Automated External Defibrillators
Ventricular Fibrillation: Definition, Etiology, and Intervention
According the American Heart Association (AHA), a ventricular fibrillation is a condition where the heart’s ventricles (thus the term “ventricular”) that are responsible for pumping of blood out of the heart contract and relax in a disorderly, unsynchronized manner. The heart “flutters” rather than beats. The heart, given its four chambers, must beat in a systematic manner, as directed by an electrical impulse (AHA).
Because of the inadequate blood supply into the client’s body parts, especially his vital organs, ventricular fibrillation may be fatal, and thus, emergency medical intervention must be provided immediately. Cardiopulmonary resuscitation must be given as soon as possible, and defibrillation must follow (Mitchell). In defibrillation, electrical shock is delivered to the heart through an automated external defibrillator (AED).
AED: Its Mode of Action and Role in Ventricular Fibrillation
An automated external defibrillator operates on two primary functions. First, it has to identify the fatal electrical rhythm that is indicative of ventricular fibrillation. Second, it needs to shock the heart with 100 kilowatts to restart the fatal rhythm to a healthy one (Kroll, Kroll, and Gilman 42).
Once the AED is switched on and the patches bearing the electrodes are attached to the patient, the device foremost identifies the presence of a ventricular fibrillation. The heartbeat is most susceptible during T wave which occurs as the heart begins to relax post contraction. If a nonfibrilling heart is shocked during the T wave, there are high chances that the heart will fibrillate. If the patch is placed in an area relatively far from the heart, such as the belly, the shock may be strong enough to fibrillate the heart but not too strong to undo the damage – to defibrillate, that is. Thus, as a solution to this, new AED models are designed to check for a pulse (Kroll et al. 44).
The detection of whether or not a fibrillation occurred rests on the heart rate. If the heart rate is greater than 150 beats per minute, a fibrillation is likely to have occurred; thus, there is a need to administer a shock. However, false positives and false negatives may occur, such as in the presence of atrial fibrillation and pacemakers respectively. An inappropriate shock might be called or called off in these scenarios. Modern AED models have provided solutions to this by creating a system that will eliminate misdiagnoses (Kroll et al. 44).
Defibrillators use the modern biphasic waveform which delivers the shock in two phases. The first phase charges the cell membranes; the second phase where the charge is reversed restores zero-voltage in the cell membranes. The second phase is theorized to reverse the current to discharge cells closest to the electrodes which have therefore received the most amount of shock, and to discharge cells that received only small amount of shock (Kroll et al. 44).
The application of shock into the heart is likened to a computer receiving a “Ctrl+Alt+Del” command. The heart is “shut down,” stopping the disorganized beating or fluttering in order for it to effectively re-establish a correct heartbeat.
Safety Issues on the Use of AED
Before the advent of the AED’s new design, a cardiac monitor that displays the heart’s waves is needed for the professional to read the presence of a ventricular fibrillation. With the new design however, it has allowed even a non-health professional to defibrillate since the AED could diagnose a ventricular fibrillation on its own. It has been designed as well to provide simple and accurate walkthroughs once the AED is turned on. The AED bears a single button to prevent confusion in a very alarming situation (Kroll et al. 44).
Manpower is vital in emergency situations. A single rescuer left in the scene is now capable of administering defibrillation since the new AED design requires only one operator. This is primarily due to the replacement of paddles with attachable patches. These patches are left attached onto the client’s skin, allowing the operator’s free hands to push the button on the device if prompted (Kroll et al. 44).
Due to the reduction in voltages needed to deliver the shock, along with the advances on the capacitors, battery, and high-voltage semiconductors, the small size and consequently, lesser weight of the AED have made it portable and more available for the use of more people (Kroll et al. 44).
AED’s Increased Public Availability: Its Cost and Benefits
Making the automated external defibrillator operable by even untrained individuals and assuring safety and efficiency of its use make emergency assistance available to the public. In a study conducted by Caffrey, Willoughby, Pepe, and Becker in 2002, AED’s for public access were effectively utilized to defibrillate patients undergoing cardiac arrest. Most of those who have assisted in cases of survivors have been identified to be volunteers from the lay and had no training prior to the use of such devices.
In 2008, San Diego Councilman James Madaffer proposed to make the installation of AED’s mandatory in large, newly constructed buildings in his county (qtd. in Upson). Such a spread in the public use of AED’s may lead to lesser health expenditures on hospitalizations rooting from fatal complications brought about by ventricular fibrillation. Although professional manpower is deemed irreplaceable in the health sector, the use of such automated devices may help alleviate the effects of manpower and resources insufficiency that lead to inadequate delivery of emergency care. Ultimately, making AED’s more available for public use may ultimately lead to lowered mortalities brought about by inadequately attended cardiac arrests (Upson).
American Heart Association. “Ventricular Fibrillation.” American Heart Association. 2009. 14 Apr. 2009 <http://www.americanheart.org/presenter.jhtml?identifier=4784>.
Caffrey, Sherry L., Paula J. Willoughby, Paul E. Pepe, and Lance B. Becker. “Public Use of Automated External Defibrillators.” The New England Journal of Medicine 347.16 (2002): 1242-1247.
Kroll, Mark W., Karl Kroll, and Byron Gilman. “Idiot-Proofing the Defibrillator.” IEEE Spectrum 45.11 (2008): 40-45.
Mitchell, L. Brent. “Ventricular Fibrillation.” The Merck Manuals: Online Medical Library. Jan. 2008. Merck & Co., Inc. 14 Apr. 2009. <http://www.merck.com/mmhe/sec03/ch027/ch027h.html>.
Upson, Sandra. “Big Push for Emergency Defibrillators in High-Rises”. IEEE Spectrum Online. Nov. 2008. 14 Apr. 2009 <http://www.spectrum.ieee.org/nov08/6970>.