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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.

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:...

ECG Interpretation of Arrhythmias I: Sinus Arrhythmias

ECG Interpretation of Arrhythmias I: Sinus Arrhythmias

Arrhythmias are disturbances in the heart's rhythm that lead to abnormal heartbeats. These irregularities can originate from different parts of the heart and are classified based on their origin and nature.
Types of Arrhythmias
Sinus Node Arrhythmias
Sinus Bradycardia: Originating from the sinoatrial (SA) node, sinus bradycardia involves slower impulses, resulting in a heart rate of less than 60 beats per minute (bpm). Causes include sleep, vagal stimulation, beta-blockers, hypothyroidism, and...

Dysrhythmias III: Characteristics of Dysrhythmias

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 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...

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Related Experiment Video

Updated: Jul 11, 2026

Generation of Murine Cardiac Pacemaker Cell Aggregates Based on ES-Cell-Programming in Combination with Myh6-Promoter-Selection

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Associated conduction disturbances in patients with symptomatic sinus node disease

H Vallin, O Edhag

Acta Medica Scandinavica

|January 1, 1981

Summary

Symptomatic sinus node disease (SND) often involves widespread conduction system issues, not just the sinus node. Electrophysiological studies reveal frequent abnormalities in the AV junction and intraventricular conduction, indicating a broader degenerative process.

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Area of Science:

Cardiology
Electrophysiology
Cardiac Electrophysiology

Background:

Symptomatic sinus node disease (SND) is a clinical diagnosis often associated with conduction system disturbances.
The full extent and distribution of these disturbances are not always clear from surface electrocardiography (ECG).

Purpose of the Study:

To electrophysiologically assess the extent and distribution of functional disturbances in the cardiac conduction system in patients with symptomatic SND.
To determine the prevalence of associated conduction abnormalities beyond the sinus node.

Main Methods:

Electrophysiological investigations were conducted in 30 patients with symptomatic SND.
Tests were performed before and after autonomic tone inhibition using propranolol and atropine.
Surface ECG findings were correlated with invasive electrophysiological data.

Main Results:

The majority of patients (80%) exhibited associated conduction abnormalities.
Atrioventricular (AV) junctional malfunction was most common (17 patients), with prolonged conduction or abnormal refractoriness.
Intraventricular conduction delays, including bundle branch blocks (BBBs), were observed in 11 patients.
Impaired automaticity of subsidiary pacemakers was suggested by prolonged cardiac arrests in 11 patients.

Conclusions:

Symptomatic sinus node disease is frequently associated with widespread conduction system abnormalities.
Electrophysiological studies reveal significant involvement of the AV junction and intraventricular conduction pathways.
Sinus node dysfunction may be a manifestation of a more generalized degenerative process affecting the entire cardiac conduction system.