Getting the heart back in rhythm

The Automated External Defibrillator (AED) - approved for home use recently by the Food and Drug Administration -can diagnose and restore normal heart rhythm to people who experience sudden cardiac arrest due to irregular heartbeat, or fibrillation. It should be operated by those trained in cardiopulmonary resuscitation (CPR).

Using the defibrillator

1. Turn on, listen to instructions.

Lift off the cover, which automatically turns on the device.*

Peel the protective seal off the cartridge and remove pads. Audio prompts direct you to remove clothing from the patient’s chest and shave area if necessary.

*Philips Heartstart model only

2. Remove backing on pads.

Take the two pads out of their cartridge and peel off the backing. Pictures on the pads show placement locations.

Pads are used on only one patient, then disguarded.

3. Place the pads, wait for diagnosis.

Normal heart rhythm, shown as an electrocardiogram (EEG).

AED will call for a shock if the person is unconscious and the heart is experiencing one of two arrythmias: (A) extremely rapid and erratic heartbeat or (B) rapid heart quivers and failure to generate a pulse.

4. Apply shock.*

If shock is appropriate, the orange button flashes and a voice prompts you to press it. Do not touch the patient at this time.

Shock stops the heart briefly, allowing it to reset itself to a normal rhythm. Device will analyze the heart again to see if more shocks are necessary. It is most effective when used with three to five minutes of the onset of cardiac arrest.

*The device will tell you if shock is not warranted (condition is not related to the heart or if arrthymia type will not respond to a shock.) CPR may be necessary.

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CPR basics

* Call 911.

* Check airway for obstruction.

* If victim is not breathing, pinch the nose and give two full breaths into mouth.

* If there is no pulse, perform chest compressions.

* All of these skills are taught in basic CPR courses.

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AED products

Cost: $1,200-$3,000; $30-$50 for replacement pads; about $125-$135 for lithium battery.

What’s included: Home model includes a set of pads, battery, manual and carrying case. Larger industrial models may include additional pads and battery.

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Why shocks require so much power

Most shocks are about 150 joules, or roughly 2,000 volts. A large shock is necessary to penetrate the skin, muscle, lungs and ribs that surround the heart.

Shocks move in both directions through the heart.

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The heart’s natural rhythm

In a normal heartbeat, naturally produced electrical impulses trigger parts of the heart to contract in a regular sequence of phases.

First phase

The heart’s upper chamber has its own natural pacemaker that produces an electrical impulse. This causes the atrium muscles to contract and push blood toward the ventricles.

Second phase

The impulse is then delayed momentarily at an inter-section before it enters the ventricle muscles. Ventricles are now filled with blood.

Third phase

As the impulse travels along special fibers (not shown) that act like electrical wires, both ventricles contract, pumping the blood out of the heart to the lungs and the rest of the body.

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Note: drawings are color-coded for clarity.

Sources: Philips Medical Systems, Heartsine Technologies, National Center for Early Defibrillation, American College of Emergency Physicians, “Anatomica,” “CIBA Collection of Medical Illustrations,” Jeffrey Curry, Los Angeles Times Safety Dept. Graphics reporting by Joel Greenberg