What is a pacemaker? Describe its structure and function. What Is An Asynchronous Cardiac Pacemaker?

Description of Pacemaker Functions:

 

 

 

 

Asynchronous cardiac pacemaker: A free-running pacemaker is called an asynchronous pacemaker. The pacemaker’s electrical stimulus appears at a uniform rate, regardless of what is happening in the heart or the rest of the body.So asynchronous pacemaker provides a fixed heart rate. The rate range for asynchronous pacemakers is 70-90 BPM. On the other hand, pacemakers that are not rate fixed typically have a range of 60-150 BPM. The following figure shows a block diagram of an asynchronous pacemaker.

 

Synchronous cardiac pacemaker: Patients often require continuous cardiac pacing, as they can establish a normal cardiac rhythm between two block periods. (Continuous stimulation of the ventricles is not necessary for all these patients. In some cases, continuous stimulation can cause serious complications.

 

 For example, if an artificial stimulus is applied during the repolarization period after spontaneous ventricular contraction. However, ventricular tachycardia or fibrillation may occur. Therefore, it is very important that the artificial pacemaker does not compete with the heart’s normal pacing function. A better way to solve such problems is to introduce the use of synchronous pacemakers. A synchronous pacemaker has a pace set at a fixed rate and the pacemaker does nothing if the patient’s heart rate maintains that fixed rate.

 

Asynchronous pacemakers, on the other hand, will fire at a set rate regardless of the patient’s heart rate. In this case there is a risk for R on T-wave phenomenon, which can lead to ventricular fibrillation. Therefore, they are rarely used. With the help of chemical impulses, the contraction of the heart is controlled.The rate at which impulses fire is controlled by the heartbeat. The cells that produce these rhythmic impulses are called pacemaker cells and they directly control the heart rate. Artificial devices that generate impulses are also called pacemakers.When the body’s pure or original conduction system is damaged Disk storage (Disk storage): Processed data or images can be stored on disk. These disks can be hard disks, floppy disks, compact disks or digital video disks. Nowadays, a patient’s ultrasound scan is stored on a disk or tape and thus the patient’s medical record can be preserved for a long time.REE ON Printers: Many ultrasound machines have thermal printers, which can be used to receive hard copies of images from the display. In the past, most ultrasound machines used film. The ultrasounds discussed so far represent a 2-D or a ‘slice’ image of a 3-D image (fetus or organ).Two other ultrasounds currently in use are Doppler imaging and 3-D ultrasound imaging. The system block diagram of the ultrasound machine is shown.

 

Doppler sonography (Doppler sonography): Doppler ultrasound, based on the Doppler effect. When the ultrasound wave is reflected by a moving object, the frequency of the echo changes. If the object moves towards the transducer, the frequency will increase and if it moves away from the transducer, the frequency will decrease. Doppler measures changes in the frequency of ultrasound echoes to calculate how fast an object is moving. This ultrasound is mainly used to measure the rate of blood flow through the heart and through the major arteries and also to detect whether these arteries are blocked by obstruction, disease or tumor.Doppler sonography can be used to determine whether blood flow is in the direction of the probe, or in the opposite direction, and its relative velocity can be determined and visualized. It is particularly useful in cardiovascular studies (sonography of blood vessels and heart). Doppler information is displayed in a graph using spectral doppler or displayed as an image using color doppler (directional doppler) or power doppler (non directional doppler). This upper shift is within the audible range and is often presented audibly using stereo speakers. An artificial pacemaker may then be used. Although all the cells of the heart have the ability to generate these electrical impulses (action potential), a special part of the heart, called the sinoatrial node (SA node), is responsible for the entire heartbeat. The SA node is a cluster of cells located on the wall of the right atrium near the entrance to the superior vena cava.Most commercial pacemakers use a single de-fibrillation protection diode and others use symmetrical two-diode type protection. In this case the diodes are connected back-to-back. The voltage of the lithium-iodine cell used in this circuit is 2.8 V and on the other hand the required output pulse of the pacemaker is about 5. V. So a voltage doubler circuit is definitely used. Choosing the right refractory period is a very difficult task.However, a refractory period of 400–500 mg is commonly set in commercial pacemakers. Selling circuit bandpass filter is designed in such a way that it passes all desired signals but attenuates unwanted signals like repolarization wave or external interference etc. The bandpass filter is usually constructed sensitive to the waveform, which rises between 8 – 30ms. For testing convenience, the amplifier/filter is tested using a standard waveform (half wave rectified 22 Hz pulse, 23 ms rise and decay time) and a 500 52 load.

The demand pulse generator sensing amplifier usually has a high input impedance, with a typical value of 5 M2 1 2 – 3 mV Most demand pacemakers are designed to sense voltages as low as the QRS signal. The lifespan of a pacemaker depends largely on pulse duration. For example, in Mirel pacemakers when the battery voltage is reduced from 2.80 to 2.0 V, the rate gradually decreases to about 8 ppm where the units are set to 72 : ppm. In this case pulse generator is recommended for modification.