks performed under anaesthetic
Used for SVT and VT if haemodynamically unstable
Implantable defibrillatior
Ventricular tachycardia and ventricular fibrillation
Defibrillation commonly used in in cardiac arrest
Catheter ablation High power radio waves used to lesion small areas known to be causing tachyarrhythmias
Electronic pacemaker
Temporary re-pace heart, permanent; usually in bradyarrhythmia
Anti-arrhythmic drugs often have a narrow therapeutic window must consider risks Vs. benefits
what are the three common arrythmias?
- supraventricular tachycardia
- atrial flutter
- atrial fibrillation
what is supra ventricular - atrial fibrillation
Most common Sustained arrhythmia atrial rate of ~350-360 bpm ventricular rate normally 160-180 AVN cannot conduct all impulses Blood pools in systemic circulation - oedema and thrombotic events Leading cause of stroke in elderly
what are the causes of supra ventricular - atrial fibrillation
Hypertension Valvular heart disease Coronary heart disease Heart failure Hyperthyroidism Pulmonary embolism Lung cancer
what are the types of AF
- paroxsymal
- persistent
- permanent
choosing between rate control and rythm control for AF
what is chadvasc score
If AF diagnosed CHA2DS2-VASc score will be assessed
Score of 2 or more anticoagulant recommended
congestive heart failure hypertension age diabetoes previous Stroke/ tia vascular disease female
