Anti-Arrhythmics - Dr. Kalai PDF

Class I agents Mechanisms...

Class I agents Mechanisms Vaughan william classification of drugs Class Ia Agents-Quinidine, Anti-arrhythmics block Na+ channel in open state & block cardiac K+ channels- prolongation of APD- precipitate torsades de’pointes procainamide, disopyramide Time of recovery of sodium channels - 1-10 ms Quinidine - cinchona plant - antimalarial action ADR- cinchonism - tinnitus, vertigo, deafness, headache, visual disturbances and mental changes DDI- should only be used with AV node blocking agent - digoxin, precipitate digitalis toxicity. verapamil, or a beta blocker MOA-decrease the slope of phase 4 (responsible CLASS II AGENTS- beta blockers- esmolol, propranolol, for automaticity) and conduction through the Procainamide - derivative of LA- AVnode procaine M- acetylation-fast and slow and metoprolol- blocks adrenaline and nor-adrenaline at the β1 receptors acetylators DOC- atrial fibrillation Uses- supraventricular tachycardia associated with WPW syndrome Esmolol - shortest acting beta blocker- i.v. - ventricular rate control in atrial fibrillation or flutter. Class IC Agents- encainide, moricizine, flecainide block Na channels in inactivated state & most potent sodium channel and propafenone possess K+ channel opening property τ < 1s - shorten the Class IB Agents-lignocaine, mexiletine, tocainide and blocking effects with negligible effect Class III agents - block the potassium channels- APD and reduce refractoriness Use- ventricular arrhythmia. phenytoin on K+ channels - τ > 10s prolonging repolarization (APD)-precipitate torsades de’pointes Lignocaine - very high first pass metabolism- i.v. maximum pro-arrhythmic property - resistant Flecainide- acute treatment of Wolff Parkinson White route. Excessive dose - neurological toxicity and life-threatening ventricular tachycardia (WPW) syndrome. [Treatment of choice for WPW (drowsiness, paraesthesia, convulsions and or ventricular fibrillation& refractory syndrome is radiofrequency ablation of the aberrant coma) and myocardial depression Amiodarone is longest acting (t1/2 = 3-8 weeks) supraventricular tachycardia pathway] DOC-ventricular arrhythmias anti-arrhythmic drug-all classes of antiarrhythmic drugs widest antiarrhythmic spectrum Mexiletine -orally active lignocaine derivative with all the properties of Uses refractory VT or VFin acute lignocaine Class IV agents - blockers of L-type voltage gated Dronedarone - non-iodinated compound ischemia. safe in cardiomyopathy and which has fewer adverse effects but also calcium channels- decrease the rate of phase 4 atrial fibrillation, to maintain normal less efficacy than amiodarone.Use- atrial depolarization in SA and AV nodes Verapamil and sinus rhythm, prophylaxis of almost all fibrillation and atrial flutter. Phenytoin - antiepileptic drug- alternative arrhythmias except torsades to lignocaine for digitalis induced diltiazem - PSVT and ventricular rate control in atrial de’pointes. ventricular arrhythmias fibrillation and flutter. Verapamil - DOC supraventricular tachycardia (SVT) and for the prophylaxis of PSVT. Tocainide -given orally but not used widely Sotalol - non-selective lipid insoluble beta - agranulocytosis blocker- both class II & class III Uses- atrial or ventricular tachyarrhythmias, AV reentrant arrhythmias. Class V agents - digoxin, adenosine, magnesium, atropine and potassium. Digoxin increases vagal activity and is used for controlling ventricular Bretylium - adrenergic neuron blocker- only rate in atrial fibrillation and flutter. parenterally for arrhythmias- Vernakalant - multi-ion channel Adenosine opens the potassium channels and lead to hyperpolarization ‘pharmacological defibrillator’ ADR- postural blocker that selectively prolongs atrial of AV node. It is the drug of choice for treatment of PSVT. It is very short hypotension refractory period without affecting acting (t1/2 = 10 seconds) drug, therefore adverse effects like flushing ventricles use- converting atrial of face and bronchospasm are also short lived. Theophylline being fibrillation of short duration (< 7 days) adenosine receptor antagonist inhibits its action whereas dipyridamole to sinus rhythm Ibutilide -structural analog of sotalol but no class II Use- atrial potentiates its action by inhibiting the reuptake of adenosine. fibrillation or atrial flutter by i.v. route only antiarrhythmic Magnesium -both congenital and acquired agent currently FDA approved for acute conversion of atrial long QT syndrome fibrillation to sinus rhythm