Alternate Names : Atrioventricular Block, AV Block, Bundle Branch Block, Complete Heart Block, First-Degree Heart Block, Second-Degree Heart Block, Third-Degree Heart Block, Cardiac Conduction Defect, Infranodal Block, Intraatrial Block, Intraventricular Block, Sinoatrial Block
Heart block is a disruption in the relay of electrical
signals that control activity of the heart muscle.
What is going on in the body?
The heart beats by using electric impulses. These impulses
follow a specific route through the heart. These
routes or pathways are sometimes grouped together into
specialized areas called nodes and bundles.
Bundles send out little fibers that go into the muscle of the
heart. The nodes, bundles, and fibers are responsible for the unified
beating of the heart and the rate at which it beats. A defect along any
of these pathways can cause a heart block. This does not mean the blood
flow or blood vessels are blocked.
There are many kinds of heart block. Each type depends on
where the damage has occurred in the electrical pathway.
First-degree heart block. This type occurs when the electrical impulse passes
through the heart slower than normal, but heartbeat and rhythm are still within a
healthy range. This type of block does not mean there is anything really
wrong with the heart.
Second-degree heart block. This occurs when some of the electrical
signals from the upper chamber of the heart, called the atrium, don't
reach the lower chamber of the heart, called the ventricle. This results in
what are called "dropped beats."
Complete heart block.This is the worst form of heart block.
In this condition, no electrical impulses pass from the upper to the lower
parts of the heart, so the lower part starts beating on its own, but at a much slower
rate than is healthy. When this occurs, the lower part of the heart may not beat
fast enough or regularly enough to keep blood flowing to the vital organs.
What are the causes and risks of the disease?
Many times, heart block is a symptom that the person
has another type of heart disease. Heart blocks are common in
people who have:
history of heart attacks
coronary artery disease
infectious diseases of the heart, such as endocarditis
hereditary defect of the heart, called congenital heart block
Certain medicines can also cause heart block if the levels in the body
build up too much. Some examples include:
beta blockers, such as propanolol or pindolol
calcium channel blockers, such as verapamil or diltiazem
digitalis glycosides, such as digoxin
Highly-trained athletes may also have the less severe forms of
heart block, but will most likely have no symptoms other than a slow heartbeat.
A block that has existed for a long time may
pose no problem. A block that appears suddenly may be due to a
new heart problem or the worsening of an old one. A change in the
heart block can alert the doctor to a change in the status of the heart.