| Bundle branches | |
|---|---|
 The left bundle branch (4) and the right bundle branch (10) | |
| Anatomical terminology |
The bundle branches, or Tawara branches, [1] are offshoots of the bundle of His in the heart's ventricle. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials from the bundle of His to the Purkinje fibers. [2]
There are two branches of the bundle of His: the left bundle branch and the right bundle branch, both of which are located along the interventricular septum. The left bundle branch further divides into the left anterior fascicle and the left posterior fascicle. These structures lead to a network of thin filaments known as Purkinje fibers. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials to the Purkinje fibers. [2]
When a bundle branch or fascicle becomes injured (by underlying heart disease, myocardial infarction, or cardiac surgery), it may cease to conduct electrical impulses appropriately, resulting in altered pathways for ventricular depolarization. This condition is known as a bundle branch block. [3]
The bundle branches were separately described by Retzer and Braeunig as early as 1904, but their physiological function remained unclear and their role in the electrical conduction system of the heart remained unknown until Sunao Tawara published his monograph on Das Reizleitungssystem des Säugetierherzens (English: The Conduction System of the Mammalian Heart) in 1906. [4] Although Tawara's monograph had demonstrated that the branches of the bundle of His may transmit cardiac action potentials to the ventricles, the functional proof for his observation was not provided until 1910, when Hans Eppinger and Carl Julius Rothberger showed that cutting off both branches to induce a bilateral bundle branch block results in a complete heart block. [5]
Electrocardiography is the process of producing an electrocardiogram, a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.
Cardioversion is a medical procedure by which an abnormally fast heart rate (tachycardia) or other cardiac arrhythmia is converted to a normal rhythm using electricity or drugs. Synchronized electrical cardioversion uses a therapeutic dose of electric current to the heart at a specific moment in the cardiac cycle, restoring the activity of the electrical conduction system of the heart. Pharmacologic cardioversion, also called chemical cardioversion, uses antiarrhythmia medication instead of an electrical shock.
A premature ventricular contraction (PVC) is a common event where the heartbeat is initiated by Purkinje fibers in the ventricles rather than by the sinoatrial node. PVCs may cause no symptoms or may be perceived as a "skipped beat" or felt as palpitations in the chest. PVCs do not usually pose any danger.
Wolff–Parkinson–White syndrome (WPWS) is a disorder due to a specific type of problem with the electrical system of the heart. About 60% of people with the electrical problem developed symptoms, which may include an abnormally fast heartbeat, palpitations, shortness of breath, lightheadedness, or syncope. Rarely, cardiac arrest may occur. The most common type of irregular heartbeat that occurs is known as paroxysmal supraventricular tachycardia.
The Purkinje fibers are located in the inner ventricular walls of the heart, just beneath the endocardium in a space called the subendocardium. The Purkinje fibers are specialized conducting fibers composed of electrically excitable cells. They are larger than cardiomyocytes with fewer myofibrils and many mitochondria. They conduct cardiac action potentials more quickly and efficiently than any other cells in the heart. Purkinje fibers allow the heart's conduction system to create synchronized contractions of its ventricles, and are essential for maintaining a consistent heart rhythm.
The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of the interatrial septum near the opening of the coronary sinus, and conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact.
The bundle of His (BH) or His bundle (HB) ( "hiss") is a collection of heart muscle cells specialized for electrical conduction. As part of the electrical conduction system of the heart, it transmits the electrical impulses from the atrioventricular node to the point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which provide electrical conduction to the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval.
The electrical conduction system of the heart transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through the body's circulatory system. The pacemaking signal travels through the right atrium to the atrioventricular node, along the Bundle of His, and through the bundle branches to Purkinje fibers in the ventricles. The Purkinje fibers transmit the signals more rapidly to stimulate contraction firstly of the right and left atrium, and then the right and left ventricles.
Ventricular tachycardia is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period of time are referred to as an electrical storm. Short periods may occur without symptoms, or present with lightheadedness, palpitations, or chest pain. Ventricular tachycardia may result in ventricular fibrillation (VF) and turn into cardiac arrest. This conversion of the VT into VF is called the degeneration of the VT. It is found initially in about 7% of people in cardiac arrest.
A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart.
A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system.
Atrioventricular block is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatrial node produces an electrical signal to control the heart rate. The signal travels from the SA node to the ventricles through the atrioventricular node. In an AV block, this electrical signal is either delayed or completely blocked. When the signal is completely blocked, the ventricles produce their own electrical signal to control the heart rate. The heart rate produced by the ventricles is much slower than that produced by the SA node.
Lown–Ganong–Levine syndrome (LGL) is a pre-excitation syndrome of the heart. Those with LGL syndrome have episodes of abnormal heart racing with a short PR interval and normal QRS complexes seen on their electrocardiogram when in a normal sinus rhythm. LGL syndrome was originally thought to be due to an abnormal electrical connection between the atria and the ventricles, but is now thought to be due to accelerated conduction through the atrioventricular node in the majority of cases. The syndrome is named after Bernard Lown, William Francis Ganong, Jr., and Samuel A. Levine.
Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked.
The electrical axis of the heart is the net direction in which the wave of depolarization travels. It is measured using an electrocardiogram (ECG). Normally, this begins at the sinoatrial node ; from here the wave of depolarisation travels down to the apex of the heart. The hexaxial reference system can be used to visualise the directions in which the depolarisation wave may travel.
A left posterior fascicular block (LPFB), also known as left posterior hemiblock (LPH), is a condition where the left posterior fascicle, which travels to the inferior and posterior portion of the left ventricle, does not conduct the electrical impulses from the atrioventricular node. The wave-front instead moves more quickly through the left anterior fascicle and right bundle branch, leading to a right axis deviation seen on the ECG.
Michel Haïssaguerre is a French cardiologist and electrophysiologist. His investigations have been the basis for development of new markers and therapies for atrial and ventricular fibrillation.
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath or chest pain. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.
Cardiac physiology or heart function is the study of healthy, unimpaired function of the heart: involving blood flow; myocardium structure; the electrical conduction system of the heart; the cardiac cycle and cardiac output and how these interact and depend on one another.
Das Reizleitungssystem des Säugetierherzens is a scientific monograph published in 1906 by Sunao Tawara. It has been recognized by cardiologists as a monumental discovery, and a milestone in cardiac electrophysiology".