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Related Concept Videos

Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

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...
Cardiac Action Potential01:30

Cardiac Action Potential

Cardiac action potentials are essential for proper heart function, enabling the rhythmic contractions needed for adequate blood circulation. Nodal cells and Purkinje fibers, specialized for electrical conduction, generate these action potentials.
The cardiac action potential process involves a series of phases characterized by the movement of ions across the cardiac cell membranes, leading to the depolarization and repolarization of the cardiac myocytes.
Ionic Basis of Cardiac Action Potentials
Dysrhythmias I: Introduction01:15

Dysrhythmias I: Introduction

Dysrhythmias refers to abnormalities in the heart's rhythm. They result from disruptions in the heart's electrical conduction system, which includes the sinoatrial(SA)node, atrioventricular(AV) node, the bundle of His, bundle branches, and Purkinje fibers.Definition and PathophysiologyDysrhythmias result from disorders of impulse formation, impulse conduction, or both. The heart contains specialized cells in the sinoatrial node, atrioventricular node, and the bundle of His and Purkinje fibers...
Dysrhythmias III: Characteristics of Dysrhythmias01:29

Dysrhythmias III: Characteristics of Dysrhythmias

Dysrhythmias, also known as arrhythmias, are irregular heart rhythms that result from abnormal electrical activity in the heart, affecting its ability to circulate blood efficiently. Tachyarrhythmias, a subset of dysrhythmias, are characterized by abnormally fast heart rates exceeding 100 beats per minute. Here are some types of tachyarrhythmias with their distinct ECG features:Sinus Tachycardia:Sinus tachycardia presents a regular heart rhythm with an increased rate of 101-180 beats per minute.
Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

Dysrhythmias IV: Characteristics of Bradyarrhythmias

Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:Sinus BradycardiaSinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).First-Degree AV...
ECG Interpretation of Arrhythmias II: Atrial, Junctional and Ventricular Arrhythmias01:25

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

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...

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Related Experiment Video

Updated: Jul 22, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
12:45

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

Published on: December 11, 2017

A characteristic precordial repolarization abnormality with intermittent left bundle-branch block.

P Denes, A Pick, R H Miller

    Annals of Internal Medicine
    |July 1, 1978
    PubMed
    Summary

    Patients with intermittent left bundle-branch block often show T-wave inversions on ECGs during normal conduction. These findings do not necessarily indicate coronary artery disease and may relate to abnormal ventricular activation patterns.

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    Real-Time Cardiac Mapping with a Noninvasive Imageless Electrocardiographic Imaging System
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    Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
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    Published on: December 11, 2017

    Ablation of Ischemic Ventricular Tachycardia Using a Multipolar Catheter and 3-dimensional Mapping System for High-density Electro-anatomical Reconstruction
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    Ablation of Ischemic Ventricular Tachycardia Using a Multipolar Catheter and 3-dimensional Mapping System for High-density Electro-anatomical Reconstruction

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    Real-Time Cardiac Mapping with a Noninvasive Imageless Electrocardiographic Imaging System
    10:17

    Real-Time Cardiac Mapping with a Noninvasive Imageless Electrocardiographic Imaging System

    Published on: April 11, 2025

    Area of Science:

    • Cardiology
    • Electrophysiology
    • Diagnostic Imaging

    Background:

    • Intermittent left bundle-branch block (iLBBB) is a cardiac condition affecting ventricular conduction.
    • Electrocardiographic (ECG) findings in iLBBB can be complex and sometimes misinterpreted.
    • The relationship between iLBBB, ECG abnormalities, and underlying heart disease requires further clarification.

    Purpose of the Study:

    • To investigate the electrocardiographic patterns in patients with intermittent left bundle-branch block during normal conduction.
    • To determine the association between these ECG patterns and the presence of organic heart disease or coronary artery disease.
    • To explore the potential mechanisms behind observed T-wave abnormalities in iLBBB.

    Main Methods:

    • Retrospective review of electrocardiograms (ECGs) from 23 patients diagnosed with intermittent left bundle-branch block.
    • Analysis of ECGs performed during periods of normal conduction.
    • Correlation of ECG findings with results from cardiac catheterization in a subset of patients.

    Main Results:

    • A distinct ECG pattern of deep, symmetrical T-wave inversions in right and mid-precordial leads was observed in 19 out of 23 patients during normal conduction.
    • Of seven patients who underwent cardiac catheterization, only two showed findings suggestive of organic heart disease, and only one had significant obstructive coronary artery disease.
    • The observed T-wave changes resemble those seen after cessation of chronic right ventricular pacing, a pattern associated with left bundle-branch block morphology.

    Conclusions:

    • Deep, symmetrical T-wave inversions in the right and mid-precordial leads during normal conduction are common in patients with intermittent left bundle-branch block.
    • These T-wave abnormalities do not necessarily indicate underlying coronary artery disease.
    • The findings suggest that abnormal ventricular activation and subsequent repolarization, as seen in iLBBB and right ventricular pacing, can lead to similar ECG patterns.