Your heart is a muscle that pumps blood steadily throughout your body, sending oxygen-rich blood and nourishment to all your body cells. It has two upper chambers, the right and left atria, and two lower chambers, the right and left ventricles (refer to figure 1.0). Blood from the body and the lungs enter the heart through the atria. The atria pump this blood into the ventricles, which then pump it to the rest of the body.
Thus, in a normal heart the atria always contract before the ventricles. This is termed Atrioventricular Synchrony & it increases the pumping efficiency of the heart by ensuring that the ventricles are properly filled with blood before they contract.
Normally, your heart’s pumping is controlled by small electrical pulses produced by your heart’s natural pacemaker, the Sinoatrial (SA) node, located in the right atrium. The SA node monitors the body’s need for oxygen and nutrients, and sends electrical pulses at a faster or slower rate based on your body’s demands. Each pulse travels through the atria, causing the atria to contract, and then to a junction in the middle of the heart called the Atrioventricular or AV node. The AV node is the only pathway available for the electrical pulses to travel from the atria to the ventricles. The pulse crosses the AV node and continues through the conduction pathways in the ventricles, causing the heart to beat. After each beat the heart rests until the next electrical pulse from the SA node begins the cycle again.
With a healthy SA node, your heart rate varies to match your body’s need for oxygen and nutrients, which in turn varies as your physical activity levels change. Normally, when you are at rest, your heart beats at rates between 60 to 80 beats per minute. When you perform activities involving moderate physical exertion, your heart rate rises to about 100 beats per minute. During sustained strenuous exertion your heart rate can rise up to 150 beats per minute or more to meet the high blood and oxygen demand of your body’s organs.
The most common medical condition needing a pacemaker is called “bradycardia”, meaning a heart rate that is too slow or irregular to meet the body’s demands.
If you suffer from bradycardia, your heart may beat as slowly as 30 beats per minute and the blood supply to your body’s organs, especially the brain, becomes inadequate. As a result you are likely to experience symptoms of bradycardia like :
Shortness of breath
Inability to exercise
These symptoms could adversely affect your quality of life and prevent you from leading a normal life.
Bradycardia is most commonly caused by one or both of the following heart rhythm disturbances :
SickSinus Syndrome :- Electrical impulses too slowly or irregularly. This results in very slow or irregular heart rates and causes symptoms. when the SA node sends out
Heart Block :- When the electrical impulse is slowed, becomes irregular, or is stopped at or below the AV node (the only pathway for impulses from the heart’s natural pacemaker to enter the ventricles). Thus, the ventricles beat very slowly or irregularly and this causes the symptoms listed above.
Slow heart rhythm problems have a variety of causes, including hereditary heart defects, certain illnesses, the ageing process, or scar tissue from heart attack or, the cause may be unknown.
Today the only therapy available to treat most slow heart rhythm problems is the implantable pacemaker.
Whenever your heart beats too slowly, the pacemaker stimulates it with precisely timed electrical pulses. These electrical pulses cause your heart to contract and restore a more or less normal heart rate that reduces or eliminates the symptoms of bradycardia.
A pacemaker is really a system that has two parts (refer to figure):
The Pulse Generator :- which is a small metal can containing electronic circuitry & a long-lasting battery
One or two insulated wires, called Leads.
The pulse generator is a “minicomputer” and contains all the electronic circuitry required to generate and control the timing of the pacing impulses. Pulse generators today are about the size of a large wrist-watch dial. The pacing leads are insulated wires that carry the electrical impulses generated by the pulse generator to the heart. One end of the lead is connected to the pulse generator and the other end is usually inserted through a vein and placed in the right ventricle or the right atrium of the heart.The electric pulses delivered by the pacemaker are very small in energy and you will not feel anything when the pacemaker paces.
In addition to pacing, the pacemaker can also “sense” or monitor the heart’s natural electrical activity. If a pacemaker senses a natural heartbeat it will not pace the heart.
Implantable pacemakers are “programmable”. After your pacemaker is implanted your heart condition may change. If it does, the pacemaker settings may be adjusted or programmed without any additional surgery or discomfort to you. The adjustments will help provide the best therapy to meet your new condition. These adjustments are made with a small computer called a programmer that transfers commands to your pacemaker by radio waves that you will not feel. The programmer is also used to regularly check the pacemaker system.
Pacing therapy is diverse because the underlying heart disorders that cause slow heart rhythm problems are different.
The general types of pacemakers available today are:
Chamber Pacemakers (without rate response)
MRI Conditional Pacemakers
Chamber Pacemakers (without rate response)
Rate Responsive Pacemakers (both single & dual chamber)
The type of pacemaker prescribed by your physician will depend on the type of slow rhythm problem you have, your overall cardiac health status and your lifestyle considerations.
No matter what type of pacemaker is implanted, they all help people live fuller lives by enabling them to participate in more activities.
Advanced pacemaker system
Canpace both atrium and ventricle
Moreefficient heart function by mimicking the functioning of the normal heart
Fewer symptoms and a more active and satisfying lifestyle
Lesslikelihood of developing other heart problems in the future
Dual chamber pacemakers typically use two leads, one placed in the right atrium and the other in the right ventricle (refer to figure).
They monitor both atrial and ventricular natural activity and pace either or both chambers whenever natural activity is not present. The electric pulses are timed so that the atria contract just before the ventricles. This timing ensures that the atria and ventricles beat in synchrony with each other, just as in the natural heart. Thus, unlike single chamber pacemakers, dual chamber pacemakers are more likely to preserve the pumping efficiency of the natural heart.
Dual chamber pacemakers function differently depending on the type of slow heart rhythm problem a patient has.
In patients whose slow heart rhythm problem is solely due to Heart Block, the SA node is healthy. It monitors the body’s blood requirements and sends electrical impulses to the atria at varying rates to match the body’s demands. The dual chamber pacemaker senses these impulses from the SA node, waits for the atria to contract and then paces the right ventricle. Therefore, in patients with complete heart block and healthy SA nodes, dual chamber pacemakers closely mimic the natural heart by
– varying the pacing rate to match the body’s demand
– maintaining the synchrony between atrial and ventricular contraction
Consequently, heart block patients treated with dual chamber pacemakers should be able to comfortably lead moderate to strenuous lifestyles so long as their hearts are strong and otherwise healthy.
Dual chamber pacemakers should enable elderly heart block patients whose hearts have weakened with age to comfortably resume most physical activities they used to perform before developing their heart block.
The two types of non-rate responsive dual chamber pacemakers available are called the VDD type and the DDD type where D stands for Dual.
The VDD type of pacemaker uses a single lead. This lead senses the rate of impulses from the SA node and paces the ventricle at the same rate. It cannot pace the atrium and hence the VDD pacemaker is prescribed only for patients who have heart block with perfectly healthy SA nodes.
It is normally not prescribed for patients who may be likely to develop SA node disease in the future. This is because patients with SA node disease are better treated by pacing in the atrium.
The DDD pacemaker uses two leads, one that can monitor and pace the atrium and another which can monitor and pace the ventricle. As compared to the VDD pacemaker, the DDD pacemaker offers the advantage of being able to continue providing optimal therapy for heart block patients even if they develop SA Node problems in the future. This is possible because the DDD pacemaker can pace both in the atrium and the ventricle.
In patients whose heart rhythm problem is due to SA node disease, DDD pacemakers prevent slow heart rates from occurring by pacing in the right atrium. They also preserve the pumping efficiency of the natural heart. As a result, most SA node disease patients with otherwise healthy and strong hearts should be able to lead moderately active lifestyles when treated with a DDD pacemaker. Similarly, most elderly patients with ageing hearts should be able to comfortably resume the activities they were accustomed to doing prior to developing their slow heart rhythm problem.
In some forms of SA node disease the sinus node is unable to increase its rate in response to increased demand by the body during physical exertion. Despite having strong hearts, patients with this type of SA node disease may be unable to lead moderate to highly active lifestyles even when treated with a dual chamber pacemaker.
Such patients require rate responsive dual chamber pacemakers.
In the normal heart, pumping efficiency is boosted because the atria and the ventricles contract in synchrony with each other. This synchrony results in better filling of the ventricles with blood before they contract. This in turn results in more blood being pumped to the organs of the body with each ventricular contraction. In patients who are treated with VVl pacemakers there is no coordination between atrial and ventricular contraction. In some patients this could cause symptoms like dizziness, shortness of breath, palpitations etc. that may significantly restrict the patient’s lifestyle. Dual chamber pacemakers maintain the synchrony between the atria and the ventricles and thus prevent these symptoms from occurring. Many clinical studies have compared patients treated with dual chamber and single chamber pacemakers. The majority of these have shown that patients with dual chamber pacemakers are likely to enjoy a significantly better cardiac health status in the long run.
MRI provides good contrast between the different soft tissues of the body, which makes it especially useful in imaging the brain, muscles, the heart, knees & shoulder cartilage etc. when compared with other medical imaging techniques such as computed tomography (CT) or X-rays. Also radiation dose scan be very high in CT, so doctors increasingly prefer MRI as the standard for non-invasive diagnosis.
MRI & PACEMAKERS
In general, it is not safe for patients with pacemakers to undergo MRI scans because the strong magnetic fields created during the MRI scan can have harmful effects on their implanted pacing systems.
Studies conducted on pacemaker patients have shown that up to 75% of them would benefit from an MRI scan for diagnosing other ailments they may develop in the course of their lifetime on pacemaker therapy. However, they are unable to have these scans because their pacemaker systems may be damaged or cause harm to the patient when exposed to an MRI scan.
MRI CONDITIONAL PACEMAKERS
In order to meet the important need for pacemaker patients to undergo MRI scans if required, specialized pacemaker systems have been developed that allow patients to avoid the harmful effects of MRI scans and thereby safely undergo MRI scans under certain conditions. Such pacemakers are called MRI conditional pacemakers and represent a major advancement in pacemaker technology.
Mostbasic type of pacemaker
Pacesone heart chamber at a fixed rate
Adequate heart rate support when you are resting or doing mild activity
A single chamber pacemaker uses only one lead, typically placed in the right ventricle, to pace the heart. Each time the pacemaker paces, the ventricles contract, causing the heart to beat. In medical terminology, such pacemakers are known as VVl pacemakers, where V stands for Ventricle.
VVI pacemakers are the most basic type of pacemakers available. They are able to pace the heart at a fixed rate whenever the natural rhythm of the heart is too slow or irregular.
VVI pacemakers are also the least expensive pacemakers available and the majority of the pacemakers implanted in India today are VVI pacemakers.
For most patients, the heart rate support provided by the VVI pacemaker should be sufficient to comfortably lead a lifestyle with low levels of physical exertion.
Unlike the natural heart which can increase its beating rate to meet increased demand during physical exertion, the VVI pacemaker paces at a fixed rate irrespective of how much you exert. Since it cannot increase the heart’s pumping rate to match your body’s requirements, the VVI pacemaker may limit the level of physical exertion you can comfortably perform.
In the normal heart, the atria contract before the ventricles. This enables better filling of the ventricles with blood, which in turn results in more blood being pumped to your body’s organs each time your ventricles contract. Since VVI pacemakers work only on the right ventricle, they are unable to preserve the contraction synchrony that exists between the atria and ventricles in the normal heart. Thus, VVI pacemakers may reduce the pumping efficiency of the heart and could result in lesser blood being pumped to your organs.
Sometimes in a single chamber pacemaker, the lead is placed in the right atrium instead of the right ventricle. When this pacemaker paces, it causes the atria to contract. The pacemaker impulse then continues to the ventricles through the patient’s healthy AV node to complete the heart beat. Thus, the atria always contract before the ventricles as in the natural heart and the heart’s pumping efficiency is preserved.
These pacemakers are called AAI pacemakers, where A stands for Atrium. AAI pacemakers are prescribed only for patients whose slow heart rhythm is solely due to SA Node problems. These patients must have healthy AV nodes that are unlikely to develop problems in the future.
Rate responsive pacemakers vary heart rate according to the body’s needs.
Single & dual chamber pacemakers that vary their pacing rate similar to the normal heart
Allow you to comfortably perform a wide range of physical activities
Essential for patients who wish to lead a fully active lifestyle
Beneficial for elderly & less active patients because they are especially dependent on heart rate increases even during mild activity
Your normal heart rhythm slows down or speeds up many times during the day. The heart beats slower while you are resting or sleeping. When you exercise or are emotionally excited your body requires a greater amount of blood to be circulated and your heart beats faster. This increased heart rate is maintained for the duration of the physical or mental stress and decreases only when you relax or return to rest.
A rate responsive pacemaker uses a special sensor to vary your heart rate in response to your body’s needs, similar to how a normal heart works. Such variations in pacing rate allow you to more comfortably perform your everyday activities. If you are engaged in physical activities such as walking, climbing stairs or exercising, the pacemaker automatically adjusts your heart rate to match your level of activity. When you slow down, rest, or sleep, the rate decreases accordingly.
You do not need to engage in very strenuous activity to benefit from a rate responsive pacemaker.
For example, the simple act of walking may require a rise in heart rate from a resting value of 70 beats to about 100 beats per minute.
A rate responsive pacemaker is able to provide this rate increase allowing the patient to walk comfortably. The same patient may feel unpleasant symptoms while walking if treated with a pacemaker that cannot vary its rate to meet the patient’s requirements.
Elderly patients, especially those who lead sedentary lifestyles and whose hearts have weakened with age, depend a lot on heart rate increases even to perform activities of mild physical exertion. These patients are likely to be able to lead far more comfortable and satisfying life-styles if they are treated with pacemakers that can automatically vary their pacing rate.
Younger patients with otherwise healthy hearts often wish to lead a moderate to highly active lifestyle including activities like playing athletic games, running, swimming, etc. In most patients, pacemakers capable of rate response are essential to comfortably carry out these activities. Rate responsive pacemakers can be single chamber or dual chamber. Both of these are able to increase their pacing rates to meet increased bodily demand. The dual chamber rate responsive pacemaker offers the additional advantages provided by dual chamber pacemakers that were discussed earlier.
The single chamber rate responsive pacemaker is also known as the VVIR pacemaker, where V stands for ventricle and R stands for rate responsive.
While VVI pacemakers may usually restrict patients to low levels of physical exertion, VVIR pacemakers should enable patients with strong hearts to comfortably lead a moderately active lifestyle. Even elderly patients should be able to more comfortably perform a wider range of physical activities when treated with a WIR pacemaker as compared to a VVI pacemaker.
All the same, like the VVI pacemaker, the VVIR pacemaker is a single chamber pacemaker. It does not maintain synchrony between atrial and ventricular contraction and compromises the heart’s pumping efficiency. This in turn could place greater restrictions on the patient’s range of activities in comparison to treatment with a dual chamber pacemaker. Moreover, WIR pacemakers may not provide the other benefits of dual chamber pacemakers discussed earlier:
Prevention of symptoms arising from the lack of atrial and ventricular coordination
The dual chamber rate responsive pacemaker or DDDR pacemaker is the most advanced type of pacemaker available today. Of all the types of pacemakers, it comes closest to working like the natural heart.
Requirements irrespective of the type of slow heart rhythm problem being treatedItadjusts its pacing rate in accordance with the body’s
It preserves the pumping efficiency of the normal heart
Patient suffers from Heart Block or SA node disease or a combination of these It is able to provide optimal pacing therapy whether the
Thus, the DDDR pacemaker is the most versatile pacemaker available today. By closely mimicking the natural heart, it provides the most optimal pacing therapy to the patient, irrespective of the nature of his or her slow heart rhythm problem.
It offers the patients all the advantages of dual chamber pacemakers and in addition also provides rate response.
Thus, it should enable patients with otherwise healthy and strong hearts to comfortably lead moderate to strenuous lifestyles, irrespective of the type of slow heart rhythm problem.
Similarly, DDDR pacemakers should allow elderly patients without strong hearts to comfortably lead the lifestyles they were accustomed to, irrespective of the type of their slow heart rhythm problem.
It is especially beneficial for SA node disease patients whose sinus nodes cannot increase their rate in response to increased demand by the body during physical exertion. In such patients, the DDDR pacemaker can increase the pacing rate to meet bodily demand and should allow them to comfortably lead moderate to highly active lifestyles.
Several studies have compared different types of pacemakers in terms of patient preference and other quality of life indicators. The majority of the patients clearly chose the DDDR pacemaker as the pacemaker they preferred most.
No matter what type of pacemaker is implanted, they all help people live fuller lives by enabling them to participate in more activities.
Your doctor will prescribe a particular type of pacemaker after careful consideration of the type of slow rhythm problem you have, your general medical history, your cardiac health status, your physical condition and your lifestyle. Your doctor’s goal in treating your slow heart rhythm problem is to provide the best possible therapy for you.
Since your life depends on your pacemaker, he or she will choose a pacemaker of high quality and reliability. When a pacemaker’s battery begins to run down, your pacemaker needs to be replaced. Therefore, your doctor will recommend a pacemaker company that offers a reliable replacement warranty.
Your pacemaker needs to be checked periodically according to your doctor’s orders. Typically, these checkups require the use of a pacemaker programmer that is provided by the pacemaker company. It also requires the inputs of a trained representative from the pacemaker company who assists in the check-up. Thus, your doctor will recommend a company that has a wide & competent service network. This will allow you to travel around the world without having to worry about your pacemaker check-up.
The pacemaker implant operation is a simple procedure that takes about an hour or so. It is not an open heart surgery and the entire procedure is done under local anesthesia.
After your pacemaker implant, you will be provided with a booklet from the pacemaker company about your pacemaker. The booklet will address a variety of aspects about living with your pacemaker and help you to make the best of the pacemaker therapy you are receiving. It is important that you read the booklet carefully and follow the suggestions provided there.
You will also receive a pacemaker identification card that you must carry at all times. In case of an accident or sudden illness, this card will inform those attending you that you have a pacemaker. This card supplies basic information about your pacemaker and identifies your doctor. Most pacemakers are implanted by inserting the lead(s) into a vein located in the upper chest area. The tip of the lead is advanced through the vein to a position on the inside of the heart. The other end of the lead(s) is connected to the pulse generator (pacemaker), which is placed under the skin in the upper chest area just below the collar bone. Wearing a pacemaker creates hardly any inconvenience – about all you will see is a small lump.
Most patients go home a few days after the implant. Upon returning home, most pacemaker wearers resume many daily activities within a few days, or at the most, a couple of weeks. Very soon, most patients even stop being aware of their pacemakers.
Pacemakers are checked periodically according to the doctor’s orders. This check-up is usually performed by your doctor in the clinic or at the hospital. Your monitoring schedule, determined by your doctor, will vary depending on the type of pacemaker you have, your general cardiac health status and the duration for which your pacemaker has been implanted. It is important that you stick to the monitoring schedule established by your doctor.
Today’s pacemakers have built-in safety features to shield them from electrical interference. This includes almost all electrical devices encountered in daily life both at the home and the office. Pacemaker patients can safely operate TVs, stereos, washing machines, microwave ovens, computers, fax machines, etc.
Today’s pacemakers are designed to last a number of years. The actual time will vary depending on the type of pacemaker, how it is programmed to pace the heart and your heart condition.
Whenever your pacemaker is checked, your doctor examines the voltage of your pacemaker battery and is able to estimate how much longer your pacemaker will last. Because the battery is permanently sealed inside the pacemaker, the entire pacemaker will be replaced when the battery runs out. Your doctor will also check the pacing leads. If the leads are functioning well, the existing leads will be connected to the new pacemaker.