Cardio - antiarrythmics and endocarditis Flashcards
What are the two mechanisms behind arrythmias?
- disturbance in impuls formation
- disturbance in impuls conduction
It could also be both
What are the mechanisms of the four classes of antiarrythmic drugs?
Class 1 - sodium channel blockade
Class 2 - blockade of sympathetic autonomic effects in
the heart,
Class 3 -prolongation of the effective refractory period
(k+ channel inhibition
Class 4 - calcium channel blockade
Name three unclassified antiarrythmic drugs
- digoxin
- adenosine
- magnesium
What is the mechanism of Class IA anti arrythmics?
- Blocks the open, active Na-channel
- slows phase 0
- prolong action potential (phase 3 - class III activity)
(slow dissociation from sodium channel)
What is the classification and clinical indications for:
- Quinidine
- Disopyramide
- Procainamide
Class 1A
Use:
- Supraventricular arrythmias
- Ventricular arrythmias
- Both
rarely used due to possible Chinconism
What are the adverse effect of class 1A antiarrythmics?
Procainamide - lupus like, hematotoxicity
Disopyramide - antimuscarinic, heart failure
Quinidine - cinchonism, M and alpha block
All: arrythmias
What is the classification and clinical indications for:
- Lidocaine
- Mexiletine
- Phenytoin
Class 1B
Use:
- ventricular arrythmias(Amiodarone DOC)
- ventricular arrythmias (oral Lidocaine)
- Anticonvulsant, digitalis - dysrythmias
What is the mechanism of class 1B antiarrythmics?
- Blocks the closed Na-channel
- slows phase 0
- shortens phase 3 repolarization
(fast dissociation from sodium channel
-> effect manifested at high firing rate)
What are the adverse effects of class 1B antiarrythmics?
CNS sedation or excitation
Mexeiletine - nausea, vomiting, dyspepsia
What is the classification and clinical indications for:
1. Flecainide
2. Propafenone
3 .Moricizine
Class 1C
Use:
1,2 - supraventricular arrythmias
3 - Ventricular arrythmias
What is the mechanism of class 1C antiarrythmics?
- Blocks all three Na channels
- slows phase 0
(slowly dissociates from Na channels
-> effects even at normal heart rate) - reduces automaticity by
increasing threshold potential
What are the adverse effects of class 1C antiarrythmics?
Proarrythmic effect
Flecainide - B-blocking properties
What is the mechanism of class II antiarrythmics?
B - blocking:
-> Diminish phase 4 repolarization
-> depress automaticity, prolong AV conduction
decrease HR and contractillity
What are the clinical indications for type II antiarrythmics?
- supraventricular arrythimas
- ventricular arrythmias
- thyrotoxicosis
- reduce mortality after MI or CHF
What is the classification and clinical indications for:
- Amiodarone
- Dronedarone
- Vernakalant
- Dofetilide, Ibutilide
- Sotalol
Class 3 antiarrythimcs
Use: 1. supraventricular/ventricular arrythmias safe in CAD and HF 2. (Increases mortality in afib and HF) 3. Cardioversion of atrial fibrilation 4. atrial fibrilation
What are the adverse effects of class III antiarrythmics?
- Amiodarone - thryoid abn., pulm. fibrosis
photodermatitis,hepatitis, corneal deposits - Dronedarone - increases mortality
- Vernakalant - altered taste, sneezing
All are potentially proarrythmic, but Amiodarone
ha a low proarrythmic affect
What is the mechanism of class III antiarrythmics?
Blockage of K+ channels
-> prolong phase 3 repolarization
- Amiodarone - shows class 1,2,3,4, and α block action
What is the antiarrythmic classification and indications for:
Verapamil
Diltiazem
Class IV: antiarrythmic
Use:
- supraventricular arrhythmias
reduce the ventricular rate in atrial fibrillation and flutter
What is the mechanism of class IV antiarrythmics?
Blockage of cardiac calcium channels
-> decrease phase 4 depolarization
-> slows conduction in SA and AV nodes
(blocks Ca-channels in phase 0)
What is the mechanism of Adenosine?
What are the uses?
less cAMP (like M2) activation of an inward K+ current and inhibition of Ca2+ current -> conduction block
Use:
acute supraventricular tachycardias
T 1/2 < 10s
Causes bronchospasm!
Antagonised by methylxanthines
synergy with dipyridamole
When is MgSO4 used in arrythmias?(I.V)
In digitalis arrythmia, Torsade de points
+ hypomagnesaemia, hypokalaemia
It is necessary for Na,Ca,K transport
across cell membranes
‘‘competes with Ca’’
When is Ca2+ used in arrythmias?
PEA caused by: hyperkalaemia, hypocalcaemia, overdose of calcium channel-blocking drugs
When is HCO3 used in arrythmias?
life-threatening hyperkalaemia,
cardiac arrest associated with hyperkalaemia,
tricyclic overdose.
When is K+ used in arrythmias?
- Digitalis toxicity
- arrythmia + low K+
What are the typical causative organisms of endocarditis?
- Streptococcus viridans (the most frequent)
- Streptococcus bovis
- Staphylococcus aureus (healthcare-associated )
- enterococci
- HACEK group
Which drugs are recommended as prophylaxis for high risk patients against endocarditis?
Amoxicillin
Clindamycin (penicillin allergy)
