ECG test - Better Health Channel
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 . Exercise stress testing · Videos & tests. Cardiac action potential, electrical impulses, ECG waves & conduction system.
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. AuflageS. 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. A standard ECG typically requires 10 electrodes in order to provide a lead view. The posterior wall in the area of the left ventricle right precordial leads VR What information can an ECG provide? Circulation problems of the coronary arteries can also be detected, which can help to diagnose a heart attack.
Clinical electrocardiography and ECG interpretation – ECG learning
These electrodes detect the electrical currents generated by the heart — these are measured and recorded by the electrocardiograph. The three major types of ECG are: No movement is allowed during the test, as electrical impulses generated by other muscles may interfere with those generated by your heart.
You are free to move around normally while the monitor is attached. This type of ECG is used for people whose symptoms are intermittent stop-start and may not show up on a resting ECG, and for people recovering from heart attack to ensure that their heart is functioning properly.
You record your symptoms in a diary, and note when they occur so that your own experience can be compared with the ECG cardiac stress test — this test is used to record your ECG while you ride on an exercise bike or walk on a treadmill. This type of ECG takes about 15 to 30 minutes to complete. This cell architecture is referred to as a syncytium, which implies that the entire network of cells functions as one unit.
It follows that if one cell in the syncytium is activated, it will activate all cells downstream provided that they are excitable. The intercalated disc is composed of cell membrane proteins that connects adjacent cells both mechanically and electrically. Electrically charged ions can flow between cells through the gap junctions. Schematic illustration of the myocardial syncytium.
Note the branched cell structure and the connections between the cells. The cardiac action potential The action potential includes a depolarization activation followed by a repolarization recovery. Thus, the action potential involves movement of ions — which are charged particles — and therefore the action potential generates an electrical current. Figure 3 below shows the appearance of the action potential in myocardial cells the action potential will be discussed in detail in the next article.
The action potential of contractile cells. Inactive resting myocardial cells have a resting membrane potential of mV. Upon stimulation, the cell depolarizes and a rapid increase in the membrane potential is noted. The cell returns to its resting state by repolarizing. These concepts are discussed in detail in the next article. Cardiac electromechanical coupling Depolarization activates the myocardial cells and induces cellular processes that lead to cell contraction.
The spread of an electrical impulse is therefore directly coupled to a mechanical event this is referred to as electromechanical coupling. Because there is an abundance of ions in the tissues and fluids surrounding the heart — and indeed in the entire human body — the electrical currents generated in the heart are transmitted all the way to the skin, where they can be recorded using electrodes.
The electrocardiograph presents these electrical events in a diagram referred to as electrocardiogram ECG. The electrical potentials generated by components of the conduction system sinoatrial node, atrioventricular node, bundle of His, Purkinje fibers are too small to be detected using surface skin electrodes. Hence, the ECG only presents activity of contractile atrial and ventricular myocardium. This is unfortunate because the conduction system plays a pivotal role in cardiac function and certainly ECG interpretation.
Luckily, it is almost always possible to draw conclusions about the conduction system based on the visible ECG waveforms and rhythm. 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.
Clinical electrocardiography and ECG interpretation
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. 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.