Electrocardiogram (ECG) | CardioSecur
While it is a relatively simple test to perform, the interpretation of the ECG tracing requires significant amounts of training. Numerous . Conducting system of the heart: SA means sinoatrial node. . Electrocardiogram (ECG) Related Articles. An electrocardiogram (ECG) is a medical test that detects heart problems by measuring congenital heart defects involving the conducting (electrical) system . The cardiac conduction system comprises of the: graph called an electrocardiogram (ECG), this is a good way to monitor the heart's cardiac conduction system.
The heart's conduction system Update your cardiac diagnostics You can record a clinical lead ECG using just 4 electrodes and an app on your iPad or iPhone. Learn more The entire process of depolarization and repolarization is depicted on the ECG.
The individual events are represented as spikes and waves, each representing a specific part of the cardiac conduction cycle.
The picture below shows the pathway of an electrical impulse as it corresponds to the spikes and waves on an ECG. To do this, the heart is shown on its side.
Clinical electrocardiography and ECG interpretation
When disturbances of the conduction system are present, this can be detected via abnormalities of the spikes and waves on an ECG. What are ECG leads? An electrocardiogram uses electrodes attached to the skinwhich are able to detect electrical currents, in order to provide us with information about the heart.
The information detected by the electrodes is used to calculate measurements, known as leads. A standard ECG includes 12 leads, i.
Each lead provides us with information about different parts of the heart. Immediately after an ECG procedure When the procedure is completed, the electrodes are removed. An ECG is completely painless and non-invasive, as the skin is not penetrated. The doctor can interpret the results of your ECG straight away based on your medical history, symptoms and clinical examination. It does not send electric current to the body. Some people may be allergic or sensitive to the electrodes, which can cause local skin reddening.
Some of the various heart problems that can be diagnosed by ECG include: A person with heart disease may have a normal ECG result if the condition does not cause a disturbance in the electrical activity of the heart.
The sinoatrial node consists of highly specialized cells with a distinct ability to depolarize spontaneously, without being stimulated. The sinoatrial node is often referred to as the primary pacemaker of the heart. The rate of spontaneous depolarization in the sinoatrial node is modified by the autonomic nervous system. Sympathetic stimulation increases the rate whereas parasympathetic stimulation lowers the rate.
The heart rate at any given instant depends on the balance between sympathetic and parasympathetic activity. Secondary latent pacemakers The sinoatrial node is the primary pacemaker of the heart. These structures are as follows: Parts of the atrial myocardium: There are clusters of atrial myocardial cells located around the crista terminalis, the entrance of the coronary sinus and the inferior vena cava, as well as cells around the mitral and tricuspid valves, which possess automaticity.
Thus, automaticity is not exclusive to cells of the conduction system.
- The Electrical Conduction System of the Heart:
Myocardium surrounding the atrioventricular AV node: It is a common misconception that the atrioventricular AV node possess automaticity, because there is no compelling evidence for that. The bundle of His and the entire Purkinje network possess automaticity. The observant reader may have noticed that the ventricular myocardium does not possess automaticity, and this is important to note as we shall see in later chapters. The reason that the sinoatrial node is the primary pacemaker is simply because it has the highest intrinsic rate of spontaneous depolarization i.
Clinical aspects of automaticity The sinoatrial node may become dysfunctional and fail to depolarize.
Clinical electrocardiography and ECG interpretation – ECG learning
This behavior is the reason why the other pacemakers are often referred to as latent pacemakers. The intrinsic rate of spontaneous depolarization in the latent pacemakers is highest in the atrial myocardium and lowest in the Purkinje fibers. Thus, automaticity appears to decline gradually with the distance from the sinoatrial node.
Should the atrial myocardium also fail, then it is most likely that the cells around the atrioventricular node will take over the rhythm.
As a last resort there is an extensive network of Purkinje fibers, starting in the bundle of His, which can establish a rhythm. This succession, from the sinoatrial node to the Purkinje fibers, is referred to as pacemaker hierarchy. Figure 4 displays the pacemaker hierarchy.Electrical Conduction System of the Heart Cardiac - SA Node, AV Node, Bundle of His
It should be noted that the automaticity discussed above is normal automaticity, which only occurs in the sinoatrial node and the latent pacemakers. However, there is also abnormal automaticity, which can arise anywhere in the heart, including in ventricular myocardium.
This is discussed later. Overview of the electrical impulse during a cardiac cycle left hand side and the pacemaker hierarchy right hand side.
The Cardiac Conduction System - Pass My Exams: Easy exam revision notes for GSCE Biology
The rate of spontaneous depolarization is highest in the sinoatrial node, which is why it is the primary pacemaker. Impulse transmission conduction, propagation The cells of the conduction system have virtually no contractile function. Conduction cells are merely responsible for spreading the depolarization rapidly and synchronously to the contractile cells, so that they can contract in concert. However, there are fewer conduction cells than contractile cells, which implies that conduction cells only communicate with a portion of the contractile myocardium.
Recall that all cells in the heart are connected, both mechanically and electrically and this enables the electrical impulse to spread from one cell to the next.
Atrial impulse transmission The conduction system is vaguely defined in the atria, as compared with the ventricles which boasts with distinct conduction structures such as the bundle of His and the bundle branches. There are, however, three rather distinct fiber bundles which appear to serve as the conduction system of the atria.