DEFIBRILLATOR AND PACEMAKERS

DEFIBRILLATOR AND PACEMAKERS

BackGrounds

PACEMAKER

It is a small device operated with batteries. Notice when the heart is beating irregularly or very slowly. This is the correct message.

Figure 1: Transcutaneous pacemaker

Figure 2: External Pacemaker

External pacemakers are employed to restart the normal rhythm of the heart in cases of cardiac standstill, in situations where short-term pacing is considered adequate, while the patient is in the intensive care unit or is awaiting implantation of a permanent pacemaker. Frequently, external pacemakers are used for patients recovering from cardiac surgery to correct temporary conduction disturbances resulting from the surgery. As the patient recovers, normal conduction returns and the use of pacemakers is discontinued.

The pacing impulse is applied through metal electrodes placed on the surface of the body. Electrode jelly is used for better contact and to avoid burning of the skin underneath. An external pacemaker may apply up to 80-mA pulses through 50-cm electrode on the chest. This procedure is painful and therefore is used only in an emergency or a temporary situation. The pulses may be delivered:

• Continuously: When it is felt that the heart rate is below the pre-set value. The impulse frequency is independent of the electrical activity of the heart.

Figure 3: Continuous Pulse

• On demand R: synchronous wave stimulation. Normally, the pacemaker does not work, but it is activated when the heart rate falls below the normal or preset value. In such a situation, a beat-to-beat examination of the time interval between two R waves is performed. When this interval exceeds the preset value, the pacemaker becomes operational.

There are three types of pacemakers based on the type of output waveform  These are:

Voltage Pacemakers: Voltage pacemakers are those in which the current in the circuit is determined by the available voltage during the entire duration of the impulse. The voltage output from the pacemaker remains constant and changes of resistance in the circuit will influence only the current.

Figure 4: Voltage Pacemaker

Current Pacemakers: In current pacemakers, throughout the impulse, the current in the circuit is determined by the internal resistance of the pacemaker.

Figure 5: constant current type pacemaker

Current Limited Voltage Pacemakers: This is primarily a voltage circuit, but the maximum current in the circuit is limited, preventing too large a current impulse to circulate when there is a low resistance in the electrode circuit. With these pacemakers, during the first part of the impulse, the current in the circuit is determined by the internal resistance of the pacemaker (constant current type) but during the second part of the impulse, the current in the circuit is determined by the voltage available (constant voltage version).

By download

Single phase: it has a current that is carried out in only one direction, which means a high dose of shock in three shocks of 200, 300 and 360 joules.

Biphasic: these are more advanced defibrillators. This means that they need up to 40% less energy and consequently produce less myocardial damage. It is a double current, because it changes polarity during the crash, with an administration of three shocks of 150. They are more efficient defibrillators and have lower energy expenditure.

Figure 7: Defibrillation by download

Type of user

Manuals: must be used by qualified personnel due to their complex functions. Only trained health personnel are authorized to use it in Europe.

Automatic: these types of defibrillators apply the discharge without prior notice, which is very dangerous for the person assisting the victim. They are increasingly disused by this aspect, but their DEA terminology is still used, since they were the only external defibrillators used in the past.

Semiautomatics: these are types of defibrillators for public use, which warn at the time of discharge and indicate that you have to separate from the patient by pressing the button that will activate the defibrillation. They are devices that require little training by the user. The device indicates the steps to be followed through sound and visual instructions.

INTERNAL DESFIBRILLATOR

Internal defibrillator or DAI (implantable cardioverter defibrillator), is the one that is implanted in the person, There are several types of DAI:

Monocameral DAI: acts only in a cardiac chamber with a pulse generator and an electrode in the right ventricle.

Bicameral DAI: acts in two chambers of the heart with a pulse generator and two electrodes, one the right ventricle and one in the right atrium.

tricameral DAI: acts in three chambers to treat ventricular arrhythmias and heart failure.

Figure 8: Internal Desfibrillator

Desing

In Figure 9 we observe the electrical circuit diagram used to perform an asynchronous pacemaker at 60 hertz and a defibrillator with two different discharge levels. To generate the pulse, the Arduino Uno board was used, a logical one (5 volts) was generated for 40 milliseconds and a logical zero (0 volts) for 960 milliseconds. At the output of pin two of the arduino a voltage divider was coupled with a potentiometer and a fixed resistance, in this way the amount of voltage supplied to the patient is varied. To simulate the patient a wave generator is used, the simulated ECG signal enters a non-inverting adder amplifier circuit with gain one, together with the generated pulse that comes from the Arduino Uno board. To create the different discharge values for the defibrillator, capacitors connected to a diode in series were used, so when loading and unloading, different load values were generated, since depending on where the selector was located, the patient received more or less voltage, that is to say, the more capacitors I had in series, the more charge they evicted, therefore, the more charge they released. Finally, to select the mode, a three-position selector is used to choose the mode: pacemaker, defroster or off.

Fugure 9: Electrical diagram of the pacemaker and the defibrillator.

Results

After carrying out the previous theoretical consultation of the operation of a pacemaker and a defibrillator, it was carried out its implementation which consisted of two parts. The first one is the pacemaker, which had an operation that consisted of an asynchronous one, that is, the stimulation is done at a constant frequency in this design was made at a frequency of 60 ppm which is equivalent to a frequency of 1 Hz because the pathology that was wanted to regulate are bradycardia, the pulse was sent by a microcontroller, Arduino each pulse has a duration of 40ms this is to what is established in the manuals, later to generate the pulse as shown in figure 1 psterior to this was done to show the pulse on the ECG signal obtained from the generator at a frequency of 500mHz as shown in figure 2.

figure 1,2

the second part was to perform the defibrillator which consists of making a discharge to different jouls, these charges were made by loading and unloading a capacitor and a discharge time calculated by means of the equation 1

t = R * C

t = 10k * 4,7uF

t = 40ms

this means that the discharge time is 40 ms as recommended in the bibliography, the charges were 12.8V and 13V

loading to nd unloading was done manually with the help of a push button. The results can be seen in figure 3 and 4.

figure 3

figure 4

Conclusions

An asynchronous pacemaker can bring different problems such as uncoordination between ventricles and atria, waste of the battery, blood flow does not depend on exercise, among others. Even in some patients it can cause fibrillation, for this reason only used externally because they are used when they are in a medical center and its use is transient.

Ventricular fibrillation (VF) is the initial rhythm in up to 90% of adult CRPs, the only effective treatment of VF is defibrillation.

It can be concluded that a defibrillator is currently very important because it can reverse some deadly damage to the heart for this reason today it is looking to improve it, that is why it is important to understand its operating principle when the time comes to manipulate it, let's know how.

BIBLIOGRAPHY

Lifetime; types of defibrillators, (2017), taken online from: https://www.desfibrilador.com/desfibrilador/tipos-de-desfibriladores/, consulted: 05/12/2019.
Webster, J. G. (2006). Encyclodex of Medical devices and instrumentation. John Wiley & sons, Inc.
Daneri, P. (2007). Electromedicine Diagnostic and Intensive Care Equipment. Editorial HASA.