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The sinoatrial node (SA node) is the primary pacemaker of the heart. It is a region of cardiac muscle on the wall of the upper right atrium near to the superior vena cava entrance. The cells that make up the SA node are specialized cardiomyocytes known as pacemaker cells that can spontaneously generate cardiac action potentials.
The primary purpose of a pacemaker is to maintain an even heart rate, either because the heart's natural cardiac pacemaker provides an inadequate or irregular heartbeat, or because there is a block in the heart's electrical conduction system. Modern pacemakers are externally programmable and allow a cardiologist to select the optimal pacing ...
Once the pacemaker potential reaches a set value, the threshold potential, it produces an action potential. [2] Other cells within the heart (including the Purkinje fibers [ 11 ] and atrioventricular node ) can also initiate action potentials; however, they do so at a slower rate and therefore, if the SA node is functioning properly, its action ...
Sinus node dysfunction (SND), also known as sick sinus syndrome (SSS), is a group of abnormal heart rhythms (arrhythmias) usually caused by a malfunction of the sinus node, the heart's primary pacemaker. [1] [2] Tachycardia-bradycardia syndrome is a variant of sick sinus syndrome in which the arrhythmia alternates between fast and slow heart ...
An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the heart. It is thus a cardiac pacemaker that is ectopic , producing an ectopic beat .
The difference between pacemakers and ICDs is that pacemakers are also available as temporary units and are generally designed to correct slow heart rates, i.e. bradycardia, while ICDs are often permanent safeguards against sudden life-threatening arrhythmias. S-ICD lead and generator position Sketch of an already-implanted cardioverter ...
The action potentials generated in the pacemaker propagate throughout the heart in a specific pattern. The system that carries this potential is called the electrical conduction system . Dysfunction of the electrical system manifests in many ways and may include Wolff–Parkinson–White syndrome , ventricular fibrillation , and heart block .
A ventricular assist device (VAD) is an electromechanical device that provides support for cardiac pump function, which is used either to partially or to completely replace the function of a failing heart.