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Questions and Answers
Procainamid may cause a lupus like syndrome with chronic therapy, including symptoms such as ______, fever, and myocarditis.
Procainamid may cause a lupus like syndrome with chronic therapy, including symptoms such as ______, fever, and myocarditis.
arthralgias
Disopyramide and quinidine can cause anticholinergic effects such as glaucoma, constipation, dry mouth, and ______.
Disopyramide and quinidine can cause anticholinergic effects such as glaucoma, constipation, dry mouth, and ______.
urinary retention
The major toxic side effect of Bretylium is ______ caused by inhibition of catecholamines release.
The major toxic side effect of Bretylium is ______ caused by inhibition of catecholamines release.
hypotension
Cardiac arrhythmias are abnormalities in the rate, regularity or site of origin of cardiac ______.
Cardiac arrhythmias are abnormalities in the rate, regularity or site of origin of cardiac ______.
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The heart contains specialized tissue that exhibit ______, allowing it to generate action potentials.
The heart contains specialized tissue that exhibit ______, allowing it to generate action potentials.
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Chronic use of dofetilide is associated with ______ prolongation, particularly in patients with renal dysfunction.
Chronic use of dofetilide is associated with ______ prolongation, particularly in patients with renal dysfunction.
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In patients with intoxication by class Ia or class I drugs, ______ may reverse cardiac depressant effects caused by inhibition of fast sodium channels.
In patients with intoxication by class Ia or class I drugs, ______ may reverse cardiac depressant effects caused by inhibition of fast sodium channels.
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Class I antiarrhythmic drugs primarily act by inhibiting the fast sodium ______ responsible for cardiac cell depolarization.
Class I antiarrhythmic drugs primarily act by inhibiting the fast sodium ______ responsible for cardiac cell depolarization.
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For Class III antiarrhythmic drugs, an example is ______, which blocks potassium channels.
For Class III antiarrhythmic drugs, an example is ______, which blocks potassium channels.
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Electrolyte ______ can trigger arrhythmias as they affect heart function.
Electrolyte ______ can trigger arrhythmias as they affect heart function.
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The SA node is known as the heart's normal ______ because it generates impulses at a regular frequency.
The SA node is known as the heart's normal ______ because it generates impulses at a regular frequency.
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In overdose, Class I drugs can markedly depress myocardial ______, conduction, and automaticity.
In overdose, Class I drugs can markedly depress myocardial ______, conduction, and automaticity.
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Type la inhibit the outward potassium channel, delaying __________.
Type la inhibit the outward potassium channel, delaying __________.
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Amiodarone is a non-competitive beta adrenergic blocker and has sodium and calcium channel __________ effects.
Amiodarone is a non-competitive beta adrenergic blocker and has sodium and calcium channel __________ effects.
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Dronedarone does not contain __________ and does not affect thyroid function.
Dronedarone does not contain __________ and does not affect thyroid function.
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Class lll drugs primarily act by blocking __________ channels to prolong the action potential duration.
Class lll drugs primarily act by blocking __________ channels to prolong the action potential duration.
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The ingestion of twice the daily therapeutic dose of certain antiarrhythmic drugs should be considered potentially __________.
The ingestion of twice the daily therapeutic dose of certain antiarrhythmic drugs should be considered potentially __________.
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Bretylium inhibits neurotransmitter release from __________ nerve endings.
Bretylium inhibits neurotransmitter release from __________ nerve endings.
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Cinchonism is a collection of symptoms associated with chronic doses of __________.
Cinchonism is a collection of symptoms associated with chronic doses of __________.
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Severe __________ may occur slightly above the therapeutic range of antiarrhythmic drugs.
Severe __________ may occur slightly above the therapeutic range of antiarrhythmic drugs.
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Class l drugs can cause cardiotoxic effects, including sinus bradycardia and __________.
Class l drugs can cause cardiotoxic effects, including sinus bradycardia and __________.
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The clinical presentation of class l drugs includes QRS or QT interval __________.
The clinical presentation of class l drugs includes QRS or QT interval __________.
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Arrhythmias may occur as a result of heart disease or from a disorder that affects ______ function.
Arrhythmias may occur as a result of heart disease or from a disorder that affects ______ function.
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Class IV antiarrhythmic drugs are known as ______ channel blockers.
Class IV antiarrhythmic drugs are known as ______ channel blockers.
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The ______ node is known as the normal pacemaker of the heart, generating impulses at a frequency of 60-100 beats per minute.
The ______ node is known as the normal pacemaker of the heart, generating impulses at a frequency of 60-100 beats per minute.
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In overdose, all class I drugs have the potential to markedly depress myocardial ______, conduction, and contractility.
In overdose, all class I drugs have the potential to markedly depress myocardial ______, conduction, and contractility.
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Class I antiarrhythmic drugs work by inhibiting the fast ______ channel responsible for initial cardiac cell depolarization.
Class I antiarrhythmic drugs work by inhibiting the fast ______ channel responsible for initial cardiac cell depolarization.
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Electrolyte imbalance can trigger ______ as they affect heart function.
Electrolyte imbalance can trigger ______ as they affect heart function.
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Class III antiarrhythmic drugs primarily act by blocking ______ channels to prolong the action potential duration.
Class III antiarrhythmic drugs primarily act by blocking ______ channels to prolong the action potential duration.
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Lidocaine can cause ______, which is a condition characterized by an abnormal level of methemoglobin in the blood.
Lidocaine can cause ______, which is a condition characterized by an abnormal level of methemoglobin in the blood.
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Chronic use of amiodarone may lead to ______ toxicity, which includes serious lung complications.
Chronic use of amiodarone may lead to ______ toxicity, which includes serious lung complications.
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The most important diagnostic test for patients with acute antiarrhythmic toxicity is ______.
The most important diagnostic test for patients with acute antiarrhythmic toxicity is ______.
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Sodium bicarbonate may be used to treat ______ and hypotension caused by intoxication with class Ia or class I drugs.
Sodium bicarbonate may be used to treat ______ and hypotension caused by intoxication with class Ia or class I drugs.
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Chronic therapy with procainamide may lead to a ______ like syndrome, characterized by arthralgias and fever.
Chronic therapy with procainamide may lead to a ______ like syndrome, characterized by arthralgias and fever.
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Amiodarone may also release ______, which can affect thyroid function.
Amiodarone may also release ______, which can affect thyroid function.
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Class ll drugs act by slowing down the heart rate by blocking sympathetic hormones such as ______.
Class ll drugs act by slowing down the heart rate by blocking sympathetic hormones such as ______.
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Class IV drugs decrease the inward current carried by ______, slowing conduction.
Class IV drugs decrease the inward current carried by ______, slowing conduction.
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Torsades de pointes is a type of ______ that can occur due to prolonged QT interval.
Torsades de pointes is a type of ______ that can occur due to prolonged QT interval.
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Quinidine can cause ______, which includes symptoms like headache and tinnitus.
Quinidine can cause ______, which includes symptoms like headache and tinnitus.
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Bretylium's major action is the inhibition of ______ release at sympathetic nerve endings.
Bretylium's major action is the inhibition of ______ release at sympathetic nerve endings.
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Amiodarone can cause ______, which may result from its bradyarrhythmic effects.
Amiodarone can cause ______, which may result from its bradyarrhythmic effects.
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Ingestion of twice the daily therapeutic dose should be considered potentially ______.
Ingestion of twice the daily therapeutic dose should be considered potentially ______.
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Patients experiencing CNS toxicity from Class I drugs may present with ______.
Patients experiencing CNS toxicity from Class I drugs may present with ______.
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Class III drugs primarily block potassium channels to prolong the duration of the ______.
Class III drugs primarily block potassium channels to prolong the duration of the ______.
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Study Notes
Antiarrhythmic Drugs Toxicity
- Antiarrhythmic drugs treat abnormal heart rhythms (arrhythmias).
- Arrhythmias stem from disturbances in impulse formation, conduction, or both.
- Factors contributing to arrhythmias include heart disease, stress, low oxygen (hypoxia), and electrolyte imbalances.
Cardiac Electrophysiology
- Specialized pacemaker cells in the heart generate action potentials (APs) spontaneously, unlike other heart cells.
- The sinoatrial (SA) node is the heart's natural pacemaker (60-100 beats/minute).
- Impulses spread from the SA node to the atria, then the atrioventricular (AV) node, and finally to the ventricles.
- Sodium and calcium currents play crucial roles in the pacemaker cells' spontaneous depolarization.
Classification of Antiarrhythmic Drugs
- Drugs are classified based on their primary effects on the action potential.
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Class I (Sodium channel blockers):
- IA: Prolong repolarization (e.g., procainamide, quinidine, disopyramide).
- IB: Shorten repolarization (e.g., lidocaine, mexiletine, phenytoin).
- IC: No change in repolarization (e.g., flecainide, propafenone).
- Class II: Beta-blockers (e.g., propranolol, metoprolol, esmolol).
- Class III: Potassium channel blockers (e.g., amiodarone, bretylium, sotalol).
- Class IV: Calcium channel blockers (e.g., diltiazem, verapamil).
Mechanism of Toxicity
- Class I: At high doses, all class I drugs can depress myocardial automaticity, conduction, and contractility. Type Ia drugs prolong the QT interval, potentially leading to polymorphic ventricular tachycardia (Torsades de pointes). Quinidine and disopyramide have anticholinergic & alpha-adrenergic blocking activity.
- Class II: Slow heart rate by blocking sympathetic hormones like adrenaline.
- Class III: Prolong the action potential & effective refractory periods, leading to QT interval prolongation.
Amiodarone and Dronedarone
- Amiodarone is a non-competitive beta-blocker, sodium channel blocker, and calcium channel blocker. Chronic use can cause altered thyroid function and pulmonary toxicity.
- Dronedarone is similar to amiodarone but lacks iodine and less likely to affect the thyroid. Chronic use increases the risk of death in patients with symptomatic heart failure.
Bretylium
- IV bretylium inhibits neurotransmitter release from sympathetic nerves, causing hypotension.
Class IV
- Class IV drugs decrease inward calcium current, slowing conduction and prolonging the AV nodal refractory period.
Toxic Dose
- Antiarrhythmic drugs generally have a narrow therapeutic index; toxicity manifests at slightly elevated levels. Doses above the therapeutic range, combined use of multiple drugs, can be life-threatening.
Clinical Presentation
- Class I: Cardiotoxicity (bradycardia, sinus arrest, QRS/QT prolongation, decreased myocardial contractility, Torsades de pointes, ventricular fibrillation), CNS toxicity (coma, respiratory depression, seizures), and quinidine-specific syndrome (Nausea, vomiting, diarrhea, cinchonism).
- Class II: Bradicardia
- Class III: Hypotension.
- Class IV: Hypo and hyperthyroidism.
Procainamide
- Chronic use can cause a lupus-like syndrome (arthralgias, fever, myocarditis).
Lidocaine
- Can cause methemoglobinemia.
Diagnosis
- ECG and serum electrolyte testing are critical for diagnosing acute antiarrhythmic toxicity. Thyroid function tests are helpful in amiodarone toxicity.
Treatment
- Class I intoxication: Sodium bicarbonate reverses cardiac depressant effects and increases serum sodium to counteract sodium channel blockage. Torsades de pointes treatment requires IV magnesium and potassium replenishment.
Decontamination
- Activated charcoal and gastric lavage can be used to remove certain drugs. Dialysis and hemoperfusion are usually not beneficial due to extensive tissue binding and large volumes of distribution. Disopyramide and procainamide can be removed by dialysis.
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Description
This quiz explores the toxicity of antiarrhythmic drugs and their classification based on effects on action potentials. It also covers the fundamentals of cardiac electrophysiology, including the role of pacemaker cells and impulse conduction. Test your knowledge on arrhythmias and the underlying mechanisms of heart function.
