Difference Between Repolarization and Depolarization in Ekg Readings

Exam of the middle'southward electric action

Electrocardiography
ECG of a heart in normal sinus rhythm
ICD-x-PCS	R94.31
ICD-9-CM	89.52
MeSH	D004562
MedlinePlus	003868
[edit on Wikidata]

Electrocardiography is the process of producing an electrocardiogram (ECG or EKG ^[a]), a recording of the centre's electrical activity.^[four] Information technology is an electrogram of the middle which is a graph of voltage versus time of the electrical action of the center^[five] using electrodes placed on the pare. These electrodes detect the pocket-size electrical changes that are a issue of cardiac musculus depolarization followed by repolarization during each cardiac bicycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances (such as atrial fibrillation^[vi] and ventricular tachycardia^[7]), inadequate coronary artery claret flow (such as myocardial ischemia^[viii] and myocardial infarction^[9]), and electrolyte disturbances (such as hypokalemia^[x] and hyperkalemia^[11]).

Traditionally, "ECG" normally means a 12-lead ECG taken while lying down as discussed below. However, other devices tin can record the electrical activity of the centre such every bit a Holter monitor but also some models of smartwatch are capable of recording an ECG. ECG signals tin can exist recorded in other contexts with other devices.

In a conventional 12-lead ECG, x electrodes are placed on the patient's limbs and on the surface of the chest. The overall magnitude of the middle's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (normally 10 seconds). In this way, the overall magnitude and direction of the heart's electric depolarization is captured at each moment throughout the cardiac cycle.^[12]

There are three principal components to an ECG: the P wave, which represents depolarization of the atria; the QRS complex, which represents depolarization of the ventricles; and the T wave, which represents repolarization of the ventricles.^[thirteen]

During each heartbeat, a healthy heart has an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads throughout the atrium, and passes through the atrioventricular node downwardly into the package of His and into the Purkinje fibers, spreading down and to the left throughout the ventricles.^[xiii] This orderly pattern of depolarization gives rise to the characteristic ECG tracing. To the trained clinician, an ECG conveys a large amount of information about the structure of the heart and the part of its electrical conduction system.^[14] Amidst other things, an ECG tin can exist used to measure out the charge per unit and rhythm of heartbeats, the size and position of the heart chambers, the presence of whatsoever damage to the heart's musculus cells or conduction organization, the effects of heart drugs, and the function of implanted pacemakers.^[15]

Medical uses [edit]

The overall goal of performing an ECG is to obtain data about the electric functioning of the heart. Medical uses for this information are varied and ofttimes need to exist combined with knowledge of the structure of the heart and physical exam signs to be interpreted. Some indications for performing an ECG include the following:

• Chest pain or suspected myocardial infarction (heart attack), such every bit ST elevated myocardial infarction (STEMI)^[16] or non-ST elevated myocardial infarction (NSTEMI)^[17]
• Symptoms such as shortness of breath, murmurs,^[18] fainting, seizures, funny turns, or arrhythmias including new onset palpitations or monitoring of known cardiac arrhythmias
• Medication monitoring (e.grand., drug-induced QT prolongation, Digoxin toxicity) and management of overdose (eastward.grand., tricyclic overdose)
• Electrolyte abnormalities, such equally hyperkalemia
• Perioperative monitoring in which any form of anesthesia is involved (e.chiliad., monitored anesthesia care, general anesthesia). This includes preoperative assessment and intraoperative and postoperative monitoring.
• Cardiac stress testing
• Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) of the heart (ECG is used to "gate" the scanning then that the anatomical position of the centre is steady)
• Clinical cardiac electrophysiology, in which a catheter is inserted through the femoral vein and tin take several electrodes along its length to tape the direction of electrical activity from within the heart.

ECGs can be recorded every bit short intermittent tracings or continuous ECG monitoring. Continuous monitoring is used for critically ill patients, patients undergoing general anesthesia,^{[19] [18]} and patients who have an infrequently occurring cardiac arrhythmia that would unlikely exist seen on a conventional x-second ECG. Continuous monitoring can be conducted by using Holter monitors, internal and external defibrillators and pacemakers, and/or biotelemetry.^[20]

Screening [edit]

A patient undergoing an ECG

Prove does not support the apply of ECGs among those without symptoms or at low run a risk of cardiovascular affliction equally an effort for prevention.^{[21] [22] [23]} This is considering an ECG may falsely bespeak the beingness of a problem, leading to misdiagnosis, the recommendation of invasive procedures, and overtreatment. Still, persons employed in certain critical occupations, such as shipping pilots,^[24] may be required to have an ECG as part of their routine wellness evaluations. Hypertrophic cardiomyopathy screening may as well exist considered in adolescents as part of a sports physical out of concern for sudden cardiac death.^{[ citation needed ]}

Electrocardiograph machines [edit]

Electrocardiograms are recorded by machines that consist of a gear up of electrodes connected to a fundamental unit.^[25] Early on ECG machines were synthetic with analog electronics, where the betoken drove a motor to impress out the signal onto paper. Today, electrocardiographs use analog-to-digital converters to convert the electrical activeness of the center to a digital signal. Many ECG machines are now portable and ordinarily include a screen, keyboard, and printer on a minor wheeled cart. Recent advancements in electrocardiography include developing even smaller devices for inclusion in fitness trackers and smart watches.^[26] These smaller devices oftentimes rely on only 2 electrodes to deliver a unmarried lead I.^[27] Portable half dozen-lead devices are also bachelor.

Recording an ECG is a safe and painless procedure.^[28] The machines are powered by mains power merely they are designed with several safety features including an earthed (ground) atomic number 82. Other features include:

• Defibrillation protection: whatsoever ECG used in healthcare may exist attached to a person who requires defibrillation and the ECG needs to protect itself from this source of energy.
• Electrostatic discharge is similar to defibrillation discharge and requires voltage protection up to xviii,000 volts.
• Additionally, circuitry chosen the right leg driver can be used to reduce mutual-fashion interference (typically the 50 or 60 Hz mains ability).
• ECG voltages measured beyond the body are very modest. This low voltage necessitates a depression racket circuit, instrumentation amplifiers, and electromagnetic shielding.
• Simultaneous lead recordings: earlier designs recorded each lead sequentially, only electric current models record multiple leads simultaneously.

Almost modern ECG machines include automated interpretation algorithms. This analysis calculates features such as the PR interval, QT interval, corrected QT (QTc) interval, PR centrality, QRS centrality, rhythm and more. The results from these automatic algorithms are considered "preliminary" until verified and/or modified by practiced interpretation. Despite recent advances, reckoner misinterpretation remains a significant problem and can result in clinical mismanagement.^[29]

Cardiac monitors [edit]

Besides the standard electrocardiograph motorcar, there are other devices capable of recording ECG signals. Portable devices have existed since the Holter monitor was produced in 1962. Traditionally, these monitors accept used electrodes with patches on the peel to record the ECG, merely new devices can stick to the chest as a single patch without demand for wires. Implantable devices such equally the artificial cardiac pacemaker and implantable cardioverter-defibrillator are capable of measuring a "far field" signal between the leads in the eye and the implanted bombardment/generator that resembles an ECG point (technically, the signal recorded in the heart is called an electrogram, which is interpreted differently). Advocacy of the Holter monitor became the implantable loop recorder that performs the same role merely in an implantable device with batteries that concluding on the order of years. Additionally, smartwatch devices are capable of recording an ECG point as well, such as with the quaternary generation Apple Sentry.

Electrodes and leads [edit]

Proper placement of the limb electrodes. The limb electrodes can exist far down on the limbs or close to the hips/shoulders as long every bit they are placed symmetrically.^[30]

Placement of the precordial electrodes

Electrodes are the bodily conductive pads attached to the body surface.^[31] Any pair of electrodes tin measure the electric potential divergence between the two corresponding locations of attachment. Such a pair forms a atomic number 82. Even so, "leads" can besides exist formed between a physical electrode and a virtual electrode, known equally Wilson's fundamental concluding (WCT), whose potential is defined as the average potential measured by three limb electrodes that are attached to the right arm, the left arm, and the left foot, respectively.^{[ citation needed ]}

Commonly, 10 electrodes attached to the body are used to grade 12 ECG leads, with each atomic number 82 measuring a specific electrical potential difference (equally listed in the table below).^[32]

Leads are broken downward into three types: limb; augmented limb; and precordial or chest. The 12-lead ECG has a total of three limb leads and three augmented limb leads bundled like spokes of a wheel in the coronal plane (vertical), and half-dozen precordial leads or breast leads that lie on the perpendicular transverse plane (horizontal).^[33]

In medical settings, the term leads is also sometimes used to refer to the electrodes themselves, although this is technically incorrect.^{[ commendation needed ]}

The x electrodes in a 12-lead ECG are listed below.^[34]

Electrode name	Electrode placement
RA	On the right arm, avoiding thick muscle.
LA	In the same location where RA was placed, but on the left arm.
RL	On the right leg, lower stop of inner attribute of calf musculus. (Avoid bony prominences)
LL	In the same location where RL was placed, only on the left leg.
Vone	In the 4th intercostal space (between ribs four and 5) just to the right of the sternum (breastbone)
Vii	In the 4th intercostal space (between ribs 4 and v) but to the left of the sternum.
Five3	Between leads Fiveii and V4.
Five4	In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line.
Fivefive	Horizontally even with 5iv, in the left inductive axillary line.
V6	Horizontally even with Five4 and V5 in the mid-axillary line.

Ii types of electrodes in common use are a flat paper-sparse sticker and a self-agglutinative round pad. The former are typically used in a unmarried ECG recording while the latter are for continuous recordings as they stick longer. Each electrode consists of an electrically conductive electrolyte gel and a silver/silver chloride conductor.^[35] The gel typically contains potassium chloride – sometimes silverish chloride too – to allow electron conduction from the pare to the wire and to the electrocardiogram.^{[ citation needed ]}

The common virtual electrode, known as Wilson's central terminal (V_W), is produced by averaging the measurements from the electrodes RA, LA, and LL to give an boilerplate potential of the body:

${\displaystyle V_{West}={\frac {one}{3}}(RA+LA+LL)}$

In a 12-lead ECG, all leads except the limb leads are assumed to be unipolar (aVR, aVL, aVF, V₁, V_ii, V₃, Five₄, V₅, and V_half-dozen). The measurement of a voltage requires two contacts and so, electrically, the unipolar leads are measured from the mutual lead (negative) and the unipolar lead (positive). This averaging for the common lead and the abstruse unipolar lead concept makes for a more challenging understanding and is complicated by sloppy usage of "lead" and "electrode". In fact, instead of beingness a constant reference, V_W has a value that fluctuates throughout the middle cycle. It also does not truly represent the center-of-heart potential due to the body parts the signals travel through.^[36]

Limb leads [edit]

The limb leads and augmented limb leads (Wilson's key last is used as the negative pole for the latter in this representation)

Leads I, Ii and Three are chosen the limb leads. The electrodes that grade these signals are located on the limbs – 1 on each arm and 1 on the left leg.^{[37] [38] [39]} The limb leads class the points of what is known equally Einthoven's triangle.^[40]

• Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode:

${\displaystyle I=LA-RA}$

• Lead Ii is the voltage between the (positive) left leg (LL) electrode and the right arm (RA) electrode:

${\displaystyle Ii=LL-RA}$

• Atomic number 82 III is the voltage betwixt the (positive) left leg (LL) electrode and the left arm (LA) electrode:

${\displaystyle III=LL-LA}$

Augmented limb leads [edit]

Leads aVR, aVL, and aVF are the augmented limb leads. They are derived from the aforementioned three electrodes equally leads I, II, and Three, simply they use Goldberger's central terminal as their negative pole. Goldberger'southward key terminal is a combination of inputs from two limb electrodes, with a different combination for each augmented lead. It is referred to immediately below as "the negative pole".

• Lead augmented vector right (aVR) has the positive electrode on the right arm. The negative pole is a combination of the left arm electrode and the left leg electrode:

${\displaystyle aVR=RA-{\frac {1}{two}}(LA+LL)={\frac {iii}{2}}(RA-V_{W})}$

• Lead augmented vector left (aVL) has the positive electrode on the left arm. The negative pole is a combination of the right arm electrode and the left leg electrode:

${\displaystyle aVL=LA-{\frac {ane}{2}}(RA+LL)={\frac {three}{ii}}(LA-V_{Due west})}$

• Lead augmented vector foot (aVF) has the positive electrode on the left leg. The negative pole is a combination of the correct arm electrode and the left arm electrode:

${\displaystyle aVF=LL-{\frac {1}{ii}}(RA+LA)={\frac {3}{two}}(LL-V_{W})}$

Together with leads I, 2, and III, augmented limb leads aVR, aVL, and aVF class the basis of the hexaxial reference organisation, which is used to calculate the heart's electrical axis in the frontal plane.^{[ citation needed ]}

Older versions of the nodes (VR, VL, VF) use Wilson's central concluding as the negative pole, but the aamplitude is also small for the thick lines of old ECG machines. The Goldberger terminals calibration up (augments) the Wilson results by 50%, at the cost of sacrificing physical correctness past not having the aforementioned negative pole for all three.^[41]

Precordial leads [edit]

The precordial leads lie in the transverse (horizontal) plane, perpendicular to the other six leads. The half dozen precordial electrodes human activity as the positive poles for the six respective precordial leads: (V₁, V₂, 5₃, V₄, V₅, and V_{half dozen}). Wilson's central last is used as the negative pole. Recently, unipolar precordial leads have been used to create bipolar precordial leads that explore the correct to left axis in the horizontal airplane.^[42]

Specialized leads [edit]

Additional electrodes may rarely be placed to generate other leads for specific diagnostic purposes. Right-sided precordial leads may be used to ameliorate study pathology of the right ventricle or for dextrocardia (and are denoted with an R (due east.g., V_5R). Posterior leads (V_seven to V₉) may exist used to demonstrate the presence of a posterior myocardial infarction. The Lewis lead or S5-atomic number 82 (requiring an electrode at the correct sternal border in the second intercostal infinite) can be used to better detect atrial activity in relation to that of the ventricles. ^[43]

An esophogeal atomic number 82 tin can exist inserted to a function of the esophagus where the distance to the posterior wall of the left atrium is only approximately 5–vi mm (remaining constant in people of dissimilar historic period and weight).^[44] An esophageal lead avails for a more than authentic differentiation between certain cardiac arrhythmias, particularly atrial flutter, AV nodal reentrant tachycardia and orthodromic atrioventricular reentrant tachycardia.^[45] Information technology can too evaluate the adventure in people with Wolff-Parkinson-White syndrome, as well as terminate supraventricular tachycardia caused by re-entry.^[45]

An intracardiac electrogram (ICEG) is essentially an ECG with some added intracardiac leads (that is, inside the heart). The standard ECG leads (external leads) are I, Ii, Three, aVL, V_ane, and V_six. Two to four intracardiac leads are added via cardiac catheterization. The give-and-take "electrogram" (EGM) without further specification normally means an intracardiac electrogram.^{[ citation needed ]}

Atomic number 82 locations on an ECG written report [edit]

A standard 12-lead ECG report (an electrocardiograph) shows a two.v second tracing of each of the twelve leads. The tracings are most ordinarily arranged in a grid of four columns and 3 rows. The starting time column is the limb leads (I, II, and Iii), the second column is the augmented limb leads (aVR, aVL, and aVF), and the last two columns are the precordial leads (Five₁ to V₆). Additionally, a rhythm strip may be included as a fourth or fifth row.^{[ citation needed ]}

The timing across the page is continuous and not tracings of the 12 leads for the same time catamenia. In other words, if the output were traced past needles on paper, each row would switch which leads as the paper is pulled nether the needle. For example, the top row would first trace lead I, then switch to lead aVR, then switch to V_ane, and so switch to V₄, and so none of these iv tracings of the leads are from the same time period as they are traced in sequence through fourth dimension.^{[ commendation needed ]}

Contiguity of leads [edit]

Diagram showing the contiguous leads in the same colour in the standard 12-lead layout

Each of the 12 ECG leads records the electric activity of the heart from a different bending, and therefore align with dissimilar anatomical areas of the centre. Two leads that look at neighboring anatomical areas are said to be face-to-face.^{[ citation needed ]}

Category	Leads	Activity
Inferior leads	Leads 2, III and aVF	Look at electric activity from the vantage bespeak of the inferior surface (diaphragmatic surface of middle)
Lateral leads	I, aVL, 55 and V6	Wait at the electrical activity from the vantage signal of the lateral wall of left ventricle
Septal leads	Vi and Five2	Await at electric activity from the vantage point of the septal surface of the heart (interventricular septum)
Anterior leads	V3 and Five4	Look at electrical activity from the vantage bespeak of the inductive wall of the right and left ventricles (Sternocostal surface of center)

In addition, any two precordial leads next to one another are considered to be contiguous. For instance, though V_four is an anterior lead and V₅ is a lateral lead, they are face-to-face considering they are side by side to 1 another.

Electrophysiology [edit]

The written report of the conduction system of the middle is called cardiac electrophysiology (EP). An EP study is performed via a right-sided cardiac catheterization: a wire with an electrode at its tip is inserted into the right middle chambers from a peripheral vein, and placed in various positions in close proximity to the conduction system so that the electric activeness of that system tin can be recorded.^{[ citation needed ]} Standard catheter positions for an EP study include "loftier correct atrium" or hRA near the sinus node, a "His" across the septal wall of the tricuspid valve to measure parcel of His, a "coronary sinus" into the coronary sinus, and a "right ventricle" in the apex of the right ventricle.

Estimation [edit]

Estimation of the ECG is fundamentally about understanding the electrical conduction system of the middle. Normal conduction starts and propagates in a anticipated pattern, and deviation from this design can be a normal variation or be pathological. An ECG does not equate with mechanical pumping activity of the heart, for instance, pulseless electric activity produces an ECG that should pump blood but no pulses are felt (and constitutes a medical emergency and CPR should exist performed). Ventricular fibrillation produces an ECG but is too dysfunctional to produce a life-sustaining cardiac output. Certain rhythms are known to have skillful cardiac output and some are known to have bad cardiac output. Ultimately, an echocardiogram or other anatomical imaging modality is useful in assessing the mechanical role of the heart.^{[ citation needed ]}

Like all medical tests, what constitutes "normal" is based on population studies. The heartrate range of between 60 and 100 beats per infinitesimal (bpm) is considered normal since information shows this to be the usual resting heart rate.^{[ citation needed ]}

Theory [edit]

QRS is upright in a lead when its axis is aligned with that lead'due south vector

Schematic representation of a normal ECG

Estimation of the ECG is ultimately that of design recognition. In society to sympathise the patterns found, it is helpful to understand the theory of what ECGs stand for. The theory is rooted in electromagnetics and boils down to the iv following points:^{[ citation needed ]}

• depolarization of the middle towards the positive electrode produces a positive deflection
• depolarization of the centre abroad from the positive electrode produces a negative deflection
• repolarization of the heart towards the positive electrode produces a negative deflection
• repolarization of the heart away from the positive electrode produces a positive deflection

Thus, the overall direction of depolarization and repolarization produces positive or negative deflection on each lead'southward trace. For case, depolarizing from right to left would produce a positive deflection in pb I considering the ii vectors point in the same direction. In contrast, that same depolarization would produce minimal deflection in V₁ and V₂ considering the vectors are perpendicular, and this phenomenon is called isoelectric.

Normal rhythm produces iv entities – a P wave, a QRS complex, a T wave, and a U wave – that each take a fairly unique pattern.

• The P wave represents atrial depolarization.
• The QRS complex represents ventricular depolarization.
• The T wave represents ventricular repolarization.
• The U wave represents papillary muscle repolarization.

Changes in the structure of the heart and its environment (including blood composition) modify the patterns of these four entities.

The U moving ridge is not typically seen and its absence is generally ignored. Atrial repolarisation is typically subconscious in the much more prominent QRS complex and ordinarily cannot be seen without boosted, specialised electrodes.

Groundwork filigree [edit]

ECGs are normally printed on a grid. The horizontal centrality represents time and the vertical axis represents voltage. The standard values on this grid are shown in the adjacent prototype at 25mm/sec:^{[ citation needed ]}

• A small box is 1 mm × 1 mm and represents 0.1 mV × 0.04 seconds.
• A large box is five mm × 5 mm and represents 0.5 mV × 0.20 seconds.

The "big" box is represented past a heavier line weight than the small-scale boxes.

The standard press speed in the The states is 25 mm per sec (5 big boxes per 2d), but in other countries information technology can exist fifty mm per sec. Faster speeds such as 100 and 200 mm per sec are used during electrophysiology studies.

Not all aspects of an ECG rely on precise recordings or having a known scaling of amplitude or fourth dimension. For example, determining if the tracing is a sinus rhythm simply requires feature recognition and matching, and non measurement of amplitudes or times (i.e., the scale of the grids are irrelevant). An example to the contrary, the voltage requirements of left ventricular hypertrophy require knowing the filigree scale.

Charge per unit and rhythm [edit]

In a normal heart, the centre rate is the rate in which the sinoatrial node depolarizes since information technology is the source of depolarization of the heart. Centre rate, similar other vital signs such as blood pressure and respiratory rate, modify with age. In adults, a normal heart rate is between sixty and 100 bpm (normocardic), whereas it is college in children. A middle rate below normal is called "bradycardia" (<lx in adults) and higher up normal is called "tachycardia" (>100 in adults). A complexity of this is when the atria and ventricles are non in synchrony and the "centre rate" must be specified as atrial or ventricular (e.thousand., the ventricular rate in ventricular fibrillation is 300–600 bpm, whereas the atrial rate tin be normal [60–100] or faster [100–150]).^{[ citation needed ]}

In normal resting hearts, the physiologic rhythm of the heart is normal sinus rhythm (NSR). Normal sinus rhythm produces the prototypical pattern of P wave, QRS complex, and T wave. Mostly, difference from normal sinus rhythm is considered a cardiac arrhythmia. Thus, the first question in interpreting an ECG is whether or not there is a sinus rhythm. A criterion for sinus rhythm is that P waves and QRS complexes appear i-to-1, thus implying that the P wave causes the QRS complex.^{[ citation needed ]}

Once sinus rhythm is established, or not, the second question is the rate. For a sinus rhythm, this is either the rate of P waves or QRS complexes since they are i-to-one. If the rate is also fast, so it is sinus tachycardia, and if information technology is too slow, then information technology is sinus bradycardia.

If it is non a sinus rhythm, so determining the rhythm is necessary before proceeding with further interpretation. Some arrhythmias with characteristic findings:

• Absent-minded P waves with "irregularly irregular" QRS complexes is the hallmark of atrial fibrillation.
• A "saw molar" design with QRS complexes is the authentication of atrial flutter.
• A sine wave pattern is the hallmark of ventricular flutter.
• Absent P waves with broad QRS complexes and a fast heart rate is ventricular tachycardia.

Decision of charge per unit and rhythm is necessary in order to make sense of further interpretation.

Axis [edit]

The heart has several axes, but the most common by far is the axis of the QRS circuitous (references to "the axis" imply the QRS axis). Each centrality tin exist computationally determined to upshot in a number representing degrees of deviation from zero, or it can exist categorized into a few types.^{[ citation needed ]}

The QRS axis is the full general direction of the ventricular depolarization wavefront (or mean electrical vector) in the frontal plane. It is oft sufficient to allocate the axis every bit one of iii types: normal, left deviated, or right deviated. Population data shows that a normal QRS centrality is from −30° to 105°, with 0° being along lead I and positive beingness inferior and negative existence superior (best understood graphically equally the hexaxial reference system).^[46] Across +105° is right axis deviation and across −thirty° is left axis difference (the third quadrant of −xc° to −180° is very rare and is an indeterminate axis). A shortcut for determining if the QRS axis is normal is if the QRS complex is mostly positive in atomic number 82 I and lead Ii (or pb I and aVF if +xc° is the upper limit of normal).^{[ citation needed ]}

The normal QRS axis is generally down and to the left, following the anatomical orientation of the heart inside the breast. An abnormal centrality suggests a change in the physical shape and orientation of the center or a defect in its conduction arrangement that causes the ventricles to depolarize in an abnormal way.^{[ citation needed ]}

Classification	Angle	Notes
Normal	−30° to 105°	Normal
Left centrality difference	−xxx° to −90°	May betoken left ventricular hypertrophy, left anterior fascicular cake, or an old junior STEMI
Right axis deviation	+105° to +180°	May indicate correct ventricular hypertrophy, left posterior fascicular block, or an old lateral STEMI
Indeterminate axis	+180° to −90°	Rarely seen; considered an 'electric no-human being's land'

The extent of a normal centrality can be +ninety° or 105° depending on the source.

Amplitudes and intervals [edit]

Animation of a normal ECG wave

All of the waves on an ECG tracing and the intervals between them have a predictable time duration, a range of acceptable amplitudes (voltages), and a typical morphology. Any deviation from the normal tracing is potentially pathological and therefore of clinical significance.^{[ citation needed ]}

For ease of measuring the amplitudes and intervals, an ECG is printed on graph paper at a standard scale: each ane mm (ane small box on the standard ECG newspaper) represents xl milliseconds of time on the x-centrality, and 0.1 millivolts on the y-axis.^{[ commendation needed ]}

Characteristic	Description	Pathology	Duration
P wave	The P wave represents depolarization of the atria. Atrial depolarization spreads from the SA node towards the AV node, and from the correct atrium to the left atrium.	The P wave is typically upright in most leads except for aVR; an unusual P moving ridge axis (inverted in other leads) tin can point an ectopic atrial pacemaker. If the P wave is of unusually long duration, it may represent atrial enlargement. Typically a large right atrium gives a tall, peaked P wave while a big left atrium gives a two-humped bifid P wave.	<80 ms
PR interval	The PR interval is measured from the start of the P moving ridge to the start of the QRS complex. This interval reflects the time the electrical impulse takes to travel from the sinus node through the AV node.	A PR interval shorter than 120 ms suggests that the electrical impulse is bypassing the AV node, as in Wolf-Parkinson-White syndrome. A PR interval consistently longer than 200 ms diagnoses first caste atrioventricular block. The PR segment (the portion of the tracing after the P wave and before the QRS circuitous) is typically completely flat, but may be depressed in pericarditis.	120 to 200 ms
QRS complex	The QRS circuitous represents the rapid depolarization of the correct and left ventricles. The ventricles have a big muscle mass compared to the atria, so the QRS complex usually has a much larger amplitude than the P moving ridge.	If the QRS complex is wide (longer than 120 ms) it suggests disruption of the heart's conduction system, such as in LBBB, RBBB, or ventricular rhythms such as ventricular tachycardia. Metabolic issues such as severe hyperkalemia, or tricyclic antidepressant overdose can also widen the QRS circuitous. An unusually tall QRS circuitous may stand for left ventricular hypertrophy while a very low-aamplitude QRS complex may stand for a pericardial effusion or infiltrative myocardial illness.	80 to 100 ms
J-point	The J-signal is the indicate at which the QRS complex finishes and the ST segment begins.	The J-point may be elevated as a normal variant. The appearance of a dissever J wave or Osborn wave at the J-point is pathognomonic of hypothermia or hypercalcemia.[47]
ST segment	The ST segment connects the QRS complex and the T wave; it represents the catamenia when the ventricles are depolarized.	It is unremarkably isoelectric, but may be depressed or elevated with myocardial infarction or ischemia. ST depression can also be acquired by LVH or digoxin. ST elevation can likewise be caused past pericarditis, Brugada syndrome, or can be a normal variant (J-point elevation).
T wave	The T moving ridge represents the repolarization of the ventricles. It is mostly upright in all leads except aVR and lead V1.	Inverted T waves can be a sign of myocardial ischemia, left ventricular hypertrophy, high intracranial pressure, or metabolic abnormalities. Peaked T waves can be a sign of hyperkalemia or very early myocardial infarction.	160 ms
Corrected QT interval (QTc)	The QT interval is measured from the beginning of the QRS circuitous to the end of the T wave. Acceptable ranges vary with middle rate, and then it must be corrected to the QTc by dividing past the foursquare root of the RR interval.	A prolonged QTc interval is a adventure factor for ventricular tachyarrhythmias and sudden expiry. Long QT can ascend every bit a genetic syndrome, or as a side upshot of certain medications. An unusually short QTc can be seen in severe hypercalcemia.	<440 ms
U wave	The U wave is hypothesized to be caused by the repolarization of the interventricular septum. It normally has a low amplitude, and even more oftentimes is completely absent-minded.	A very prominent U wave can exist a sign of hypokalemia, hypercalcemia or hyperthyroidism.[48]

Limb leads and electrical conduction through the heart [edit]

Formation of limb waveforms during a pulse

The animation shown to the right illustrates how the path of electrical conduction gives rising to the ECG waves in the limb leads. Recall that a positive current (every bit created by depolarization of cardiac cells) traveling towards the positive electrode and away from the negative electrode creates a positive deflection on the ECG. Likewise, a positive current traveling away from the positive electrode and towards the negative electrode creates a negative deflection on the ECG.^{[49] [50]} The carmine arrow represents the overall management of travel of the depolarization. The magnitude of the reddish arrow is proportional to the amount of tissue being depolarized at that instance. The ruby-red arrow is simultaneously shown on the centrality of each of the 3 limb leads. Both the direction and the magnitude of the red arrow's projection onto the axis of each limb lead is shown with blue arrows. And so, the management and magnitude of the blue arrows are what theoretically decide the deflections on the ECG. For example, as a blue arrow on the axis for Pb I moves from the negative electrode, to the right, towards the positive electrode, the ECG line rises, creating an upwardly wave. As the blue arrow on the axis for Lead I moves to the left, a downward wave is created. The greater the magnitude of the blue arrow, the greater the deflection on the ECG for that particular limb lead.^{[ citation needed ]}

Frames 1–3 depict the depolarization beingness generated in and spreading through the Sinoatrial node. The SA node is too small for its depolarization to be detected on most ECGs. Frames iv–10 depict the depolarization traveling through the atria, towards the Atrioventricular node. During frame seven, the depolarization is traveling through the largest amount of tissue in the atria, which creates the highest indicate in the P moving ridge. Frames 11–12 depict the depolarization traveling through the AV node. Like the SA node, the AV node is too small for the depolarization of its tissue to be detected on most ECGs. This creates the flat PR segment.^[51]

Frame 13 depicts an interesting phenomenon in an over-simplified style. It depicts the depolarization equally it starts to travel down the interventricular septum, through the Bundle of His and Bundle branches. After the Package of His, the conduction system splits into the left bundle branch and the right bundle co-operative. Both branches conduct activity potentials at about 1 chiliad/s. Interestingly, however, the action potential starts traveling downward the left parcel branch near v milliseconds before it starts traveling down the right bundle branch, as depicted by frame 13. This causes the depolarization of the interventricular septum tissue to spread from left to correct, as depicted past the red arrow in frame 14. In some cases, this gives rise to a negative deflection afterward the PR interval, creating a Q wave such equally the 1 seen in pb I in the animation to the right. Depending on the mean electrical centrality of the heart, this phenomenon can event in a Q wave in lead II besides.^{[52] [53]}

Post-obit depolarization of the interventricular septum, the depolarization travels towards the apex of the eye. This is depicted past frames fifteen–17 and results in a positive deflection on all three limb leads, which creates the R moving ridge. Frames 18–21 then describe the depolarization equally it travels throughout both ventricles from the apex of the middle, following the activeness potential in the Purkinje fibers. This phenomenon creates a negative deflection in all three limb leads, forming the S wave on the ECG. Repolarization of the atria occurs at the same time as the generation of the QRS circuitous, but it is not detected by the ECG since the tissue mass of the ventricles is so much larger than that of the atria. Ventricular wrinkle occurs between ventricular depolarization and repolarization. During this fourth dimension, there is no movement of charge, so no deflection is created on the ECG. This results in the flat ST segment later on the South wave.^{[ citation needed ]}

Frames 24–28 in the blitheness depict repolarization of the ventricles. The epicardium is the commencement layer of the ventricles to repolarize, followed by the myocardium. The endocardium is the last layer to repolarize. The plateau phase of depolarization has been shown to last longer in endocardial cells than in epicardial cells. This causes repolarization to showtime from the noon of the eye and move upwardly. Since repolarization is the spread of negative current as membrane potentials decrease back downward to the resting membrane potential, the crimson pointer in the animation is pointing in the direction opposite of the repolarization. This therefore creates a positive deflection in the ECG, and creates the T moving ridge.^[54]

Ischemia and infarction [edit]

Ischemia or non-ST elevation myocardial infarctions (non-STEMIs) may manifest every bit ST low or inversion of T waves. Information technology may also bear on the high frequency band of the QRS.

ST pinnacle myocardial infarctions (STEMIs) take dissimilar feature ECG findings based on the amount of time elapsed since the MI outset occurred. The earliest sign is hyperacute T waves, peaked T waves due to local hyperkalemia in ischemic myocardium. This then progresses over a period of minutes to elevations of the ST segment past at least 1 mm. Over a period of hours, a pathologic Q wave may announced and the T wave will invert. Over a flow of days the ST elevation volition resolve. Pathologic Q waves generally volition remain permanently.^[55]

The coronary artery that has been occluded can be identified in an STEMI based on the location of ST height. The left anterior descending (LAD) artery supplies the anterior wall of the heart, and therefore causes ST elevations in anterior leads (V₁ and V₂). The LCx supplies the lateral attribute of the heart and therefore causes ST elevations in lateral leads (I, aVL and V_{half dozen}). The correct coronary artery (RCA) usually supplies the inferior aspect of the middle, and therefore causes ST elevations in junior leads (2, III and aVF).^{[ citation needed ]}

Artifacts [edit]

An ECG tracing is affected past patient motion. Some rhythmic motions (such as shivering or tremors) can create the illusion of cardiac arrhythmia.^[56] Artifacts are distorted signals caused past a secondary internal or external sources, such as musculus movement or interference from an electrical device.^{[57] [58]}

Distortion poses significant challenges to healthcare providers,^[57] who employ various techniques^[59] and strategies to safely recognize^[60] these false signals.^{[ medical citation needed ]} Accurately separating the ECG artifact from the true ECG point can accept a significant impact on patient outcomes and legal liabilities.^{[61] [ unreliable medical source? ]}

Improper lead placement (for example, reversing two of the limb leads) has been estimated to occur in 0.4% to 4% of all ECG recordings,^[62] and has resulted in improper diagnosis and treatment including unnecessary use of thrombolytic therapy.^{[63] [64]}

Diagnosis [edit]

Numerous diagnoses and findings can exist made based upon electrocardiography, and many are discussed above. Overall, the diagnoses are made based on the patterns. For case, an "irregularly irregular" QRS complex without P waves is the hallmark of atrial fibrillation; even so, other findings can exist nowadays likewise, such as a bundle branch block that alters the shape of the QRS complexes. ECGs can be interpreted in isolation merely should be applied – like all diagnostic tests – in the context of the patient. For instance, an ascertainment of peaked T waves is not sufficient to diagnose hyperkalemia; such a diagnosis should be verified past measuring the blood potassium level. Conversely, a discovery of hyperkalemia should be followed past an ECG for manifestations such as peaked T waves, widened QRS complexes, and loss of P waves. The post-obit is an organized list of possible ECG-based diagnoses.^{[ citation needed ]}

Rhythm disturbances or arrhythmias:^{[ citation needed ]}

• Atrial fibrillation and atrial flutter without rapid ventricular response
• Premature atrial wrinkle (PACs) and premature ventricular contraction (PVCs)
• Sinus arrhythmia
• Sinus bradycardia and sinus tachycardia
• Sinus interruption and sinoatrial arrest
• Sinus node dysfunction and bradycardia-tachycardia syndrome
• Supraventricular tachycardia
  • Atrial fibrillation with rapid ventricular response
  • Atrial flutter with rapid ventricular response
  • AV nodal reentrant tachycardia
  • Atrioventricular reentrant tachycardia
  • Junctional ectopic tachycardia
  • Atrial tachycardia
    • Ectopic atrial tachycardia (unicentric)
    • Multifocal atrial tachycardia
    • Paroxysmal atrial tachycardia
  • Sinoatrial nodal reentrant tachycardia
• Torsades de pointes (polymorphic ventricular tachycardia)
• Wide circuitous tachycardia
  • Ventricular flutter
  • Ventricular fibrillation
  • Ventricular tachycardia (monomorphic ventricular tachycardia)
• Pre-excitation syndrome
  • Lown–Ganong–Levine syndrome
  • Wolff–Parkinson–White syndrome
• J wave (Osborn wave)

Heart block and conduction problems:

• Aberration
• Sinoatrial block: kickoff, second, and third-degree
• AV node
  • First-degree AV block
  • Second-degree AV block (Mobitz [Wenckebach] I and 2)
  • Third-degree AV block or complete AV cake
• Right packet
  • Incomplete correct bundle co-operative block
  • Complete correct bundle co-operative cake (RBBB)
• Left bundle
  • Complete left package co-operative cake (LBBB)
  • Incomplete left package branch block
  • Left anterior fascicular block (LAFB)
  • Left posterior fascicular block (LPFB)
  • Bifascicular block (LAFB plus LPFB)
  • Trifascicular block (LAFP plus FPFB plus RBBB)
• QT syndromes
  • Brugada syndrome
  • Short QT syndrome
  • Long QT syndromes, genetic and drug-induced
• Correct and left atrial aberration

Electrolytes disturbances and intoxication:

• Digitalis intoxication
• Calcium: hypocalcemia and hypercalcemia
• Potassium: hypokalemia and hyperkalemia
• Serotonin Toxicity

Ischemia and infarction:

• Wellens' syndrome (LAD occlusion)
• de Wintertime T waves (LAD apoplexy) ^[65]
• ST elevation and ST depression
• Loftier Frequency QRS changes
• Myocardial infarction (heart attack)
  • Non-Q wave myocardial infarction
  • NSTEMI
  • STEMI
  • Sgarbossa's criteria for ischemia with a LBBB

Structural:

• Acute pericarditis
• Right and left ventricular hypertrophy
• Correct ventricular strain or S1Q3T3 (can be seen in pulmonary embolism)

History [edit]

An early commercial ECG device (1911)

• In 1872, Alexander Muirhead is reported to have fastened wires to the wrist of a patient with fever to obtain an electronic record of their heartbeat.^[66]
• In 1882, John Burdon-Sanderson working with frogs, was the first to capeesh that the interval between variations in potential was non electrically quiescent and coined the term "isoelectric interval" for this period.^[67]
• In 1887, Augustus Waller^[68] invented an ECG auto consisting of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate that was itself fixed to a toy train. This immune a heartbeat to be recorded in real time.
• In 1895, Willem Einthoven assigned the letters P, Q, R, Due south, and T to the deflections in the theoretical waveform he created using equations which corrected the bodily waveform obtained by the capillary electrometer to compensate for the imprecision of that musical instrument. Using letters dissimilar from A, B, C, and D (the messages used for the capillary electrometer'southward waveform) facilitated comparison when the uncorrected and corrected lines were drawn on the aforementioned graph.^[69] Einthoven probably chose the initial alphabetic character P to follow the case fix by Descartes in geometry.^[69] When a more than precise waveform was obtained using the string galvanometer, which matched the corrected capillary electrometer waveform, he continued to use the letters P, Q, R, S, and T,^[69] and these letters are still in utilise today. Einthoven as well described the electrocardiographic features of a number of cardiovascular disorders.
• In 1897, the string galvanometer was invented past the French engineer Clément Ader.^[70]
• In 1901, Einthoven, working in Leiden, the netherlands, used the string galvanometer: the start practical ECG.^[71] This device was much more sensitive than the capillary electrometer Waller used.
• In 1924, Einthoven was awarded the Nobel Prize in Medicine for his pioneering piece of work in developing the ECG.^[72]
• By 1927, Full general Electric had developed a portable appliance that could produce electrocardiograms without the use of the cord galvanometer. This device instead combined amplifier tubes like to those used in a radio with an internal lamp and a moving mirror that directed the tracing of the electric pulses onto film.^[73]
• In 1937, Taro Takemi invented a new portable electrocardiograph car.^[74]
• In 1942, Emanuel Goldberger increases the voltage of Wilson's unipolar leads past l% and creates the augmented limb leads aVR, aVL and aVF. When added to Einthoven's three limb leads and the vi breast leads we go far at the 12-lead electrocardiogram that is used today.^[75]
• In the belatedly 1940s Rune Elmqvist invented an inkjet printer - thin jets of ink deflected by electrical potentials from the heart, with good frequency response and direct recording of ECG on paper - the device, called the Mingograf, was sold past Siemens Elema until the 1990s.^[76]

Etymology [edit]

The discussion is derived from the Greek electro, meaning related to electric activity; kardia, meaning heart; and graph, meaning "to write".^{[ citation needed ]}

See also [edit]

• Point-averaged electrocardiogram
• Electrical conduction system of the eye
• Electrogastrogram
• Electropalatography
• Electroretinography
• Emergency medicine
• Forward trouble of electrocardiology
• Eye rate
• Heart charge per unit monitor
• KardiaMobile
• Wireless convalescent ECG

Notes [edit]

1. ^ The version with '-Thou-', more commonly used in American English than in British English, is an early-20th-century loanword from the German language acronym EKG for Elektrokardiogramm (electrocardiogram),^[1] which reflects that German language physicians were pioneers in the field at the time. Today, AMA style and – under its stylistic influence – most American medical publications use ECG instead of EKG.^[2] The German term Elektrokardiogramm as well as the English equivalent, electrocardiogram, consist of the New Latin/international scientific vocabulary elements elektro- (cognate electro- ) and kardi- (cognate 'cardi-'), the latter from Greek kardia (heart).^[three] The '-Chiliad-' version is more often retained nether circumstances where there may be verbal confusion between ECG and EEG (electroencephalography) due to like pronunciation.

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External links [edit]

Wikimedia Commons has media related to ECG.

• The whole ECG class on 1 A4 paper from ECGpedia, a wiki encyclopedia for a grade on interpretation of ECG
• Wave Maven – a big database of practice ECG questions provided by Beth Israel Deaconess Medical Center
• PysioBank – a free scientific database with physiologic signals (here ecg)
• EKG University – free EKG lectures, drills and quizzes
• ECG Learning Center created by Eccles Health Sciences Library at University of Utah

colealinst.blogspot.com

Source: https://en.wikipedia.org/wiki/Electrocardiography

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