Pacemakers and Defibrillators

Mar 24, 2012 , Translated by Kristina Knazko

kardiostimulator-a-defibrilator.jpg - kopie
kardiostimulator-a-defibrilator.jpg - kopie
Pacemakers and defibrillators are devices that influence the electrical signal in the heart. Pacemakers directly influence the formation of electrical impulses in the heart, along with the heart rate. A defibrillator is used in order to return correct impulse conduction in the heart, in the event of arrhythmia.

Pacemakers and Defibrillators

Pacemakers and defibrillator are devices that are implanted and connected to the heart of patients with heart rhythm disorders. In a healthy heart, the sinus node functions as the pacemaker. The sinus node is a cluster of specialized cells in the right atrium which form electrical impulses. These impulses spread among cells of the atrium, to the atrioventricular node, which slows the impulses slightly and transfers it into the ventricles. This results in coordinated contractions of the atria, followed by the ventricles. Only this kind of regulated formation and transportation of electrical signals leads to correct function of the heart. If the heart's activity is too slow and the transfer of impulses is interrupted between the cells of the atrium, the heart needs to be stimulated by a pacemaker. In the case of faulty signal conductions in the heart's chambers, a cardioverter – defibrillator is implanted as treatment for ventricular fibrillation.

Pacemakers

If the formation of impulses is malfunctioning in the sinus node, or conduction of the impulse to the atrial cells is faulty, the condition is manifested by sudden loss of consciousness from insufficient blood supply to the brain, or dizziness and fatigue. The body does not receive enough blood and the heart needs to be stimulated with either medications, or by the insertion of electrodes, i.e. a pacemaker. A pacemaker is a device used to stimulate the heart. If the heart is beating too slowly, it functions as an artificial sinus node. Electrodes are introduced into the heart to replace the malfunctioning sinus node or faulty conduction of impulses between cells. The stimulation can be temporary or permanent. Some patients are completely dependent on external stimulations.

Implanting a Pacemaker

A pacemaker looks like a small box that is implanted under the skin in the subclavian area, under local anesthesia. A pacemaker contains batteries, a microcomputer and is attached to an electrode or electrodes, depending on where the heart needs to be stimulated. Electrodes can be inserted into one chamber of the heart, known as a single-chamber pacemaker, or two chambers, known as a dual-chamber pacemaker. The electrodes are usually stored in the right atrium and right ventricle. Electrodes monitor the electrical activity of the cardiac cells, and if it drops below a certain threshold, they send electrical impulses stimulating the heart to contract. Most patients do not feel these impulses. A pacemaker is also able to adapt to increased stress on the heart during physical activity, and increased heart rate.

Risks of a Pacemaker

The pacemaker is checked at every visit to the doctor to determine whether it is functioning properly and whether its battery is sufficiently charged. The battery gradually loses its charge, requiring the device to be replaced. Complications that accompany treatment with a pacemaker are linked to the setting of the speed of the stimulations which can be too fast or too slow. These can also include technical problems such as a low battery, damage to the stimulation electrodes or their shifting from their original position in the heart. Other risks for patients include infection, as bacteria often settle on foreign material. Another risk includes the risk of pressure sores due to the pressure of the device on the skin and oppression of blood supply. This requires the pacemaker to be removed, the condition to be treated, and implanting a new pacemaker on the opposite side of the chest. When leading the electrodes through the veins, blood clots can form in the venous blood stream. It is important to avoid strong magnetic and electrical fields which can interfere with the pacemaker's function, such as industrial generators, arc welders, metal detectors or various security systems. Magnetic resonance imaging (MRI) is also strictly forbidden. Mobile phones do not endanger the patient.

Cardioverter – Defibrillator

Patients endangered by ventricular tachycardia or ventricular fibrillation, when the ventricles begin to act chaotically or their activation is increased to the extent that they no longer contract properly, are in a life-threatening situation. These conditions prevent blood from being expelled into the circulatory system, causing a halt to the system and the individual needing to be resuscitated and defibrillated. In order to prevent this, a cardioverter – defibrillator is implanted into the heart. A cardioverter – defibrillator is a device that is implanted into patients in danger of sudden heart failure from ventricular tachycardia or fibrillation. The chaotic formation of electrical impulses can be interrupted by an intensive electric shock, which restores the cells back in sync and leads to a regular heartbeat; because the electrical impulses will again spread in the correct way and the heart begins to contract again.

Cardioverter – Defibrillator and its Function

A cardioverter- defibrillator is able to monitor the heart's activity via its electrodes. If an irregularity in the rhythm is detected, the device activates and sends a shock. All information is stored so that the course of arrhythmia and whether the device responded as it should have can be analyzed later on. The device is implanted into the left side of the chest and electrodes are lead into the heart. The patient may feel weakness during arrhythmia, or heart palpitations, and in severe cases he or she can fall unconscious before the device sends a shock. If the individual is conscious, the shock can be felt in the chest. Some patient may not be able to tolerate this shock. Complications can arise as with pacemaker implanting. There is a risk of infection, pressure sores on the skin and vein thrombosis. Electrodes can be damaged or they can shift. The device lasts for approximately 5 years and its settings and batteries must be checked regularly in a specialized center.

Conclusion

Pacemakers and cardioverter – defibrillators increase the quality of life for patients with heart rhythm disorders. Each case is assessed by an expert committee, which grants consent to this treatment method. The implantation and monitoring of the patient is the responsibility of the specialized implant center.

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