Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). a portable machine that can be used with no previous training. That is possible because the machine produces pre-recorded voice instructions that guide the user. The device automatically checks the patient's condition and applies the correct electric shocks. There also exist written instructions that explain the procedure step-by-step.

Outcomes

Survival rates for out-of-hospital cardiac arrests in North America are poor, often less than 10%.

Placement

thumb|upright|Anterior-apex placement of electrodes for defibrillation

Resuscitation electrodes are placed according to one of two schemes. The anterior-posterior scheme is the preferred scheme for long-term electrode placement. One electrode is placed over the left precordium (the lower part of the chest, in front of the heart). The other electrode is placed on the back, behind the heart in the region between the scapula. This placement is preferred because it is best for non-invasive pacing.

The anterior-apex scheme (anterior-lateral position) can be used when the anterior-posterior scheme is inconvenient or unnecessary. In this scheme, the anterior electrode is placed on the right, below the clavicle. The apex electrode is applied to the left side of the patient, just below and to the left of the pectoral muscle. This scheme works well for defibrillation and cardioversion, as well as for monitoring an ECG.

Researchers have created a software modeling system capable of mapping an individual's chest and determining the best position for an external or internal cardiac defibrillator.

Cardiac cells require a strong electrical stimulus to raise their transmembrane potential to the activation threshold. The widespread depolarization from the shock interrupts these circuits, stopping the erratic propagation of electrical signals. This allows the heart's natural pacemaker, the sinoatrial node, to resume control of the rhythm. During this period, ion pumps actively restore the normal distribution of ions, re-establishing the resting membrane potential.

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General and cited references

  • Sudden Cardiac Arrest Foundation
  • Center for Integration of Medicine and Innovative Technology
  • American Red Cross: Saving a Life is as Easy as A-E-D
  • FDA Heart Health Online: Automated External Defibrillator (AED)