What is the key difference between a heart attack and cardiac arrest?

Many media outlets incorrectly referred to the event as a “heart attack” or used the terms interchangeably.

Cardiac arrest and heart attack are distinct but overlapping concepts associated with the heart.

With some background on how the heart works, we can see how they differ and how they relate.

Understanding the heart

The heart is a muscle that contracts to function as a pump. When it contracts, it pumps blood, which contains oxygen and nutrients, to all the tissues in our body.

In order for the heart muscle to function effectively as a pump, it needs to receive its own blood supply, which comes from the coronary arteries. If these arteries are blocked, the heart muscle does not receive the blood it needs.

This can cause the heart muscle to become damaged or die and the heart to not pump properly.

Heart attack or cardiac arrest?

In simple terms, a heart attack, technically known as a myocardial infarction, describes an injury or death of the heart muscle.

Cardiac arrest, sometimes called sudden cardiac arrest, is when the heart stops beating or, put another way, stops functioning as an effective pump.

In other words, both are related to the heart not working as it should, but for different reasons. As we will see later, one can lead to the other.

Why do they occur? Who is at risk?

Heart attacks are often caused by blockages in the coronary arteries. This is sometimes called coronary artery disease, but in Australia we usually call it ischaemic heart disease.

The underlying cause in about 75% of people is a process called atherosclerosis, in which fatty and fibrous tissue builds up on the walls of the coronary arteries, forming plaque. The plaque can block the blood vessel or, in some cases, cause a blood clot to form.

Atherosclerosis is a stealthy, long-term process, with a number of risk factors that can surprise anyone. High blood pressure, high cholesterol, diet, diabetes, stress and genes are all involved in this plaque-forming process.

Other causes of heart attacks include spasms of the coronary arteries (causing them to narrow), chest trauma, or anything else that reduces blood flow to the heart muscle.

Regardless of the cause, blockage or reduced blood flow through these tubes can result in the heart muscle not receiving enough oxygen and nutrients, which can damage or kill heart muscle cells.

However, cardiac arrest is the result of irregularities in the heart rhythm, which makes it difficult for the heart to effectively pump blood throughout the body. These irregularities in the heart rhythm are usually due to electrical faults in the heart. There are four distinct types:

• ventricular tachycardia: A rapid, abnormal heart rhythm in which the heart rate is greater than 100 beats per minute (normal adult resting heart rate is usually 60 to 90 beats per minute). This rapid heart rate prevents the heart from filling with blood and therefore pumping properly.

• ventricular fibrillation: Instead of a regular heartbeat, the heart quivers or “fibrillates,” resembling a bag of worms, resulting in an irregular heart rhythm of more than 300 beats per minute.

• pulseless electrical activity: It occurs when the heart muscle does not generate enough pumping force after electrical stimulation, resulting in no pulse.

• asystole: the classic flat heart rhythm seen in movies, indicating no electrical activity in the heart.

Cardiac arrest can be caused by numerous underlying conditions, both cardiac and non-cardiac, including drowning, trauma, asphyxiation, electric 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 cardiac arrest, ischemic heart disease, such as myocardial infarction, stands out as the most common cause, accounting for 70% of all cases.

So how can a heart attack cause cardiac arrest? You'll recall that during a heart attack, the heart muscle can be damaged or parts of it can die. This damaged or dead tissue can disrupt the heart's ability to conduct electrical signals, increasing the risk of developing arrhythmias, possibly causing cardiac arrest.

While a heart attack is a common cause of cardiac arrest, cardiac arrest does not usually cause a heart attack.

What are they like?

Because cardiac arrest results in the sudden loss of the heart's effective pumping, the most common signs and symptoms are sudden loss of consciousness, absence of pulse or heartbeat, stopping of breathing, and pale or bluish skin.

But the most common signs and symptoms of a heart attack include chest pain or discomfort, which can appear in other areas of the body such as the arms, back, neck, jaw or stomach. Shortness of breath, nausea, dizziness, paleness and sweating are also common.

What is the final message?

Although both heart attack and cardiac arrest are heart-related disorders, they differ in their mechanisms and outcomes.

A heart attack is like a blockage in the pipes that supply water to a house. But a cardiac arrest is like an electrical fault in the wiring of the house.

Despite their different nature, both conditions can have serious consequences and require immediate medical attention.

(Michael Todorovic, Associate Professor of Medicine, Bond University and Matthew Barton, Senior Lecturer, School of Nursing and Midwifery, Griffith University)

(This article is republished from The Conversation under a Creative Commons license. Read the original article.)