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 your 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.
Overview
Heart block is a type of
arrhythmia (ah-RITH-me-ah). An arrhythmia is any problem with the rate or
rhythm of the heart.
You can be born with heart block or you can develop
it. If you're born with it, it's called congenital (kon-JEN-i-tal) 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.
Outlook
The symptoms and severity of heart block depend on
which type you have. 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 make you feel dizzy
or faint.
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.
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 your doctor can
study your 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
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 (AY-tree-um), 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 (VEN-trih-kuls). 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.
The animation below shows how your heart's
electrical system works. Click the "start" button to play the animation.
Written and spoken explanations are provided with each frame. Use the buttons
in the lower right corner to pause, restart, or replay the animation, or use
the scroll bar below the buttons to move through the frames.
The animation shows how an
electrical signal moves through your heart and how an EKG records your heart's
electrical activity.
For more information on the heart's electrical
system, go to the Diseases and Conditions Index
How
the Heart Works article.
Types of Heart Block
You can be born with heart block (congenital) or you
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 delay is shown as a line (called the PR
interval) between the P and QRS waves. The line gets longer and longer until
the QRS wave doesn't follow the next P 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.
The animation below shows how your heart's
electrical system works and what happens during second-degree, Mobitz type I
heart block. Click the "start" button to play the animation. Written and spoken
explanations are provided with each frame. Use the buttons in the lower right
corner to pause, restart, or replay the animation, or use the scroll bar below
the buttons to move through the frames.
The first part of this animation is the same as the
animation in the section on understanding the heart’s electrical system
and EKG results. If you want to skip directly to the frames on Mobitz type I,
click the "skip intro" link above the start, pause, and replay buttons.
The first part of the animation
shows how an electrical signal moves through your heart and how an EKG records
your heart's electrical activity. The second part of the animation shows how a
pause in the heart’s electrical signal can delay and momentarily block the
contraction of the ventricles.
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
you get a permanent pacemaker.
What Causes Heart Block?
Heart block has a number of causes. You 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, you shouldn't change the way you take your medicines unless your
doctor tells you to.
Who Is At Risk for Heart Block?
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.
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 raise your 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.
What Are the Signs and Symptoms of Heart
Block?
Signs and symptoms depend on the type of heart block
you have. 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 you have milder symptoms, talk to your doctor right
away to find out whether you need prompt treatment.
How Is Heart Block Diagnosed?
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).
Your doctor will diagnose heart block based on your
family and medical histories, a physical exam, and results from tests.
Specialists Involved
Your primary care doctor may be involved in
diagnosing heart block. However, if you have the condition, you may need 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)
Family and Medical Histories
To find out your family and medical histories, your
doctor may ask whether:
You have any health problems, such as heart
disease
Any of your family members have been diagnosed
with heart block or other health problems
You're taking any medicines, including herbal
remedies and prescription and over-the-counter medicines
You smoke or use alcohol and drugs
Your doctor also may ask about other health habits,
such as how much physical activity you do.
Physical Exam
During the physical exam, your doctor will listen to
your heart's rhythm. He or she will listen carefully for abnormal rhythms or
heart
murmurs (extra or unusual sounds heard during heartbeats).
Your doctor also may:
Check your pulse to find out how fast your heart
is beating
Check for swelling in your 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. (For more information, see
“Types of Heart Block.”)
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,
your doctor may have you wear a
Holter
or event monitor.
Holter and event monitors are similar to EKGs, but
they're portable devices. You can wear a Holter or event monitor while you do
your normal daily activities. This allows the device to record your 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 your groin (upper thigh) or arm to
your heart. The wire records your heart's electrical signals.
Other Tests
To diagnose heart block, your doctor may need to do
tests to rule out other types of
arrhythmias
(irregular heartbeats). For more information, see
"How
Are Arrhythmias Diagnosed?"
How Is Heart Block Treated?
Treatment depends on the type of heart block you
have. First-degree heart block usually needs no treatment.
If you have second-degree heart block, you may need
a pacemaker.
A pacemaker is a small device that's placed under the skin of your chest
or abdomen. This device uses electrical pulses to stimulate the heart to beat
at a normal rate.
If you have third-degree heart block, you will need
a pacemaker. In an emergency, a temporary pacemaker may be used until you can
get a permanent one. 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, you shouldn't change the way you take your medicines unless your
doctor tells you to.
Living With Heart Block
First-degree heart block may not cause any symptoms
or require treatment. If you've been diagnosed with this condition, ask your
doctor whether you need to take any special measures to control it. Your doctor
can tell you whether you need ongoing care or whether you need to change the
way you take certain medicines.
If you have second-degree heart block that doesn't
require a pacemaker, talk to your doctor about keeping your heart healthy. Your
doctor will tell you whether you need ongoing care for your condition.
Living With a Pacemaker
People who have third-degree heart block and some
people who have second-degree heart block need
pacemakers.
If you have a pacemaker, you should 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
your pacemaker from working properly.
Let all of your doctors, dentists, and medical
technicians know that you have a pacemaker. You also should 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.
Your doctor may need to check your 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.
Ask your doctor about what types of physical
activity are safe for you. A pacemaker usually won't limit you from doing
sports and physical activity. But you may need to avoid full-contact sports,
such as football, that can damage the pacemaker.
For more information on living with a pacemaker, see
the Diseases and Conditions Index
Pacemaker
article.
Key Points
Heart block is a problem that occurs with the
heart's electrical system. This system controls the rate and rhythm of
heartbeats.
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. The process repeats with
each new heartbeat.
Heart block occurs when the electrical signal is
slowed or disrupted as it moves through the heart.
You can be born with heart block or you can
develop it. If you're born with it, it's called congenital heart block. If it
develops after birth, it's called acquired heart block. Acquired heart block is
more common.
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 your doctor can review it.
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. Third-degree heart block may be fatal and requires prompt
treatment.
Heart block has a number of causes. Autoimmune
diseases and
congenital heart defects may cause congenital heart block. Diseases,
surgery, medicines, and other conditions may cause acquired heart block.
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 with recovery.
Signs and symptoms depend on the type of heart
block you have. 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, and chest pain.
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). Your doctor will diagnose heart block based on your family and
medical histories, a physical exam, and results from tests.
Treatment depends on the type of heart block you
have. First-degree heart block usually needs no treatment. People who have
third-degree heart block and some people who have second-degree heart block
need
pacemakers.
A pacemaker is a small device that's placed under the skin of your chest or
abdomen. This device uses electrical pulses to stimulate the heart to beat at a
normal rate.
If you have heart block or symptoms of heart
block, it's important to talk to your doctor. He or she can tell you whether
you need treatment and whether you should have ongoing medical care for your
condition. If you have severe symptoms, you should call 9–1–1 or go
to the hospital right away.
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