Automated external defibrillators (AEDs) automatically analyze the heart rhythm of a victim. If ventricular fibrillation (VF or V-fib) or ventricular tachycardia (VT or V-tach) are detected, the device will automatically deliver a shock. Semi-automatic AEDs will prompt the rescuer to administer a shock. The shock can help reset or restore a normal heart rhythm.
In some cases, an AED may indicate (via audio or text prompts) that a shock is not advised. Although VF is the most common rhythm detected in cardiac arrest, it is not the only one. An AED is designed to deliver a shock only when VF or VT rhythms are detected. However, there are other heart rhythms associated with sudden cardiac arrest (SCA) that cannot be treated with a shock from an AED.
Therefore, a "No Shock Advised" message doesn’t necessarily mean that the heart rhythm is back to normal; instead, it may mean that the victim is experiencing asystole or pulseless electrical activity; neither of which are treatable by shock.
While it’s difficult to imagine an AED not delivering a shock to someone experiencing SCA, it also means that potential rescuers should rest assured that an AED will not shock a person unless they require defibrillation.
What is Ventricular Fibrillation?
When a heart is in VF, it is still receiving nerve impulses from the brain. These impulses are simply firing so chaotically that the heart cannot produce a beat that’s strong enough to pump enough blood to keep the circulatory system flowing through the body.
The heart will continue its uncoordinated twitching or fluttering until it is no longer receiving electrical impulses from the brain and stops altogether. Unless the heart is shocked back into a normal rhythm, which is where an AED comes in. An AED stops the heart from its spasm by shocking it. This allows the nerve impulses a chance to resume their normal pattern, which, in turn, allows the heart to resume beating at its normal pace.
What Causes Ventricular Fibrillation and Ventricular Tachycardia?
V-fib can have several root causes, including:
- Insufficient blood flow to the heart muscle
- Damage to the heart muscle (from a heart attack, for example)
- Problems with the aorta
- Drug toxicity
- Electrolyte imbalance
- Sepsis (severe body infection)
Source: American Heart Association and Mayo Clinic
Should I Leave the Pads On If No Shock is Advised?
Yes, whether a shock has been delivered successfully or the AED initially indicates “no shock advised,” you should always leave the electrode pads on. The victim may go into VF a second time or the device may recognize a shockable rhythm. Always leave an AED on until emergency medical personnel have taken over.
To learn more about V-fib and V-tach and how to effectively use an AED, get your CPR and AED certifications! Contact Cardio Partners at 866-349-4362 to learn more. We also welcome your emails, and you can reach us at firstname.lastname@example.org.
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