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Related Concept Videos

Mechanism of Cardiac Arrhythmias01:28

Mechanism of Cardiac Arrhythmias

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Arrhythmias are irregular heart rhythms occurring when the heart's electrical impulses become abnormal. These disturbances can lead to various symptoms, depending on their severity and the underlying cause. Some common factors contributing to arrhythmias include hypoxia, ischemia, electrolyte imbalances, excessive catecholamine exposure, drug toxicity, and muscle overstretching. Arrhythmias can be classified into two main types based on the rate and site of origin of abnormal heart rhythms.
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Disturbances in Heart Rhythm01:29

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Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
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Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

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

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

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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,...
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Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

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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...
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Related Experiment Video

Updated: Dec 21, 2025

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents
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Real-Time Closed-Loop Suppression of Repolarization Alternans Reduces Arrhythmia Susceptibility In Vivo.

Faisal M Merchant1,2, Omid Sayadi2, Kwanghyun Sohn2

  • 1Cardiology Division, Emory University School of Medicine, Atlanta, GA (F.M.M.).

Circulation. Arrhythmia and Electrophysiology
|May 22, 2020
PubMed
Summary

We developed a closed-loop system to control repolarization alternans (RA) and reduce arrhythmia risk. Pacing during the absolute refractory period suppressed RA, significantly lowering susceptibility to ventricular arrhythmias in a swine model.

Keywords:
alternanspacingpreventionrepolarizationventricular arrhythmias

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Area of Science:

  • Cardiovascular Electrophysiology
  • Cardiac Arrhythmia Mechanisms
  • Biomedical Engineering

Background:

  • Repolarization alternans (RA) is linked to ventricular arrhythmias and sudden cardiac death.
  • Understanding RA's role is crucial for developing antiarrhythmic strategies.

Purpose of the Study:

  • To develop and evaluate a real-time, closed-loop system for recording and analyzing RA.
  • To assess the system's ability to control RA and reduce arrhythmia susceptibility in vivo.

Main Methods:

  • Developed a closed-loop system for real-time RA analysis from intracardiac leads.
  • Delivered R-wave triggered pacing during the absolute refractory period.
  • Evaluated system efficacy in a swine model (n=9 for induction, n=7 for suppression).

Main Results:

  • R-wave triggered pacing modulated RA magnitude, influenced by pacing parameters (amplitude, pulse width, vector).
  • Pacing-induced RA changes (alternans voltage, Kscore) correlated with pacing charge.
  • Spontaneously occurring RA was suppressed, leading to reduced arrhythmia susceptibility (lower Srank score).

Conclusions:

  • A novel closed-loop method effectively modulated RA in a swine model.
  • Suppression of RA via pacing directly reduced arrhythmia susceptibility.
  • RA plays a critical role in arrhythmogenesis, and its modulation is a viable therapeutic strategy.