Why do I Need a Pacemaker?, Conduction Disease

Why do I need a pacemaker?

Pacemakers are implanted in the body when its heart beat becomes very slow or unreliable. The medical term to describe this condition is a bradyarrhythmia. Brady- means slow, and arrthytmia is any rhythm that the heart gets into that is different than the normal one. To understand why this can happen, we need to look at the heart’s electrical conduction system.

The conduction system of the heart

The heart is an electrical organ. Electricity in the heart starts in the sinus node, known as the heart’s pacemaker. This structure produces an electrical pulse that travels through tissues to distribute the electricity throughout the heart’s structure, all the way down to the ventricles. The electrical pulse first contracts both top chambers of the heart, then travels to the center of the heart where it slows down to allow for blood flow to catch up. After that, it moves into the ventricles, making them contract and push the blood out into the body and lungs. Problems with the heart’s conduction system can appear along any of its parts and for different reasons. Doctors can have an idea of the location and severity of the problem by looking at the ECG. Conduction abnormalities are named depending on the location where they happen.

The electrical conduction system of the heart - Doctabet

The beating of the heart is produced by the heart’s very own pacemaker, located in the right atrium. Think of the pacemaker as both the spark plug that starts the heart’s engine and the conductor of the heart’s rhythm.

The sinus node, conductor of spark plugs - Doctablet

The pacemaker is a structure within the heart known as the “sinus node.” It is located in the upper right corner of the heart, which is the cardiac chamber where blood first enters. The sinus node produces a regular electrical pulse that travels down the heart and makes its muscle contract in the rhythmic fashion we all know. The sinus node is controlled by the body’s nervous system, and its pulse can be speeded up or slowed down depending on what the body is doing. You can say the body “drives the heart” through the pacemaker, pushing down on gas pedals and brakes to accelerate it or slow it down. Blood pressure in the body is maintained in part by the heartbeat our pacemaker produces, because without this regular beat, the heart cannot pump blood. If the heart beats very slowly or if the beating becomes unsteady, it can cause an unstable blood pressure situation the body may have trouble adapting to. People who develop severely slow or unsteady heartbeats can feel lightheaded, dizzy, very tired and out of breath, and the condition can also be fatal.

Types of electrical blocks the heart can experience

First degree heart block

Electrical problems that originate at the upper parts of the electrical conduction system create a pattern known as a “first degree block.” The upper parts of the conduction system are made up of the atrium, the atrioventricular node (AV node) and the His-Purkinje system. First degree blocks can be caused by abnormalities in the structure of the atria that prolong the amount of time it takes for the electricity to reach other parts of the heart—for example, if the atrium enlarges in size. Most of the time, this type of pattern is caused by a delay in conduction across the atrioventricular node.

This type of block does not need a pacemaker.

Second degree heart block

Second degree blocks appear at or near the AV node. The AV node is another important part of the heart’s conduction system. It is responsible for slowing down the electrical impulse so the heart can contract in a rhythm. The AV node is called this because it is located at the junction between the atria and the ventricle. Second degree heart blocks cause breaks in the communication between the top and the bottom parts of the conduction system. Different things can cause second degree blocks, including the body’s own nervous system’s effect on the heart and different types of drugs.

An expert is needed to decide if a pacemaker will help with this block

Third degree blocks

This type of block is the most dangerous. Third degree blocks are permanent breaks between the top and the bottom parts of the conduction system. These breaks can happen at the AV node or in the “wires” below it. Without a signal from the top, the bottom parts of the heart usually beat on their own with unpredictable rhythms that originate within the lower parts of the heart. These backup rhythms are known as ventricular or junctional escape rhythms, and are very unreliable. In fact, some patients who develop third degree heart blocks will fail to generate these backup rhythms and die as a result.

This type of block always needs a pacemaker

Sinus node dysfunction

The sinus node itself, known as the main pacemaker of the heart, can fail as a result of a variety of conditions. Its ability to generate an impulse can be either diminished or suppressed. Also, the tissue surrounding the SA node can degenerate resulting in a loss of the signal this pacemaker generates

An expert is needed to decide if a pacemaker will help with this block

What causes cardiac conduction disease?

Many different things cause abnormalities of the conduction system of the heart. Some conduction problems are temporary or treatable, while others are permanent. Let’s review some of the most common causes:

Structural heart disease describes a medical problem that occurs from abnormalities in the size of the heart or its valves. Enlargement of the heart’s chambers and valvular abnormalities like stenosis or regurgitation are examples of structural heart disease. It is important to remember that hypertension is an important cause of structural heart disease, and therefore it can also lead to conduction disease.

Autoimmune medical conditions like scleroderma, polymyositis and lupus can lead to the development of antibodies directed against one’s own heart. These antibodies can cause inflammation and destruction of different parts of the cardiac structure, including the conduction system. Two conditions in this category are especially important: amyloidosis and cardiac sarcoidosis. Amyloidosis is the result of the accumulation of an abnormal protein in the heart tissue, which leads to its dysfunction. Cardiac sarcoidosis is an inflammatory process that occurs within the heart tissue which results in conduction blocks and deterioration of the heart muscle.

Lyme disease is an infection transmitted by ticks that affects many different parts of the body. One rare manifestation of Lyme disease involves an infection of the heart tissue by the organism Borrelia burgdorferi. Carditis (inflammation of the heart) caused by Lyme causes a progressive block in the heart’s conduction system. More serious infections of the heart, known as endocarditis, can also cause conduction problems, as bacteria and the abscesses they form tend to destroy the structure necessary to conduct electricity.

And in general lack of blood flow to the heart; If the heart muscle dies as a result of a heart attack, part of the conduction system of the heart can die or diminish its function, too. This can be seen in an ECG and present itself in different types of heart blocks.

The thyroid hormone is an important driver of metabolism and cell function in the body. This effect extends to the cardiac muscle cell. Both hypothyroidism (low) and hyperthyroidism (high) can cause different types of heart blocks. Up to 24 percent of people with low thyroid and 14 percent with high thyroid can have a conduction disease related to this condition. Whether or not treatment of the thyroid abnormality results in normalization of the conduction abnormality remains an area of active research.

How are conduction problems in the heart treated?

If a specific cause of the conduction problem, like drugs or an infection, is present, removing or treating these can often result in a cure. For permanent conduction problems or those that cause severe symptoms, doctors often recommend an artificial pacemaker.

About the Author

Jose Taveras M.D. F.A.C.C.

Dr Taveras works as a cardiologist caring for spanish speaking communities in the Bronx. He completed a dual residency in Internal Medicine and Pediatrics and then served as chief resident of internal medicine at the St. Vincent’s Catholic Medical Center of New York. He went on to specialize in cardiovascular disease at NYU Winthrop Hospital , under the mentorship of Dr. Kevin Marzo, chief of Cardiology at Winthrop. He is board certified in both internal medicine and cardiovascular diseases, and sub specializes in echocardiography, nuclear cardiology and computed tomography of the heart. Apart from his work in community outreach, Dr. Taveras' career focuses on innovation and technology. Dr. Taveras is a fellow of the American College of Cardiology.