Physics
Electrocardiography
Electrocardiography is a medical technique used to record the electrical activity of the heart over a period of time. It involves placing electrodes on the skin to detect the heart's electrical signals, which are then displayed as a graph called an electrocardiogram (ECG). This non-invasive procedure is commonly used to diagnose heart conditions and monitor cardiac health.
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11 Key excerpts on "Electrocardiography"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 15 Electrocardiography Image showing a patient connected to the 10 electrodes necessary for a 12-lead ECG ________________________ WORLD TECHNOLOGIES ________________________ 12 Lead ECG of a 26-year-old male. Electrocardiograph ( ECG, or EKG [from the German Elektrokardiogramm ]) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from the Greek electro , because it is related to electrical activity, cardio , Greek for heart, and graph , a Greek root meaning to write. In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG. The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heart beat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through intrinsic conduction pathways and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
eBook - PDF- Andrew G. Webb(Author)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
5 Electrocardiography 5.1 Electrical Activity in the Heart 141 5.2 Electrode Design and Einthoven ’ s Triangle 145 5.2.1 Standard Twelve-Lead Con fi guration 146 5.3 ECG System Design 149 5.3.1 Common-Mode Signals and Other Noise Sources 150 5.3.2 Reducing the Common-Mode Signal 152 5.3.2.1 Instrumentation Ampli fi er 153 5.3.2.2 Driven Right Leg Circuit 153 5.3.3 Design of Lead-Off Circuitry 154 5.3.4 Filtering and Sampling 155 5.4 Signal Processing of the ECG Signal and Automatic Clinical Diagnosis 156 5.4.1 University of Glasgow (Formerly Glasgow Royal In fi rmary) Algorithm 157 5.5 Examples of Abnormal ECG Recordings and Clinical Interpretation 158 5.6 ECG Acquisition During Exercise: Detection of Myocardial Ischaemia 161 5.7 High-Frequency (HF) ECG Analysis 163 140 Introduction An ECG, also sometimes referred to as an EKG from the original German word ‘ electrokardiogram ’ , measures the electrical activity of the heart [ 1 ]. This elec-trical activity produces the contractions and relaxations of the cardiac muscles required to pump blood around the body. An ECG is recorded over a series of cardiac cycles (heartbeats) and shows the different phases of the cardiac cycle. The ECG indirectly measures transmembrane voltages in myocardial cells that depolarize and repolarize within each cardiac cycle. These depolarization and repolarization events produce ionic currents within the body, and these are transduced into voltages by electrodes (described in Chapter 2 ) placed on the surface of the chest and thorax, as shown in Figures 5.1(a) and (b) . Up to twelve different lead voltages are recorded, with the magnitude of the voltages being in the low mV range, Figure 5.1(c) , and a frequency spectrum between 0 and 30 Hz, as shown in Figure 5.1(d) . The ECG signal has many distinct features, such as the P-wave, QRS-complex and T-wave, illustrated in Figure 5.1(c) .
eBook - ePubBasic Cardiovascular Physiology
From Molecules to Translational Medical Science
- Pasquale Pagliaro, Claudia Penna, Raffaella Rastaldo(Authors)
- 2022(Publication Date)
- River Publishers(Publisher)
10 Electrocardiogram10.1 The Definition of Electrocardiogram and Dipole Theory
The electrical activity of the heart produces electric fields transmitted to the surface of the body. The electrocardiogram (ECG) can be defined as the graphic recording of these electric fields by electrodes placed on the skin.The electrical activity of the heart is due to the processes of depolarization and repolarization during a heartbeat. Both processes propagate from a region to the other of the heart. Indeed, the ECG is the recording of origin and diffusion of both heart excitement (depolarization) and its recovery to resting conditions (repolarization). Therefore, ECG is not the registration of action potentials as such but the consequence on the surface of the body of the processes of the traveling of depolarization and repolarization within the heart, which result in several variations of the electric field that determine a modular repetition of similar waves.While the electrical activity is located in several parts of the heart (sinusatrial node, sinoatrial, interatrial and atrioventricular conduction systems, myocardium), the ECG is the result of the processes of depolarization and repolarization traveling within the various parts of the heart that produces cyclic variations of the electric field on the body surface. These cyclic electrical fields can be registered by electrodes on the surface of the body. From these considerations on the definition of ECG, it emerges that ECG can give information on the diffusion of the impulse (the traveling depolarization/ripolarization) within the heart mass but cannot give direct indications on the mechanical activity of the heart.Since we record a phenomenon occurring outside of the cells, for the ECG we can consider only the electrical phenomena on outer sides of the fibers. In Chapter 3.1 we have seen that a resting myocardial fiber is polarized, that is, it has positive charges outside and negative charges inside the cell membrane (Figure 3.1A
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 4 Electrocardiography 12 Lead ECG of a 26 -year-old male ________________________ WORLD TECHNOLOGIES ________________________ Image showing a patient connected to the 10 electrodes necessary for a 12-lead ECG Electrocardiograph ( ECG, or EKG [from the German Elektrokardiogramm ]) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from the Gre ek electro , because it is related to electrical activity, cardio , Greek for heart, and graph , a Greek root meaning to write. In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG. The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heart beat. At rest, ________________________ WORLD TECHNOLOGIES ________________________ each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through intrinsic conduction pathways and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 17 Electrocardiography 12 Lead ECG of a 26-year-old male ________________________ WORLD TECHNOLOGIES ________________________ Image showing a patient connected to the 10 electrodes necessary for a 12-lead ECG Electrocardiograph ( ECG, or EKG [from the German Elektrokardiogramm ]) is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device. The etymology of the word is derived from the Greek electro , because it is related to electrical activity, cardio , Greek for heart, and graph , a Greek root meaning to write. In English speaking countries, medical professionals often write EKG (the abbreviation for the German word elektrokardiogramm) in order to avoid confusion with EEG. The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heart beat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarization, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial ________________________ WORLD TECHNOLOGIES ________________________ node, spreads out through the atrium, passes through intrinsic conduction pathways and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.
eBook - PDF- Joseph D. Bronzino, Donald R. Peterson(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
45 -1 45.1 Introduction The electrocardiogram (ECG) is the recording of the electrical activity generated by the heart on the body surface It was originally observed by Waller in 1889 [1] using his pet bulldog as the signal source and the capillary electrometer as the recording device In 1903 Einthoven [2] improvised the technology by using the string galvanometer as the recording device and employing human subjects with a variety of cardiac abnormalities Einthoven is chiefly responsible for introducing some concepts still in use today, including the labeling of the various waves, defining some of the standard recording sites using the arms and legs, and developing the first theoretical construct whereby the heart is modeled as a single time-varying dipole We also owe the “EKG” acronym to Einthoven writing in German where the root word “cardio” is spelled with a “k” To record an ECG waveform, a differential recording between two points on the body are made Traditionally each differential recording is referred to as a lead Einthoven defined three leads numbered with the Roman numerals I, II, and III They are defined as: I II III LA RA LL RA LL = -= -= -V V V V V V LA where RA = right arm, LA = left arm, and LL = left leg Because the body is assumed to be purely resis-tive, at ECG frequencies, the four limbs can be thought of as wires attached to the torso Hence, lead I could be recorded from the respective shoulders without a loss of cardiac information Note that these are not independent and the following relationship II = I + III holds For 30 years the evolution of the ECG proceeded when FN Wilson [3] added concepts of a “unipolar” recording He created a reference point by tying the three limbs together and averaging their potentials so that individual recording sites on the limbs or the chest surface would be differentially recorded with the same reference point
eBook - PDF- Robert Splinter(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
23.2 Electrocardiogram: Electrical Signal of the Cardiovascular System 23.2.1 Brief History of the Development of Electrocardiogram Recording Th e fi rst observations of the electric current accompanying each heart beat were made in 1842 by Carlo Matteucci. Marey used a capillary electrometer to record the electrical activity of the frog heart i n 1 876 . Th e fi rst h uman ele ctrocardiogram ( ECG) w as recorded w ith Li ppmann’s c apillary e lectrometer i n 1 887 b y Augustus D. Waller . Th is simple ECG revealed only two de fl ec-tions i ndicating t he v entricular e vents. H owever, t he ter m “electrocardiogram” w as e stablished l ater i n 1 893 b y Wi llem Einthoven as well as the terms P, Q, R, S, and T denoting di ff er-ent de fl ections of the ECG. Einthoven invented a new galvanom-eter for the accurate recording of the ECG and published th e fi rst ECG re corded w ith it in 1902. He re ceived t he N obel prize in 1924 for his life’s work in developing the ECG. Electrocardiogram 23 -3 23.2.2 Origin of the ECG Th e ECG is a g raphic i mage of t he su m of t he electric currents generated in the heart. Th ese currents spread over the tissues sur-rounding the heart and reach the surface of the body . Th er efore they can be recorded using surface electrodes and visualized a ft er appropriate amplifying. As the mass of the pacemaker cells and the specialized conductive tissues is small, the ECG mainly rep-resents the electrical activity of the working muscle. 23.2.3 ECG Electrode Placement Th e standard 12-lead ECG measures the heart from 12 di ff erent directions throughout t he recording of t he potential di ff erence between electrode pairs (Figure 23.1).
eBook - PDF- John G. Webster(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
Cardiology: Electrocardiography ◾ 67 before reaching a plateau. When exercise is stopped, heart rate quickly recovers. Both the ability to reach the target heart rate during exercise (220 − age) and the speed of recovery once stopping exercise are indicators of cardiovascular health. 3.12 CARDIAC MAPPING The surface ECG provides composite information of the heart’s electrical activity in its entirety. However, this “global” view of the electrical activity may not offer sufficient enough detail of the activation sequences of the heart to pinpoint the locations responsible for certain arrhythmias. This detail is particularly needed for radio-frequency ablation procedures, where catheters are used to deliver radio-frequency energy to specific areas of the heart to destroy the culprit tissue. Local electrical activity can be recorded by elec-trodes that are in contact directly with the heart tissue. These contact electrical recordings are known as electrograms. In a cardiac electrophysiologic study, catheters with electrodes at the tip are guided through a vein or artery to the heart. X-ray machines that produce real-time images displayed on monitors are used to guide the catheters. The catheter used for radio-frequency ablation can also be used to record electrograms. A mapping system is used to amplify, filter, display, and record electrogram signals. Mapping systems also allow the selection of channels to perform pacing via an electrical stimulator. 3.12.1 Electrograms Contact electrograms again differ from surface ECG recordings as they reflect local electri-cal activity at the site of recording. Electrograms are most commonly either unipolar or bipolar recordings. Unipolar electrograms are differential recordings made from a single electrode in contact with the heart referenced to a distant electrode not in contact with the heart. Figure 3.21 shows the typical waveform of a unipolar electrogram and how it relates to an activation wavefront.
eBook - PDF- Rishi Aggarwal, Emily Ferenczi, Nina Muirhead(Authors)
- 2007(Publication Date)
- CRC Press(Publisher)
THE ELECTROCARDIOGRAM SECTION 4 • RECORDING AN ELECTROCARDIOGRAM 34 • LEADS AND PAPER 36 • BASIC ELECTROCARDIOGRAM INTERPRETATION (I) 38 • BASIC ELECTROCARDIOGRAM INTERPRETATION (II) 40 • RATE AND AXIS 42 • FIRST-DEGREE ATRIOVENTRICULAR BLOCK 44 • SECOND-DEGREE ATRIOVENTRICULAR BLOCK 46 • THIRD-DEGREE ATRIOVENTRICULAR BLOCK (COMPLETE HEART BLOCK) 48 • RIGHT BUNDLE BRANCH BLOCK 50 • LEFT BUNDLE BRANCH BLOCK 52,70 • ANATOMY AND TERRITORIES OF THE CORONARY ARTERIES (I) 54 • ANATOMY AND TERRITORIES OF THE CORONARY ARTERIES (II) 56 • ARRHYTHMIAS 58 • ATRIAL FIBRILLATION 60 • NARROW COMPLEX TACHYCARDIA (I) 62 • NARROW COMPLEX TACHYCARDIA (II) 64 • BROAD COMPLEX TACHYCARDIA (I) 66 • BROAD COMPLEX TACHYCARDIA (II) 68 • ECG POINTERS 70 ICS, intercostal space THE ELECTROCARDIOGRAM SECTION 4 1. Label the diagram below to show where you would place the chest leads to obtain an ECG 2. Name the important bony landmark that allows correct positioning of the precordial leads 3. For each chest lead, describe which aspect of the heart it looks at 4. Describe Einthoven’s triangle and how it is used to view the heart’s vertical plane 5. In the UK, specific colours are used to represent ECG limb leads. Using the options provided, match each of the limb leads with its correct colour Options A. Right shoulder C. Upper part of left thigh B. Left shoulder D. Upper part of right thigh 1. Red 4. Green 7. Orange 2. Blue 5. Brown 8. Purple 3. Yellow 6. Grey 9. Black The electrocardiogram 35 EXPLANATION: RECORDING AN ELECTROCARDIOGRAM An electrocardiograph is an instrument used to measure the intrinsic electrical impulses of the heart via elec-trodes placed on the body surface. The recording is an electrocardiogram , which represents the activity as a series of oscillations. Oscillations from a normal cardiac cycle are named P , Q , R , S and T and follow in alpha-betical order. Additional letters may be necessary for other distinct waveforms.
- Leif Sörnmo, Pablo Laguna(Authors)
- 2005(Publication Date)
- Academic Press(Publisher)
While the diagnostic accuracy of a modern system is very good, the ECG print-out is usually checked by a physician to assure that the diagnosis is correct. Once a resting ECG has been diagnosed, the signal is stored in a database for retrieval, if necessary, at a later date. Database storage facilitates serial ECG analysis in which two or more successive ECG recordings from the same patient are compared to reveal possible changes related, for example, to myocardial infarction. Unfortunately, interrecording changes in the ECG caused by nonphysiological factors, such as different electrode placement or positional changes of the heart, degrade the reliability of serial analysis. 444 Chapter 6. The Electrocardiogram--A Brief Background 6.6.2 Intensive Care Monitoring A patient who has suffered myocardial infarction or undergone heart surgery is placed in an intensive care unit (ICU) or coronary care unit (CCU). Such a unit has a number of beds wired to a central computer so that the ECG of each individual patient can be continuously monitored. The objective of ECG monitoring is primarily to detect life-threatening arrhythmias, such as ventricular fibrillation, at a very early stage. It is also important to detect episodes of acute myocardial ischemia by monitoring changes in the ST segment. Of the five ECG applications discussed in this section, intensive care monitoring is the only one which is critically dependent on real-time signal processing: a serious event such as cardiac arrest must be detected within a few seconds so that the staff can be alerted to immediately begin emergency life-saving procedures. The ECG signal is recorded under conditions associated with consider- able amounts of noise and artifacts caused by, for example, muscle activity and changes in body position. Poor signal quality produces an increased number of false alarms and reduced diagnostic performance.
eBook - PDF- Umashankar Lakshmanadoss(Author)
- 2020(Publication Date)
- IntechOpen(Publisher)
ECG signal is a fundamental tool commonly used in the heart medical domain to treat patients suffering from cardiac diseases. By measuring the potential difference between electrodes posed in well-known places in the patient skin, these signals are usually obtained. The ECG signal can be single channel or multichannel depending on how many electrodes are used, one or several. Important knowledge is obtained by cardiologists about the patient ’ s heart function only by analyzing a minute feature of these signals. The ECG signal has a well-defined P, QRS, and T signatures that represent each heartbeat. The duration, shape, and amplitude of these waves are considered as major features in time domain analysis. Changes in the normal rhythmicity of a human heart may result in different cardiac arrhythmias, which may be immediately fatal or cause irreparable damage to the heart when sustained over a long period of time. The following subsections present the different normal and abnormal ECG signals chosen for this study. These data were obtained from [19]. 2.3.1 Normal ECG Figure 1 shows the time domain of a normal ECG signal. The sampling frequency for this normal ECG signal was 128 samples/s and the signal length 8 s. 2.3.2 Atrial fibrillation ECG Figure 2 shows a length of 4 s of an abnormal atrial fibrillation ECG signal obtained from a patient with malignant ventricular arrhythmia. The sampling frequency for this signal was 250 samples/s. The atrial rate exceeds 350 beats per minute in this type of arrhythmias. This arrhythmia occurs due to an uncoordinated activation and contraction of different parts of the atrial which leads to ineffective pumping of blood into the ventricles. 2.3.3 Ventricular tachyarrhythmia ECG Figure 3 shows a length of 4 s of a ventricular tachyarrhythmia ECG signal with a 250 samples/s sampling frequency. This abnormal signal presents a misalignment of the third QRS complex. 26 Practical Applications of Electrocardiogram
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