ECG apparatus (electrocardiograph): types, principle of operation

Electrocardiography is a method of examining the work of the heart muscle. With the help of the ECG-device, the formed electric fields are fixed with further derivation of the results in the form of a graphic image on thermal paper (in most cases). The first ECG-device recorded data on a photographic film, then there were ink recorders. If the device is completely electronic, then the data can be stored in the computer's memory.

Use of electrocardiographs

The procedure of electrocardiography is carried out with the following purposes:

• Determination of the frequency and regularity of contractions of the heart muscle;
• If it is necessary to determine the presence of ischemic disease or infarction;
• If it is necessary to confirm or deny the presence of electrolyte deficiency;
• Clarification of the presence of cardiac blockades;
• The evaluation of the state in dynamics when carrying out samples with a load;
• If it is necessary to clarify the anatomical and physiological features of the heart (for example, hypertrophy of the left ventricle) ;
• If it is necessary to confirm or disprove the development of pulmonary embolism;
• For preventive purposes during the period of medical examination of the population.

Modern devices

Another 20-30 years ago, the ECG device was an immense machine that was difficult to transport and occupied a lot of space indoors. Modern technologies allowed to reduce the dimensions of devices (up to portable ones) without loss of quality in functionality.

The device for ECG can record one or several channels at the same time, on which the division into groups is based. In addition, it must be provided with certain software:

• Syndromic conclusion based on the results of the data;
• In case of cardiac rhythm disturbances, special leads should be switched on automatically;
• The presence of a device for defibrillation and its manual control;
• Monitoring of the heart for a long time with the recording of results in the memory of the device;
• Possibility to make an ECG to several patients and simultaneous fixing of this data in the memory of the device;
• Remote control.

Single-channel devices

They are used practically in all state and private medical and preventive institutions, ambulance services. Such a portable electrocardiograph has a weight of up to 1 kg. The device is equipped with a mini printer, which provides ECG data on thermal paper. There is the possibility of automatic diagnosis. Such an ECG device can function from a network or from an internal battery.

There are even smaller models (about 800 g), which are popular among paramedics. It is possible to record a small amount of data in the device memory for ECG. The price of single-channel devices is in the range of 22-30 thousand rubles.

Three-channel devices

Such electrocardiographs are endowed with a thermal printer and three-channel deducing of the results of the study. They have the following features:

• Calculations are carried out automatically, control of the device is not needed;
• Thermal printer has a significant expansion, which, in addition to the graphic data of the electrocardiogram, indicate personal information about the patient, the electrofilter used, the level of increase in the amplitude of the study;
• The results can be transferred to a personal computer for calculating additional indicators;
• There is the possibility of defibrillation.

The cost of three-channel electrocardiographs is within 50 thousand rubles.

Six-channel devices

Such an ECG device has a wider scope of application. It is used by employees of rescue services, military hospitals, emergency services, private clinics. ECG can be removed on two types of six-channel devices: portable (portable) and computer.

Features:

• Saving about 1000 survey results (there is a hard disk with 10 GB);
• Possibility to examine 150 patients without recharging the device;
• High speed printing, which is carried out automatically;
• The possibility of using several paper sizes to record the results.

Among other things, this device for ECG, whose price is within 75 thousand rubles, shows the status of the device: battery charge, memory, disconnection of electrodes, gives warning about the imminent end of the paper.

Twelve-channel electrocardiographs

They are used in orthopedics, therapy, surgery, in urgent conditions, during rehabilitation after surgical interventions, during physiotherapeutic manipulations. Removing the ECG on this device has many advantages. The device allows you to make an hourly record of data for one patient, enter data about the patient, and also control the electrocardiograph from the computer.

An interesting point is that it is possible to drive these norms, and in case of determining deviations in the survey, the device will give a signal about violations. Make an ECG allows a set that consists of the following elements:

• electrocardiograph;
• A computer that can communicate with an ECG device through a wired or wireless connection;
• A printer that allows you to print diagnostic data;
• Veloergometer - a device with which you can evaluate the work of the heart muscle with a load, connects to an electrocardiogram via Bluetooth;
• software.

The cost of twelve-channel devices varies from 100 to 500 thousand rubles, which depends on the country of the manufacturer and the kit bundle.

Conducting research

To measure the potential difference, electrodes used for ECG are disposable, which are superimposed on certain parts of the body. On the fixation area, a gel is applied, which improves the conductivity of the skin. So they do now, but earlier they used napkins made of gauze, moistened in salt water.

The cells of the heart muscle are small electric generators, which when charged with excitation wave are charged and discharged. The electrocardiogram is the final indicator of the functional abilities of these generators, which reflects the propagation of electrical impulses in the heart.

What does the doctor see on the cardiogram?

Usually, the following indicators can be determined on the ECG:

1. The tooth P - is a reflection of atrial depolarization.
2. QRS - a complex that denotes depolarization of the ventricles.
3. ST and tine T - repolarization of the ventricles.
4. Wave U - experts have different opinions about her appointment. Some believe that the wave is caused by the repolarization of Purkinje fibers, while others talk about the penetration of potassium into the cardiac cells during the relaxation period.

It is important to know about the location of the leads, due to which the potential difference is measured. The first three leads are placed on the limbs (red electrode on the right hand, yellow on the left, green on the left leg). On the right foot a black electrode is applied, which does not measure the indicators, but is grounded.

Breast leads, on which ECG electrodes are applied (disposable):

• V1 - right edge of the sternum in the 4th intercostal space;
• V2 - the left edge of the sternum in the 4th intercostal space;
• V3 - in the middle between V2 and V4;
• V4 - mid-clavicular line in the 5th intercostal space;
• V5 - in the anterior axillary line at the intersection with the horizontal level V4;
• V6 - on the middle axillary line at the intersection with the horizontal level V4;
• V7 - on the back axillary line at the intersection with the horizontal level V4;
• V8 - along the median-scapular line at the intersection with the horizontal level V4;
• V9 - along the paravertebral line at the intersection with the horizontal level V4.

Other ECG methods

There is a significant number of techniques. For example, electrocardiography through the esophagus. The electrode is injected into the lumen of the esophagus in the active state. This method is informative for various cardiac blockades.

Vector cardiography is a diagnostic method that allows to fix the electrical vector of the functionality of the heart muscle in the form of a projection of three-dimensional figures on a flat surface.

Daily monitoring by Holter - the evaluation of the heart muscle in the dynamics for a long time. A positive aspect is the possibility of carrying it out not only in stationary, but also at home. At the end of the diagnosis, the data is transferred to the computer, where the doctor is already studying them.

Gastrokardiomonitorirovanie - there is a simultaneous fixation of ECG and gastrogram data for 24 hours. Together with the device for electrocardiography, the patient is administered a nasogastric tube, through which data on acidity in the esophagus or stomach are obtained.

Medicine in general and cardiology in particular do not stand still. Every year, diagnostic equipment is improved, transforming into advantages those moments that were previously shortcomings.