You immediately lose consciousness
When the heart stops beating or pumping blood, that individual loses consciousness and falls to the ground. Many people who have had a cardiac arrest say they had no symptoms at all just before they collapsed.
“Other people may report that they felt dizzy, tired, cold, or weak right before they passed out,” says Dr. Gulkarov. An onlooker may notice the person’s eyes rolling back and/or witness a seizure.
“The heart is tasked with pumping blood to all parts of the body including the brain, and when the brain doesn’t get blood, a person can seize or pass out,” he says. “The first cells to die during cardiac arrest are brain cells.”
Your heart’s natural pacemaker malfunctions
The sinus node, located in your heart’s upper right chamber, is a specialized group of cells that generate electrical impulses through the heart, explains Iosif Gulkarov, MD, a cardiothoracic surgeon at the Heart Institute, Staten Island University Hospital in Staten Island, New York.
This cluster of cells functions as your heart’s natural pacemaker; they produce electrical signals that tells the muscles when to contract. Normally, the heart’s upper chambers contract first, then the lower chambers, which results in the familiar “lub dub” of a heart beat. The “dub” part of the beat is the sound of the heart valves closing after the muscular lower heart chambers, the ventricles, push blood to where it needs to go in the body.
When the cells misfire, you get an arrhythmia. There is an impairment in your heart’s rhythm that interferes with the job of pumping blood and maintaining circulation. With a cardiac arrest, the heart stops beating due to this electrical disturbance.
Your heart may be quivering, but not pumping blood
There are abnormal rhythms that can cause the heart to pump blood abnormally, including ventricular tachycardia, which is marked by a quickened heartbeat (above 100 beats per minute). In this case, the lower heart chambers beat out of sync with the heart’s upper chambers. Ventricular tachycardia symptoms include a racing heart or heart palpitations, breathlessness, fainting, fatigue, and dizziness.
Brachycardia is a heart rate that has slowed below 60 beats per minute. (A normal heart rate is 60 to 100 beats per minute.) Bradycardia symptoms can include dizziness, fainting, shortness of breath, or confusion because the heart is not pumping an adequate amount of blood to the brain.
Neither of these heart arrhythmias are necessarily life threatening, but need to be checked out. (There are also other kinds of tachycardia and arrhythmias that are less serious, and arrhythmias can be treated with medication and surgery.)
In some cases, however, you can progress to a potentially lethal arrhythmia that is associated with cardiac arrest—ventricular fibrillation. This is a quick and chaotic rhythm in which the heart quivers with uncoordinated contractions, bringing your circulation to a halt.
When that happens, you need a defibrillator—a device that shocks the heart—to reset its natural rhythm.
Your pulse will stop
What is a pulse? A pulse, or your heart rate, is the number of times your heart beats in a minute. You can easily measure this by laying two fingers on any part of the body where you can feel a heartbeat—the side of the neck, a wrist, or inside an elbow. Just do it for 60 seconds and count the beats. (Never use your thumb, however, it has a pulse of its own.)
To check someone’s pulse, place your index and middle finger on the inside of their wrist, just below the thumb. Press gently, and count the number of beats in 30 seconds. Double it for the heart rate—so 30 beats in 30 seconds would mean the person has a heart rate of 60 beats per minute.
When someone is having a cardiac arrest, the pulse is weak or nonexistent because the heart is no longer beating. This is one of the quickest ways to tell if someone who is unconscious needs cardiopulmonary resuscitation (CPR).