Silent killer or sudden stop: Know your heart risks
In July 2023, rising US basketball star
Bronny James collapsed on the court during practice and was sent to hospital.
The 18-year-old athlete, son of famous LA Lakers' veteran LeBron James, had
experienced a cardiac arrest.
Many media outlets incorrectly referred to
the event as a “heart attack” or used the terms interchangeably. A cardiac
arrest and a heart attack are distinct yet overlapping concepts associated with
the heart. With some background in how the heart works, we can see how they
differ and how they're related.
Understanding the heart
The heart is a muscle that contracts to
work as a pump. When it contracts it pushes blood – containing oxygen and
nutrients – to all the tissues of our body.
For the heart muscle to work effectively
as a pump, it needs to be fed its own blood supply, delivered by the coronary
arteries. If these arteries are blocked, the heart muscle doesn't get the blood
it needs.
This can cause the heart muscle to become
injured or die, and results in the heart not pumping properly.
Heart attack or cardiac arrest?
Simply put, a heart attack, technically
known as a myocardial infarction, describes injury to, or death of, the heart
muscle.
A cardiac arrest, sometimes called a
sudden cardiac arrest, is when the heart stops beating, or put another way,
stops working as an effective pump.
In other words, both relate to the heart
not working as it should, but for different reasons. As we'll see later, one
can lead to the other.
Why do they happen? Who's at risk?
Heart attacks typically result from
blockages in the coronary arteries. Sometimes this is called coronary artery
disease, but in Australia, we tend to refer to it as ischaemic heart disease.
The underlying cause in about 75 per cent
of people is a process called atherosclerosis. This is where fatty and fibrous
tissue build up in the walls of the coronary arteries, forming a plaque. The
plaque can block the blood vessel or, in some instances, lead to the formation
of a blood clot.
Atherosclerosis is a long-term, stealthy
process, with a number of risk factors that can sneak up on anyone. High blood
pressure, high cholesterol, diet, diabetes, stress, and your genes have all
been implicated in this plaque-building process.
Other causes of heart attacks include
spasms of the coronary arteries (causing them to constrict), chest trauma, or
anything else that reduces blood flow to the heart muscle.
Regardless of the cause, blocking or
reducing the flow of blood through these pipes can result in the heart muscle
not receiving enough oxygen and nutrients. So cells in the heart muscle can be
injured or die.
But a cardiac arrest is the result of
heartbeat irregularities, making it harder for the heart to pump blood
effectively around the body. These heartbeat irregularities are generally due
to electrical malfunctions in the heart.
There are four distinct types:
1. ventricular tachycardia: a rapid and
abnormal heart rhythm in which the heartbeat is more than 100 beats per minute
(normal adult, resting heart rate is generally 60-90 beats per minute). This
fast heart rate prevents the heart from filling with blood and thus pumping
adequately
2. ventricular fibrillation: instead of
regular beats, the heart quivers or “fibrillates”, resembling a bag of worms,
resulting in an irregular heartbeat greater than 300 beats per minute 3.
pulseless electrical activity: arises when the heart muscle fails to generate
sufficient pumping force after electrical stimulation, resulting in no pulse 4.
asystole: the classic flat-line heart rhythm you see in movies, indicating no
electrical activity in the heart.
Cardiac arrest can arise from numerous
underlying conditions, both heart-related and not, such as drowning, trauma,
asphyxia, electrical shock and drug overdose. James' cardiac arrest was
attributed to a congenital heart defect, a heart condition he was born with.
But among the many causes of a cardiac
arrest, ischaemic heart disease, such as a heart attack, stands out as the most
common cause, accounting for 70 per cent of all cases.
So how can a heart attack cause a cardiac
arrest? You'll remember that during a heart attack, heart muscle can be damaged
or parts of it may die. This damaged or dead tissue can disrupt the heart's
ability to conduct electrical signals, increasing the risk of developing
arrhythmias, possibly causing a cardiac arrest.
So while a heart attack is a common cause
of cardiac arrest, a cardiac arrest generally does not cause a heart attack.
What do they look like?
Because a cardiac arrest results in the
sudden loss of effective heart pumping, the most common signs and symptoms are
a sudden loss of consciousness, absence of pulse or heartbeat, stopping of
breathing, and pale or blue-tinged skin.
But the common signs and symptoms of a
heart attack include chest pain or discomfort, which can show up in other
regions of the body such as the arms, back, neck, jaw, or stomach. Also
frequent are shortness of breath, nausea, light-headedness, looking pale, and
sweating.
What's the take-home message?
While both heart attack and cardiac arrest
are disorders related to the heart, they differ in their mechanisms and
outcomes.
A heart attack is like a blockage in the
plumbing supplying water to a house. But a cardiac arrest is like an electrical
malfunction in the house's wiring.
Despite their different nature both
conditions can have severe consequences and require immediate medical
attention.
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