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Related Concept Videos

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

1.5K
Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of...
1.5K
Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

1.2K
Class IV antiarrhythmic drugs, such as verapamil and diltiazem, block calcium channels. They primarily affect the heart, slowing the conduction in calcium-dependent tissues like the SA and AV nodes. These drugs manage reentrant supraventricular tachycardia (SVT) and reduce ventricular rate in atrial flutter/fibrillation.
Verapamil, a calcium channel blocker, inhibits calcium movement across myocardial cell membranes and vascular smooth muscle. This results in the dilation of coronary and...
1.2K
ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias

253
Arrhythmia is a condition characterized by an irregular heart rhythm, with ECG changes that differ based on its origin and nature. The types of arrhythmias discussed below include atrial, junctional, and ventricular arrhythmias.Atrial ArrhythmiasPremature Atrial Complexes (PACs): PACs are early atrial beats caused by stress, caffeine, alcohol, electrolyte imbalances, hypoxia, hyperthyroidism, or certain medications (e.g., bronchodilators and decongestants). The ECG shows early P waves with an...
253
Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

1.1K
Adrenergic stimulation generally impacts cardiac rate and rhythm. Specifically, stimulation of the β-adrenoceptors triggers an increase in intracellular calcium ion influx and pacemaker currents, which may cause arrhythmias. Catecholamines like adrenaline also demonstrate β2-adrenoceptor-mediated hypokalemia, impacting cardiac action potential and disrupting the normal cardiac rhythm. Class II antiarrhythmic drugs are β-adrenoceptor antagonists or β-blockers, which...
1.1K
Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers01:22

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

2.2K
Class I antiarrhythmic drugs are used to treat various types of arrhythmias or irregular heart rhythms. These drugs block the sodium (Na+) channels in the cardiac cells, thereby affecting the movement of electrical impulses across the heart. Class I antiarrhythmic drugs are divided into three subgroups: Class IA, Class IB, and Class IC, each with distinct mechanisms of action and effects on the heart.
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
2.2K
Desensitization and Tachyphylaxis01:20

Desensitization and Tachyphylaxis

2.7K
Tachyphylaxis is described as a rapid decrease in response to a drug after repeated or continuous administration of the same drug dose. It is a phenomenon where the body becomes less responsive to a particular substance or intervention over time, requiring higher doses or stronger interventions to achieve the same effect. It results from adaptive changes in the body's receptors, signaling pathways, or physiological processes that occur in response to prolonged exposure to a stimulus.
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Related Experiment Videos

QT Dispersion and Drug-Induced Torsade de Pointes.

Ari Friedman1, Jeremy Miles2, Jared Liebelt3

  • 1Medicine, Jacobi Medical Center/Albert Einstein College of Medicine, Bronx, USA.

Cureus
|March 1, 2021
PubMed
Summary
This summary is machine-generated.

Amiodarone causes less torsade de pointes (TdP) than other Class III antiarrhythmics. This study found amiodarone increases QT dispersion, suggesting its TdP-reducing effect stems from decreased early afterdepolarizations (EADs), not repolarization homogeneity.

Keywords:
antiarrhythmic agentsarrhythmiaearly after depolarizationsqt dispersiontorsade de pointes

Related Experiment Videos

Area of Science:

  • Cardiology
  • Pharmacology
  • Electrophysiology

Background:

  • Amiodarone exhibits a lower incidence of drug-induced torsade de pointes (TdP) compared to other Class III antiarrhythmics.
  • Proposed mechanisms for amiodarone's reduced TdP risk include less repolarization heterogeneity and/or decreased early afterdepolarizations (EADs).
  • QTc dispersion on ECG reflects spatial heterogeneity of ventricular repolarization.

Purpose of the Study:

  • To compare QT dispersion between amiodarone and other Class III antiarrhythmics.
  • To investigate the underlying etiology of TdP with these antiarrhythmics.

Main Methods:

  • Retrospective observational study of adult patients on amiodarone, dofetilide, or sotalol with prolonged QT intervals.
  • ECG analysis by blinded observers to calculate QT and QTc dispersion using Bazett and Framingham formulas.
  • Statistical comparison using ANOVA with Bonferroni correction.

Main Results:

  • A total of 77 ECGs met inclusion criteria from 447 reviewed.
  • Amiodarone showed significantly higher average QT dispersion (0.050) and QTc dispersion (Bazett: 0.053; Framingham: 0.049) compared to dofetilide and sotalol (p<0.01 for all).
  • Increased QT dispersion with amiodarone was observed.

Conclusions:

  • Heterogeneous ventricular repolarization, indicated by QTc dispersion, does not explain amiodarone's lower TdP incidence.
  • Amiodarone's ability to decrease EADs through sodium-channel blockade is the more probable reason for its reduced risk of drug-induced TdP.
  • This finding challenges the repolarization heterogeneity theory for amiodarone's safety profile.