Despite what many may think, it is not a heart attack, but can occur during a heart attack.
Sudden cardiac arrest occurs when the electrical system to the heart malfunctions and suddenly the heart beats dangerously fast.
Most cases of SCD are related to cardiac arrhythmias.
"There are young people, athletes for example, who die suddenly on the basketball court or football field," says cardiac electrophysiologist Dr. Tom Wallace. "They aren't necessarily having a heart attack but rather their heart rhythm becomes life threatening. They go into a rhythm called ventricular tachycardia or ventricular fibrillation. It's a condition that the heart beats so fast that it doesn't have enough time between beats to fill up with blood. So, it doesn't have enough time then to squeeze blood out to the brain and the rest of the body. So in essence, the heart just quivers, it doesn't move blood. Ultimately, there's not enough blood flow to the brain and the person loses consciousness."
There are medications to help prevent this, but Dr. Wallace recommends anyone who has had a life-threatening rhythm to consider getting a defibrillator.
The device is implanted just underneath the skin in the chest and is able to pace the heart and shock the heart if it goes into a life-threatening rhythm.
"If someone is having palpitations or a fluttering in their chest, that's a concern," Dr. Wallace says. "That's usually not from a life-threatening heart rhythm but rather from a heart rhythm abnormality coming from the atrium or top chamber of the heart. But if you've passed out and have a history of heart disease, then you should be checked out quickly by your cardiologist to make sure that you don't have ventricular tachycardia."
There are several risk factors for SCD, with the main two being a previous heart attack and coronary artery disease.
In the event of cardiac arrest, CPR and an external defibrillator are the best chances at survival.