The human heart has a natural pacemaker in the sinus node or the sinoatrial node, which is a group of cells that trigger electrical signals to stimulate the rhythmic contraction of the heart. In 1958, the first artificial cardiac pacemaker was surgically implanted by Dr. Ake Senning. An artificial pacemaker is a type of cardiac conduction device that is surgically implanted to control and rectify an abnormal heartbeat, with the help of electrical pulses. In the world, there are more than 3 million people with pacemakers and on an average in India, 20,000 patients are implanted with pacemaker devices each year. The pacemaker has a generator that is operated by a 2.5 V lithium-iodine battery and is connected by electrical wires to either one or two leads that are connected to the heart. The generator weighs approximately 20 g and is enclosed in a case that is made up of titanium. The pacemaker is placed under the skin usually just below the collarbone.
A pacemaker is normally used to treat arrhythmia of the heart
, a condition where there is alteration in the rate and/or rhythm of heartbeats. When the heart beats slowly, it is called bradycardia. Tachycardia is a condition when the heart beats fast. When the heart beats with an abnormal rhythm, the blood may not be pumped into the body at a uniform rate. This leads to fatigue, fainting, or dizziness. A pacemaker tries to rectify the abnormalities in the heartbeat and thus prevents the secondary conditions.
Types of Pacemakers
Pacemakers can be distinguished based on the number of leads used and the approach to pacing. Based on the number of leads, the pacemakers are classified as follows:
In a single-chamber pacemaker, one lead is connected to the right atrium in cases of sinus node disease or the right ventricle in cases of atrial fibrillation
. Single-chamber atrial pacemakers are used when sinoatrial disease causes a slow heartbeat. Though the sinoatrial node does not fire appropriately, there is no problem in the conduction between the atria and the ventricles. On the other hand, the single-chamber ventricular pacemakers are used when the conduction between the atrium and the ventricle is impaired.
In a dual-chamber pacemaker, one lead is connected to the right atrium and the second lead is connected to the right ventricle. The wires simultaneously transmit electrical pulses to pace the atrium and the ventricle, thus coordinating the contractions between the 2 chambers of the heart. This device is normally used for patients with heart blocks. If the leads are not appropriately placed, the pacemaker does not function well and there is a recurrence of symptoms.
A biventricular pacemaker is also called a cardiac resynchronization therapy device (CRT). In this type of pacemaker, electrical pulses are transmitted from the wires of the generator to both the ventricles and sometimes an atrium, resulting in coordination between the 2 ventricles. This type of pacemaker is used to treat patients with refractory heart disease that is associated with dys-synchrony in the ventricles. Bi-ventricular pacemakers are now being explored to treat individuals with the lethal condition of congestive heart failure. Research has shown that reduced morbidity and reduced hospitalization are some of the benefits of using biventricular pacemakers to treat congestive heart failure.
Leadless Cardiac Pacemakers
This is a recent advance in technology where pacemakers do not have the conventional lead electrodes that are connected to wires. Instead, the pacemaker is the size of an AA battery. However, it needs to be approved by the Food and Drug Administration (FDA) for use in the United States.
Pacemaker Threshold Testing
Pacemakers are monitored for their optimum pacing outputs or thresholds in order to maintain their efficiency. The Autocapture algorithm was the first to be introduced in pacemakers to monitor the pacing threshold in the ventricles of the heart. There are two types of pacemaker programming:
The pacemaker adjusts the heartbeat rate based on the activity of the individual. The pacing threshold is established with the help of an algorithm that is present in the computer-based generator. For example, if the individual is exercising, the pacemaker adjusts the heart rate for the activity. The pacemaker assesses the sinus node pulse, the temperature of the blood, and the breathing pattern of the individual.
In this condition, the pacemaker adjusts the heart rate if the heart misses a beat or beats too slowly.
How Does a Pacemaker Work?
The basic pacemaker consists of a battery-operated generator that is covered by a thin titanium box. The generator is connected to the heart by electrical wires with lead electrodes. The lead electrodes monitor the heartbeat by transmitting the signals to the generator. When there is any abnormality in the rate (e.g., bradycardia or tachycardia) or rhythm, the generator detects these changes and transmits electrical pulses to correct this abnormality in the heartbeat.
The computer in the pacemaker’s generator keeps a record of the electrical activity and the rhythm of the individual’s heart. This record enables the doctor to understand the working of the individual’s heart and to adjust the pacemaker to work better for the individual. The adjustments can be made externally without any surgical procedure.
The surgical procedure to implant pacemakers is a minor surgery that lasts for 1 to 2 hours with a risk rate of 1% to 2% in surgical complications. The transvenous surgical procedure is performed with local anesthesia. The wires are first positioned in the heart with the help of imaging techniques before connecting them to the pacemaker that is placed below the skin usually under the collarbone. A small bump is observed in patients at the site of implantation. Extreme motion with the arm, near the location where the pacemaker is inserted, is discouraged for a few weeks. Similarly, heavy lifting is also discouraged for a few weeks. The patients can resume their normal activity in a few days.
Doctors should examine their patients with pacemakers every 3 to 6 months. The battery of a pacemaker lasts for 6 to 8 years following which, surgery should be performed to replace the old pacemaker. Individuals should always carry an information card stating the type of pacemaker inserted and the number of leads used, to show medical professionals or security officials at airports.
Pacemaker Vs Defibrillator
Severe conditions, such as tachyarrhythmias, can be treated with an alternate device known as an implantable cardioverter defibrillator (ICD). The ICD has a defibrillator
that delivers shock to the heart muscles to generate a normal rhythm in the heartbeat. In addition, electrical impulses are also delivered to the heart muscles to maintain the steady rhythm. There are 2 types of ICDs: subcutaneous (S-ICDs) and transvenous (T-ICDs) based on where the lead electrodes are located. Patients who do not require pacing adjustments for bradycardia or tachycardia, can be fitted with an ICD. One also finds ICDs coupled with single or dual-chamber pacemakers to generate and manage the normal rhythm of the heart.
The difference between an ICD and a pacemaker is that an ICD can use either low-energy or high-energy electrical stimuli to control arrhythmias of the heart, while a pacemaker uses only low-energy impulses.
Advantages of Pacemakers
Pacemakers have many advantages and they are listed below:
- Pacemakers maintain a normal heartbeat with a continuous rhythm in conditions where the heartbeat slows down, such as bradycardia.
- Pacemakers coordinate the pumping of atria and ventricles or maintain the coordination between the 2 ventricles.
- Pacemakers prevent arrhythmias in life-threatening conditions such as long QT syndrome.
- People with pacemakers can lead normal lives and use cellphones, microwaves, and other electrical objects as long as they are not in close contact with the region of the pacemaker. They are prevented from working in high-voltage areas, playing contact sports, or being exposed to magnetic resonance scanners, or welding equipment.
- Pacemakers with rate-responsive pacing can evaluate an individual’s rate of breathing, and the temperature of the blood and thus, adjust the heartbeat according to the activity of the individual.
- Temporary pacemakers are used for short-term heart conditions with a slow heartbeat induced by a drug overdose, a heart attack, or a heart surgery. Individuals with temporary pacemakers remain in the hospital until the condition is stabilized or until a permanent pacemaker is inserted.
- Permanent pacemakers are used for long-term heart conditions, such as slowing of the heart rate due to bradycardia or an increase in the heart rate due to tachycardia.
Risks of Pacemakers
The risks of pacemakers are minimal compared with the advantages. Some of the risks include:
- Discontinued, kinked, or pinched electrical wires
- Diathermy (generation of high-frequency electrical current) as therapy during dental surgery or for arthritis may cause damage to the pacemaker.
- Collapse of a lung during surgery
- Rupture of a blood vessel or a nerve during the surgery
- Swelling, infection, intracardiac thrombosis, or bleeding in the region of the inserted pacemaker
- A hypersensitive reaction to the medications used during the surgery