Related Experiment Video
Updated: Jul 20, 2026
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
Left septal fascicular block: myth or reality?
1Division of Cardiology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1679, USA. rmacalpi@ucla.edu
Indian Pacing and Electrophysiology Journal
|September 1, 2006
Summary
This study explores left septal fascicular block, a controversial conduction defect. It proposes electrocardiogram criteria for recognizing this condition, which can explain unexplained ECG abnormalities.
Area of Science:
- Cardiology
- Electrophysiology
- Human Anatomy
Background:
- The left bundle branch in the human heart typically trifurcates into anterior, posterior, and septal fascicles.
- Electrocardiogram (ECG) interpretation commonly includes conduction abnormalities of the anterior and posterior fascicles.
- Conduction defects of the third left fascicle, the septal or median fascicle, lack established diagnostic criteria and remain debated.
Purpose of the Study:
- To review existing evidence regarding the septal fascicle of the left bundle branch.
- To propose specific electrocardiogram (ECG) criteria for identifying left septal fascicular block.
- To present illustrative cases demonstrating left septal fascicular block as a distinct entity.
Main Methods:
- Literature review of anatomical and electrophysiological studies on left bundle branch fascicles.
- Analysis of 12-lead electrocardiogram (ECG) patterns associated with conduction delays.
- Development and validation of proposed ECG criteria for left septal fascicular block using case examples.
Main Results:
- Anatomical studies confirm the trifascicular nature of the left bundle branch in most individuals.
- Proposed electrocardiogram (ECG) criteria can identify specific conduction defects within the left septal fascicle.
- Case studies demonstrate that left septal fascicular block can manifest as unique, previously unexplained ECG abnormalities.
Conclusions:
- Left septal fascicular block is a recognizable clinical entity with distinct electrocardiogram (ECG) findings.
- The proposed diagnostic criteria aid in identifying this specific conduction defect.
- Recognition of left septal fascicular block can improve the understanding of complex electrocardiogram (ECG) abnormalities.
Related Concept Videos
01:18Dysrhythmias 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...
01:25Dysrhythmias VI: Management of Dysrhythmias
Dysrhythmia management involves a multifaceted approach, incorporating pharmacological treatments, medical procedures, surgical interventions, lifestyle modifications, and patient education.Pharmacological ManagementAntiarrhythmic Drugs:Class I (Sodium Channel Blockers): This class includes quinidine and procainamide, which reduce the speed of impulse conduction in the heart, stabilize the cardiac membrane, and control arrhythmias. Quinidine and procainamide are Class IA agents that prolong the...
01:23Mitral Stenosis II: Clinical features and Diagnostic Tests
Mitral stenosis is a heart condition in which the mitral valve, which allows blood to flow from the left atrium to the left ventricle, becomes narrowed or stenotic. This narrowing hinders blood flow and leads to clinical symptoms requiring specific medical evaluations and management strategies. The following overview outlines the clinical symptoms, assessments, diagnostic findings, prevention methods, and treatments for mitral stenosis.Clinical ManifestationsDyspnea (shortness of breath): This...
01:29Disturbances 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...
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
01:29Cardiomyopathy III: Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy, or HCM, is an autosomal dominant genetic disorder characterized by asymmetric left ventricular hypertrophy without ventricular dilation. It is more common in men and is typically diagnosed in young, athletic adults.EtiologyHCM is primarily genetic and is caused by mutations in genes encoding sarcomeric proteins. Researchers have identified over 1400 mutations across at least 11 different genes. Among these, the most frequently occurring mutations are found in the...
01:22Mitral Stenosis I: Introduction
Mitral Valve Stenosis (MVS) is a heart condition where the mitral valve narrows, impeding blood circulation from the left atrium to the left ventricle. The etiology and pathophysiology of this condition are multifaceted, leading to a cascade of cardiovascular complications.Causes of Mitral Valve StenosisRheumatic Heart Disease: It is the main cause of mitral valve stenosis, particularly in developing nations. This condition arises from rheumatic fever, an inflammatory illness resulting from...