What Causes Sudden Cardiac Arrest?
Most cases of sudden cardiac arrest (SCA) are due to
an
arrhythmia called ventricular fibrillation (v-fib). In v-fib,
the ventricles (the large pumping chambers of the heart) quiver very rapidly
and irregularly instead of beating normally. When this happens, the heart pumps
little or no blood to the body. Death results if the arrhythmia is not treated
within a few minutes.
Other electrical problems that can cause SCA are
extreme slowing of the rate of the heart's electrical signals or when heart
muscle stops responding to the electrical signals.
Several factors can cause the electrical problems
that lead to SCA. These factors include:
Coronary Artery Disease
CAD occurs when the arteries that supply blood to
the heart muscle (the coronary arteries) become hardened and narrowed, causing
less blood to flow to the muscle. The arteries harden and narrow because a
material called plaque (plak) builds up on their inner walls. As the plaque
increases in size, the insides of the coronary arteries narrow, and less blood
flows through them to the heart muscle. Eventually, the heart muscle is not
able to receive the amount of blood and oxygen that it needs. Reduced blood
flow or no blood flow to the heart muscle can result in a
heart
attack. During a heart attack, some heart tissue dies and turns into scar
tissue. This can damage the heart's electrical system, increasing the risk for
dangerous arrhythmias and SCA.
Physical Stress
Certain physical stresses can cause the heart's
electrical system to fail. The physical stresses that cause this to happen
include:
- Major blood loss.
- Severe lack of oxygen.
- Very low blood levels of potassium or
magnesium.
- Intense exercise. The hormone adrenaline
released during intense exercise can trigger SCA in people who have other heart
problems.
Inherited Disorders
A tendency to develop arrhythmias runs in some
families. This tendency is inherited, which means it is passed from parents to
children. Members of these families might have an increased chance of having
SCA. Other people are born with inherited structural defects in their hearts
that may increase their chance of having SCA.
Structural Changes in the Heart
Changes in the heart's normal size or structure can
affect its electrical system. Such changes include a heart enlarged by blood
pressure or advanced heart disease. Heart infections also can cause structural
changes in the heart.
Several research studies are under way to try to
understand these possible causes of SCA and to find other causes. |