12 Lead ECG of a 26 year old male.

An electrocardiogram (ECG or EKG, abbreviated from the German Elektrokardiogramm) is a graphic produced by an electrocardiograph, which records the electrical activity of the heart over time. Analysis of the various waves and normal vectors of depolarization and repolarization yields important diagnostic information. QRS Records is a United States record label which produced notable jazz and blues recordings in the early twentieth century. ... Image File history File links Size of this preview: 800 × 313 pixel Image in higher resolution (1040 × 407 pixel, file size: 73 KB, MIME type: image/jpeg) I captured this 12 lead ECG from a friend of mine during a training class at the fire station. ... Image File history File links Size of this preview: 800 × 313 pixel Image in higher resolution (1040 × 407 pixel, file size: 73 KB, MIME type: image/jpeg) I captured this 12 lead ECG from a friend of mine during a training class at the fire station. ... Lightning strikes during a night-time thunderstorm. ... The heart and lungs, from an older edition of Grays Anatomy. ... In biology, depolarization is the event a cell undergoes when its membrane potential grows more positive with respect to the extracellular solution. ... In neuroscience, repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. ...

• It is the gold standard for the diagnosis of cardiac arrhythmias^[1]
• It guides therapy and risk stratification for patients with suspected acute myocardial infarction^[2]
• It helps detect electrolyte disturbances (e.g. hyperkalemia and hypokalemia)^[3]
• It allows for the detection of conduction abnormalities (e.g. right and left bundle branch block)^[4]
• It is used as a screening tool for ischemic heart disease during a cardiac stress test^[5]
• It is occasionally helpful with non-cardiac diseases (e.g. pulmonary embolism or hypothermia)^[3]

The electrocardiogram does not directly assess the contractility of the heart. However, it can give a rough indication of increased or decreased contractility.^[6] In medicine, a gold standard test is the diagnostic test that is regarded as definitive in determining whether an individual has a disease process. ... Cardiac arrhythmia is a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... Hyperkalemia is an elevated blood level (above 5. ... Hypokalemia is a potentially fatal condition in which the body fails to retain sufficient potassium to maintain health. ... Bundle branch block refers to a disorder of the hearts electrical conducting system. ... Ischaemic heart disease is a disease characterized by reduced blood supply to the heart. ... A cardiac stress test is a medical test performed to evaluate relative arterial blood flow increases to the left ventricular heart muscle during exercise, as compared to resting blood flow rates (i. ... Hypothermia refers to any condition in which the temperature of a body drops below the level required for normal metabolism and/or bodily function to take place. ... Myocardial Contractility: is a term used in to describe the performance of cardiac muscle. ...

History

ECG as done by Willem Einthoven. Electromechanical technology.

In 1856 Kollicker and Mueller discovered the electrical activity of the heart when a frog sciatic nerve/gastrocenemius preparation fell onto an isolated frog heart and both muscles contracted synchronously.^[7] Image File history File links I think this is public domain by now, not completely sure, as I couldnt find out who the author is. ... Image File history File links I think this is public domain by now, not completely sure, as I couldnt find out who the author is. ...

The Cambridge Simpliscribe, a popular ECG instrument of the 1950's and 1960's. Vacuum tube technology.

Alexander Muirhead attached wires to a feverish patient's wrist to obtain a record of the patient's heartbeat while studying for his DSc (in electricity) in 1872 at St Bartholomew's Hospital^[8] This activity was directly recorded and visualized using a Lippmann capillary electrometer by the British physiologist John Burdon Sanderson.^[9] Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Alexander Muirhead (1848-1920) Born Saltoun, East Lothian, Scotland was an electrical engineer specialising in wireless telegraphy. ...

The first to systematically approach the heart from an electrical point-of-view was Augustus Waller, working in St Mary's Hospital in Paddington, London.^[10] His electrocardiograph machine consisted of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate which was itself fixed to a toy train. [2] This allowed a heartbeat to be recorded in real time. In 1911 he still saw little clinical application for his work. Augustus Desiré Waller FRS (12 July 1856 - 11 March 1922) was a British scientist and the son of Augustus Volney Waller. ... St Marys Hospital QEQM building (above) and old section (below) (Photographs by username Hegster) Although there must be many hospitals named St Marys Hospital, the most famous is probably located in Paddington, West London, England. ... A street in Paddington including a pub, a restaurant targeted at tourists and Paddington Station in the background. ... This article is about the capital of England and the United Kingdom. ... A Lipman electrometer is a device for detecting small rushes of electric current. ...

The Cambridge VS4, a popular ECG instrument of the 1970's and 1980's. Solid state technology.

The breakthrough came when Willem Einthoven, working in Leiden, The Netherlands, used the string galvanometer invented by him in 1901, which was much more sensitive than the capillary electrometer that Waller used.^[11] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Willem Einthoven Willem Einthoven (May 21, 1860 – September 29, 1927) was a Dutch doctor and physiologist. ... Leyden redirects here. ... Motto: Je Maintiendrai (Dutch: Ik zal handhaven, English: I Shall Uphold) Anthem: Wilhelmus van Nassouwe Capital Amsterdam1 Largest city Amsterdam Official language(s) Dutch2 Government Parliamentary democracy Constitutional monarchy  - Queen Beatrix  - Prime minister Jan Peter Balkenende Independence Eighty Years War   - Declared July 26, 1581   - Recognised January 30, 1648 (by Spain... The String galvanometer was one of the earliest instruments capable of detecting and recording the very small electrical currents produced by the human heart and provided the first practical Electrocardiogram (ECG). ... 1901 (MCMI) was a common year starting on Tuesday (link will display calendar) of the Gregorian calendar (or a common year starting on Wednesday of the 13-day-slower Julian calendar). ...

Einthoven assigned the letters P, Q, R, S and T to the various deflections, and described the electrocardiographic features of a number of cardiovascular disorders. In 1924, he was awarded the Nobel Prize in Medicine for his discovery.^[12] List of Nobel Prize laureates in Physiology or Medicine from 1901 to the present day. ...

Though the basic principles of that era are still in use today, there have been many advances in electrocardiography over the years. The instrumentation, for example, has evolved from a cumbersome laboratory apparatus to compact electronic systems that often include computerized interpretation of the electrocardiogram.

ECG graph paper

ECG graph paper

A typical electrocardiograph runs at a paper speed of 25 mm/s, although faster paper speeds are occasionally used. Each small block of ECG paper is 1 mm². At a paper speed of 25 mm/s, one small block of ECG paper translates into 0.04 s (or 40 ms). Five small blocks make up 1 large block, which translates into 0.20 s (or 200 ms). Hence, there are 5 large blocks per second. A diagnostic quality 12 lead ECG is calibrated at 10 mm/mV, so 1 mm translates into 0.1 mV. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ...

Filter selection

Modern ECG monitors offer multiple filters for signal processing. The most common settings are monitor mode and diagnostic mode. In monitor mode, the low frequency filter (also called the high-pass filter because signals above the threshold are allowed to pass) is set at either 0.5 Hz or 1 Hz and the high frequency filter (also called the low-pass filter because signals below the threshold are allowed to pass) is set at 40 Hz. This limits artifact for routine cardiac rhythm monitoring. The low frequency (high-pass) filter helps reduce wandering baseline and the high frequency (low pass) filter helps reduce 50 or 60 Hz power line noise (the power line network frequency differs between 50 and 60 Hz in different countries). In diagnostic mode, the low frequency (high pass) filter is set at 0.05 Hz, which allows accurate ST segments to be recorded. The high frequency (low pass) filter is set to 40, 100, or 150 Hz. Consequently, the monitor mode ECG display is more filtered than diagnostic mode, because its bandpass is narrower.^[13] Worldwide, many different mains power systems are found for the operation of household and light commercial electrical appliances and lighting. ...

Leads

Graphic showing the relationship between positive electrodes, depolarization wavefronts (or mean electrical vectors), and complexes displayed on the ECG.

An electrocardiogram is obtained by measuring electrical potential between various points of the body using a biomedical instrumentation amplifier. A lead records the electrical signals of the heart from a particular combination of recording electrodes which are placed at specific points on the patient's body. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Electrical potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential or the electric potential, typically measured in volts. ... Typical instrumentation amplifier schematic An instrumentation amplifier is a type of differential amplifier that has been specifically designed to have characteristics suitable for use in measurement and test equipment. ...

• When a depolarization wavefront (or mean electrical vector) moves toward a positive electrode, it creates a positive deflection on the ECG in the corresponding lead.

• When a depolarization wavefront (or mean electrical vector) moves away from a positive electrode, it creates a negative deflection on the ECG in the corresponding lead.

• When a depolarization wavefront (or mean electrical vector) moves perpendicular to a positive electrode, it creates an equiphasic (or isoelectric) complex on the ECG. It will be positive as the depolarization wavefront (or mean electrical vector) approaches (A), and then become negative as it passes by (B).

There are two types of leads—unipolar and bipolar. The former have an indifferent electrode at the center of the Einthoven’s triangle (which can be likened to a ‘neutral’ of the wall socket) at zero potential. The direction of these leads is from the “center” of the heart radially outward and includes the precordial (chest) leads and limb leads— VL, VR, & VF. The latter, in contrast, have both the electrodes at some potential and the direction of the corresponding electrode is from the electrode at lower potential to the one at higher potential, e.g., in limb lead I, the direction is from left to right. These include the limb leads--I, II, and III.

Note that the colouring scheme for leads varies by country.

Limb

Lead I

Lead II

Leads I, II and III are the so-called limb leads because at one time, the subjects of electrocardiography had to literally place their arms and legs in buckets of salt water in order to obtain signals for Einthoven's string galvanometer. They form the basis of what is known as Einthoven's triangle.[3] Eventually, electrodes were invented that could be placed directly on the patient's skin. Even though the buckets of salt water are no longer necessary, the electrodes are still placed on the patient's arms and legs to approximate the signals obtained with the buckets of salt water. They remain the first three leads of the modern 12 lead ECG. EKG 2: time-strip My heart, my leads applied to my body with my hands, scanned on my scanner and converted to PNG on my computer. ... EKG 2: time-strip My heart, my leads applied to my body with my hands, scanned on my scanner and converted to PNG on my computer. ... EKG lead I My heart, my leads applied to my body with my hands, scanned on my scanner and converted to PNG on my computer. ... EKG lead I My heart, my leads applied to my body with my hands, scanned on my scanner and converted to PNG on my computer. ... Willem Einthoven in 1906 Willem Einthoven (Semarang, May 21, 1860 – Leiden, September 29, 1927) was a Dutch doctor and physiologist. ... The String galvanometer was one of the earliest instruments capable of detecting and recording the very small electrical currents produced by the human heart and provided the first practical Electrocardiogram (ECG). ...

• Lead I is a dipole with the negative (white) electrode on the right arm and the positive (black) electrode on the left arm.
• Lead II is a dipole with the negative (white) electrode on the right arm and the positive (red) electrode on the left leg.
• Lead III is a dipole with the negative electrode (black) on the left arm and the positive (red) electrode on the left leg.

The Earths magnetic field, which is approximately a dipole. ...

Augmented limb

Proper placement of the limb leads.

Leads aVR, aVL, and aVF are augmented limb leads. They are derived from the same three electrodes as leads I, II, and III. However, they view the heart from different angles (or vectors) because the negative electrode for these leads is a modification of Wilson's central terminal, which is derived by adding leads I, II, and III together and plugging them into the negative terminal of the EKG machine. This zeroes out the negative electrode and allows the positive electrode to become the "exploring electrode" or a unipolar lead. This is possible because Einthoven's Law states that I + (-II) + III = 0. The equation can also be written I + III = II. It is written this way (instead of I + II + III = 0) because Einthoven reversed the polarity of lead II in Einthoven's triangle, possibly because he liked to view upright QRS complexes. Wilson's central terminal paved the way for the development of the augmented limb leads aVR, aVL, aVF and the precordial leads V1, V2, V3, V4, V5, and V6. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A vector going from A to B. In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a direction. ...

• Lead aVR or "augmented vector right" has the positive electrode (white) on the right arm. The negative electrode is a combination of the left arm (black) electrode and the left leg (red) electrode, which "augments" the signal strength of the positive electrode on the right arm.
• Lead aVL or "augmented vector left" has the positive (black) electrode on the left arm. The negative electrode is a combination of the right arm (white) electrode and the left leg (red) electrode, which "augments" the signal strength of the positive electrode on the left arm.
• Lead aVF or "augmented vector foot" has the positive (red) electrode on the left leg. The negative electrode is a combination of the right arm (white) electrode and the left arm (black) electrode, which "augments" the signal of the positive electrode on the left leg.

The augmented limb leads aVR, aVL, and aVF are amplified in this way because the signal is too small to be useful when the negative electrode is Wilson's central terminal. Together with leads I, II, and III, augmented limb leads aVR, aVL, and aVF form the basis of the hexaxial reference system, which is used to calculate the heart's electrical axis in the frontal plane. The hexaxial reference system is a diagram that is used to determine the hearts electrical axis in the frontal plane. ...

Precordial

Proper placement of the precordial leads.

The precordial leads V1, V2, V3, V4, V5, and V6 are placed directly on the chest. Because of their close proximity to the heart, they do not require augmentation. Wilson's central terminal is used for the negative electrode, and these leads are considered to be unipolar. The precordial leads view the heart's electrical activity in the so-called horizontal plane. The heart's electrical axis in the horizontal plane is referred to as the Z axis. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Leads V1, V2, and V3 are referred to as the right precordial leads and V4, V5, and V6 are referred to as the left precordial leads.

The QRS complex should be negative in lead V1 and positive in lead V6. The QRS complex should show a gradual transition from negative to positive between leads V2 and V4. The equiphasic lead is referred to as the transition lead. When the transition occurs earlier than lead V3, it is referred to as an early transition. When it occurs later than lead V3, it is referred to as a late transition. There should also be a gradual increase in the amplitude of the R wave between leads V1 and V4. This is known as R wave progression. Poor R wave progression is a nonspecific finding. It can be caused by conduction abnormalities, myocardial infarction, cardiomyopathy, and other pathological conditions.

• Lead V1 is placed in the fourth intercostal space to the right of the sternum.
• Lead V2 is placed in the fourth intercostal space to the left of the sternum.
• Lead V3 is placed directly between leads V2 and V4.
• Lead V4 is placed in the fifth intercostal space in the midclavicular line (even if the apex beat is displaced).
• Lead V5 is placed directly between leads V4 and V6.
• Lead V6 is placed horizontal with V4 in the midaxillary line.

The apex beat is the furthermost point outwards (laterally) and downwards (inferiorly) from the sternum at which the cardiac impulse can be palpated. ...

Ground

An additional electrode (usually green) is present in modern four-lead and twelve-lead ECGs. This is the ground lead and is placed on the right leg by convention, although in theory it can be placed anywhere on the body. With a three-lead ECG, when one dipole is viewed, the remaining lead becomes the ground lead by default.

Waves and intervals

Schematic representation of normal ECG

A typical ECG tracing of a normal heartbeat (or cardiac cycle) consists of a P wave, a QRS complex and a T wave. A small U wave is normally visible in 50 to 75% of ECGs. The baseline voltage of the electrocardiogram is known as the isoelectric line. Typically the isoelectric line is measured as the portion of the tracing following the T wave and preceding the next P wave. Image File history File links SinusRhythmLabels. ... Image File history File links SinusRhythmLabels. ...

Rhythm analysis

There are some basic rules that can be followed to identify a patient's heart rhythm. What is the rate? Is it regular or irregular? Are P waves present? Are QRS complexes present? Is there a 1:1 relationship between P waves and QRS complexes? Is the PR interval constant?

P wave

During normal atrial depolarization, the mean electrical vector is directed from the SA node towards the AV node, and spreads from the right atrium to the left atrium. This turns into the P wave on the ECG, which is upright in II, III, and aVF (since the general electrical activity is going toward the positive electrode in those leads), and inverted in aVR (since it is going away from the positive electrode for that lead). A P wave must be upright in leads II and aVF and inverted in lead aVR to designate a cardiac rhythm as Sinus Rhythm. In anatomy, the atrium (plural: atria) is the blood collection chamber of a heart. ... In anatomy, the atrium (plural: atria) is the blood collection chamber of a heart. ...

• The relationship between P waves and QRS complexes helps distinguish various cardiac arrhythmias.
• The shape and duration of the P waves may indicate atrial enlargement.

Cardiac arrhythmia is a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. ...

PR interval

The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It is usually 120 to 200 ms long. On an ECG tracing, this corresponds to 3 to 5 small boxes.

• A prolonged PR interval may indicate a first degree heart block.
• A short PR interval may indicate a pre-excitation syndrome via an accessory pathway that leads to early activation of the ventricles, such as seen in Wolff-Parkinson-White syndrome.
• A variable PR interval may indicate other types of heart block.
• PR segment depression may indicate atrial injury or pericarditis.
• Variable morphologies of P waves in a single ECG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia

First degree heart block is a disease of the electrical conduction system of the heart. ... Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles of the heart due to an accessory pathway known as the Bundle of Kent. ... A heart block is a disease in the electrical system of the heart. ... Pericarditis is inflammation of the sac surrounding the heart, the pericardium. ... This atrial arrhythmia occurs when the natural cardiac pacemaker site shifts between the SA node, the atria, and/or the AV node. ... Multifocal atrial tachycardia is a cardiac arrhythmia, specifically a type of supraventricular tachycardia. ...

QRS complex

Various QRS complexes with nomenclature.

See also: Electrical conduction system of the heart

The QRS complex is a structure on the ECG that corresponds to the depolarization of the ventricles. Because the ventricles contain more muscle mass than the atria, the QRS complex is larger than the P wave. In addition, because the His/Purkinje system coordinates the depolarization of the ventricles, the QRS complex tends to look "spiked" rather than rounded due to the increase in conduction velocity. A normal QRS complex is 0.06 to 0.10 sec (60 to 100 ms) in duration. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (Cardiac muscle). ...

Not every QRS complex contains a Q wave, an R wave, and an S wave. By convention, any combination of these waves can be referred to as a QRS complex. However, correct interpretation of difficult ECGs requires exact labeling of the various waves. Some authors use lowercase and capital letters, depending on the relative size of each wave. For example, an Rs complex would be positively deflected, while a rS complex would be negatively deflected. If both complexes were labeled RS, it would be impossible to appeciate this distinction without viewing the actual ECG.

• The duration, amplitude, and morphology of the QRS complex is useful in diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, myocardial infarction, electrolyte derangements, and other disease states.

• Q waves can be normal (physiological) or pathological. Normal Q waves, when present, represent depolarization of the interventricular septum. For this reason, they are referred to as septal Q waves, and can be appreciated in the lateral leads I, aVL, V5 and V6.

• Q waves greater than 1/3 the height of the R wave, greater than 0.04 sec (40 ms) in duration, or in the right precordial leads are considered to be abnormal, and may represent myocardial infarction.

Animation of a normal ECG wave.

A cardiac arrhythmia, also called cardiac dysrhythmia, is a disturbance in the regular rhythm of the heartbeat. ... Although ventricular hypertrophy may occur in either the left or right or both ventricles of the heart , left ventricular hypertrophy (LVH) is more commonly encountered. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... Image File history File links Size of this preview: 525 × 600 pixel Image in higher resolution (700 × 800 pixel, file size: 664 KB, MIME type: image/gif) Prinzip der EKG-Darstellung, schnell en: Priniple of ECG formation de: Prinzip der EKG-Darstellung Autor: Kalumet, selbst erstellt, 28. ... Image File history File links Size of this preview: 525 × 600 pixel Image in higher resolution (700 × 800 pixel, file size: 664 KB, MIME type: image/gif) Prinzip der EKG-Darstellung, schnell en: Priniple of ECG formation de: Prinzip der EKG-Darstellung Autor: Kalumet, selbst erstellt, 28. ...

ST segment

See Electrocardiogram in Main article: Myocardial infarction

The ST segment connects the QRS complex and the T wave and has a duration of 0.08 to 0.12 sec (80 to 120 ms). It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the T wave. However, since it is usually difficult to determine exactly where the ST segment ends and the T wave begins, the relationship between the ST segment and T wave should be examined together. The typical ST segment duration is usually around 0.08 sec (80 ms). It should be essentially level with the PR and TP segment. Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ...

• The normal ST segment has a slight upward concavity.
• Flat, downsloping, or depressed ST segments may indicate coronary ischemia.
• ST segment elevation may indicate myocardial infarction. An elevation of >1mm and longer than 80 milliseconds following the J-point. This measure has a false positive rate of 15-20% (which is slightly higher in women than men) and a false negative rate of 20-30%.^[14]

Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... A false positive, also called false alarm, exists when a test reports, incorrectly, that it has found a signal where none exists in reality. ... In statistics, a false negative, also called a Type II error or miss, exists when a test incorrectly reports that a result was not detected, when it was really present. ...

T wave

The T wave represents the repolarization (or recovery) 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). A terahertz (THz) is 1012 hertz or a thousand gigahertz, a measure of frequency. ...

In most leads, the T wave is positive. However, a negative T wave is normal in lead aVR. Lead V1 may have a positive, negative, or biphasic T wave. In addition, it is not uncommon to have an isolated negative T wave in lead III, aVL, or aVF.

• Inverted (or negative) T waves can be a sign of coronary ischemia, Wellens' syndrome, left ventricular hypertrophy, or CNS disorder.
• Tall or "tented" symmetrical T waves may indicate hyperkalemia. Flat T waves may indicate coronary ischemia or hypokalemia.
• The earliest electrocardiographic finding of acute myocardial infarction is sometimes the hyperacute T wave, which can be distinguished from hyperkalemia by the broad base and slight asymmetry.
• When a conduction abnormality (e.g., bundle branch block, paced rhythm) is present, the T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance.

Ischaemic heart disease is a disease characterized by reduced blood supply to the heart. ... Left ventricular hypertrophy (LVH) is the abnormal thickening of the myocardium (muscle) of the left ventricle of the heart. ... A diagram showing the CNS: 1. ... Hyperkalemia is an elevated blood level (above 5. ... Hypokalemia is a potentially fatal condition in which the body fails to retain sufficient potassium to maintain health. ... Hyperkalemia is an elevated blood level (above 5. ...

QT interval

See main article: QT interval

The QT interval is measured from the beginning of the QRS complex to the end of the T wave. A normal QT interval is usually about 0.40 seconds. The QT interval as well as the corrected QT interval are important in the diagnosis of long QT syndrome and short QT syndrome. The QT interval varies based on the heart rate, and various correction factors have been developed to correct the QT interval for the heart rate. Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled. ... Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled. ... The long QT syndrome (LQTS) is a heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. ... Short QT syndrome is a genetic disease of the electrical system of the heart. ...

The most commonly used method for correcting the QT interval for rate is the one formulated by Bazett and published in 1920.^[15] Bazett's formula is , where QTc is the QT interval corrected for rate, and RR is the interval from the onset of one QRS complex to the onset of the next QRS complex, measured in seconds. However, this formula tends to be inaccurate, and over-corrects at high heart rates and under-corrects at low heart rates. 1920 (MCMXX) was a leap year starting on Thursday. ... In medicine, specifically cardiology, the study of the heart, the QT interval is a measure of the time between the start of the Q wave and the end of the T wave in the hearts electrical cycle. ...

U wave

The U wave is not always seen. It is typically small, and, by definition, follows the T wave. U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers. Prominent U waves are most often seen in hypokalemia, but may be present in hypercalcemia, thyrotoxicosis, or exposure to digitalis, epinephrine, and Class 1A and 3 antiarrhythmics, as well as in congenital long QT syndrome and in the setting of intracranial hemorrhage. An inverted U wave may represent myocardial ischemia or left ventricular volume overload.^[16] Papillary muscles: attached to chordae tendineae, their function is to open and close both the bicuspid and the tricuspid valves, which are located between the atrias and their respective ventricles. ... Purkinje fibers (or Purkyne tissue) are located in the inner ventricular walls of the heart, just beneath the endocardium. ... Hypokalemia is a potentially fatal condition in which the body fails to retain sufficient potassium to maintain health. ... Hypercalcaemia is an elevated calcium level in the blood. ... Hyperthyroidism (thyrotoxicosis or fast thyroid gland) is the clinical syndrome caused by an excess of circulating free thyroxine (T4) and free triiodothyronine (T3), or both. ... Species About 20 species, including: Digitalis cariensis Digitalis ciliata Digitalis davisiana Digitalis dubia Digitalis ferruginea Digitalis grandiflora Digitalis laevigata Digitalis lanata Digitalis leucophaea Digitalis lutea Digitalis obscura Digitalis parviflora Digitalis purpurea Digitalis thapsi Digitalis trojana Digitalis viridiflora Digitalis is a genus of about 20 species of herbaceous biennials, perennials and... Adrenaline redirects here. ... Antiarrhythmic agents are a group of pharmaceuticals that are used to suppress fast rhythms of the heart (cardiac arrhythmias), such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation. ... The long QT syndrome (LQTS) is a heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. ...

Clinical lead groups

Diagram showing the contiguous leads in the same color

See Electrocardiogram in Main article: Myocardial infarction

There are twelve leads in total, each recording the electrical activity of the heart from a different perspective, which also correlate to different anatomical areas of the heart for the purpose of identifying acute coronary ischemia or injury. Two leads that look at the same anatomical area of the heart are said to be contiguous (see color coded chart). Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ...

• The inferior leads (leads II, III and aVF) look at electrical activity from the vantage point of the inferior (or diaphragmatic) wall of the left ventricle.
• The lateral leads (I, aVL, V₅ and V₆) look at the electrical activity from the vantage point of the lateral wall of left ventricle. Because the positive electrode for leads I and aVL are located on the left shoulder, leads I and aVL are sometimes referred to as the high lateral leads. Because the positive electrodes for leads V5 and V6 are on the patient's chest, they are sometimes referred to as the low lateral leads.
• The septal leads, V₁ and V₂ look at electrical activity from the vantage point of the septal wall of the left ventricle. They are often grouped together with the anterior leads.
• The anterior leads, V₃ and V₄ look at electrical activity from the vantage point of the anterior wall of the left ventricle.
• In addition, any two precordial leads that are next to one another are considered to be contiguous. For example, even though V4 is an anterior lead and V5 is a lateral lead, they are contiguous because they are next to one another.
• Lead aVR offers no specific view of the left ventricle. Rather, it views the inside of the endocardial wall from its perspective on the right shoulder.

The anatomical planes The anatomical position is a schematic convention for describing the relative morphology of the human body. ... In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ... The term lateral can refer to: an anatomical definition of direction. ... In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ... In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ...

Axis

Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the heart's electrical axis in the frontal plane.

The heart's electrical axis refers to the general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane. It is usually oriented in a right shoulder to left leg direction, which corresponds to the left inferior quadrant of the hexaxial reference system, although -30^o to +90^o is considered to be normal. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The hexaxial reference system is a diagram that is used to determine the hearts electrical axis in the frontal plane. ...

• Left axis deviation (-30^o to -90^o) may indicate left anterior fascicular block or Q waves from inferior MI.
• Right axis deviation (+90^o to +180^o) may indicate left posterior fascicular block, Q waves from high lateral MI, or a right ventricular strain pattern.
• In the setting of right bundle branch block, right or left axis deviation may indicate bifascicular block.

Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ... Right bundle branch block (RBBB) is a cardiac conduction abnormality seen on electrocardiogram (EKG). ... Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked. ...

Representation in culture

The ECG has become so familiar to the general population that it is part of the logo of many medical organizations, representing the technical side of medicine vs. the Rod of Asclepius or caduceus, which are more traditional. Being an electrical representation, it signifies vitality and urgency. The Rod of Asclepius is an ancient Greek symbol associated with medicine. ... The Caduceus Two caduceuses without wings as decoration of door portal in Ztracená street in Olomouc (Czech Republic). ...

In various television medical dramas, an isoelectric ECG (no cardiac electrical activity, also known as flatline) is often used as a symbol of death or at least extreme medical peril. This is technically known as asystole, a form of cardiac arrest with a particularly bad prognosis. Though sometimes shown on television, defibrillation, which can be used to correct arrythmias such as ventricular fibrillation and pulseless ventricular tachycardia, does not correct asystole and is not an indicated therapy. The term flatline is usually used to describe an electrical measurement that shows no activity and therefore when represented, shows a flat line instead of a moving one. ... In medicine, asystole is a state of no cardiac electrical activity, hence no contractions of the myocardium and no cardiac output or blood flow. ... Typical view of the defibrillator operator. ...

The Digital Imperative

Recent regulatory developments have thrust cardiac safety to the forefront of clinical development due to the fact that QT effects of new drugs is now the most common cause of drug withdrawal from the market and delays in or lack of regulatory approval for marketing. The resultant "Digital ECG Imperative for Cardiac Safety" requires innovative strategies on the part of both drug development organizations and ECG services providers.

On November 15, 2002, the FDA and Health Canada published regulatory guidance in the form of a concept paper entitled The Clinical Evaluation of QT/QTc Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic Drugs, which was reviewed and discussed on January 13-14, 2003.

Overall, the new regulatory guidance on ECGs in clinical research will require more robust and uniform cardiac safety assessments across virtually all segments of the drug development industry. It will drive increased reliance on ECG core laboratories. In turn, such laboratories will need to respond with not only increased capacity and capability, but also an enhancement of methodologies employed. While scientific expertise will remain of prime importance, core ECG laboratories will need to demonstrate mastery in new core competencies of a technical and logistical nature.

See also

• Advanced cardiac life support (ACLS)
• Ballistocardiograph
• Cardiac cycle
• EKG tech
• Electrical conduction system of the heart
• Electroencephalography
• Electrogastrogram
• Electroretinography
• Heart rate monitor
• Holter monitor
• Myocardial infarction

Advanced cardiac life support or (ACLS) refers to a set of clinical interventions for the urgent treatment of cardiac arrest and other life threatening medical emergencies, as well as the knowledge and skills to deploy those interventions. ... Ballistocardiograph or BCG detects and measures recoil of the human body due to the momentum of the blood that the heart is currently pumping. ... Cardiac cycle is the term used to describe the sequence of events that occur as a heart works to pump blood through the body. ... An EKG tech (short for electrocardiogram technician) is a member of the health care team whose primary duty is the performance of EKGs on patients. ... The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (Cardiac muscle). ... Girl wearing electrodes for electroencephalography Person wearing electrodes for electroencephalography Portable recording device for electroencephalography Electroencephalography is the neurophysiologic measurement of the electrical activity of the brain by recording from electrodes placed on the scalp or, in special cases, subdurally or in the cerebral cortex. ... An electrogastrogram (EGG) is similar in principle to an electrocardiogram (ECG) in that sensors on the skin detect electrical signals indicative of muscular activity within. ... Electroretinography, is used to measure the electrical responses of various cell types in the retina, including the light-sensitive cells (rods and cones) and the ganglion cells. ... Photo of a heart rate monitor (made by Polar) showing chest strap and watch Photo of a Prevention MF-180 strapless heart rate monitor This article refers to a device used by laypersons. ... Holter monitor In medicine, a Holter monitor (also called an ambulatory electrocardiography device), named after its inventor, Dr. Norman J. Holter, is a portable device for continuously monitoring the electrical activity of the heart for 24 hours or more. ... Acute myocardial infarction (AMI or MI), more commonly known as a heart attack, is a disease state that occurs when the blood supply to a part of the heart is interrupted. ...

References

External links

• The whole ECG - A really basic ECG primer
• 12-lead ECG library
• Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
• ECG information from Children's Hospital Heart Center, Seattle.
• ECG Challenge from the ACC D2B Initiative
• ECG simulator
• National Heart, Lung, and Blood Institute, Diseases and Conditions Index
• Digital Imperative
• A summarized extensive history of electrocardiography
• Interpretation of electrocardiograms in infants and children.