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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.
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 IV: Characteristics of Bradyarrhythmias

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...

Electrophysiology of Normal Cardiac Rhythm

Electrophysiology of Normal Cardiac Rhythm

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 of...

Conduction System of the Heart

Conduction System of the Heart

Autorhythmicity is a term that refers to the heart's inherent ability to generate electrical signals and instigate muscle contractions. This self-regulating conduction system within the heart consists of two key components: the pacemaker cells and specialized conducting cells.
The pacemaker cells are located in two primary nodes: the sinoatrial (SA) node and the atrioventricular (AV) node. The SA node pacemaker cells can autonomously depolarize, triggering an action potential that leads to the...

Conduction System of the Heart

Conduction System of the Heart

The cardiac conduction system produces and transmits electrical impulses that prompt myocardial contraction, ensuring efficient heart function. This intricate system ensures that the heart beats in a coordinated and efficient manner, beginning with the atria and then the ventricles. The conduction system optimizes cardiac output by maintaining this precise sequence, which is crucial for adequate blood circulation.
This system relies on the unique properties of nodal and Purkinje cells:...

Electrocardiogram Fundamentals

Electrocardiogram Fundamentals

Introduction
An electrocardiogram (ECG) is a diagnostic tool for identifying cardiac conditions such as arrhythmias, conduction abnormalities, and myocardial ischemia.
Definition
An electrocardiogram (ECG) visualizes the heart's electrical activity by tracing the electrical movement associated with each heartbeat on a graph or monitor. As the heart beats, an electrical wave passes through it, correlating with the cardiac cycle events.
Parts of an ECG
An ECG utilizes electrodes on the skin to...

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Related Experiment Video

Updated: May 22, 2026

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

Published on: December 28, 2012

PR Interval Alternans and the Mystery of Inverse Decremental Conduction.

Alyssa Zakala¹, Mohammed Hussein Kamareddine¹, Farah Olleik¹

¹Lankenau Medical Center, Main Line Health, Wynnewood, Pennsylvania, USA.

JACC. Case Reports

|May 21, 2026

Summary

A rare heart condition called Yan conduction, characterized by inverse decremental conduction, can cause PR alternans in patients with right bundle branch block. This may precede sudden cardiac arrest from atrioventricular block.

Keywords:

Yan conduction inverse decremental conduction left bundle branch block paroxysmal AV block right bundle branch block

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

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Published on: April 11, 2025

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Last Updated: May 22, 2026

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

A Research Method For Detecting Transient Myocardial Ischemia In Patients With Suspected Acute Coronary Syndrome Using Continuous ST-segment Analysis

Published on: December 28, 2012

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

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

Published on: April 11, 2025

Area of Science:

Cardiology
Electrophysiology
Medical Devices

Background:

Severe aortic stenosis necessitates intervention, often transcatheter aortic valve replacement (TAVR).
Preexisting right bundle branch block (RBBB) can complicate cardiac conduction post-TAVR.
Intermittent atrioventricular (AV) block is a potential complication after TAVR.

Purpose of the Study:

To describe a case of PR alternans and subsequent proximal AV block in a patient with RBBB after TAVR.
To elucidate the electrophysiological mechanism of inverse decremental conduction (Yan conduction) in this context.

Main Methods:

Case report of a 73-year-old male with severe aortic stenosis and RBBB undergoing TAVR.
Post-TAVR monitoring with mobile cardiac outpatient telemetry.
Electrocardiogram (ECG) analysis revealing PR interval alternans and RBBB.

Main Results:

The patient developed intermittent AV block post-TAVR.
ECG showed PR alternans, with PR interval length inversely related to preceding RP interval length.
The patient experienced sudden cardiac arrest due to proximal AV block.

Conclusions:

Inverse decremental conduction (Yan conduction) exhibits an inverse relationship between conduction time and upstream stimulation frequency.
In RBBB, inverse decremental conduction in the left bundle branch may present as PR alternans.
PR alternans in this setting can herald proximal AV block and cardiac arrest.