ELECTROCARDIOGRAPHY: CLASSICS IN CARDIAC FUNCTION ASSESSMENT

Quality of life and the life itself depend on heart function. Regular check-up helps to detect disorders as early as possible and prevent dangerous complications. Besides, the heart is a main body muscle. It is the first line of response to increased physical activity, so it is necessary to check the cardiac muscle (myocardium) before any training. Electrocardiography is considered as a classical method of assessment of the cardiovascular system. It enables to detect abnormalities fast, determine contraindications to the certain types of physical activity or health improvement procedures. Electrocardiograph registers electrical signals produced by the heart. Measurement results are recorded as a graph of electrical signals, electrocardiogram (ECG).

There are a lot of portable electrocardiograph types. Some of them are designed only for the electrocardiography, while others combine different technologies. For example, HSC Bioscanner Wellness makes it possible to calculate the heart rate variability (HRV) when recording one-channel ECG (by the standard leads only). Usually HRV is performed during pulseoximetry using the finger sensor, but sometimes data cannot be registered (for instance, because of opaque nail polish or when there is no a limb). Therefore, Bioscanner enables you to receive information for the HRV calculation both from finger sensor and from arm and leg electrodes while recording ECG.

Operating principle of any electrocardiograph is similar, but some technical features can impact the quality and accuracy of ECG recording. Digital and analogue filters distinguish the electrocardiograph of Bioscanner and make it possible to record a high-quality ECG.

HOW THE METHOD WORKS
The heart is a kind of generator of electrical impulses. They can be “skimmed” from the body surface with the use of electrodes (sensors). They are placed on the certain skin areas in such a way as to register the change in difference of potentials produced by the heart between two points, i. e. between two electrodes. That potential difference is called a lead. There are standard leads (electrodes are placed on legs and arms) and chest leads (electrodes are placed on the chest).

During ECG recording the following leads are registered:

— three standard leads (I, II, III),
— six standard chest leads ((V1-V6),
— three unipolar extremity leads (аVR, аVL and аVF).

So the first standard lead is a potential difference between electrodes on the right and left arms. The second standard lead is a potential difference between a left leg and a right arm. The third standard lead is a potential difference between a left leg and a left arm. The electrode on the right leg is necessary to ground.

Electrocardiogram makes it possible to assess cardiac muscle state, impulse conductance (cardiac conduction disturbances affect the normal heart function) as well as a cardiac rhythm and a heart rate. Bioscanner Wellness provides ECG recording in 3 or 12 leads: 3-channel or 12-channel electrocardiogram, respectively.

WHAT IT IS USED FOR
Any cardiac muscle damage (for example, when necrotic region (myocardial infarction) or heart inflammation (myocarditis) appears), large vessel disorders or mineral deficiency, affecting the heart function (potassium, magnesium, calcium), are reflected in the ECG immediately. Many life-threatening conditions at their early stages have no symptoms. Even myocardial infarction may not be manifested by sharp pain and other typical signs. It is important to be examined by means of electrocardiography on a regular basis, because cardiac disorders, undetected in time, are often causes of sudden death. This is particularly important for pregnant women and athletes due to sharp increasing stress on the heart. Electrocardiography is used actively as a screening diagnostics. It is well known that probability of cardiac and vessel disorders increases with age, especially a person has overweight problems, high blood cholesterol or other risk factors, including smoking. These days the telehealth is being actively developed. It enables a physician to have a long-distance contact with a patient via telecommunication technologies such as Internet. Electrocardiogram recording by means of Bioscanner makes it possible to record and send ECG to the clinician by Zoom, Skype, email etc. It facilitates regular preventive check-up significantly.

Electrocardiography helps to assess the preparedness of the body for the certain training level (both for the evaluation of professional athletes and unexercised people) or to check health state of drivers, high-rise building construction workers, crane operators, train drivers, pilots and other professionals, whose work relates to high-risk activity.

Besides, ECG is required to control the treatment course, especially if a person has chronic cardiovascular disease (arterial hypertension, coronary heart disease, etc.). If a person feels worse, at occurrence or increased pain in the heart region, appearance of shortness of breath, abnormal or irregular heartbeat, it is necessary to record the electrocardiogram immediately and seek medical assistance.

One-channel ECG in 3 leads is usually a method of screening diagnostics, when there are no complaints related to the heart function, but it is necessary to evaluate possible latent disorders fast. To determine the cause of the cardiac rhythm disorder or detect a particular location of the cardiac muscle damage, you should record ECG in 12 leads. Use of additional three unipolar limb leads on the chest makes it possible to detect even low-grade changes.
To do that, six additional electrodes are placed on the chest. They can provide more information, including myocardium enlargement (it often points to cardiac failure) and abnormal focuses in remote heart regions (for instance, in posterior wall of the heart).

PRINCIPLE OF METHOD
The heart is a hollow muscular organ, consisting of two ventricles and two atria. When left ventricle contracts, it pushes the blood into aorta. From the aorta oxygen-rich blood moves to all organs and then returns to the right atrium. From the right atrium the blood goes to the right ventricle. When it contracts, the blood moves to the pulmonary artery (to become oxygenated in lungs), then the blood returns to the left atrium to go to the left ventricle. This sequence of myocardium contraction and relaxation regulated by nervous impulse produced by the heart, is called a cardiac cycle and reflects on the electrocardiogram.

So called ECG reading can be challenging, so the nuances should be left to the professionals of functional diagnostics. However, the basics of electrocardiography, if desired, almost everyone can learn.

ECG CONTOUR ANALYSIS
The hardware-software complex Bioscanner Wellness makes it possible to perform the ECG contour analysis. This module is intended to find diagnostically significant points on ECG graph as well as calculate the cardiogram parameters. The obtained data help to detect different heart disorders.

Normal ECG graph depends on a person’s body type, level of training and other factors. However, normal sequence and position of certain waves and segments are always similar. To evaluate ECG, it is necessary to compare the values of wave height, duration and deviation of segments to normal values.

To work successfully with the module of contour analysis, you should be familiar with the basic principles of the cardiosignal structure. Standard ECG graph includes a lot of repetitive, similar segments called cardiointervals. Each cardiointerval in turn consists of set of peaks and lows (waves) specific to the different time intervals of cardiac activity.

More detailed about the contour analysis you can read in a separate article. Please note that the contour analysis takes into account the base ECG characteristics only and cannot be considered as a ground for the establishment of clinical diagnosis. In case you suspect a disorder, a cardiologist must read the ECG.

HOW THE PROCEDURE IS PERFORMED
Connect Bioscanner Wellness to a laptop or a computer using USB port. Accumulator or batteries are not required for operation. An electric shock hazard is excluded, because the device is not connected to 220 V line. The device can be used anywhere if there is a possibility to connect Bioscanner to a laptop.

There is no discomfort during the procedure. To provide the best contact, the corresponding skin areas before electrodes placement should be wiped with alcohol solution. After that moisten the contact surfaces of electrodes as well as skin under them with hypertonic solution. To prepare it, you should dissolve a whole teaspoon of salt in 100 ml of cooled boiled water.

PLACEMENT OF THE CHEST ELECTRODES (video)

Standard leads:
Right arm — red electrode
Left arm — yellow electrode plug
Left leg — green electrode
Right leg — black electrode plug

Chest leads:
V1 — IV intercostal space to the right of the sternum,
V2 — IV intercostal space to the left of the sternum,
V3 — between IV and V intercostal spaces along the left parasternal line (it passes in a vertical direction along the left border of the sternum),
V4 — V intercostal space along the left medioclavicular line (it passes in a vertical direction through the middle of the collar bone),
V5 — V intercostal space along the anterior axilar line (it passes in a vertical direction along the anterior border of the underarm),
V6 — V intercostal space along the middle axilar line (it passes in a vertical direction through the middle of the underarm).

Electrocardiogram displays with the clear reference grid (grid-like squares). There is a possibility of automatic wave and segment size measurement. There is also a possibility to print the electrocardiogram.

CONTRAINDICATIONS
Electrocardiography does not affect the body, because ECG is a registration of the electric signals produced by the heart itself. There are no contraindications. Electrocardiography can be performed at any age, during pregnancy, in any diseases. Skin damage in the areas of electrode placement can be considered as a relative contraindication.

One hour before the ECG recording an examined person should not smoke, eat, drink tea or coffee. Before electrode placement it is necessary to lie down for several minutes to exclude the impact of physical activity.