A pacemaker is an electrical device that is used to control an individuals heartbeat. It sends electrical impulses to the heart to help the heart muscle contract at a normal rate. There are three main components of a pacemaker: a battery, a generator, and wires with specific electrodes attached to them. The wires are placed deep down into the chambers of the heart. If the heart suddenly goes into an irregular pattern, the electrodes attached to the end of the wire can detect this type of irregular activity and “notify” the generator. The generator can then fire an electrical signal back to the heart, helping the muscle contract and establish normal function.
Different Types of Pacemakers
A single chamber pacemaker is the simplest of all the pacemakers and uses the electrical impulses to help set the rate of one chamber of the heart. It uses a single lead, known as a pacing lead, which is most commonly placed in the right ventricles, or sometimes the right atrium. This pacemaker can be used for a patient who has a minor heart issue, such as sporadic arrhythmia’s.
Dual Chamber Pacemakers
A dual chamber pacemaker is the most common type of pacemaker and commonly treats individuals with heart blockages. A heart block is a type of conduction disorder in which the electrical signal that is sent from the atrium of the heart is damaged and is then poorly transmitted to the ventricles. A dual chamber pacemaker can set the rate of two chambers of the heart by placing one lead in the atrium and one lead in the ventricle. If the heart is beating irregularly, the generator sends an impulse to the first lead in the atrium, stimulating contraction and then another impulse is sent to the ventricle. This can help regulate the amount of blood flow to the ventricles as well.
Bi-ventricular Pacemaker/Triple-chambered Pacemaker
These types of pacemakers are used to treat patients with severe heart failure. It has three leads: one in the right atrium, one in the right ventricle, and one in the left ventricle. Like other pacemakers, it resets the rhythm pattern of the ventricles, allowing increased blood flow.
Normal Sinus Rhythm
The heart contracts in a specific sequence which allows it to effectively push blood out of the heart. Unlike skeletal muscle, cardiac muscle does not uses electrical signals from the brain. Instead, it has its owns cells known as “pacemaker cells” that trigger specific action potentials that diffuse across the heart. This cycle is carried about by a specific system called the intrinsic cardiac conduction system. As impulses are generated, it starts at the atria, causing it to contract first. When this happens the blood is pumped into the ventricles. The impulse then travels to the ventricles where it contracts again. This results in the blood being pushed out of the heart to the arteries.
The Five Components of the Intrinsic Conduction System
Sinostrial (SA) Node
- The SA node is located on the top of the right atrium, just below the superior vena cava. This is where the impulse is generated and ultimately determines the heart rate.
Atrioventricular (AV) Node
- The AV node is located at the bottom the the right atrium. When the impulse travels to this node, it is delayed about 0.1 second. This delay allows the atria to contract and allows more time for the blood to fill the ventricle.
Atrioventricular (AV) Bundle
- The AV bundle is where the impulse from the AV node is transferred from the atria to the ventricle.
Right and Left Bundle Branches
- The bundle branches separate into two different pathways in the interventricular septum that carry in the impulse towards the bottom of the heart.
- These fibers finish the pathway by carrying the impulse towards the ventricle walls.
Cardiac Conduction System and its Relationship with ECG
The implantation of a pacemaker is a very minor procedure. There are two different types of implantation methods. The first and most common is the endocardial (transvenous) approach. In this method, the skin around the collar bone is numbed. An incision is made and a small wire is placed into the vein.
How Do I Know If I Need a Pacemaker?
The majority of patients who have pacemakers are diagnosed with some type of arrhythmia. There are many tests that can detect whether or not a patient has an arrhythmia.
Coronary artery disease can also lead to arrhythmia’s. Arrhythmia’s are known as irregular changes in the normal sinus rhythm. Although most arrhythmia’s are not deadly, there are some that can be severe if not treated properly.
Different Types of Arrhythmias
A heart block is a type of conduction disorder in which the electrical signal that is sent from the atrium of the heart is damaged and poorly transmitted. In some cases, the signal is not received by the ventricles at all. There are different levels of heart block that indicate the severity of this condition.
Bradycardia is when the heart rate is slower (less than 60 beats per minute) than the average.
Atrial Tachycardia is a disturbance to the standard rhythm of the heart within the atria itself.
Ventricular Tachycardia is when the ventricles are beating at a faster rate than normal. If left untreated, the patient may go into ventricular fibrillation.
Ventricular fibrillation is the most severe type of arrhythmia. Instead of the ventricles contracting normally, they contract in an uncoordinated manner, which makes the ventricles shake and unable to pump blood.
Atrial Fibrillation occurs when both atriums contract irregularly and at increased rates. This causes the atriums to fill with blood and cannot enter the ventricles.