Electrocardiography (2. LF UK)

ECG Practical
Electrocardiography

1. Introduction

The human heart is a 4 chamber muscular structure in the thoracic cavity, pumping oxygenated blood to all body parts, in a regular yet non-stoping rhythm.

Although being controlled by parts of the Central Nervous System, for rate regulation, the heart generates it’s contractions by itself, this happens by electrical signals (action potentials) taking place in special sites of the heart tissue, called the Electrical conduction system of the heart, the impulse is then transported to all cardiac tissue, causing the heart to contract, and blood to be ejected.

These electrical signals can be detected in some other areas in the body, such as the skin, by using special electrodes, giving a view on the electrical activity of the heart, and the different phases of a cardiac cycle, the procedure of detection of the cardiac electrical impulses through the skin by electrodes placed on the chest and limbs is called Electrocardiography (ECG).

2. Importance in clinical medicine

Electrocardiograph is used mainly for detecting problems related to the heart, mainly in it’s electrical activity which causes the pumping of blood to the lungs and rest of the body. The electrical pulse started by the SA node, or cardiac pacemaker is produced by the heart causing contraction of the heart in a specific area and can be detected and shown as ascending and descending lines, or waves. Since the heart is widely interactive with the lungs, problems in breathing may have something to do with the heart and vice versa.

ECG can be used generally to detect most problems involving the heart or heartbeat. If a patient is experiencing chest pains, dizziness, shortness of breath, bradycardia (slow heartbeat) or tachycardia (fast heartbeat), ECG may be used to diagnose the hearts electrical activity to find the cause. ECG may be also used to detect cardiac side effects of diseases or conditions such as high blood pressure, high cholesterol, cigarette smoking, diabetes, and a family history of early heart disease or also of specific medication. If an artificial pacemaker is installed in the heart, ECG can be used to follow up the function of the device in case it is not working properly.

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What are its advantages and disadvantages?

Electrocardiography has remarkable advantages and some disadvantages (for resting and stress test).

First of all, it can function as an important indicator of potential causes and consequences of a cardiac disease.

This can be enormously significant, because it can discover and prevent, for example heart arrhythmia, Hypertrophy (thickness of heart muscle) or heart infarction. Additionally, it is a valid diagnostic tool for the detection of an electrophysiological dysfunction or disorder.

In respective to the procedure, it is crucial to emphasise that it is a relatively easy procedure to apply and to perform. Moreover, it is a non-invasive and a painless method, which is resulting in a fast and most of the time accurate diagnosis/diagnostic outcome.

However, it is important to mention that obtaining and analysing the results can be time-consuming, if not having an analysis program.

In addition, for measuring the results the examiner has to be presence every second to control the program and to look after the patient.

In some cases the results do not discover a structural damage or disorder.

Therefore, the program shows results, which do not match the clinical facts. (false negative or false positive results)

For that you need clinical experience to interpret the results.

(One point, regarding the stress test can be a possible heart attack or dysrhythmia due to an exhausting exercise.)

How does it work?

Electrodes will be attached to the skin of the patient on the limbs and chest area. A conductive gel is also used with the electrodes to aid in the measurement of the electrical activity of the heart. The electrodes record the potentials produced by the polarity changes of the myocardium in MILLIvolt (mV). There are different ECG machines: 3-lead, 5-lead and 12-lead ECG. The 12-lead ECG gives a more complete measurement and has in total 10 electrodes, that together provide 12 different angles from the heart. Each different angle is called a lead. These 12 leads are: 3 bipolar limb Einthoven's leads, 3 unipolar limb augmented leads and 6 unipolar precordial leads. For the test, 6 electrodes are located in the chest area around the heart and 4 are symmetrically attached to each of the limbs. The data collected by the electrodes are printed on a graph and analysed by the physician. The test usually takes 5 to 10 minutes.

Are there any risks involved in it’s use (for patients and the clinical staff)?

First of all the ECG is procedure without any risk factors. It represents a simple and painless way to measure the electrical activity of the heart. However, one type of ECG can cause some hazards. During the stress test the patient has to perform physically exhausting exercises. Therefore, a treadmill or a cardio glider is used. The level of the strain depends on the age and the fitness of the patient._ Sometimes the patient get some medication that mimics the effects of exercise._

During the stress test irregular heartbeats, breathlessness, dizziness, drop or rise in blood pressure or chest pain can occur. The physician has to monitor the electrocardiogramm, the blood pressure and the pulse. In addition the stress test must not be performed if the patient suffers from certain diseases like myocardial inflammation, unstable angina pectoris, very high blood pressure at rest or lung edema.

All things considered the ECG is a safe procedure. Although the stress test, which includes high exercise, can lead to effects like dysrhythmia or in extremely rare cases heart attack. Important is, that those effects are not caused by the Electrocardiography, but rather by high exercise.

Are there ethical issues associated with the topic?

In general, the ECG does not have any ethical issues.

Some people do not want to perform an ECG. One reason can be that those people do not want to know if they have any cardiac diseases. In that case, the dilemma of the physician is to decide whether to accept the decision of the patient or not. It could be neglected, if the physician is absolutely sure that the patient could suffer from a cardiac disease.

(A very controversial ethic issue which can be mentioned is also that in some culture the man is in charge of the woman decision.)

4. The equipment

1. BTL-08 ECG apparatus

The electrocardiograph records and detects the heart’s electrical activity and is used in cardio-diagnostics. The heart produces electrical impulses which spread through the heart muscle to make the heart contract. These impulses are in a range of hundreds of microvolts up to AROUND 1 millivolt and  can be detected by the ECG machine. It measures  the tiny electrical changes on the skin caused by the heart muscles‘ depolarisation during each heart action. Therefore the machine has to be very percise. The signals can be transformed to waves and recorded to a paper or computer.

The BTL-08 ECG apparatus offers the possibility to record the ECG curve automatically or manually.

2. Electrodes

The electrodes are the detectors placed at the patient’s body and they are connected to the ECG apparatus with a wire for each electrode. For a conventional 12-leads ECG, 10 electrodes are placed on the patient’s chest and limbs. The overall magnitude of the heart's electrical potential is measured from 12 different leads and is recorded over a certain period of time. In our project, we only use 4 limb electrodes with different colored tongs positioned as followed:

4 limb electrodes with tongs (R, L, F, N) and connected electrode cables

- R: (red) right wrist

- L: (yellow) left wrist

- F: (green) right ankle

- N: (black) left ankle

3. Computer with the BTL 08 Win program

The computer is connected to the ECG and the software evaluates the recorded signals and transforms it into wave diagrams. It provides a detailed analysis, diagnostics and printing of the recorded electrocardiogram. It also offers the possibility to change between automatic and manual measurement.

 

 

 

5. Methodology

Task 1

1.      Turn on the computer

2.      Open the ECG file and click on the folder of your group

3.      Create a new patient and fill in the personal data

-     in the ID field you are supposed to put in your birth number. In case you don’t have it, you can put in a not controllable birth number, such as: 010101/999

-     in the Comment field you should fill in personal information, that could influence the heart rate, such as: smoking, drinking alcohol, doing sports, medication, personal anamnesis and family anamnesis

1.      Plug the cables in the limb electrodes (red, yellow, green and black clips) and place them on the cot

2.      The examined person lies down and the electrodes get attached on the moistened skin. Red - right wrist, yellow - left wrist, green - left ankle, black - right ankle

3.      Turn on the ECG device

4.      Start the New standard ECG examination (it might take a while, until signal stabilizes)

5.      Check if the parameters are set correctly

-     Time base (posuv): speed usually 25 mm/s, can be increased to 50 mm/s

-     Amplitude (zesílení): usually 10 mm/mV, can be set up and down

-     Filter (filtr): 50 Hz

-     Time constant (časová konstanta): choose as long as possible (3.2 s)

1.      Save a 10 sec. period by pressing the Enter button. Wait a little and repeat this twice

2.      Terminate recording by pressing the Esc button

3.      Turn off the ECG device and remove the electrodes from examined person

4.      Print the three measurements

-     Parameter setting:

-     Grid (mřížka): normal

-     Time base (posuv): 25 mm/s

-     Amplitude (amplituda): large enough to not overlap the curves, usually 10 mm/mV

-     Print leads (tisknout svody): all recorded (usually all)

-     Wave length (délka záznamu): 5 sec

-     Diagnosis (diagnóza): automatic diagnosis (intervals); approved diagnosis (leave empty)

-     Image export: not important

Graphical interpretation of measurements:

1.      Choose one lead (best readable one) for further evaluation

2.      Measure individual requested intervals and amplitudes in the printed record, fill in the appropriate report section; watch given units

3.      Calculate average R-R interval and heart-rate (frequency) in both required units

4.      Draw the lengths of amplitudes of QRS vectors to the scheme of Einthoven triangle; using these projections in individual leads restore the vector of the electric axis of the heart (example given in Figure below)

5.      Evaluate amplitude [mV] and slope [º] of the axis vector from the drawing

6.      Compare the results to those of automatic evaluation and discuss the possible differences and the method itself

Task 2

1.      Attach the electrodes to examined person like in Task 1

2.      Turn on the ECG device

3.      Start the New long ECG examination

4.      Choose lead II and set the interval for 3 min.

5.      The examined person needs to breathe in consistently for 5 sec. and then breathes out for another 5 sec. Inhaling and exhaling phases should be announced by the examiner, in order that the „patient“ can relax and the ECG can record the heart rate according to the respiration. DO NOT EXAMINE AN EPILEPTIC PERSON!

6.      Wait until signal is stabilized

7.      Start the ECG with the Enter button; heart in the lower right corner turns red, showing that the measurement has started

8.      If the time is up, the ECG window will automatically close

9.      Turn off the ECG device and remove the electrodes from examined person

10.   Print the measurements (one recorded minute on each sheet)

'6. Conclusion

What are the possible impacts on medicine?

The first heart rhythm measurements were made in the end of the 18th century. In 1984 the international society for computerized Electrocardiology (ISCE) was found with the aim to unite academia, industry and physicians and patients. Therefore they invite every year for their Annual conference where scientists, clinicians, engineers and policy makers can discuss the newest developments in cardiology. If we hadn’t societies which care above the future like the ISCE does, today’s cardiology would not be that successful in diagnosing heart rhythm abnormalities, infarctions et cetera and millions of lives could not be saved.

What future developments are envisaged in the area?

At this moment a new ECG machine is discussed and developed, called “CombynTM Function and Spaces-ECG“, with which it will be possible to diagnose several diseases in only three minutes. On the one hand the expensive time of doctors and patients will be reduced. On the other hand illnesses like cardiac insufficiency or the state of the aorta, oedema (accumulation of water) and the mass of muscles can be distinguished via this new technique.

References:

http://www.isce.org

http://steiermark.orf.at/news/stories/2742996/

https://de.wikipedia.org/wiki/Elektrokardiogramm

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