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Related Concept Videos

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers01:22

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

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,...
Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

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 indirectly block calcium...
Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

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 the heart's...
Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

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...
Heart Failure Drugs: β-Blockers01:22

Heart Failure Drugs: β-Blockers

β-adrenergic antagonists, commonly known as β-blockers, block the effects of sympathetic neurotransmitters such as noradrenaline (NA) and adrenaline (ADR). They have several beneficial effects in heart failure treatment. They reduce heart rate, the force of contraction, and cardiac muscle relaxation. They also slow the atrial-ventricular conduction rate and raise the threshold for arrhythmias. The concentration of β-blockers determines their effects on bronchodilation, vasodilation, and...
Mitral Stenosis I: Introduction01:22

Mitral Stenosis I: Introduction

Mitral Valve Stenosis (MVS) is a heart condition where the mitral valve narrows, impeding blood circulation from the left atrium to the left ventricle. The etiology and pathophysiology of this condition are multifaceted, leading to a cascade of cardiovascular complications.Causes of Mitral Valve StenosisRheumatic Heart Disease: It is the main cause of mitral valve stenosis, particularly in developing nations. This condition arises from rheumatic fever, an inflammatory illness resulting from...

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Related Experiment Video

Updated: Jun 23, 2026

Echocardiographic Evaluation of Atrial Communications before Transcatheter Closure
07:41

Echocardiographic Evaluation of Atrial Communications before Transcatheter Closure

Published on: February 8, 2022

Gap junction blockers decrease defibrillation thresholds without changes in ventricular refractoriness in isolated

X Qi1, P Varma, D Newman

  • 1Department of Medicine, St Michael's Hospital, University of Toronto, Toronto, Ont, Canada.

Circulation
|September 26, 2001
PubMed
Summary
This summary is machine-generated.

Gap junction blockers like 16-DSA and 1-heptanol significantly decrease defibrillation threshold (DFT) and ventricular fibrillation cycle length (VFCL) dispersion. In contrast, lidocaine increases DFT, despite similar effects on conduction velocity.

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Bidirectional Electrical and Optoelectronic Interfaces in Healthy and Ischemic Ex Vivo Rat Hearts
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Area of Science:

  • Cardiovascular Electrophysiology
  • Pharmacology
  • Medical Physics

Background:

  • Reentry arrhythmias depend on tissue properties like refractoriness and conduction velocity.
  • The impact of Na(+) and K(+) channel blockers on electrophysiology and defibrillation threshold (DFT) is known, but gap junction blockers' effects are less understood.

Purpose of the Study:

  • To investigate the effects of gap junction blockers (16-doxyl-stearic acid and 1-heptanol) and a sodium channel blocker (lidocaine) on defibrillation threshold (DFT) and electrophysiological properties in isolated rabbit hearts.

Main Methods:

  • Defibrillation threshold (DFT) measurements were taken before and after administering 16-doxyl-stearic acid (16-DSA), 1-heptanol, or lidocaine in isolated perfused rabbit hearts.
  • Electrophysiological parameters including ventricular fibrillation cycle length (VFCL), QRS duration, and ventricular effective refractory period were assessed.

Main Results:

  • 16-DSA and 1-heptanol significantly decreased DFT by 23% and 21%, respectively. Lidocaine increased DFT by 26%.
  • All agents increased VFCL and QRS duration, and decreased VFCL dispersion. Refractoriness was unchanged by gap junction blockers but increased with lidocaine.
  • Control hearts showed no significant changes in DFT or electrophysiological variables.

Conclusions:

  • Electrical uncoupling via 16-DSA and 1-heptanol reduces DFT and VFCL dispersion without affecting refractoriness.
  • Lidocaine, while slowing conduction similarly, increases DFT, highlighting differential effects of channel blockers on cardiac electrical stability.