What Causes Sudden Cardiac Arrest?
Most cases of sudden cardiac arrest (SCA) are due to
ventricular fibrillation (v-fib). V-fib is a type of
arrhythmia.
In v-fib, the ventricles (the heart's lower chambers) don't beat normally.
Instead, they quiver very rapidly and irregularly.
When this happens, the heart pumps little or no
blood to the body. V-fib is fatal if not treated within a few minutes.
Other electrical problems in the heart also can
cause SCA. For example, SCA can occur if the rate of the heart's electrical
signals becomes very slow and stops. SCA also can occur if the heart muscle
doesn't respond to the heart's electrical signals.
Several factors can cause the electrical problems
that lead to SCA. These factors include:
-
Coronary
artery disease (CAD), which reduces blood flow to the heart muscle
- Severe physical stress, which raises the risk for
abnormal electrical activity in the heart
- Inherited disorders that disrupt the heart's
electrical activity
- Structural changes in the heart that cause
electrical signals to spread abnormally
Several research studies are under way to try to
find the exact causes of SCA and how to prevent them.
Coronary Artery Disease
CAD occurs when a fatty material called plaque
(plak) builds up in the coronary arteries. These arteries supply your heart
muscle with oxygen-rich blood.
Plaque narrows the arteries and reduces blood flow
to your heart muscle. Eventually, an area of plaque can rupture, causing a
blood clot to form on the surface of the plaque.
A blood clot can mostly or completely block the
flow of oxygen-rich blood to the part of the heart muscle fed by the artery.
This causes a
heart
attack.
During a heart attack, some heart cells die and are
replaced by scar tissue. This damages the heart's electrical system. The scar
tissue may cause electrical signals to spread abnormally throughout the heart.
These changes increase the risk for dangerous ventricular arrhythmias and
SCA.
CAD seems to be the cause of most cases of SCA in
adults. Many of these adults, however, have no signs or symptoms of CAD before
having SCA.
Physical Stress
Certain types of physical stress can cause your
heart's electrical system to fail. Examples include:
- Intense physical activity. The hormone adrenaline
is released during intense physical activity. This hormone can trigger SCA in
people who have other heart problems.
- Very low blood levels of potassium or magnesium.
These minerals play an important role in your heart's electrical
signaling.
- Major blood loss.
- Severe lack of oxygen.
Inherited Disorders
A tendency to have arrhythmias runs in some
families. This tendency is inherited, which means it's passed from parents to
children. Members of these families may be at increased risk for SCA.
An example of an inherited disorder that makes you
more likely to have arrhythmias is
long
QT syndrome (LQTS). LQTS is a disorder of the heart's electrical activity
due to problems with tiny pores on the surface of heart muscle cells. LQTS can
cause sudden, uncontrollable, dangerous heart rhythms.
People who inherit structural heart problems also
may be at increased risk for SCA. Many cases of SCA in children are due to
these problems.
Structural Changes in the Heart
Changes in the heart's normal size or structure may
affect its electrical system. Examples of such changes include an enlarged
heart due to
high
blood pressure or advanced heart disease. Heart infections also may cause
structural changes in the heart. |