Defibrillator

What is a Defibrillator?

The heart is a very vital organ in the body; just as its location, it has a high central function in maintaining life. The heart is composed of very special muscle tissue that will never get tired, so that is could pump blood all over the body without stopping for any rest. By average the heart beats 72 times per minute pumping around 70 milliliters per heart beat. Therefore an average heart pumps 1.3 gallons (5 Liters) per minute. In other words it pumps 1,900 gallons (7,200 Liters) per day, almost 700,000 gallons (2,628,000 Liters) per year, or 48 million gallons (184,086,000 liters) by the time someone is 70 years old. That’s not bad for a 10-ounce pump, is it?

which is responsible for propelling of the blood through the blood vessels to tissues and organs all over the body. If this process stops at least for half a minute the consequences can be critical.
The very function of the heart is a very simple process of pumping which is to take oxygenated blood from the lungs and send it to all the tissues and organs in the body, and then the deoxygenated blood that is collected from the body is pumped back to the lungs to be oxygenated.

By this circulatory function of the heart, we can divide the circulatory system into 1) greater circulation; the part which sends and receives blood all over the body and the 2) lesser circulation; that sends and receives blood from the lungs. The heart has four chambers or rooms for this function from which it pumps blood to these greater and lesser circulation. The muscles of these chambers as mentioned before are, unlike any other muscle in the body, well connected to each other which never exhausts. It also has special cells which produces electrical impulses spreaded throughout the heart walls that cause the heart to beat in a regular rhythmic fashion that makes the heart pump the blood out of it.

In very simple terms any defect in this electrical impulses caused by any of the number of heart diseases present can cause the heart to start beating in an irregular, arrhythmic manner, leading to a very unfavorable outcome. This is where the defibrillator comes into play, and just like its name it DE- Fibrillates where fibrillation basically means uncoordinated twitching of the heart muscle fibers.

How does the defibrillator work?

Like I mentioned before a defibrillator is a medical device that is used to defibrillate a heart, this is achieved by electrically shocking the heart with two electrodes that are placed on the skin of the patient in the area of the heart. These electrodes are normally sticky pads or paddles and each electrode is placed on one side of the heart.

This electric shock, to put in simple terms, resets or restarts the electric impulses produced in the heart and causes the heart to start beating again in regular rhythmic pattern. There are many conditions of the heart that can cause this sort of electrical disturbance, namely ventricular fibrillation and ventricular tachycardia could be named as a common few.

The ventricular fibrillation is a condition where there is a huge electrical chaos in the conduction system of the heart. The normal contraction of the of the heart muscles are disturbed and causes the heart to stop pumping blood to the body properly, which in turn causes something that is called circulatory arrest and death within a few minutes from hypoxia to the brain when proper circulation is not restored. The electric current from the defibrillator puts a stop to all electrical activity of the heart by depolarizing it. This lets the heart’s normal impulses regain the control of the heart’s muscle tissue.

More commonly to be diverting from a medical point of view, the defibrillator is the first resort to those whose heart has stopped beating. It helps the heart to start beating properly again.

This amazing machine was born when two physiologists from Switzerland, Prevost and Batelli, demonstrated that a small electric shock could induce ventricular fibrillation on a dog, and that a larger charge would reverse the condition. Until the early 1950’s defibrillation was only possible when the heart cavity was opened and since alternating current was generated from large transformers, these units were very hard to transport. In the early 1950’s the closed chest method was developed, where electrodes containing alternating current of greater voltage than 1000 volts were applied externally through the chest.

In 1959, Bernard Lown’s research brought about the technique involving the use of charged capacitors to approximately 1000 volts to deliver a 100 -200 joule heavily damped sinusoidal wave for a duration of about 5 milliseconds. As a result it brought about the new generation of defibrillators.

The Lown waveform was the standard of defibrillation until the late 1980’s before the dawn of the Biphasic truncated waveform (BTE) which was able to efficiently deliver lower levels of energy to produce defibrillation. This significantly reduced the weight of the machines.

The major breakthrough in defibrillators came in the 1960’s when defibrillators were added to ambulances. Today portable defibrillators are one of the most important tools carried in ambulances. They are the only proven way to resuscitate a person who has had a cardiac arrest. The next turn in defibrillators was the invention of implantable devices, known as implantable cardioverter- defibrillators (ICD). The invention of implantable units is invaluable to some regular sufferers of heart problems, although they are generally only given to those people who have already had a cardiac episode.

What are the Types of defibrillators?

Today there a many types of defibrillator available, let’s look at a common few below that are frequently used.

Manual External defibrillator – this unit is commonly inbuilt with an ECG machine where medical personals can use to diagnose medical conditions. The clinician needs to know the charge in joules to be used, which would be delivered through pads or paddles onto the patient’s chest. As a detailed medical knowledge and background is of high priority they are found only in Hospitals and some ambulances. As a rule paramedics are trained to recognize lethal arrhythmias and deliver appropriate electrical therapy with a manual defibrillator.

Manual internal Defibrillators – they are identical to the manual external defibrillators except that the charge is delivered by direct contact to the heart and is exclusively found in operating theatres.

Automated external defibrillators (AED) – is definitely the modern generation of defibrillators. It’s a user friendly unit bundled with computer technology designed to analyze the heart rhythm and advise you on whether a shock is required. They are intended to be used by anyone with the least amount of training required, hence being generally limited in its function and not used by health professionals. But definitely valuable instrument in times of crisis and are generally found in public access units in large corporate building, government offices, shopping centers, airports, restaurants and other public places.

Semi- automated External defibrillators- these units are a compromise between a full manual unit and an automated unit, which are used by pre-hospital care professionals such as paramedics. They are fitted with the automated features of AED but at the same time keeping important features that aids in clinical diagnosis and a manual override.

The last would be Implanted Cardioverter-defibrillators(ICD) – these devises are implanted into the patient and acts quite like a pacemaker, many a times being able to perform a pacemaker’s function. They constantly keep check of the patient’s heart rhythm and automatically administer a current in regard to various needed conditions.

Who are the major manufacturers of automatic external defibrillators (AED)?

There are many AED products available in today’s market; the following are the comparison of three models of popular brand names for AED that is approved for public use.

Philips
Heartstream FR2 Medtronic
Physio-control
LIFEPAK500 Zoll
AED Plus
How many Buttons to operate? Two – on and shock Two – on and shock Two – on and Treatment
Is there voice prompt? Yes with visual Yes with visual Yes with visual
Is there a protection against shocking patients not in cardiac arrest? Yes Yes Yes
Does it detect motion that could interfere with analysis? Yes Yes YEs
Can it be used on children under 8 years Yes with special pediatric pads No No
Strength of the shock given All shocks are at 150J but vary in duration and waveform 200 and 300 J 120,150 and 200J
What happens if the electrodes are reversed? AED with function but ECG display will be inverted AED will function but ECG data will be upside down One Piece electrode reduce the chances of incorrect placement
Could the pads be pre connected so it’s ready to be used? No Yes Yes
Battery life
Electrode pads 5 years
2 years 5 years
2 years 2 ½ years
4 years
What arrhymias can be treated? Ventrical Fib
Ventrical Tachycardia Ventrical Fib
Ventrical Tachycardia
Supra Ventrical Tachycardia Ventrical Fib
Ventrical Tachycardia
Does it have prompt on how to perform CPR? No No Yes with visual and voice prompt
How is service? AED sent to factory Onsite service AED is sent to the factory

The other Known brands would be Cardiac Science POWERHEART AED and Access Cardio Systems Access AED.

Every AED brand like any instrument produced commercially has its Plus sides over the competitive counterparts hence it is unable to say which the overall best AED.

Defibrillator placement

The resuscitation electrodes of the defibrillator are placed on the patient according to two of the presently existing schemes. Of this the more preferred scheme would be what is called the anterior posterior scheme for long term electrode placement. Where one electrode is placed on the lower part of the chest, in front of the heart, while the other electrode is placed on the back behind the heart, in the region close to the scapula. This is preferred because it is the best situation for non-invasive pacing.

The second scheme is the anterior-apex scheme which is normally used if the first is of inconvenience. Here, the anterior electrode is placed right below the clavicle and the apex electrode is placed on the left side of the patient.

Today AEDs are found more commonly in many locations for easy accessibility for the public. Although it’s mainly used by trained personals, it is possible to be used by a layman too in times of emergency. Public access units can be found in places including corporate and government offices, shopping centers, airports, restaurants, casinos, hotels, sports stadiums, schools and universities, community centers, fitness centers, health clubs and any other location where people may congregate.
Many emergency vehicles and ambulances are too, likely to carry an AED along with a semi automatic manual defibrillator.

Today, as it has become more affordable, a trend that is developing would be to purchase an AED to be used at home, especially by those with known existing heart conditions.

AED- Are they simple to use? And what are the Risks of AED?

The modern models of AED available are very simple to use with highly complex computer technology that makes it very simple to manure and handle without any previous experience.

The AED from the time it is turned on will instruct the user in a step-by-step procedure of how the machine should be utilized. Once instructed how to apply the pads, the user and everyone around should avoid any contact with the patient as it would give rise to a false reading. Once the AED is analyzed the patient is instructed if he/she needs an electric shock to restore a proper rhythm. If the device determines that a shock is warranted, it will then charge the internal capacitor using its batteries. When it is on charge, the device instructs the users to ensure that no one is touching the victim before pressing the button to deliver the current. Most models then re-assess the patient and instruct either CPR or the need of another shock.

Many AED units come with their own event memory which keeps record of event details, number and strength of the shock delivered. Some come with the added feature of having a voice recorder for monitoring the actions taken by the personnel.
Since the AED presently available to the public is fixed with all the physical precaution methods available, it could be said that the AED is quite Risk free.

However, if the operators have not been trained to avoid touching the patient while giving the electric shock, they may run in to risks including abnormal heart rhythms, skin burns from electrodes and blood clots. But these can be eliminated through proper training for the life saving function that is provided by the AED should not be compromised in any way!

About the Author: The author is a freelance writer with many years of experience.

This is not a substitute for professional medical advice. Seek the guidance of a licensed physician if you need medical advice.

Defibrillator Resources

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