Heart Block

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Heart block is a problem that occurs with the heart's electrical system. This system controls the rate and rhythm of heartbeats. ("Rate" refers to the number of times the heart beats in a minute.)

With each heartbeat, an electrical signal spreads across the heart from the upper to the lower chambers. As it travels, the signal causes the heart to contract and pump blood. This process repeats with each new heartbeat.

Heart block occurs when the electrical signal is slowed or disrupted as it moves through the heart.

Heart block is a type of arrhythmia. An arrhythmia is any problem with the rate or rhythm of the heart.

A person can be born with heart block or they can develop it. THis is called a congenital heart block. If it develops after birth, it's called acquired heart block.

Acquired heart block is more common. Damage to the heart muscle or to the heart's electrical system causes acquired heart block. Diseases, surgery, or medicines can cause this damage.

Congenital heart block may be found before or after a baby is born. If certain diseases occur during pregnancy, they may cause a baby to be born with heart block. Some congenital heart defects also may cause congenital heart block. Often, doctors don't know what causes these defects.

The three types of heart block are: first degree, second degree, and third degree. First degree is the least severe and third degree is the most severe. This is true for both congenital and acquired heart block.

Doctors use a test called an EKG (electrocardiogram) to help diagnose heart block. This test detects and records the heart's electrical activity. It records the data on a graph so the doctor can review it.

The symptoms and severity of heart block depend on which type is present. First-degree heart block rarely causes severe symptoms.

Second-degree heart block may result in the heart skipping a beat or beats. This type of heart block also can cause dizziness or fainting.

Third-degree heart block limits the heart's ability to pump blood to the rest of the body. This type of heart block may cause fatigue (tiredness), dizziness, and fainting. Third-degree heart block requires prompt treatment, because it can be fatal.

A medical device called a pacemaker is used to treat third-degree heart block and some cases of second-degree heart block. This device uses electrical pulses to make the heart beat at a normal rate.

Contents

Understanding the Heart's Electrical System and EKG Results

Doctors use a test called an EKG (electrocardiogram) to help diagnose heart block. This test detects and records the heart's electrical activity. An EKG records the strength and timing of electrical signals as they pass through each part of the heart.

The data is recorded on a graph so that the doctor can study the heart's electrical activity. Different parts of the graph show each step of an electrical signal's journey through the heart.

A Healthy Heart Cross-Section

Source:NIH

The illustration shows a cross-section of a healthy heart and its inside structures. The blue arrow shows the direction in which oxygen-poor blood flows from the body to the lungs. The red arrow shows the direction in which oxygen-rich blood flows from the lungs to the rest of the body.

Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the right atrium, which is the upper right chamber of the heart. In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute.

From the SA node, the signal travels to the right and left atria. This causes the atria to contract and pump blood into the heart's two lower chambers, the ventricles. This is recorded as the P wave on the EKG.

The signal passes between the atria and ventricles through a group of cells called the atrioventricular (AV) node. The signal slows down as it passes through the AV node. This slowing allows the ventricles time to finish filling with blood. On the EKG, this is the flat line between the end of the P wave and beginning of the Q wave.

The electrical signal then leaves the AV node and travels along a pathway called the bundle of His. From there the signal travels into the right and left bundle branches. On the EKG, this is the Q wave.

As the signal spreads across the right and left ventricles, they contract and pump blood out to the lungs and the rest of the body. On the EKG, R marks the contraction of the left ventricle and S marks the contraction of the right ventricle.

The ventricles then relax (shown as the T wave on the EKG). This entire process continues over and over with each new heartbeat.

Types

A person can be born with heart block (congenital) or they can acquire it. Acquired heart block is more common.

The three types of heart block are: first degree, second degree, and third degree. First degree is the least severe and third degree is the most severe. This is true for both congenital and acquired heart block.

First-Degree Heart Block

In first-degree heart block, the electrical signal is slowed as it moves through the heart. When this occurs between the atria and the ventricles, it appears as a slightly longer, flatter line between the P and the R waves on the EKG.

First-degree heart block rarely causes any symptoms. Well-trained athletes and young people are at higher risk for first-degree heart block caused by an overly active vagus nerve. Activity in this nerve slows the heart rate. Some medicines, such as digitalis, also may trigger first-degree heart block.

First-degree heart block usually doesn't require treatment.

Second-Degree Heart Block

In this type of heart block, electrical signals between the atria and ventricles are slowed to a large degree. Some signals can't reach the ventricles. On an EKG, the QRS wave doesn't follow each P wave as it normally would.

If the signal is blocked before it reaches the ventricles, they won't contract and pump blood to the lungs and the rest of the body.

Second-degree heart block is divided into two different types, Mobitz type I and Mobitz type II.

Mobitz Type I

In this type (also known as Wenckebach's block), the electrical signals are delayed more and more with each heartbeat, until the heart skips a beat. On the EKG, the flat line between the P and the QRS waves gets longer and longer until there's no QRS wave.

Sometimes people with Mobitz type I feel dizzy or have other symptoms. This type of second-degree heart block is less serious than Mobitz type II.

Mobitz Type II

In this type, some of the electrical signals also don't reach the ventricles. However, the pattern is less regular than it is in Mobitz type I. Some signals move between the atria and ventricles normally, while others are blocked. On an EKG, the QRS wave follows the P wave at a normal speed. Sometimes, though, the QRS wave is missing (when a signal is blocked).

Mobitz type II is less common than type I, but it's usually more severe. Some people with type II need medical devices called pacemakers to maintain their heart rates.

Third-Degree Heart Block

In this type of heart block, none of the electrical signals reach the ventricles. This type also is called complete heart block or complete AV block.

When complete heart block occurs, special areas in the ventricles may create electrical signals to cause the ventricles to contract. This natural backup system is slow and isn't coordinated with the contraction of the atria. On an EKG, the normal pattern is disrupted. The P waves occur at a faster rate than the QRS waves.

Complete heart block can be fatal. It can result in sudden cardiac arrest and death. This type of heart block needs emergency treatment. A temporary pacemaker may be used to keep the heart beating until a permanent pacemaker can be put in place.

Signs and Symptoms

Signs and symptoms depend on the type of heart block. First-degree heart block rarely causes symptoms.

Symptoms of second- and third-degree heart block include:

  • Fainting
  • Feeling dizzy or lightheaded
  • Fatigue (tiredness)
  • Shortness of breath
  • Chest pain

These symptoms may point to other health problems as well. If these symptoms are new or severe, call 9–1–1 or go to the hospital emergency room. If the symptoms are milder, talk to a doctor right away to find out whether prompt treatment is needed.

Causes

Heart block has a number of causes. A person can be born with this disorder (congenital) or acquire it.

Congenital Heart Block

One form of congenital heart block occurs in the babies of women who have autoimmune diseases, such as lupus. People who have these diseases make proteins called antibodies.

In pregnant women, these antibodies can cross the placenta. (The placenta is the organ that attaches the umbilical cord to the mother's womb.) They can damage the baby's heart and lead to congenital heart block.

Congenital heart defects (problems with heart's structure) also may cause congenital heart block. Often, doctors don't know what causes these defects.

Acquired Heart Block

A number of factors, such as diseases, surgery, medicines, and other conditions, can cause acquired heart block.

The most common cause of acquired heart block is damage to the heart from a heart attack. Other diseases that can cause heart block include coronary artery disease, myocarditis (inflammation of the heart muscle), heart failure, rheumatic fever, and cardiomyopathy.

Other diseases may increase the risk for heart block. These include sarcoidosis and the degenerative muscle disorders, Lev's disease and Lenegre's disease.

Certain types of surgery also may damage the heart's electrical system and lead to heart block.

Exposure to toxic substances and taking certain medicines, including digitalis and beta blockers, also may cause heart block. Doctors closely watch people who are taking these medicines for signs of problems.

In some cases, atrioventricular (AV) heart block has been linked to genetic mutations (changes in the genes).

An overly active vagus nerve can cause first-degree heart block. Activity in this nerve slows the heart rate. Well-trained athletes and young people are at higher risk for first-degree heart block due to this cause.

In some cases, acquired heart block may go away if the factor causing it is treated or resolved. For example, heart block that occurs after a heart attack or surgery may go away after recovery.

Also, if a medicine is causing heart block, the condition may go away if the medicine is stopped or the dosage is lowered. However, do not change the way the medicines are being taken unless instructed to do so by a doctor.

Chances of Developing

Risk factors

The risk factors for congenital and acquired heart block are different.

Congenital Heart Block

If a pregnant woman has an autoimmune disease, such as lupus, her fetus is at risk for heart block.

Autoimmune diseases can cause the body to make proteins called antibodies that can cross the placenta. (The placenta is the organ that attaches the umbilical cord to the mother's womb.) These antibodies may damage the baby's heart and lead to congenital heart block.

Congenital heart defects (problems with the heart's structure) also may result in congenital heart block. Most of the time, doctors don't know what causes these defects.

Heredity may play a role in certain heart defects. For example, a parent who has a congenital heart defect may be more likely than other people to have a child with the condition.

Acquired Heart Block

Acquired heart block can occur in people of any age. However, most types of the disorder are more common in older people. This is because many of the risk factors are more common in older people.

People who have a history of heart disease or heart attacks are more likely to have heart block. Examples of heart disease that can lead to heart block include heart failure], coronary artery disease], and cardiomyopathy].

Other diseases also may raise the risk for heart block. These include sarcoidosis and the degenerative muscle disorders, Lev's disease and Lenegre's disease.

Exposure to toxic substances or taking certain medicines, such as digitalis, can increase the risk for heart block.

Well-trained athletes and young people are at higher risk for first-degree heart block caused by an overly active vagus nerve. Activity in this nerve slows the heart rate.

Diagnosis

Heart block may be diagnosed as part of a routine doctor's visit or during an emergency situation (third-degree heart block is an emergency).

A doctor will diagnose heart block based on family and medical histories, a physical exam, and results from tests.

A primary care doctor may be involved in diagnosing heart block. However, if heart block exists, it may be necessary to see a heart specialist. Heart specialists include:

  • Cardiologists (doctors who treat adults with heart problems)
  • Pediatric cardiologists (doctors who treat babies and youths with heart problems)
  • Electrophysiologists (cardiologists or pediatric cardiologists who specialize in the heart's electrical system)

Exams and Tests

Family and Medical Histories

To find out family and medical histories, the doctor may ask whether:

  • There are any signs or symptoms of heart block
  • There are any health problems, such as heart disease
  • If any family members have been diagnosed with heart block or other health problems
  • If any medicines are being taken, including herbal remedies and prescription and over-the-counter medicines
  • If there is a history of smoking, alcohol use, or drugs

The doctor also may ask about other health habits, such as the amount of physical activity.

Physical Exam

During the physical exam, the doctor will listen to he heart's rhythm. He or she will listen carefully for abnormal rhythms or heart murmurs (extra or unusual sounds heard during heartbeats).

The doctor also may:

  • Check the pulse to find out how fast the heart is beating
  • Check for swelling in the legs or feet, which could be a sign of an enlarged heart or heart failure
  • Look for signs of other diseases that could be causing a problem with the heart's rate or rhythm (such as coronary artery disease)

Diagnostic Tests and Procedures

EKG (Electrocardiogram)

Doctors usually use a test called an EKG (electrocardiogram) to help diagnose heart block. This simple test detects and records the heart’s electrical activity. It shows how fast the heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through each part of the heart.

The data is recorded on a graph. Different types of heart block have different patterns on the graph. A standard EKG test only records the heart’s activity for a few seconds.

Holter and Event Monitors

To diagnose first- or second-degree heart block, the doctor may have the patient wear a Holter or event monitor.

Holter and event monitors are similar to EKGs, but they're portable devices. A Holter or event monitor can be worn while doing normal daily activities. This allows the device to record the heart's electrical activity for a longer time than an EKG.

Electrophysiology Study

For some cases of heart block, doctors may do electrophysiology studies (EPS). During an EPS, a thin, flexible wire is passed through a vein in the groin (upper thigh) or arm to the heart. The wire records the heart's electrical signals.

Other Tests

To diagnose heart block, the doctor may need to do tests to rule out other types of arrhythmias (irregular heartbeats).

Treatment

Treatment depends on the type of heart block you have. First-degree heart block usually needs no treatment.

A person with a second-degree heart block may need a pacemaker. A pacemaker is a small device that's placed under the skin of the chest or abdomen. This device uses electrical pulses to stimulate the heart to beat at a normal rate.

A person with a third-degree heart block will need a pacemaker. In an emergency, a temporary pacemaker may be used until a permanent one can be placed. Most people who have third-degree heart block need pacemakers for the rest of their lives.

Some people with third-degree congenital heart block don't need a pacemaker for many years. Others may need a pacemaker at a young age or during infancy.

In some cases, acquired heart block may go away if the factor causing it is treated or resolved. For example, heart block that occurs after a heart attack or surgery may go away.

Also, if a medicine is causing heart block, the condition may go away if the medicine is stopped or the dosage is lowered. However, this shouldn't change the way that the medicines are taken unless the doctor says that there should be a change made.

Living With Heart Block

First-degree heart block may not cause any symptoms or require treatment. Anyone who has been diagnosed with this condition should ask therir doctor whether they need to take any special measures to control it. The doctor will discuss the need for ongoing care or changing the way certain medicines are taken.

A person with second-degree heart block that doesn't require a pacemaker should talk to their doctor about keeping their heart healthy. The doctor discuss whether ongoing care is needed.

Living With a Pacemaker

People who have third-degree heart block and some people who have second-degree heart block need pacemakers. Anyone who has a pacemaker will need to take special care to avoid things that may interfere with it.

Avoid close or prolonged contact with electrical devices and devices that have strong magnetic fields. These objects can keep a pacemaker from working properly.

Let all doctors, dentists, and medical technicians know that about the pacemaker. It is important to notify airport screeners.

Certain medical procedures can disrupt pacemakers. These include MRI (magnetic resonance imaging), electrocauterization during surgery, and shock-wave lithotripsy to get rid of kidney stones.

The doctor may need to check the pacemaker several times a year to make sure it's working properly. Some pacemakers must be checked in the doctor's office, but others can be checked over the phone.

Clinical Trials

Other Resources

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