Chapter 39: Automated External Defibrillation

INTRODUCTION

Cardiovascular disease is the most common cause of death in the developed world. It is responsible for 350,000 deaths per year in the United States.¹ Approximately 40% of those with out-of-hospital cardiac arrest (OOHCA) have an initial presenting rhythm of ventricular fibrillation.² Early defibrillation increases the chances of survival in these situations.

The American Heart Association (AHA) undertook a program in 1991 dedicated to increasing the rate of survival from OOHCA with education regarding the concept of a “chain of survival.”³ The chain is a series of actions that give the highest chances of survival. The links of the chain include calling 911, performing early cardiopulmonary resuscitation (CPR), providing rapid defibrillation, and survival. Inherent are the concepts of early defibrillation and “time is muscle.”

The AHA had further advocated in 1995 the use of automated external defibrillators (AEDs) by laypersons as a key link in the chain (Figure 39-1).² This allowed all but early advanced life support by laypersons. The AED automatically analyzes the heart rhythm and delivers an electrical shock to restore the heart to a normal rhythm.⁴

Most cardiac arrests occur outside the hospital. Ventricular fibrillation is the most common rhythm in OOHCA. There has been a concerted effort in the United States to increase the availability of AEDs in public spaces (e.g., airports, casinos, stadiums) and to responding police officers, resulting in a much higher survival in ventricular fibrillation arrest.^5-11 The approximate 10% survival rate after OOHCA and in-hospital sudden cardiac arrest remains dismally low.¹² The rates versus historical norms in bystander-witnessed ventricular fibrillation arrest have been much improved to as high as 31% in some studies by this effort.^13,14

Health care professionals often use traditional manual defibrillators (Chapter 40). These are not widely available outside of the hospital. The Emergency Physician must interpret the heart rhythm, know when cardioversion or defibrillation is appropriate, and manually operate the defibrillator. A thorough understanding of how to properly operate AEDs is important. Some AEDs switch modes to become manual defibrillators.

ANATOMY AND PATHOPHYSIOLOGY

The heart is composed of two systems, a physical pump driven by the rhythmic discharge of the electrical system. The electrical system is a conduit composed of the sinus node, the atrioventricular node, the bundle of His, and the left and right bundle branches (Figure 39-2). ...