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Heart pacemakers explained

What is a Pacemaker?

A pacemaker is a device that generates electrical impulses that are delivered to the heart muscle to maintain or control heart rate and rhythm. They are used to treat many heart conditions but mainly used for arrhythmias (abnormal heart rhythm or rate).

heartpacemaker

The Heart’s Electrical System

For the heart to work in a coordinated manner and pump the right volume of blood to different organs, it has to maintain a rate and adjust it based on our activity. The atria (upper chambers) and the lower chambers (ventricles) have to contract and relax alternately to receive the blood into the heart and pump it out of it to the lungs and into the blood vessels supplying different parts of the body. The electrical system of the heart is a power generating and conducting system that makes this coordinated activity possible.

heart-electrical-system

The electrical activity of the heart originates in the sinoatrial (SA) node located in the right atrium. From here, the impulse travels through the walls of the atria causing them to contract.

The electrical impulse then travels through the AV node located between the atria and ventricles. The AV node behaves like a gate and slows the electrical signals before it enters the ventricles. This delay allows the atria to complete its contraction before the ventricles contract.

From the AV node, the electrical impulse passes through the His-Purkinje network, a pathway of specialised fibres conducting electricity. When the impulse travels into the muscular walls of the ventricles, ventricles contract.

This chain of activity repeats with every heartbeat (at a rate of 60-100 times per minute).

How does a pacemaker work?

A pacemaker contains a computerised pulse generator, a battery and electrodes. The electrodes sense your heart’s electrical activity and send this data to the computer in the pacemaker via the wires. The battery powers the generator, and these components are contained in a box; the wires connect the generator to the heart.

The function of the pacemaker is to monitor and control your heartbeat. When the heart rhythm is abnormal, the computer will detect it through the sensors and instruct the generator to send electrical impulses to your heart. These impulses will travel through the wires to your heart and control the abnormal rhythm.

The computer within the pacemaker can record the electrical activity and rhythm of the heart. Your doctor can use this information to adjust the pacemaker to suit your requirements best. This adjustment is done using an external device without any needles or direct contact with the pacemaker. Your doctor can set a minimum heart rate (lowest heart rate). If the heart rate drops below this rate, the pacemaker sends impulses that pass to the heart muscle and creates heartbeats to maintain the heartbeat.

The newer pacemakers also have technology to sense blood temperature, breathing, and other factors. They can alter the heart rate to match the changes in your activity.

Types of pacemakers

Pacemakers can have one to three wires which are positioned in different chambers of the heart. Based on the number of wires and positioning, there are different types of pacemakers (single chamber pacemaker, dual chamber pacemaker, biventricular pacemaker, leadless pacemaker).

  • Single chamber pacemaker: The wires carry the pulses from the generator to the right ventricle (The right lower chamber).
  • Dual chamber pacemaker: The wires carry electrical impulses from the generator to the upper right chamber (right atrium) and the right lower chamber (right ventricle). These signals assist in coordinating the timing of contractions of these two chambers.
  • Biventricular pacemaker: The wires carry pulses from the generator to one atrium and both the ventricles. The signals help coordinate electrical signalling between the two ventricles. This type of pacemaker is also called a cardiac resynchronization therapy (CRT) device.
  • Leadless pacemaker: This is a self-contained device without any wires, doesn’t need any skin pocket for placement in the chest and is inserted into the right lower chamber of the heart.

Your doctor will decide the best-suited pacemaker for you based on the condition you have.

What are the conditions in which pacemakers are used?

Pacemakers may be used for many conditions. The most common indications are:

  • Bradycardia: Heartbeats are slower than normal. Slow heart rhythms can occur as a result of diseases of the heart’s conduction system (such as the SA node, AV node or His-Purkinje network).
  • Heart block: Electrical signal transmission is very delayed or interrupted as it moves through the heart. Heart block can result because of ageing, injury caused by a heart attack, neuromuscular disorders or other conditions that damage the electrical conduction system of the heart.

The other conditions for which the pacemakers are used include:

  • Sick Sinus Syndrome: Old age or heart disease causes the sinus node to function slower than usual, and it doesn’t set the correct pace for your heartbeat. The heartbeat may be slower than normal or long pauses may be there between the heartbeats. Also, there may be alternate slow and fast rhythms.
  • After medical management of atrial fibrillation, a pacemaker may be used to regulate your heartbeat.
  •  Slow heart beat caused as a side-effect of certain medications such as beta blockers that are given for heart diseases.
  • Fainting attacks. Syncopal attacks (fainting attacks) caused by slow heart rate.
  • Heart muscle problems. Electrical signals travel too slowly through your heart muscle. You may need CRT treatment for this.
  • Long QT syndrome. This is a type of syndrome that puts the person at high risk of dangerous arrhythmias.
  • Some types of congenital heart diseases may need a pacemaker.
  • After a heart transplant, some patients may need a pacemaker.

Procedure for pacemaker placement

A minor surgery is required to place a pacemaker, which is usually performed in a hospital or a special heart clinic. Before the procedure, you may be given an injection to calm and help you relax.
The area where the pacemaker needs to be inserted is numbed, so that you do not feel any pain. A needle will be inserted into a large vein near the shoulder and used to thread the pacemaker wires into the vein and position them correctly into the heart. X-ray images will be taken to see the wires pass through the vein to your heart. Once the wires are in position, the doctor will make a small cut in the skin of your chest or abdomen. The metal box of the pacemaker (containing the battery and pulse generator) is placed in this pocket and connected to the wires that are placed in the heart. After checking the proper functioning of the pacemaker, the skin will be stitched back.

After the procedure, you may have to stay overnight in the hospital to check your heart beats and whether the pacemaker is working properly. You may experience mild pain and swelling at the site where the pacemaker is placed, which can be relieved with simple pain killers. You can return to normal activities after few days of surgery. You may be advised to avoid strenuous activities and lifting of heavy weights for about one month after the procedure.

Complications of pacemaker implantation procedure

Pacemaker implantation surgery is usually safe. Some of the complications that can happen with this procedure include:

  • Allergic reaction to dyes (contrast agent) injected during the procedure.
  • Swelling, bruising and bleeding at the skin area where the pacemaker is buried, especially if the patient is taking any blood thinning agents.
  • Injury to blood vessels and nerves where the pacemaker is inserted.
  • Infection can occur in the area where the pacemaker is placed.
  • The collapse of the lung.

Consult a top Cardiologist

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References

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  • National Heart Lung and Blood Institute. Pacemakers. Accessed at https://www.nhlbi.nih.gov/health/health-topics/topics/pace/howdoes on 28 June 2016.
  • American Heart Association. Living With Your Pacemaker. Accessed at http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/Living-With-Your-Pacemaker_UCM_305290_Article.jsp#.V3NQ2JN94b0 on 29 June 2016.
  • Cleveland Clinic. Permanent Pacemaker. Accessed at http://my.clevelandclinic.org/services/heart/services/arrhythmia-treatment/permanent-pacemaker on 29 June 2016.

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