Your heart is one of the most important organs in your body — if not the most important.
It pumps blood to every other organ, providing the constant supply of oxygen and nutrients these systems need to function. This process is also involved in removing harmful metabolic waste, like carbon dioxide.
If the heart stops working properly, as is the case with cardiac arrest, your entire body starts shutting down.
"Cardiac arrest is when the heart suddenly develops a severe arrhythmia, causing it to beat inefficiently," explains Dr. Kevin Lisman, a cardiologist at Houston Methodist.
An arrhythmia is an issue with the heart's electrical system that affects the rhythm at which the heart beats. Not all arrhythmias are immediately harmful. But some, including ventricle fibrillation (V-fib) and ventricular tachycardia, can develop suddenly and lead to cardiac arrest.
"These types of irregular rhythms disrupt the heart's ability to pump blood effectively," explains Dr. Lisman. "When the brain, lungs and other vital organs aren't getting adequate blood flow, it leads to loss of consciousness and breathing, as well as organ damage and injury."
Unsurprisingly, cardiac arrest is a medical emergency — life-threatening if not treated immediately. Cardiac arrest is treated by shocking the heart back into a normal rhythm using a defibrillator device.
"In the meantime, though, anyone can administer life-saving care by performing cardiopulmonary resuscitation (CPR)," says Dr. Lisman. "It's why I strongly recommend everyone take a course on how to provide basic life support."
What causes cardiac arrest?
"By far and away, the most common cause of cardiac arrest is heart attack," explains Dr. Lisman. "As blood flow to the heart is reduced, the injury experienced can set off cardiac arrest by triggering one of these dangerous rhythms."
But a person with no known heart issues can also experience sudden cardiac arrest.
"There are genetic disorders that can make a person more prone to arrhythmias and, therefore, cardiac arrest," explains Dr. Lisman. "For instance, cardiac channelopathy disorders affect how electricity transverses through heart, setting a person up for arrhythmias."
In rare cases, commotio cordis — Latin for "agitation of the heart" — can cause cardiac arrest. It happens when a person is hit in the chest in such a way that disrupts the heart's normal rhythm and induces a severe arrhythmia.
"It's not just being hit in the chest, though," adds Dr. Lisman. "To cause such an extreme arrhythmia, the blow must occur in a specific spot at the exact time of a heartbeat. It's incredibly uncommon, usually seen only on rare occasions in athletes."
Cardiac arrest vs. heart attack: What's the difference?
The terms heart attack and cardiac arrest are frequently used as synonyms, but in fact they're unique conditions that should be understood distinctly.
Where cardiac arrest is an electrical problem that affects blood flow to every organ in the body, heart attack is an issue with blood flow to the heart, specifically, that occurs when the arteries become blocked.
Failure to deliver enough oxygenated and nutrient-rich blood to the heart leads to the damage of heart muscle. That in turn can affect the heart's rhythm and cause cardiac arrest.
Heart attack itself is almost always caused by coronary artery disease (CAD), a common heart condition in which the coronary arteries narrow over time as a result of plaque buildup, a process called atherosclerosis.
How to prevent cardiac arrest
Since a heart attack is its most common cause, cardiac arrest is best prevented by taking steps to reduce your risk of developing coronary artery disease or working with your doctor to establish an effective plan for managing the condition if you already have it.
These behaviors can also reduce your risk of developing health issues that can lead to coronary artery disease, including:
Since cardiac arrest can occur in people who don't have coronary artery disease, you may be wondering whether cardiac arrest is a condition that can be screened for.
"We have ways to screen for the severe arrhythmias that can lead to cardiac arrest, but screening isn't appropriate for everyone," adds Dr. Lisman. "Since we know these issues tend to run in families, there are questions we ask first to help determine a person's risk."
Having a family member with an arrhythmia or who died suddenly before the age of 40 almost always prompts screening. Your doctor will use a test called an electrocardiogram (ECG or EKG) to record the electrical signals of your heart and detect potential issues.
"EKGs catch around 80% of people prone to arrhythmia," says Dr. Lisman.
Despite what we know about preventing cardiac arrests, they still happen. It's why Dr. Lisman reminds us of the importance of taking a course to learn how to perform CPR.
"For instance, if your neighbor collapses while mowing the lawn and goes unconscious, being able to provide basic life support until medical professionals arrive can absolutely be life-saving," Dr. Lisman reiterates.