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Cardiac Action Potential

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.
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Ionic Basis of Cardiac Action Potentials

Correlation between ECG and Cardiac Cycle

Correlation between ECG and Cardiac Cycle

The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac cycle.
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...

Electrocardiogram

Electrocardiogram

An electrocardiogram (ECG or EKG) is a critical diagnostic tool that records the electrical signals produced by the heart during each heartbeat. This recording is achieved through electrodes placed strategically on the arms, legs, and chest. The electrocardiograph amplifies these signals and produces 12 distinct tracings, offering a comprehensive understanding of the heart's electrical activity.
Three major waveforms are present in a typical ECG recording: the P wave, the QRS complex, and...

Electrophysiology of Normal Cardiac Rhythm

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The normal cardiac rhythm is a synchronized electrical activity that facilitates the regular and coordinated contraction of the heart muscle. This process is essential for efficient blood circulation throughout the body. The fundamental elements involved in establishing and maintaining this rhythm include the unique electrical properties of cardiac muscle cells, the sinoatrial (SA) node's pacemaker function, the specialized conducting system, and the ionic mechanisms underlying each phase...

Mechanism of Cardiac Arrhythmias

Mechanism of Cardiac Arrhythmias

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.

Myocarditis I: Introduction

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Myocarditis is inflammation of the myocardium, which is the muscular layer of the heart.EtiologyMyocarditis has a diverse etiology, including a wide range of infectious and non-infectious causes:Infectious CausesViral: Common viruses include Coxsackie A and B, adenovirus, parvovirus B19, enteroviruses, and influenza A.Bacterial: Examples include infections caused by Streptococcus, Staphylococcus, and Mycoplasma species.Rickettsial: Infections like Rocky Mountain spotted fever can result in...

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Related Experiment Video

Updated: Feb 17, 2026

Dual-Dye Optical Mapping of Hearts from RyR2R2474S Knock-In Mice of Catecholaminergic Polymorphic Ventricular Tachycardia

Dual-Dye Optical Mapping of Hearts from RyR2R2474S Knock-In Mice of Catecholaminergic Polymorphic Ventricular Tachycardia

Published on: December 22, 2023

Is myocardial repolarization duration associated with repolarization heterogeneity?

Keith A Marill¹, Pat Dorsey², Anthony Holmes²

¹Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.

Annals of Noninvasive Electrocardiology : the Official Journal of the International Society for Holter and Noninvasive Electrocardiology, Inc

|December 3, 2017

Summary

Prolongation of myocardial repolarization, measured by the heart rate-corrected J-to-T peak interval (JTpkc), is not associated with repolarization dispersion. This suggests dispersion may not be a key factor linking QTc prolongation to Torsades de Pointes (TdP).

Keywords:

QT interval cohort studies dispersion repolarization torsades de pointes

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Published on: June 16, 2020

Area of Science:

Cardiology
Electrophysiology
Medical Imaging

Background:

Repolarization dispersion is theorized to link myocardial repolarization prolongation with lethal Torsades de Pointes (TdP).
Investigating the relationship between repolarization duration and heterogeneity is crucial for understanding TdP mechanisms.

Purpose of the Study:

To determine if prolonged myocardial repolarization (JTpkc) correlates with repolarization heterogeneity (transmural dispersion, TpTe).
To assess the association between JTpkc and QT dispersion (QTd).

Main Methods:

Retrospective cohort study of 874 emergency department patients with ECG.
Automated ECG interval measurements including JTpkc, TpTe, QTd, QTc, QRS, and RR.
Multiple linear regression analysis adjusted for QRS and RR intervals.

Main Results:

No positive association was found between JTpkc and TpTe (coefficient -0.10).
No significant association was found between JTpkc and QTd (coefficient 0.03).
Clinical TdP factors were more strongly associated with JTpkc than TpTe.

Conclusions:

Prolonged repolarization duration (JTpkc) is not positively associated with repolarization dispersion (TpTe or QTd).
Repolarization dispersion may not be a critical mechanistic link between QTc prolongation and TdP.