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Ekg signal: Electrocardiogram (ECG or EKG) – Mayo Clinic


Electrocardiogram (ECG or EKG) – Care at Mayo Clinic

Mayo Clinic’s approach

At Mayo Clinic, electrophysiologists and rhythm analysis technicians use their expertise in electrocardiograms and other types of heart rhythm monitoring to provide exactly the care you need.

  • Individualized approach. Mayo Clinic specialists in the Heart Rhythm Clinic will talk with you about the types of heart rhythm monitoring available and which one meets your needs. They will develop an approach that fits with your life and condition.
  • Latest technology. Mayo Clinic has every type of heart-monitoring device available. Some of them use wireless technology, so your ECG test can be downloaded and interpreted immediately and in your medical record within minutes. In addition, Mayo Clinic helped develop and was among the first to use mobile cardiac outpatient telemetry. This method uses wireless ECG technology to continuously monitor your heart rhythm from your home.
  • ECG interpretation service. High-quality ECG interpretation has been offered at Mayo Clinic for nearly 50 years. Mayo Clinic’s Heart Rhythm and Physiological Monitoring Laboratory in Rochester, Minnesota, offers interpretation of ECG exams for adults, adolescents and children. ECG interpretations are available 24 hours a day, seven days a week. In urgent situations, ECG interpretations are available within minutes.
  • Innovative research. Doctors at Mayo Clinic research innovative uses of ECG diagnostic techniques to benefit people with heart disease. Doctors in Mayo Clinic’s Cardiovascular Research Center study and adopt new techniques for and uses of electrocardiography.

Monitoring ECG readings

A nationally certified rhythm analysis technician at Mayo Clinic monitors and interprets ECG readings.

Expertise and rankings

Implantable loop recorder consultation

A heart rhythm specialist holds the tiny implantable part of a loop recorder as he explains the risks and benefits of this method of remote heart monitoring.

Heart rhythm disorders expertise

Mayo Clinic specialists in the Heart Rhythm Clinic are experts in diagnosing heart rhythm disorders with monitoring devices, including Holter monitors and implantable loop recorders. Mayo Clinic performs many thousands of all types of heart rhythm monitoring each year.

These tests are interpreted with a team-based approach by Mayo Clinic doctors trained in heart rhythm disorders (electrophysiologists) and nationally certified rhythm analysis technicians in the Heart Rhythm and Physiological Monitoring Laboratory at Mayo Clinic’s campus in Rochester, Minnesota.

Mayo Clinic heart specialists write textbooks, such as Mayo Clinic Cardiology, and lead seminars for other doctors on the use of electrocardiograms to diagnose complex heart rhythm disorders.

Nationally recognized expertise

Mayo Clinic in Rochester, Minn., and Mayo Clinic in Phoenix/Scottsdale, Ariz., are ranked among the Best Hospitals for heart and heart surgery by U.S. News & World Report. Mayo Clinic Children’s Center in Rochester is ranked the No. 1 hospital in Minnesota, and the five-state region of Iowa, Minnesota, North Dakota, South Dakota and Wisconsin, according to U.S. News & World Report’s 2021–2022 “Best Children’s Hospitals” rankings.

Learn more about Mayo Clinic’s cardiovascular surgery and cardiovascular medicine departments’ expertise and rankings.

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What is an electrocardiogram (ECG)? – InformedHealth.org

Whether during routine examinations or heart diagnostics, many people have already had an electrocardiogram (ECG or EKG). But what does it actually measure, and what does the ECG curve show us?

Our nerve and muscle cells communicate with each other using electrical and chemical signals. Regular electrical signals also control our heartbeat. These signals are sent by a group of cells in the right atrium of the heart known as the sinoatrial node (SA node), and they spread through the heart muscle tissue as tiny electrical impulses. This causes first the atria and then the ventricles of the heart to contract. The way that these signals spread through the heart can also be measured on the surface of our skin. An ECG measures these changes in electrical signals (or, in fact, voltage) on different areas of skin and plots them as a graph. The resulting ECG graph is called an electrocardiogram.

When is this test offered?

An ECG is used to see how the heart is functioning. It mainly records how often the heart beats (heart rate) and how regularly it beats (heart rhythm). It can give us important information, for instance about possible narrowing of the coronary arteries, a heart attack or an irregular heartbeat like atrial fibrillation.

What does an ECG show?

If the heart is beating steadily, it will produce the typical ECG pattern: The first peak (P wave) shows how the electrical impulse (excitation) spreads across the two atria of the heart. The atria contract (squeeze), pumping blood into the ventricles, and then immediately relax. The electrical impulse then reaches the ventricles. This can be seen in the Q, R and S waves of the ECG, which is called the QRS complex. The ventricles contract. Then the T wave shows that the electrical impulse has stopped spreading, and the ventricles relax once again.

Heart diseases and irregular heartbeats can be detected in ECGs. What they look like and how they develop can help us find out what the underlying causes are.

Course of the QRS complex in a normal heartbeat

What does the test involve?

The electrical activity of the heart can be measured on the surface of the skin – even as far from the heart as on your arms or legs. The standard “12-lead ECG” uses a total of ten electrodes: six on your chest, and then one each on your lower arms and calves. If there is too much body hair, these areas are shaved first; other than that, no preparation is needed. These electrodes are connected by cables to an ECG machine. The machine converts the signals it receives into an ECG graph and saves it. Some machines can also print the graphs out.

What types of ECG tests are done?

Resting ECG: This involves lying still on your back with a bare chest. It is important that you lie calmly and comfortably during the test because tensing your muscles, moving, coughing or shaking can affect the results. The actual measurement takes about one minute, or five minutes at most.

Exercise ECG: Here the electrical activity of your heart is measured while you are physically active. This usually involves riding an exercise bike. The amount of exertion is steadily increased to a high level by making it increasingly difficult to turn the pedals. The test is stopped earlier if any irregularities in the ECG occur. In addition to the ECG graph, this test also provides data on the power that was generated in Watts. Your blood pressure is also checked regularly.

Holter monitor: The electrical activity of the heart is typically recorded over a period of 24 hours. Three or four electrodes are attached to your chest, and a small recording device is worn on a belt or hung around your neck. The ECG data are then transferred to a computer later on at the doctor’s office for analysis. To do this, the doctor also needs information about your daily schedule (like unusual events, physical activity and sleep). A Holter monitor may be used if, for instance, you only have an irregular heartbeat some of the time and it doesn’t show up in a “normal” ECG.

What do the results of a 12-lead ECG show?

The 12-lead ECG takes advantage of the fact that signals sent by the heart don’t travel evenly over your skin. The device compares the strength of the signals between two electrodes – doctors call these measurements “leads.” For example, one of the leads is measured based on the two electrodes on your arms. A 12-lead ECG, as its name implies, is used to measure twelve leads.

Depending on which lead shows irregularities, experts can find out things like in which part of the heart muscle an infarction has occurred, or whether a heart rhythm problem is coming from the left or right ventricle.

Normal ECG – Left: the leads from the arms and legs, Right: the leads from the chest wall. Source: CCB Frankfurt a.M.


  • Schmidt R, Lang F, Heckmann M. Physiologie des Menschen: mit Pathophysiologie. Berlin: Springer; 2017.

  • Trappe HJ, Schuster HP. EKG-Kurs für Isabel. Stuttgart: Thieme; 2017.

  • IQWiG health information is written with the aim of helping
    people understand the advantages and disadvantages of the main treatment options and health
    care services.

    Because IQWiG is a German institute, some of the information provided here is specific to the
    German health care system. The suitability of any of the described options in an individual
    case can be determined by talking to a doctor. We do not offer individual consultations.

    Our information is based on the results of good-quality studies. It is written by a
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Basic principles of the ECG. The normal ECG

Author(s): Dr Dallas Price

Consultant Cardiologist, St Mary’s Hospital, Isle of Wight, UK


The electrocardiogram (ECG) is one of the simplest and
oldest cardiac investigations available, yet it can provide a wealth of useful
information and remains an essential part of the assessment of cardiac

With modern machines, surface ECGs are quick and easy to
obtain at the bedside and are based on relatively simple electrophysiological
concepts. However junior doctors often find them difficult to interpret.

This is the first in a short series of articles that aim to:

  • Help
    readers understand and interpret ECG recordings.
  • Reduce
    some of the anxiety juniors often experience when faced with an ECG.

Basic principles

What is an ECG?

An ECG is simply a representation of the electrical activity
of the heart muscle as it changes with time, usually printed on paper for
easier analysis. Like other muscles, cardiac muscle contracts in response to
electrical depolarisation of the
muscle cells. It is the sum of this electrical activity, when amplified and
recorded for just a few seconds that we know as an ECG.

Basic Electrophysiology of the Heart (see
Figure 1)

The normal cardiac cycle begins with spontaneous
depolarisation of the sinus node, an area of specialised tissue situated in the
high right atrium (RA). A wave of electrical depolarisation then spreads
through the RA and across the inter-atrial septum into the left atrium (LA).

The atria are separated from the ventricles by an
electrically inert fibrous ring, so that in the normal heart the only route of
transmission of electrical depolarisation from atria to ventricles is through
the atrioventricular (AV) node. The AV node delays the electrical signal for a
short time, and then the wave of depolarisation spreads down the
interventricular septum (IVS), via the bundle of His and the right and left
bundle branches, into the right (RV) and left (LV) ventricles. Hence with normal
conduction the two ventricles contract simultaneously, which is important in
maximising cardiac efficiency.

After complete depolarisation of the heart, the myocardium
must then repolarise, before it can
be ready to depolarise again for the next cardiac cycle.

Figure 1. Basic
electrophysiology of the heart

Electrical axis and recording lead vectors (see
Figures 2 and 3)

The ECG is measured by placing a series of electrodes on the
patient’s skin – so it is known as the ‘surface’ ECG.

The wave of electrical depolarisation spreads from the atria
down though the IVS to the ventricles. So the direction of this depolarisation
is usually from the superior to the inferior aspect of the heart. The direction
of the wave of depolarisation is normally towards the left due to the leftward
orientation of the heart in the chest and the greater muscle mass of the left
ventricle than the right. This overall direction of travel of the electrical
depolarisation through the heart is known as the electrical axis.

A fundamental principle of ECG recording is that when the
wave of depolarisation travels toward a recording lead this results in a
positive or upward deflection. When it travels away from a recording lead this
results in a negative or downward deflection.

The electrical axis is normally downward and to the left but
we can estimate it more accurately in individual patients if we understand from
which ‘direction’ each recording lead measures the ECG.

Figure 2. Orientation of
the limb leads showing the direction from which each lead ‘looks’ at the heart

By convention, we record the standard surface ECG using 12
different recording lead ‘directions,’ though rather confusingly only 10
recording electrodes on the skin are required to achieve this. Six of these are
recorded from the chest overlying the heart – the chest or precordial leads. Four are recorded from the limbs – the limb leads. It is essential that
each of the 10 recording electrodes is placed in its correct position,
otherwise the appearance of the ECG will be changed significantly, preventing
correct interpretation.

The limb leads record the ECG in the coronal plane, and so
can be used to determine the electrical axis (which is usually measured only in
the coronal plane). The limb leads are called leads I, II, III, AVR, AVL and
AVF. Figure 2 shows the relative directions from which they ‘look’ at the
heart. A horizontal line through the heart and directed to the left (exactly in
the direction of lead I) is conventionally labelled as the reference point of 0
degrees (0 o). The directions from which other leads ‘look’ at the
heart are described in terms of the angle in degrees from this baseline.

The electrical axis of depolarisation is also expressed in
degrees and is normally in the range from -30 0 to + 90 0.
A detailed explanation of how to determine the axis is beyond the scope of this
article but the principles mentioned here should help readers to understand the
concepts involved.

The chest leads record the ECG in the transverse or
horizontal plane, and are called V1, V2, V3, V4, V5 and V6 (see Figure 3).

Figure 3. Transverse
section of the chest showing the orientation of the six chest leads in relation
to the heart

Voltage and timing intervals

It is conventional to record the ECG using standard measures
for amplitude of the electrical signal and for the speed at which the paper
moves during the recording. This allows:

  • Easy
    appreciation of heart rates and cardiac intervals and
  • Meaningful
    comparison to be made between ECGs recorded on different occasions or by
    different ECG machines.

The amplitude, or voltage, of the recorded electrical signal
is expressed on an ECG in the vertical dimension and is measured in millivolts
(mV). On standard ECG paper 1mV is represented by a deflection of 10 mm. An
increase in the amount of muscle mass, such as with left ventricular hypertrophy
(LVH), usually results in a larger electrical depolarisation signal, and so a
larger amplitude of vertical deflection on the ECG.

An essential feature of the ECG is that the electrical
activity of the heart is shown as it varies with time. In other words we can
think of the ECG as a graph, plotting electrical activity on the vertical axis
against time on the horizontal axis. Standard ECG paper moves at 25 mm per
second during real-time recording.   This
means that when looking at the printed ECG a distance of 25 mm along the
horizontal axis represents 1 second in time.

ECG paper is marked with a grid of small and large squares.
Each small square represents 40 milliseconds (ms) in time along the horizontal
axis and each larger square contains 5 small squares, thus representing 200 ms.
Standard paper speeds and square markings allow easy measurement of cardiac
timing intervals. This  enables
calculation of heart rates and identification of abnormal electrical conduction
within the heart (see Figure 4).

Figure 4. Sample of
standard ECG paper showing the scale of voltage, measured on the vertical axis,
against time on the horizontal axis

The normal ECG

It will be clear from above that the first structure to be
depolarised during normal sinus rhythm is the right atrium, closely followed by
the left atrium. So the first electrical signal on a normal ECG originates from
the atria and is known as the P wave.
Although there is usually only one P wave in most leads of an ECG, the P wave
is in fact the sum of the electrical signals from the two atria, which are
usually superimposed.

is then a short, physiological delay as the atrioventricular (AV) node slows
the electrical depolarisation before it proceeds to the ventricles. This delay
is responsible for the PR interval, a short period where no electrical activity
is seen on the ECG, represented by a straight horizontal or ‘isoelectric’ line.

Depolarisation of the ventricles results in usually the
largest part of the ECG signal (because of the greater muscle mass in the
ventricles) and this is known as the QRS

  • The
    Q wave is the first initial downward or ‘negative’ deflection
  • The
    R wave is then the next upward deflection (provided it crosses the isoelectric
    line and becomes ‘positive’)
  • The
    S wave is then the next deflection downwards, provided it crosses the
    isoelectric line to become briefly negative before returning to the isoelectric

In the case of the ventricles, there is also an electrical
signal reflecting repolarisation of the myocardium. This is shown as the ST segment and the T wave. The ST segment is normally isoelectric, and the T wave in
most leads is an upright deflection of variable amplitude and duration (see
Figures 5 and 6).

Figure 5. The major
waves of a single normal ECG pattern

Figure 6. Example of a
normal 12 lead ECG; notice the downward deflection of all signals recorded from
lead aVR. This is normal, as the electrical axis is directly away from that

Normal intervals

The recording of an ECG on standard paper allows the time
taken for the various phases of electrical depolarisation to be measured,
usually in milliseconds. There is a recognised normal range for such

  • PR interval (measured from the
    beginning of the P wave to the first deflection of the QRS complex). Normal
    range 120 – 200 ms (3 – 5 small squares on ECG paper).
  • QRS duration (measured from first
    deflection of QRS complex to end of QRS complex at isoelectric line). Normal
    range up to 120 ms (3 small squares on ECG paper).
  • QT interval (measured from first
    deflection of QRS complex to end of T wave at isoelectric line). Normal range
    up to 440 ms (though varies with heart rate and may be slightly longer in

Heart rate estimation from the ECG

Standard ECG paper allows an approximate estimation of the
heart rate (HR) from an ECG recording. Each second of time is represented by
250 mm (5 large squares) along the horizontal axis. So if the number of large
squares between each QRS complex is:

  • 5
    – the HR is 60 beats per minute.
  • 3
    – the HR is 100 per minute.
  • 2 – the HR is 150 per minute.


Electrocardiograms (ECG, EKG) & Other Specialized EKG Tests

An electrocardiogram (also called EKG or ECG) is a test that records the electrical activity of your heart through small electrode patches attached to the skin of your chest, arms, and legs. An EKG may be part of a routine physical exam or it may be used as a test for heart disease. An EKG can be used to further investigate symptoms related to heart problems.

EKGs are quick, safe, painless, and inexpensive tests that are routinely performed if a heart condition is suspected.

Your doctor uses the EKG to:

  • Assess your heart rhythm
  • Diagnose poor blood flow to the heart muscle (ischemia)
  • Diagnose a heart attack
  • Evaluate certain abnormalities of your heart, such as an enlarged heart


How Should I Prepare for an EKG?

To prepare for an EKG:

  • Avoid oily or greasy skin creams and lotions the day of the test. They interfere with the electrode-skin contact.
  • Avoid full-length hosiery, because electrodes need to be placed directly on the legs.
  • Wear a shirt that can be easily removed to place the leads on the chest.

What Happens During an EKG

During an EKG, a technician will attach 10 electrodes with adhesive pads to the skin of your chest, arms, and legs. Men may have chest hair shaved to allow a better connection. You will lie flat while the computer creates a picture, on graph paper, of the electrical impulses traveling through your heart. This is called a “resting” EKG. This same test may also be used to monitor your heart during exercise.

It takes about 10 minutes to attach the electrodes and complete the test, but the actual recording takes only a few seconds.

Your EKG patterns will be kept on file for later comparison with future EKG recordings.

If you have questions, be sure to ask your doctor.


What Is a Holter Monitor?

In addition to the standard EKG, your doctor may recommend other specialized EKG tests, including a holter monitor or a signal-averaged electrocardiogram.

A holter monitor is a portable EKG that monitors the electrical activity of a person’s heart, generally for one to two days, 24 hours a day. It is most often used when the doctor suspects an abnormal heart rhythm or ischemia (not enough blood flow to the heart muscle).

It is a painless test; electrodes from the monitor are taped to the skin. Once the monitor is in place, you can go home and perform all of your normal activities (except showering). You will be asked to keep a diary of your activities and any symptoms you experience and when they occur.

What Is an Event Monitor?

If your symptoms are infrequent your doctor may suggest an event monitor. This is a device that, when you push a button, will record and store the heart’s electrical activity for a few minutes. Each time you develop symptoms you should try to get a reading on the monitor. Event monitors are typically used for one month. This information can later by transmitted by telephone to the doctor for interpretation.

What Is a Signal-Averaged Electrocardiogram?

This is a painless test used to assess whether a person is at high risk of developing a potentially fatal heart arrhythmia. It is performed in a similar manner to the EKG, but uses sophisticated technology to look for risk of heart arrhythmias.


Routine EKG Finding Could Signal Serious Heart Problem


A common test that records the heart’s electrical activity could predict potentially serious cardiovascular illness, according to a UC San Francisco-led study.

Gregory Marcus, MD

A cardiac condition called left anterior fascicular block (LAFB), in which scarring occurs in a section of the left ventricle, may not be as benign as currently thought and could increase the likelihood of heart failure, sudden cardiac death or atrial fibrillation.

In a study published on April 17 in the Journal of the American Medical Association (JAMA), UCSF researchers and their colleagues at Wake Forest School of Medicine and the University of Washington, Seattle, analyzed data on 1,664 people over the age of 65 who were medically followed for 16 years.

The researchers selected those who had no evidence of cardiovascular disease from the National Institutes of Health-sponsored Cardiovascular Health Study. People with heart failure, high blood pressure or diabetes, or who had heart attacks, were excluded from the study sample.

“We then compared those with LAFB to those with a normal electrocardiogram (EKG),” said senior author Gregory Marcus, MD, an electrophysiologist with the UCSF Division of Cardiology and an associate professor in residence with the UCSF School of Medicine. “We found that those who had LAFB indeed had a higher risk of atrial fibrillation, congestive heart failure and death.”

After adjusting for other potential confounding variables, LAFB posed a 57 percent greater risk for sudden cardiac death, an 89 percent greater risk for atrial fibrillation, and a 143 percent greater risk for heart failure.

LAFB is a blockage of one of the electrical branches that delivers electrical signals to a part of the left ventricle, one of two chambers in the heart. Small studies suggest it is associated with fibrosis or scarring of the left ventricle, but the clinical ramifications of this have not been previously studied. It is unknown how many people LAFD affects.

“We now have come to realize that important cardiovascular diseases like atrial fibrillation, heart failure and maybe sudden cardiac death, are related to fibrosis of the left side of the heart,” said Marcus, who sees cardiology patients at the UCSF Medical Center. “So we sought to test the hypothesis that LAFB, even in those people who are otherwise healthy, might be a readily available marker that any doctor can see on an EKG, of a propensity to left-heart fibrosis. And it therefore might predict those at risk for atrial fibrillation, heart failure and death.”

The top EKG shows a reading of a person with a healthy heart. The bottom EKG shows a reading of a person with left anterior fascicular block (LAFB), previously thought to be benign but found by a UCSF-led team to potentially signal a serious heart condition.

There currently is no treatment for people with LAFB. However, this new finding potentially could open up a new area of research in cardiology, according to Marcus.

“Currently there is a therapy for people with heart failure and a left bundle branch block using a special pacemaker called a biventricular pacemaker or cardiac resynchronization therapy,” Marcus said. “So one question we have to explore is whether people with LAFB and heart failure, for example, might benefit from a specialized pacemaker.”

Patients also can reduce their overall cardiovascular risk with lifestyle modifications, such as choosing a healthy diet, exercising regularly and eliminating tobacco products.

“This study may suggest that LAFB, even in the absence of known high blood pressure or diabetes, should be thought of as a cardiovascular risk factor,” Marcus said. “Those patients with LAFB perhaps should be considered the same as someone with an established cardiovascular risk factors.”

Co-authors include Mala Mandyam of the UCSF Division of Cardiology, Electrophysiology Section; Eric Vittinghoff, PhD, of the UCSF Department of Epidemiology and Biostatistics; Elsayed Z. Soliman, MD, of the Wake Forest School of Medicine; and Susan R. Heckbert, MD, PhD, of the University of Washington, Seattle.

This study was supported by the National Center for Research Resources, the National Center for Advancing Translational Sciences, and the Office of the Director, National Institutes of Health, through grant TL1 RR024129 to UCSF’s Clinical and Translational Science Institute (CTSI). This research was also supported by contracts HHSN268201200036C, N01HC85239, N01HC55222, N01HC85079, N01HC85080, N01HC85081, N01HC85082, N01HC85083, N01HC85086, and grants HL080295 and HL068986 from the National Heart, Lung, and Blood Institute, with additional contributions from the National Institute of Neurological Disorders and Stroke. Additional support was provided by grant AG023629 from the National Institute on Aging and the Joseph Drown Foundation.

Researchers reported no conflicts of interest to disclose.

ECG Small Signal General and Analysis

Electrocardiogram (ECG or EKG) is the most common way to identify various ailments, especially when the ailment is related to the heart. To perform an ECG, the medical personnel places the leads on the patient’s skin. The leads measure the heart’s electrical activity of one heartbeat cycle and record it as a continuous line tracing on paper to produce a graph. The ECG signal may indicate:

  • Cause of unexplained chest pain
  • Cause of symptoms of heart disease
  • How well medicines are working for the patient
  • How well implants such as pacemakers are working
  • Other heart-related disease

Figure 1. The superposition of all the heart action potentials of the QRS complex signal is formed to produce the ECG signal.

Today, there is a wide array of cardiac equipment that displays and interprets ECG signal patterns, and medical equipment designers need a flexible, reliable, and accurate way to seamlessly generate ECG signal patterns to verify their designs (Figure 1).

ECG Signal Generation

In this scenario, a maker of cardiac monitoring equipment needs to test its latest design’s ability to capture and interpret ECG signals. The company’s design engineers want to simulate gradual changing sequences of normal and abnormal ECG signals to test and tune the design’s input signal and condition hardware and firmware interpretation algorithms to ensure the design does not produce false positives or life-threatening false negatives. A few key factors need to be taken into consideration when generating ECG signal, such as:

  • Low-amplitude signal ±1mV or ±0.5mV
  • Large offset due to half potential developed at electrode
  • System noise (50/60Hz) from the power lines that forms the common mode signal
  • Complex ECG signal pattern

The firmware design of the ECG equipment can resolve the offset developed by electrode and common mode signal from power lines. The designer needs to use firmware to remove the power line noise, implement a filter to remove the electrode offset, and correct noise.

Figure 2. Simple voltage divider.

This article focuses on two considerations of ECG signal generation: the clean, low-amplitude signal generation; and the complexity of the ECG pattern generation. The best solution for this is to use an Arbitrary Waveform Generator (AWG).

Very-Low-Amplitude Signal

Real-world cardiac signals typically are very low in amplitude — often only a couple of millivolts or even less. This poses a problem for simulation using AWGs because typically their lowest amplitude setting is between 10 mV and 1 mV. When they are used at their lowest amplitude, the AWG’s signal-to-noise ratio can become a problem. One way to overcome this drawback is to use a voltage divider at the output of the AWG. Since ECG signals are at such low frequencies, the divider only needs resistors, as reactive effects can be ignored. When constructing the voltage divider, it is important to remember that the amplitude accuracy of the divider’s output signal depends on the precision of the resistors used in the divider. For example, a voltage divider that uses a 10-kohm resistor and a 10- ohm resistor will reduce amplitude of 1 V down to 1 mV, as shown in Figure 2.

Complex ECG patterns

There are various methods to create and store an ECG on an AWG, including:

  1. User can use a digitizer or an oscilloscope to capture the actual ECG signal from a patient and upload the points to the AWG. Most modern AWGs are able to support this.
  2. User can use mathematical software such as MATLAB. 3. The AWG has the built-in typical ECG waveform.

Figure 3. Example ECG waveform sequence.

In a real-life scenario, the ECG waveform is not standard or typical; rather, it is a dynamic signal that varies from one to another, and seamless transition from one complex pattern to another is an important feature that a designer would desire. In addition, arb sequencing ability is very important to the designer. This allows an actual ECG waveform cycle to run continuously and further stimulate an actual ECG signal for the designer to test the ECG equipment (Figure 3).

In the medical industry, a precision oscilloscope is very important test equipment that the ECG designer needs for their design and verification phases. The oscilloscope needs to be able to capture, display, and analyze the ECG patterns.

Figure 4. A noisy environment on the displayed waveform under normal acquisition mode. This is a typical display for most ECG waveforms using a normal oscilloscope.

Measuring Very-Low-Amplitude Signals

One of the key test challenges for a test engineer is to capture the ECG signal, especially in a noisy environment and most importantly, the low amplitude of the signal. Typically, the amplitude value is in the 0.5 mV to 1 mV range for heart rate between 60 beats per minute and 100 beats per minute. Hence a designer normally uses an amplifier to strengthen the signal, set an offset to the scope channel, and even use waveform averaging to capture an accurate ECG signal. Waveform averaging is not suitable for noise reduction due to the fact that the ECG signal is not repetitive, and the signal needed is too weak and no signal can be observed (Figure 4).

The best solution is to select an oscilloscope with a fast waveform update rate in order to capture the intermittent signal anomalies. The faster the waveform update rate, the shorter the “dead time” or the time the oscilloscope misses the signal completely. Hence during acquisition mode, extra samples are averaged in order to reduce random noise and produce a smoother trace, and effectively increase vertical resolution, as shown in Figure 5.

Figure 5. A captured ECG signal with 1 mV and 0.5 mV amplitude in the high-resolution acquisition mode.

A mask test is one of the best ways to verify a healthy ECG signal against the measures signal. The oscilloscope’s display defines the region where the waveform must remain in order to comply with the golden signal. This helps a designer to visually identify any abnormality in the measured signal instantly.

Solution for ECG Signal Generation

Keysight’s InfiniiVision 4000 X-series oscilloscope.

State-of-the-art AWGs have arb sequencing capability and deep arb memory to provide an excellent solution for ECG simulation. The sequencing provides the ability to seamlessly transition through various ECG signal conditions. The deep arb memory complements the sequencing capability to allow storage of a large library of ECG waveforms. This allows an engineer to add subtle changes from waveform to waveform for high-resolution testing of designs.

An oscilloscope is the best tool in analyzing very-low-amplitude signals (such as ECG signals) with superb accuracy and suitability for medical application. Designers can analyze the full spectrum of the signal in high-resolution acquisition. The signal analysis is also economical in that it does not require additional accessories to achieve high vertical resolution for the ECG signal amplitude. In addition to this, masking the golden signal allows designers to identify anomalies in the ECG pattern with ease.

This article was written by Kah-Meng Chew and Doris Lau of Keysight Technologies, Santa Rosa, CA. For more information, Click Here .

Test & Measurement Tech Briefs Magazine

This article first appeared in the December, 2016 issue of Test & Measurement Tech Briefs Magazine.

Read more articles from this issue

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Why is my EKG trace noisy? Why doesn’t my EKG trace look like the trace in the book?

If you are using the Go Direct® EKG Sensor (GDX-EKG) make sure you are using the EKG channel.

If you are using the EKG Sensor (EKG-BTA) you should update to the most recent version of Logger Pro or LabQuest App. The most recent versions of these two programs automatically filter data collected with an EKG Sensor.

If you are using an older version of Logger Pro, you can open an experiment file that has been set up to automatically filter the data. There are two experiment files that will work. To find the files

1. In Logger Pro, choose Open from the File menu.
2. Open either “Analyzing Heart EKG” in the “Human Physiology w Vernier” folder or “Monitoring EKG” in the “Biology w Vernier” folder.

If problems persist, check the following:

There are several things that can increase the noise in an EKG trace. Most of these issues can be addressed using proper electrode placement and placement of the sensor. Software filtering can also be used to clean up a noise signal as well. See the instructions below.

Is an EKG trace visible? If the QRS complex (big spike) in the EKG trace is not visible then there is either a problem with the EKG sensor or a problem with the subject. To test the EKG sensor, collect data while shaking the leads when they are not attached to the subject. You should see a change in the trace. If you do not see a change, something could be wrong with the leads or the sensor. Call technical support.

In a few cases (less than 12%) the subject’s skin may not be conductive enough to pick up a good EKG trace. Abrasive / conductive electrode gel and clinical grade EKG electrodes may need to be used in this case. The easiest way to test this is to record an EKG from another individual. If you get a good EKG from another subject then skin conductivity is the problem.

If the EKG trace is visible but is noisy there are several things that you can do to decrease the noise.

If you are using a LabQuest or laptop computer, use the battery power (remove the AC adapter). This should decrease the noise.

Let the electrodes sit on the skin for 1-2 minutes before you begin recording. This will increase the strength of the signal.

Place the grounding electrode on the ulnar process of the wrist. If you are recording from the chest, place the grounding lead on the clavicle. This will increase the strength of the signal and should decrease any noise.

Do not place the EKG sensor near computers, cell phones, power outlets or the LabQuest. The EKG sensor is not shielded and can pick up electronic interference and noise. The best location for the EKG sensor is on the subject’s lap or knee during a recording.

If problems persist, please contact Technical Support.

(PDF) Dividing the electrocardiogram signal into cycles


methods of obtaining estimates of the cross-correlation function, although the results of

analysis in such cases are somewhat lower.

Methods based on digital filtering. The approach based on

using digital filtering for QRS complex recognition,

can be considered as one of the options for a simplified implementation of

correlation methods.In this case, the recognition procedure is divided into

two interrelated stages. First, the signal is passed through a digital filter

(or filter chain) with a frequency response

corresponding to the spectrum of the QRS complex, obtained by averaging

spectral estimates of a large number of complexes of different morphologies. This

is adequate for calculating the cross-correlation function between the signal and

by some “typical” ventricular complex, the shape of which

corresponds to the impulse response of the applied CF.At the next

stage of the analysis according to the algorithm based on threshold rules,

the QRS complex is preliminarily detected and its reference point

is determined, which serves to align the current complex in time with

averaged samples of previously found complexes related to

different classes of form. The coefficients of cross-correlation

between the detected complex and all available samples are calculated. On

, based on the results obtained, the analyzed complex either belongs to

one of the pre-existing classes, or is considered the first

representative of a new form class, or is rejected as an artifact.

The procedure described for the algorithm based on digital filtering,

is used in one form or another in many developments, since

is the result of a compromise between the fundamentally achievable high

quality of QRS complex detection using correlation methods,

and limited performance of widespread

microprocessors. The comparative computational simplicity of the described

method is explained by the fact that in this case, easily implementable

DFs are usually used, and the calculation of the correlation function is performed for each sample

at one single point (i.e.That is, it is not a function that is calculated, but the cross-correlation coefficient


Consider the algorithm for recognizing the QRS complex based on digital

filtering. This algorithm can be conditionally subdivided into three

successively performed stages:

– identification of the QRS complex (improving the conditions for detecting


– detecting the QRS complex (establishing the fact of its presence),

– determining the QRS reference point -complex (used to measure

duration of cardiocycles),

– recording data on signal splitting.

Isolation of the QRS complex. We receive a signal that has passed the

filtering procedure from interference. One of the digital filtering methods is

differentiation. With the help of this filter, it is possible to select

high-frequency sections of the input signal falling on the QRS complex.

HART.ZONE | Skolkovo project participant

Hart.Zon LLC has developed a technology for continuous monitoring of electrocardiogram (ECG) for wearable devices and accessories such as headphones, glasses, watches, hats, clothing accessories and jewelry.

Heart.Zone LLC was founded in 2017 after the founders moved from Vancouver to Moscow. The roots of the project go back to 2011, when the first ECG headphone system entered the top ten Bluetooth Innovation World Cup projects. The company employs an international team of 12 people in America, Europe, China, Oceania and Russia.

About the Project

In September 2018, Apple introduced Apple Watch with ECG measurement and cardiac arrhythmia recognition. This presentation opened a new page for the mass production of personal ECG instruments.However, the Apple Watch only provides intermittent, non-continuous ECG monitoring. Major players are currently looking for continuous ECG monitoring technologies for wearable gadgets.

Heart.Zone ™ continuous ECG monitoring technology monitors heart load in real time and alerts the user to cardiac stress. The Heart.Zone ™ continuous ECG monitoring technology is offered to electronics manufacturers in the form of a micromodule and API for a mobile application.

The Heart.Zone ™ micro-module is a miniature single-channel ECG sensor with electrodes that touch the human skin. They can be discreetly integrated into wearable devices and accessories such as headphones, glasses, caps, helmets, watches and bracelets.

Unlike other portable ECG devices, devices with the Heart.Zone ™ ECG micro-module provide:

• continuous monitoring of the heart in motion without limiting the user’s mobility and comfort;

• warning the user about the load on the heart, cardiac stress and emotional state;

• record ECG together with sound accompaniment: voice and breathing;

Features of the Heart ECG continuous monitoring technology.Zone ™:

• USB Type-C ™ headphones without internal power supply transmit an analog ECG signal over the microphone line in the ultrasonic range. The user can simultaneously listen to music, record his feelings through the microphone and ECG;

• Wireless headphones, glasses, hats, helmets, necklaces and pendants with miniature batteries can use Bluetooth to simultaneously record voice and ECG;

• Heart.Zone ™ ECG modules built into smart watches, bracelets and other headsets can measure ECG using wireless electrodes at two or more points on the human body, for example, in the ear and on the wrist;

Problems with recording the ECG signal

If the electrode cable is damaged, the contact of the electrodes with each other will not affect the shape of the ECG signal – it will still remain chaotic.But even if this did not happen and the signal took the form of a flat line, you should make sure that this is not a coincidence and the cable is really intact.

To do this, keeping both electrodes close to each other with one hand, gently bend (but not breaking them!) The electrode cables along their entire length with the other hand, while controlling the shape of the ECG signal on the screen. Most often, careless use damages the cable next to its attachment to the electrode pins, in the place where the plug braid ends and the cable itself begins.

If, during the bending of the cables, the ECG signal becomes chaotic or the contact of the electrodes with each other does not lead to a flat line on the ECG graph at all, then the cable of the electrodes has an internal break and requires replacement. Repeat the above procedure again to make sure that the problem is in the cable, and, for example, not in poor contact of the electrodes with each other. After that, you should contact the Technical Support Service of the Dinamika company and provide the technical support operator with access to your computer.After that, under his guidance, do again everything that is described above in the “Breakdown Diagnostics” section to eliminate the possibility of an error.

After a technical support specialist confirms that the problem is indeed a damaged electrode cable, there are several options for the development of events.

You can send your cardiorecorder to replace the cable to the Dinamika company at the following address:

196158, Russian Federation, city of St. Petersburg,
Moskovskoe shosse, house 14, building 1, office 166,
tel.+7 (911) 925-27-77.

We strongly recommend not to use the Russian Post for sending, but to use the services of any courier service.