How to Identify Shockable Heart Rhythms During Cardiac Arrest
Posted by Sydney Pulse, APRN at 9:24 am 0 Comment Print
On January 2, 2023, Buffalo Bills safety Damar Hamlin collapsed on the field at Paycor Stadium in Cincinnati. His heart had stopped beating normally. Medical staff started CPR within seconds and used an AED to shock his heart back into rhythm. He survived because responders recognized a shockable heart rhythm and acted fast.
Most cardiac arrests never make the evening news. They happen at home, at work, or on a Cincinnati sidewalk. Knowing how to identify shockable heart rhythms during cardiac arrest can mean the difference between life and death, and you don’t need a medical degree to help.
What Is a Shockable Heart Rhythm?
A shockable heart rhythm happens when the heart’s electrical system misfires. Instead of pumping blood, the heart muscle quivers uselessly. Two rhythms fall into this category: ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). Both respond to an electrical shock from a defibrillator. Without that shock, blood stops reaching the brain and vital organs.
Shockable vs. Non-Shockable Rhythms
Not every cardiac arrest rhythm responds to a shock. Asystole means the heart shows no electrical activity at all. Pulseless electrical activity (PEA) means the monitor shows an organized rhythm, but the heart still isn’t pumping. Neither rhythm responds to defibrillation. These patients need immediate, uninterrupted CPR instead.
According to the 2025 CARES National Registry, nearly one in five out-of-hospital cardiac arrests present in a shockable rhythm. That split matters. Shockable rhythms carry a far better chance of survival, but only when someone acts within the first few minutes.
Recognizing Sudden Cardiac Arrest
Before you ever reach for an AED, you have to recognize the emergency. Sudden cardiac arrest looks different from fainting or a seizure. Look for these signs:
- Sudden collapse, with no response to shouting or shaking
- No normal breathing, or only occasional gasping
- No pulse you can feel at the neck or wrist
If you see these signs, call 911 immediately. Then start chest compressions and send someone to find the nearest AED. Every second without compressions lowers the odds of survival.
How an AED Detects a Shockable Rhythm
A layperson cannot read a heart rhythm the way a paramedic can, and that’s fine. An automated external defibrillator (AED) does the reading for you. Once you attach the pads, the device analyzes the heart’s electrical signal in seconds.
The AED then tells you, in plain language, whether a shock is needed. If it says “shock advised,” it has detected VF or pulseless VT. If it says “no shock advised,” it has detected asystole, PEA, or a normal rhythm. You never have to guess, and you never have to diagnose anything yourself.
What to Do When the AED Calls for a Shock
First, call 911 or have someone else call while you grab the AED. Next, turn the device on and follow its voice prompts. Attach the pads to the bare chest, exactly where the pictures show. Stand clear while the device analyzes the rhythm.
If the AED advises a shock, press the button and resume compressions right away. Don’t pause to check for a pulse. High-quality, continuous chest compressions keep oxygen moving to the brain between shocks and improve the odds of a positive outcome.
Why Every Second Counts
The American Heart Association reports that survival from a shockable rhythm drops by 7% to 10% for every minute defibrillation is delayed. A widely cited Circulation study found that bystander-delivered shocks in public settings led to a 66.5% survival-to-discharge rate, compared with just 43% when EMS delivered the first shock. Speed saves lives just as much as skill does.
Ohio’s bystander CPR rate hovers near 33%, trailing the 2025 national CARES average of 42.5%. That gap means fewer Hamilton County residents receive compressions before EMS arrives. Hands-on training closes that gap one class, and one rescuer, at a time.
Common Questions About Shockable Rhythms
Can a shock restart a stopped heart? Not exactly. A defibrillator doesn’t jump-start a flatlined heart the way movies suggest. Instead, it stops the chaotic electrical activity of VF or VT for a split second. That pause gives the heart’s natural pacemaker a chance to take back control and resume a normal beat.
Is it safe for an untrained bystander to use an AED? Yes. Modern AEDs walk you through every step out loud. The device won’t deliver a shock unless it detects a shockable rhythm, so you can’t shock someone who doesn’t need it. That built-in safeguard is exactly why AHA courses teach rescuers to trust the machine.
What if I’m not sure whether someone is in cardiac arrest? Attach the AED anyway and let it analyze the rhythm. You lose nothing by checking, and you may save a life by acting instead of waiting for certainty.
Who Should Learn This Skill?
Anyone can face a cardiac emergency. Parents, coaches, office workers, and gym members in Cincinnati all stand a chance of witnessing sudden cardiac arrest. Healthcare workers face an even higher likelihood, which is why hospitals and clinics across Hamilton County require current certification. Front desk staff, teachers, and fitness instructors benefit just as much from AED and CPR training, since they’re often first on the scene long before EMS arrives.
Get Trained. Be Ready.
Reading this article helps, but muscle memory saves lives. CPR Cincinnati is an American Heart Association training site offering initial certification and renewal in BLS for Healthcare Providers, ACLS, PALS, and CPR and First Aid. Every class stays hands-on and stress-free, so you walk out ready to act, not just ready to pass a test.
Sign up for CPR certification in Cincinnati today to learn hands-on compressions and AED use in a relaxed, supportive classroom.
Already work in a hospital, clinic, or care facility? Enroll in ACLS certification in Cincinnati to meet your employer’s requirements and refresh your skills before they expire.