A pacemaker is an implantable device that stimulates the heart in order to generate a heartbeat.
A smaller and smaller device
This electronic device powered by a battery that is slightly thicker than a 2-dollar coin. The pacemaker is generally implanted beneath the skin just below the left collarbone.
Small intervention necessary
A short surgery – lasting only a few minutes - needs to be done to implant a pacemaker. General anesthesia is not necessary; local anesthesia is sufficient.
A box and electric wires
This apparatus includes the pacemaker generator (the “box”) and between one and three electric wires. The device produces an electric pulse that stimulates the heart’s contraction.
The pacemaker only needs to work when the heart rate is slower than the programmed settings.
At that point the pacemaker turns on in order to accelerate and regulate the heartbeat. But, if the heart rate is faster than the pacemaker, then the pacemaker is not needed.
An electric system of its own for the heart
We must remember that the heart possesses its own electrical system.
This system is used to generate its heart beat, or contraction. The frequency of these beats is the responsibility of a specialized region of the electric system in the top right heart chamber (the right atrium) called the sinoatrial node.
This area can be thought of as the conductor of the heartbeat.
Once this electric impulse travels through the two top chambers (the left and right atria), it is transmitted through a wire towards the ventricles. This specialized passage can be thought of as a special bridge of electrical wires. It is known as the atrioventricular node. The atrioventricular node allows for the electrical impulses to reach the ventricles.
But the atrioventricular node also regulates the heart beat by ensuring that the heart beats can’t travel too fast to the ventricles.
The electric impulses then travel from the atrioventricular node down a rapid conduction system to the bottom chambers of the heart (the ventricles).
This is like a specialised highway for the electronic impulses that allows the ventricles to contract in a way that is most efficient to push the blood out of the heart and around the body.
Many factors influence the electric system
The orchestra conductor (sinoatrial node) and the electrical bridge (atrioventricular node) are influenced by multiple factors that can slow down or block electric impulsions.
- Certain components of the blood called electrolytes like potassium, sodium and calcium
- Certain medication like beta-blockers and calcium channel blockers
- The aging and condition of the electric system
- Injury to the heart muscle like a myocardial infaction
- Certain valvar diseases
Sometimes the electrical abnormalities in the heart can be corrected. Sometimes that means correcting for an electrolyte disorders.
Sometimes non-essential medications can be modified.
However, in other occasions the problem in the electrical system of the heart cannot be corrected, and a pacemaker is necessary to normalise the heartbeat.
Varied and vague symptoms
The symptoms of an electrical conduction disturbance can vary. Most often people will experience:
- Being out of breath more easily during physical activity
- Loss of consciousness, sometimes suddenly
These symptoms are the consequence of an abnormally slow heart beat.
Taking your pulse helps with the diagnostic
The patient can facilitate the diagnosis by taking their own pulse or blood pressure. The heart’s rhythm may be abnormally low when it is below 50 beats per minute.
The ECG shows the problem
The diagnosis can be confirmed with the help of an electrocardiogram.
Sickness sometimes discovered by accident
Some patients can be asymptomatic. Sometimes the diagnostic is found through testing, which may have been done routinely or for the investigation of other health problems.
Can the situation be corrected?
Once the doctor confirms the diagnosis, they will verify if there is a reversible cause to this condition.
Necessary to install a pacemaker
If there isn’t a reversible cause, then the risks and benefits of pacemaker implantation will be explained.
Different types of pacemakers
The health professional responsible for the implantation will determine the type of pacemaker needed.
The pacemaker electrodes (or wires) are placed inside the cardiac chambers.
- Single chamber pacemaker
A generator with only one electrode is called a single chamber pacemaker. This is because the pacemaker is only able to stimulate only one cardiac chamber. Usually this type of pacemaker is placed in the bottom right chamber, or the right ventricle.
- Dual chamber pacemaker
A box containing two electrodes is called a dual chamber pacemaker.
The two electrodes stimulate two cardiac chambers (the right atrium and right ventricle).
- Bi-Ventricular pacemaker
A box containing 3 electrodes is used with certain patients suffering with heart failure. These patients’ hearts are often large. Most often the electrical conduction system is abnormal.
This anomaly in the electric conduction means that the synchronisation of the contraction in the two ventricles is lost. This impairs the “squeezing” function of the heart.
To re-coordinate the contraction in the two ventricles, an electrode is deposited in the right atrium, a second one in the right ventricle and a third one on the left ventricle. The wire to the left ventricle is placed in the heart’s big vein (the coronary sinus).
How it works
The dual chamber pacemaker is the most commonly implanted device.
The electrodes in the right atrium and the right ventricle send the information recorded on the electric activity to the generator.
In the situation where there isn’t any electric activity received from the atria, then the pacemaker sends an electric impulse through the electrode (or wire) to the right atrium. This electric impulse is transmitted through the atria and then, to the ventricles. In the event that it does not make it to the ventricles, the pacemaker will send another impulse via the ventricular electrode (or wire).
The pacemaker is programmed in such a way that there is a pause between the two impulses to allow the heart to normally function as much as possible.
Many combinations are possible with a pacemaker.
Keeping in mind the previous example, when the electric activity travels from the atriums to the ventricles, the ventricular activity is perceived by the ventricular electrode (or wire). The pacemaker does not send an electric impulse to the ventricular electrode (or wire).
It is possible that the electrical activity is generated by the natural pacemaker and transmitted normally to the atriums. This information is perceived by the atrial electrode (or wire). The pacemaker doesn’t need to send an impulse. It waits for the information from the ventricular electrode (or wire). In the event that there isn’t any activity transmitted to the ventricles, and electric impulse is sent to the ventricles.
A small computer under the skin
The pacemaker can therefore be seen as a small computer placed under the skin., This computer receives electrical information from the heart, analyses it, and responds by withholding or delivering an electrical impulse back to the heart. Its activity is complementary to the natural system already in place.
The battery’s lifespan
The battery’s lifespan is dependant on the pacemaker’s use. In general, a pacemaker battery can last around 10 years, but this depends how often it is being used.
Necessary verifications of the pacemaker
The pacemaker function will be verified on a regular basis.
An appointment for the analysis is necessary once or twice per year.