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T Wave Alternans
T wave alternans (TWA) is a periodic beat-to-beat variation in the amplitude or shape of the T wave in an electrocardiogram (ECG or EKG) TWA was first described in 1908. At that time, only large variations ("macroscopic" TWA) could be detected. Those large TWAs were associated with increased susceptibility to lethal ventricular tachycardias. Most modern references to TWA refer to microvolt T wave alternans (MTWA), a non-invasive heart test that can identify patients who are at increased risk of sudden cardiac death. It is most often used in patients who have had myocardial infarctions (heart attacks) or other heart damage to see if they are at high risk of developing a potentially lethal cardiac arrhythmia. Those who are found to be at high risk would therefore benefit from the placement of a defibrillator device which can stop an arrhythmia and save the patient's life. The TWA test uses an electrocardiogram (ECG) measurement of the heart's electrical conduction using electro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T-wave Alternans
T wave alternans (TWA) is a periodic beat-to-beat variation in the amplitude or shape of the T wave in an electrocardiogram (ECG or EKG) TWA was first described in 1908. At that time, only large variations ("macroscopic" TWA) could be detected. Those large TWAs were associated with increased susceptibility to lethal ventricular tachycardias. Most modern references to TWA refer to microvolt T wave alternans (MTWA), a non-invasive heart test that can identify patients who are at increased risk of sudden cardiac death. It is most often used in patients who have had myocardial infarctions (heart attacks) or other heart damage to see if they are at high risk of developing a potentially lethal cardiac arrhythmia. Those who are found to be at high risk would therefore benefit from the placement of a defibrillator device which can stop an arrhythmia and save the patient's life. The TWA test uses an electrocardiogram (ECG) measurement of the heart's electrical conduction using electro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T Wave
In electrocardiography, the T wave represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the ''absolute refractory period''. The last half of the T wave is referred to as the ''relative refractory period'' or ''vulnerable period''. The T wave contains more information than the QT interval. The T wave can be described by its symmetry, skewness, slope of ascending and descending limbs, amplitude and subintervals like the Tpeak–Tend interval. In most leads, the T wave is positive. This is due to the repolarization of the membrane. During ventricle contraction (QRS complex), the heart depolarizes. Repolarization of the ventricle happens in the opposite direction of depolarization and is negative current, signifying the relaxation of the cardiac muscle of the ventricles. But this negative flow causes a positive T wave; although the cell becomes more negatively charged, the net effect is in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ventricular Tachycardia
Ventricular tachycardia (V-tach or VT) 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. Ventricular tachycardia can occur due to coronary heart disease, aortic stenosis, cardiomyopathy, electrolyte problems, or a heart attack. Diagnosis is by an electrocardiogram (ECG) showing a rate of greater than 120 beats per minute and at least three wide QRS complexes in a row. It is classified as non-sustained versus sustained based on whether it lasts le ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to the lungs. In humans, the heart is approximately the size of a closed fist and is located between the lungs, in the middle compartment of the chest. In humans, other mammals, and birds, the heart is divided into four chambers: upper left and right atria and lower left and right ventricles. Commonly the right atrium and ventricle are referred together as the right heart and their left counterparts as the left heart. Fish, in contrast, have two chambers, an atrium and a ventricle, while most reptiles have three chambers. In a healthy heart blood flows one way through the heart due to heart valves, which prevent backflow. The heart is enclosed in a protective sac, the pericardium, which also contains a small amount of fluid. The wall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sudden Cardiac Death
Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possibly defibrillation are needed until further treatment can be provided. Cardiac arrest results in a rapid loss of consciousness, and breathing may be abnormal or absent. While cardiac arrest may be caused by heart attack or heart failure, these are not the same, and in 15 to 25% of cases, there is a non-cardiac cause. Some individuals may experience chest pain, shortness of breath, nausea, an elevated heart rate, and a light-headed feeling immediately before entering cardiac arrest. The most common cause of cardiac arrest is an underlying heart problem like coronary artery disease that decreases the amount of oxygenated blood supplying the heart muscle. This, in turn, damages the structure of the muscle, which can alter its function. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myocardial Infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck or jaw. Often it occurs in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat or feeling tired. About 30% of people have atypical symptoms. Women more often present without chest pain and instead have neck pain, arm pain or feel tired. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, cardiogenic shock or cardiac arrest. Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardiac Arrhythmia
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. Arrhythmias are often categorized into four groups: extra beats, supraventricular tachycardias, ventricular arrhythmias and bradyarrhythmias. Extra beats include premature atrial contractions, premature ventricular contra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Defibrillator
Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current (often called a ''counter-shock'') to the heart. Although not fully understood, this process depolarizes a large amount of the heart muscle, ending the arrhythmia. Subsequently, the body's natural pacemaker in the sinoatrial node of the heart is able to re-establish normal sinus rhythm. A heart which is in asystole (flatline) cannot be restarted by a defibrillator, but would be treated by cardiopulmonary resuscitation (CPR). In contrast to defibrillation, synchronized electrical cardioversion is an electrical shock delivered in synchrony to the cardiac cycle. Although the person may still be critically ill, cardioversion normally aims to end poorly perfusing cardiac arrhythmias, such as supraventricular tachycardia. Defibrillators can be external, transvenou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vector (geometric)
In mathematics, physics, and engineering, a Euclidean vector or simply a vector (sometimes called a geometric vector or spatial vector) is a geometric object that has magnitude (or length) and direction. Vectors can be added to other vectors according to vector algebra. A Euclidean vector is frequently represented by a '' directed line segment'', or graphically as an arrow connecting an ''initial point'' ''A'' with a ''terminal point'' ''B'', and denoted by \overrightarrow . A vector is what is needed to "carry" the point ''A'' to the point ''B''; the Latin word ''vector'' means "carrier". It was first used by 18th century astronomers investigating planetary revolution around the Sun. The magnitude of the vector is the distance between the two points, and the direction refers to the direction of displacement from ''A'' to ''B''. Many algebraic operations on real numbers such as addition, subtraction, multiplication, and negation have close analogues for vectors, operations whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplitude (see below), which are all functions of the magnitude of the differences between the variable's extreme values. In older texts, the phase of a periodic function is sometimes called the amplitude. Definitions Peak amplitude & semi-amplitude For symmetric periodic waves, like sine waves, square waves or triangle waves ''peak amplitude'' and ''semi amplitude'' are the same. Peak amplitude In audio system measurements, telecommunications and others where the measurand is a signal that swings above and below a reference value but is not sinusoidal, peak amplitude is often used. If the reference is zero, this is the maximum absolute value of the signal; if the reference is a mean value (DC component), the peak amplitude is the maximu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding the National Advisory Committee for Aeronautics (NACA), to give the U.S. space development effort a distinctly civilian orientation, emphasizing peaceful applications in space science. NASA has since led most American space exploration, including Project Mercury, Project Gemini, the 1968-1972 Apollo Moon landing missions, the Skylab space station, and the Space Shuttle. NASA supports the International Space Station and oversees the development of the Orion spacecraft and the Space Launch System for the crewed lunar Artemis program, Commercial Crew spacecraft, and the planned Lunar Gateway space station. The agency is also responsible for the Launch Services Program, which provides oversight of launch operations and countdown management f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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