Defibrillators are one of the most commonly seen and useful innovations in cardiology. Designed to treat cardiac dysrhythmias, ventricular fibrillation and pulseless ventricular tachycardia, these devices have saved countless lives over the years. These irregularities in the heart’s sinus rhythm result in a weaker than necessary contraction of the heart muscles, meaning that blood does not get pumped fully through the body and can potentially cause unconsciousness and death. This paper will outline the history, various designs, advantages and disadvantages of defibrillators.
The concept of a defibrillator was first proposed when two Swiss scientists observed that small electrical shocks applied to a dog would induce ventricular fibrillation, and that if a larger shock was used on a dog experiencing this condition, it would be reversed. Thirty years later, the first predecessor of the modern device was built in New York, and used a hollow needle to transport an insulated wire to the heart. The device was never used on a human, but in 1947 Claude Beck used electrical paddles on either side of the heart to restore normal rhythm on a child undergoing open-heart surgery.
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Massively more powerful devices were quickly produced to allow usage without an open chest cavity, and Irish scientists quickly made them portable. Two final innovations were realized when the Automated External Defibrillator and implantable cardioverter-defibrillator were developed. These will be discussed later in the paper.
Modern defibrillators generally consist of electrodes in the form of paddles with insulated handles. Some highly portable forms use self-adhesive pads in the place of paddles, as the former require more time to be applied properly. One paddle is placed over the left precordium on the chest and the other between the scapula on the back in order to achieve maximum efficiency. The DC circuit then delivers approximately 1000 volts of power characterized by a biphasic waveform, which decreases the amount of energy needed to correct the irregular rhythm, preventing burns and heart damage from the process.
While movies and television would lead most people to believe that a defibrillator is a panacea for any problem remotely related to a heart attack, this is not true. As noted in the introduction, there are three major problems that can be corrected with the use of a defibrillator: cardiac dysrhythmias, ventricular fibrillation and pulseless ventricular tachycardia. Without going into complex medical discussions, these are all very specific and irregular heartbeats. If one of these heartbeats is identified, the defibrillator sends a shock of predetermined power in order to momentarily stop the heart, allowing the body to restart the organ, restoring normal sinus rhythm. It is possible that the rhythm will not restart in a regular manner, or for the shock to be insufficient to stop the heart. In manual defibrillators, the doctors can choose to increase the voltage, and with an AED, it will automatically increase voltage to the highest allowed amount in order to attempt a successful restart of the heart.
The process by which the heart is restarted is referred to as electrical cardio-version. Electrical cardio-version consists of the heart being actually stopped for a short period of time. The heart rhythm is a cycle, and while the irregular rhythm is unnatural, the heart does not recognize that and simply continues to send the same stimulus, repeating the incorrect heartbeat. When the irregularity is stopped along with the heart, the same stimulus will generate correct sinus rhythm unless an additional problem is present. With atrial fibrillation, the most common condition correctable with a defibrillator, success rates are over 90% in non-emergency situations, although 20-30% of those patients revert to their former irregular dysrhythmia
As noted earlier, there are several types of defibrillators. The most basic, yet often the most useful, type is the manual external defibrillator. Nearly every hospital and ambulance in the modern world carries they units in order to provide treatment for dysrhythmias, ventricular fibrillation, and pulseless ventricular tachycardia. The devices almost always include two paddles and a control unit. A very similar type is the manual internal defibrillator, designed for use in open-heart surgery. The only difference is that internal paddles directly touching the heart deliver the charge.
A relatively recent innovation that has saved countless lives is the automated external defibrillator (AED). This device is designed to be used by people with minimal medical training and automatically diagnoses the dysrhythmia and determines the appropriate charge to apply. It has been shown that interrupting chest compressions for this activity is worthwhile. These devices are very user-friendly and can be operated without confusion by laymen.
Common AED with a user friendly design
Finally, the implantable cardioverter-defibrillator can be placed inside a patient like a pacemaker to constantly monitor rhythms and administer shocks automatically when needed. These can be used to treat chronically irregular heartbeats, most commonly presented as atrial fibrillation, with occasional shocks to correct dysrhythmia or as a device to restart the heart after sudden cardiac arrest. This device is similar to a pacemaker in that it monitors heart rhythms and can give the low-energy pulses necessary to correct some dangerous dysrhythmias. Unlike a pacemaker, however, an ICD can give a high-energy pulse to correct more serious dysrhythmias and sudden cardiac arrest. (NIH 2013)
ICD and Pacemaker Design and Implantation (NIH 2013)
Defibrillators of all types provide an excellent tool for doctors and EMTs across the globe. Unfortunately they are not what the popular media depicts them as. Defibrillators can only treat specific types of heart irregularities and often are not successful at this function. Heart conditions are often very difficult to treat unless the treatment is applied extremely quickly. For this reason, many people applaud the increasing popularity of AEDs, as the chances of a defibrillator being located near a patient are much higher.
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- Eftestol, T. “Effects Of Interrupting Precordial Compressions On The Calculated Probability Of Defibrillation Success During Out-of-hospital Cardiac Arrest.” ACC Current Journal Review 11.6 (2002): 74-75. Print.
- Kastor, John A.. Arrhythmias. 2nd ed. Philadelphia: W.B. Saunders, 2000. Print.
- Timmons, Stephen, Brian Crosbie, and Russell Harrison-Paul. “Displacement Of Death In Public Space By Lay People Using The Automated External Defibrillator.” Health & Place 16.2 (2010): 365-370. Print.
- Trayanova, N.. “Defibrillation Of The Heart: Insights Into Mechanisms From Modelling Studies.” Experimental Physiology 91.2 (2005): 323-337. Print.
