CH 52: antidysrhythmic drugs

Dysrhythmia

An abnormality in the rhythm of the heartbeat; caused by impulse formation disturbances.

Reentry

A heart impulse that keeps circulating instead of dying.

SA node

The pacemaker of the heart.

P wave in ECG

Represents depolarization of the atria.

QRS complex in ECG

Represents depolarization of the ventricles.

T wave in ECG

Represents repolarization of the ventricles.

Common ventricular dysrhythmias

Sustained ventricular fibrillation and torsades de pointes.

Quinidine

Sodium channel blocker that Slows impulse conduction and Delays repolarization.

Therapeutic uses of Quinidine

Supraventricular and ventricular dysrhythmias

Adverse effects of Quinidine

Diarrhea, cinchonism (quinidine toxicity), cardiotoxicity, arterial embolism, alpha-adrenergic blockade leading to hypotension.

Drug interactions with Quinidine

Digoxin

Procainamide 

a sodium channel blocker with effects similar to quinidine 

Adverse effects: symptoms of lupus syndrome 

Lidocaine

A medication that slows conduction in the atria, ventricles, and His-Purkinje system, reducing automaticity.

Accelerates repolarization

Adverse effects of Lidocaine

CNS effects, Drowsiness, Confusion, Paresthesias  

Phenytoin

Sodium channel blocker that is an Antiseizure medication used to treat digoxin induced dysrhythmias

Mexiletine

Sodium channel Blocker used for symptomatic ventricular arrhythmias

Overall effects and MOA of Propranolol

Beta blocker that decreases automaticity of SA node, conduction through AV node and myocardial contractility.

Therapeutic uses of Propranolol

Dysrhythmias caused by excessive sympathetic stimulation and supraventricular tachydysrhythmias.

Adverse effects of Propranolol

Heart block, Heart failure, AV block, Sinus arrest , Hypotension, Bronchospasm (in asthma patients)

Amiodarone

A potassium channel blocker used for life-threatening ventricular dysrhythmias.

Adverse effects of potassium channel blockers

Prolonged half life, Pulmonary toxicity, Cardiotoxicity, Toxicity in pregnancy and breast feeding, Corneal microdeposits, Optic neuropathy

Drug interactions with potassium channel blockers

Quinidine, Diltiazem, Cyclosporin, Digoxin, Procainamide, Phenytoin, Warfarin, Lovastatin, simvastatin, atorvastatin, Liver toxicity 

grapefruit juice and CYP3A4 inhibitors (can Increase Amiodarone levels)

Cholestyramine (decreases Amiodarone absorption)

Diuretics (increase risk of severe dysrhythmias because they reduce levels of potassium and magnesium) 

Verapamil and Diltiazem 

Calcium channel blocker used to slow Ventricular rate and Terminate supraventricular tachycardia caused by an AV nodal reentrant circuit

Adverse effects of Calcium Channel Blockers

Bradycardia, Hypotension, AV block, Heart failure, Peripheral Edema , Constipation, Elevate digoxin levels 

Adenosine

Calcium channel blocker that decreases the automaticity of the SA node and slows AV nodal conduction used to treat  paroxysmal SVT.

Adverse effects of Adenosine 

Sinus Bradycardia, Dyspnea, Hypotension, Facial flushing, Chest discomfort 

Interactions with Adenosine 

Methylxanthines, Dipyridamole

Digoxin

Calcium Channel Blocker where the Primary indication is Heart failure but treats supraventricular arrhythmias and Ventricular arrhythmias.

Main adverse effect for digoxin 

Cardiotoxicity (risk increased by hypokalemia)

Class 1 agent

Sodium channel blockers used to treat dysrhythmias.

Class 2 agent

Beta blockers used to manage cardiac dysrhythmias.

Class 3 agent

Potassium channel blockers that prolong repolarization.

Class 4 agent

Calcium channel blockers for tachycardia prevention.