anti-arrhythmic drugs Flashcards
what is the vaughan-williams classification?
a drug classification based on the site of action
problems with the vaughan-williams classification (4)
many useful drugs don’t fit in the classification; lots of new receptors and ion channels discovered; drugs act on multiple targets; pathology is often multifactorial and affects multiple channels
vaughan-williams classification and examples
I - Na+ ch blockers e.g. disopyramide (Ia), lidocane (Ib), flecanide (Ic);
II - B-andrenogen receptor antagonist (B-blockers) e.g. Sotalol
III - K+ ch blockers e.g. amioderone
IV - Ca2+ ch blockers e.g. verapamil
Ia MOA, indications and adverse effects
MOA: Binds to Na channel and block ability to depolarise 🡪 slower A, Prolongs ERP, reduce cardiac excitability, increase AP duration;
indications: Maintain sinus rhythm post MI
Treat SVT or Ventricular tachycardias;
adverse effects: Prolonged repolarisation can increase risk of arrythmias – Torsade’s de pointes
Ib MOA, indications and adverse effects
MOA: Na channel atagonist 🡪 reducing depolarisation 🡪 slower HR, Decreased ERP and AP duration;
indications: Acute cardiopulmonary resuscitation;
adverse effects: Do NOT give in AV block
Bradycardia
Convulsion
Ic MOA, indications and adverse effects
MOA: preferential block of open Na+ channels, Reduces contractility, most potent, Normal ERP and AP duration
indications: Tachycardia, paroxysmal AF, Ventricular tachycardia
adverse effects: ½ dose if used with amiodarone, dont give if ischaemic or structural heart disease
II MOA, indications and adverse effects
MOA: Beta adrenergic receptor antagonists, Block effects of NA and Adrenaline (Catecholamines) on the SAN, Slow pacemaker activity, Decrease cardiac conduction and contractility, increased PR interval;
indications: AF, SVT;
adverse effects: Can prolong QT interval causing AV blocks - must monitor ECG and U&Es; bronchocontrisction
III MOA, indications and adverse effects
MOA: Slow repolarisation, Reduced cardiac excitability, Increased ERP and AP duration, blocks K+ channels to delay repol;
indications: SVT, ventricular tachycardia, atrial flutter, AF, Ventricular fibrillation, AVNRT (wolff-Parkinson White);
adverse effects: Can prolong QT interval, tremor, ataxia, fatigue, headache, insomnia; amiodarone - long acting (half life of weeks), pulmonary fibrosis, liver damage, photosensitivity, thyroid malfunction
IV MOA, indications and adverse effects
MOA: Less muscle contraction, decrease CO, Supress cardiac conduction across AVN 🡪 decrease HR, slower overall, Increased PR interval and ERP;
indications: Supraventricular tachycardia, AF
adverse effects: DO NOT use in pt with heart failure or beta blockers
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V (other - atropine) MOA, indications and adverse effects
MOA: Antagonist of the muscarinic Ach receptors (dampens down parasympathetic activity) and therefore positively chronotropic (increases heart rate);
indications: Bradycardia
adverse effects: eye pain, blindness etc.
V (other - adenosine) MOA, indications and adverse effects
MOA: inhibits Ca2+ Ch opening, activates G-couples adenosine receptors, K+ Ch activation = repolarisation, Slow pacemaker activity;
indications: paroxysmal SVT, Allow for diagnosis of AVRT or AVNRT through restoring sinus rhythm
adverse effects: flushing, chest pain, dyspnoea, bronchospasam
V (other - magnesium sulphate) MOA, indications and adverse effects
MOA: Reduce muscle contractions, Inhibit Ca influx through L-type Ca channel;
indications: Emergency arrhythmia treatment
adverse effects: don’t give with heart block or cardiac ischaemia
indication for MgCl
ventricular arrythmias (emergency)
what drugs act on phase 4 (pacemaker depol) of the myocyte AP
adenosine, metoprolol, propanolol
