ECG, EKG

Overview:

An electrocardiogram (ECG1) refers to the imaging of cardiac electrical events associated with each heart beat. As the heart’s atria and ventricles alternate between relaxation and contraction, changes in the polarity of the electrical field surrounding the heart can be detected using dermal electrodes placed on the chest and limbs. The resulting ECG waveform can then be used to provide information about normal and pathophysiological heart beat and rhythm.

 

1. Also referred to by the German abbreviation ‘EKG’ (Electrokardiogramm)

Method:

Cardiac monitoring lead systems

Several different lead configurations exist differing in the number and placement of skin electrodes. In addition, two types of leads may be recorded:

  • Bipolar – measures the potential difference between two electrodes on either side of the heart.
  • Unipolar – measures the potential variation of a single electrode with respect to a reference potential obtained by averaging the potentials at other lead sites. This includes the augmented limb leads: aVR, aVL and aVF and the precordial leads (V1-6).

 

3-electrode 3-lead system

The oldest and simplest ECG system uses three leads (Fig 1.): Lead I (LA, +ve; RA, -ve), Lead II (LL, +ve; RA, -ve), Lead III (LL, +ve; LA, -ve). The 3-lead system is sufficient for tracking heart rate change, R-wave detection, and ventricular fibrillation, but is less sensitive than 6- and 12-lead systems in the detection of arrhythmia monitoring for the reason that no true V1 lead is present (see below). Alternative electrode placements may be used if limb movements are expected to cause movement artifacts. For example, LA and RA can be placed in the left and right infraclavicular fossa, respectively; similarly RL may be placed on the right iliac fossa. Three bipolar recording leads are obtained as follows:

  • Lead I (LA +ve, RA -ve), lead II (RA -ve, LL +ve), and lead III (LA -ve, LL +ve)

Figure 1. Wrist/ankle placements for a 3-electrode 3-lead system. The lead created by each bipolar pair is labeled with an accompanying example waveform. The advantages of the wrist/ankle positions is that there is less underlying muscle that might otherwise contribute to movement artifacts, and electrode locations are more accessible. Alternatively, equivalent torso locations may provide better a signal-to-noise ratio.

 

5-electode 6-lead system

Commonly used in clinical practice and in research, the 5 electrode system can be used to obtain 6 ECG leads including one precordial lead (e.g., V1). Bipolar electrode placement is similar to the 3-lead system, except that an additional LL electrode is placed on the left ankle (or left iliac fossa in the case of torso placement; see Fig. 2). Thus, with the 5-electrode system there are LA, RA, LL, and RL electrodes, with one additional precordial electrode. The precordical electrode is unipolar and may be placed in any of the standard V1 to V6 locations, but in general V1 is preferred because of its sensitivity in arrhythmia monitoring. The location of V1 is the 4th intercostal space at the right sternal margin. Six recording leads are obtained as follows:

  • Bipolar leads I, II, III are as per the 3-lead system.
  • Two additional unipolar leads are obtained by measuring the potential variation at a single electrode with respect to a reference potential (see below). The reference potential (indifferent electrode) is obtained by connecting two other limb electrodes through a resistance:
    • aVR = RA (+ve) to [LA and LL] (-ve)
    • aVL = LA (+ve) to [RA and LL] (-ve)
    • aVF = LL (+ve) to [RA and LA] (-ve)
  • A single precordial lead2 (e.g., V1, although V2, V3, V4, V5, or V6 could also be used). The indifferent electrode is the sum of the potentials at LA, RA, and LL. Since these form a near equilateral triangle with current source at its center, connecting LA, RA, and LL to a common terminal through a resistance creates an indifferent electrode that remains close to zero potential.

Figure 2. Wrist/ankle placements for computing the augmented limb leads for a 6-lead system. Equivalent torso electrode positions may be substituted for wrist/ankle positions.

 

10-electrode 12-lead system

There are two variations to the 10-electrode 12-lead system: the Mason-Likar 12-lead ECG system, named after the researchers who proposed it in 1966; and the standard 10-electrode 12-lead system. The difference between the two is that whereas the standard system uses wrist/ankle electrode positions for the limb electrodes, the Mason-Likar system places limb electrodes on the torso. Thus, there are the usual 4 limb leads (LA, RA, LL, RL); but instead of a single precordial lead as in the 5-electrode 6-lead system, there are 6 precordial leads (V1-V6; see Fig. 3). This gives a total of 12 recording leads as follows:

  • Bipolar leads I, II, III
  • Unipolar leads aVR, aVL, aVF
  • Precordial leads V1, V2, V3, V4, V5, V6

Advantages of the Mason-Likar and standard 12-lead system over 6- and 3-lead systems include the additional sensitivity to detecting myocardial ischaemia and ST segment changes, as well as being able to monitor >1 precordial lead.

Figure 3. The six precordial leads V1-V6. The configuration for the 12-lead system also includes the standard limb leads and augmented limb leads, as indicated in figures 1 and 2. The indifferent electrode for the precordial leads are LA, RA, and LL combined.

 

3-electrode-single lead system in rats and other small animals

ECG Leads I or II or III can be obtained noninvasively using spring clip electrodes attached to the limbs: 

  • Lead I: LA (+ve), RA (-ve)
  • Lead II: RA (-ve), LL (+ve)
  • Lead III: LA (-ve), LL (+ve)
    • The ground lead may be placed in any convenient location

For long-term monitoring in behaving animals, the Telemetry Research wireless system may be used. Electrodes can be positioned for equivalent ECG leads I or II or III by subcutaneous implantation. 

For acute invasive applications, needle electrodes placed on limbs or torso may be used for lead I, or II, or II recordings.

2 A precordial lead is also an example of a unipolar lead. ‘Precordium’ refers to the area of the torso that covers the heart and lower chest.

Software:

The LabChart Advantage:

(may require additional Modules and Extensions)

  • LabChart data files can be marked with events using the Comments feature
  • Parameters such as heart rate, mean heart rate and R-R interval can be calculated and displayed in real-time using LabChart's Cyclic Measurements function and the Data Pad
  • If any two signals of Lead I or Lead II or Lead III are recorded, then LabChart's Arithmetic function can be used to generate aVR, aVL, and aVF signals simultaneously on different channels.
  • Macros can automate many tedious and repetitive analysis tasks
  • Automated extraction of data from recordings using online Timed Add to Data Pad or offline using Multiple Add to Data Pad
  • The LabChart ECG Analysis Module enables real-time or offline analysis and data extraction of ECG parameters, such as PQRST component amplitudes, RR, PR, JT, QT and QTc intervals
  • The LabChart HRV Module enables real-time or offline detection and analysis of R waves and RR interval variation
  • Extracted parameters in the Data Pad or ECG Table View can be easily exported for further analysis, e.g in Excel or Matlab

LabChart

LabChart software (for Windows and Macintosh) together with a PowerLab data acquisition system offers up to 32 channels of real-time data acquisition, data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Additional acquisition and analysis functionality is provided with the use of specialized LabChart Extensions and LabChart Modules. Modules are available as part of LabChart Pro while Extensions are free for download from the website for existing LabChart users.

ECG Analysis Module

The ECG Analysis Module (Windows) provides a comprehensive set of tools that automatically detects and reports values of ECG recordings. The software can be used with ECG recordings taken from humans and many species of animals from pigs through to mice.

It provides

  • Beat classifier view based on
    • QRS form factor vs RR interval
    • Activity vs isoelectric noise
  • Real-time analysis and data extraction of ECG parameters, such as
    • PQRST component amplitudes
    • RR, PR, JT, QT and QTc intervals
  • Automated detection and averaging of ECG cycles
  • Automated tabulation of ECG parameters in Table view
  • Automated real-time or offline ECG Plots
    • Graphical QT vs RR, QT vs Time, and RR vs Time plots
    • Waterfall plot (3-D plot of stacked averaged ECG cutouts)

 

Heart Rate Variability (HRV) Module

The HRV Module (Windows and Macintosh) provides a comprehensive set of tools for the analysis and display of variation in the interval between heartbeats in human and animal ECG recordings.

It provides:

  • Detection and analysis of R waves and RR interval variation in real-time or offline
  • Includes or excludes ectopic beats from analysis
  • Adds R waves or remove artifacts from analysis
  • Exports data analysis
    • NN Intervals, RR Intervals, Spectrum NN Intervals & Report
  • HRV Analysis Plots
    • Poincaré Plot, Tachogram & Spectrum
    • Period Histogram and Delta N-N Histogram
  • Frequency-domain analysis: 
    • High frequency (HF) spectral power - a measure of vagal (parasympathetic) tone
    • Low frequency (LF) spectral power - a measure of sympathetic tone
    • LF/HF ratio - sympathovagal balance
  • Time-domain analysis:
    • Average HR, RR range, SDNN, SD of delta NN, RMSSD, pNN50
  • Full HRV report generated containing all time and frequency domain parameters
 

Cardiac Axis Extension

Cardiac Axis is a LabChart extension (Windows and Macintosh) that automates the calculation of the 6-lead ECG system and displays the direction and magnitude of ventricular depolarization in the vertical plane (vectorcardiogram).

It provides:

  • Automatic channel calculations for leads III, aVL, aVR, and aVF (from leads I and II)
  • Instantaneous cardiac vector
  • Mean cardiac vector

Cardiac Axis Vectorcardiogram (VCG)

 
GLP and 21 CFR Part 11

For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Hardware:

PowerLab Data Acquisition Systems

The PowerLab is a high-performance data acquisition unit capable of recording at speeds of up to 400,000 samples per second continuously to disk (aggregate). PowerLab units are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other third-party companies. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. Research PowerLab units include:

Research Systems

Wireless ECG in Small Animals

PL3516B109 Telemetry Small Animal Foundation System: A wireless monitoring system for physiological signals including intravascular or intralumen pressure signals, biopotentials such as ECG, EMG, EOG or EEG signals. Suitable for small conscious animals > 200 g (especially in rats). Note: Telemeters purchased separately.

Signal Conditioners

Bio Amplifiers

The ECG biopotentials are typically very small in amplitude (mV). Therefore accurate recording, display and analysis of an ECG require a suitable bioamplifier. ADInstruments offer a range of Bio Amplifiers, when connected a PowerLab data acquisition unit and, are certified safe for use with humans or used with animals. These bioamplifiers are fully software-controlled using LabChart or Scope. The following ADInstruments' biological amplifiers are fully isolated for connection to human or animal subjects:

FE132 Bio Amp

FE135 Dual Bio Amp

ML408 Dual Bio Amp/Stimulator


If a Dual Bio Amp is used to record any two signals of Lead I or Lead II or Lead III, then the Arithmetic function of the LabChart software can be used to generate aVR, aVL, and aVF signals simultaneously on different channels. The MLA0115/S ECG 12 Lead Switch Box (with a ML132 Single Bio Amp) or MLA0115/D ECG 12 Lead Switch Box (with a Dual Bio Amp) can be used to record all 12 ECG leads as shown in multi-lead recording.

ML138 Octal Bio Amp

  • A differential amplifier that consists of eight electrically isolated differential input AC amplifiers
  • A shared ground connection across all eight inputs.
  • Supplied with two packets of MLA0310 Lead Wires (1.8 m, 10 snap on)

GT201/F 16 Channel Bio Amp

The following ADInstruments' biological amplifiers for use with animals (i.e. pithed toad, or anaesthetized rat/mouse) only:

FE136 Animal Bio Amp

Transducers and Accessories

ECG Switch Boxes

  • For multi-lead recordings, ADInstruments Bio Amps (Bio Amp, Dual Bio Amp, Dual Bio Amp/Stim) can be used with the ECG Switch Boxes (MLA0115/S or MLA0115/D)
  • Quickly change between limb and augmented limb leads (I, II, II, aVR, aVL, aVF) and precordial leads (V1 - V6) on Ch1 in LabChart
  • Lead II is recorded on Ch2 by default

Bio Amp Cables & Lead Wires


Leads compatible with both shielded (MLA2340 & MLA2540) and unshielded (MLA1340 & MLA1540) cables:


Leads compatible with shielded cables (MLA2340 & MLA2540) only:


Leads that directly connect to the Dual Bio Amp


Leads that directly connect to the Animal Bio Amp


Electrodes

Wireless Biopotential Telemeters

Wireless biopotential telemeters are suitable for measuring ECG (and other types of biopotentials) plus temperature in small laboratory animals ≥200 g (ideally suited to rats).

Single lead wireless EEG: 

Dual lead wireless EEG

Alterations in cerebral blood flow and cerebrovascular reactivity during 14 days at 5050 m
S.J. E. Lucas, K.R. Burgess, K.N. Thomas, J Donnelly, K.C. Peebles, R.A. I. Lucas, J-L Fan, J.D. Cotter, R Basnyat and P.N. Ainslie, Journal of Physiology, 741-753, 2011

Heart Rate Variability Dynamics for the Prognosis of Cardiovascular Risk
Ramirez-Villegas JF, Lam-Espinosa E, Ramirez-Moreno DF, Calvo-Echeverry PC, Agredo-Rodriguez W., PLoS ONE, e17060, 2011

Citations Database


The material on this page is provided in good faith and believed accurate at the time of writing. No responsibility will be taken, or liability accepted, for damages arising from the use of information herein. Readers are urged to check with respective manufacturers the accuracy of all product related information.

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