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Successful outcomes in ACLS rely on fast response, making it crucial for clinicians to recognize and know which cardiac rhythms are treated with defibrillation.
It is common for laypeople to think that “shocking” (defibrillating) is the main treatment involved in an ACLS or Code Blue situation. Contrary to portrayals in the media and public perceptions, defibrillation is only used in very specific situations — and is specifically contraindicated in many clinical situations.
It is vital for ACLS-prepared clinicians to quickly recognize when defibrillation is needed, prepare equipment, and deliver shocks promptly. Along with high-quality CPR, it is critical for successful patient outcomes that ACLS teams promptly give the right treatment in the form of medications and defibrillation. Per the ACLS protocol, once a patient is found in cardiac distress and is verified to be pulseless and unresponsive, help is called, and CPR is initiated. If defibrillation is indicated, the next action is to deliver shocks immediately. This protocol is the same whether the patient is in a medical facility or in an out-of-hospital community setting.
A study from the American Journal of Emergency Medicine showed that patients defibrillated within 5 minutes of collapse showed an average 58% neurological recovery rate. For each 1-minute delay, a significant decrease in the likelihood of neurological recovery was found. With certain types of defibrillators becoming more commonly available, it is more important than ever for ACLS clinicians and laypeople alike to understand what rhythms are shockable and how to treat them.
Let’s take a closer look at the rhythms that call for defibrillation, how they work, and how to treat them according to ACLS guidelines.
There are three main types of defibrillators:
Over the years, the availability of AEDs has increased, with units commonly found in stores, sports arenas, schools, airports, and anywhere large crowds gather. This dramatically increases the likelihood of a defibrillator being available in any situation — and the chances that a clinician will encounter situations in which it is appropriate to use one.
The word defibrillation means to deliver an electric shock to the heart to stop an arrhythmia, with the intention of returning the heart to a productive heart rhythm. A productive heart rhythm is one which contracts heart muscle, pumps blood throughout the body, and maintains a sustainable blood pressure. To understand exactly how defibrillation works, it is important to review the heart’s electrical conduction system.
The cells of the cardiac conduction system generate electrical impulses and then carry that signal throughout the heart along a route from the top of the heart muscle (atria) to the bottom (ventricles). The signal is conducted at very specific speeds, which controls how the different parts of the heart beat in coordination to pump blood.
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Image source: https://www.al.com/heart-beat/2013/12/expert_corner_normal_heart_rhy.html
You can see in the figure above that the electrical signal originates in the right atrium at the Sinoatrial node (SA) node, called the pacemaker. The path then moves in this order down through to the ventricles:
A normal cardiac conduction pathway is represented visually on a cardiac monitor as Sinus Rhythm (SR). (meaning it originates in the SA node)
Normal Sinus Rhythm
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Image source: https://infogram.com/normal-sinus-rhythm-1gq3plxlv8o6p1g
When a cardiac condition occurs (such as a vascular heart blockage, heart failure, trauma, genetic condition, or other factor) the electrical pathway can be disrupted, meaning that the signal no longer travels in the way it should. This can lead to a variety of problems, such as:
The most dangerous rhythm disruptions originate in the ventricles, bypassing most of the “pump action” of the heart. In ventricular rhythms, the bottom of the heart is not being pumped full of blood, so the chambers either pump rapidly without filling (pulseless Ventricular Tachycardia) or fibrillate rapidly without filling (Ventricular Fibrillation). This causes rapid collapse, loss of blood pressure, loss of consciousness, and cardiac arrest.
When the heart is stuck in a ventricular rhythm pattern (fibrillation), a defibrillator is used to deliver an electrical shock to restore a normal heart beat. Defibrillation is unsynchronized, meaning that it is not timed to the heart rhythm at all. For this reason, it is often termed “unsynchronized cardioversion”. Other types of treatments that use electrical current, like synchronized cardioversion and external and internal pacemakers, are synchronized, meaning that the shock is carefully timed with the heart’s current.
When defibrillation occurs, the shock depolarizes the cardiac muscle and allows the body’s natural pacemaker, the SA node, to re-establish a proper rhythm. It serves as a “reset button” for the heart’s electrical conduction pathways.
The first external defibrillators were monophasic, passing only one wave of current through the heart from right to left. Biphasic defibrillators use a lower dose of energy (measured in Joules), and the shock has two waves of energy — one from right to left and one from left to right, making the shock more effective.
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Image Source: https://electro-medical.blogspot.com/2015/11/monophasic-and-biphasic-defibrillation.html
In general, biphasic defibrillators have been found to be more effective and less likely to burn the patient. They also don’t use as much battery power to deliver, meaning that portable units can last longer throughout a resuscitation period. It is safe to say that most defibrillators in use today are biphasic, but there are always exceptions.
NOTE: It is vital that you know what type of defibrillator you have in your facility or area of work and know the manufacturer’s recommendations for use.
Ventricular arrhythmias are severely abnormal heart rhythms, in which the blood is not pumping through the heart to the body. Unless immediately treated, these rhythms cause death. Ventricular Fibrillation (VF) is responsible for 75% to 85% of sudden deaths in persons with heart problems. About 10% of the ability to restart the heart is lost with every minute that the heart fibrillates.
When the heart is in ventricular tachycardia (VT), the QRS complexes will be wide and rapid. Monomorphic VT means that the electrical impulse is being generated from one part of the ventricles, thus all the QRS waves look the same.
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Image source: https://acls-algorithms.com/rhythms/pulseless-ventricular-tachycardia/comment-page-5/
Patients can either be stable or unstable while in Monomorphic VT, although the condition usually deteriorates. Always check for a pulse and treat the patient accordingly. If unstable, the ACLS algorithm should be followed (pulse check – call for help – CPR – shock).
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Image source: https://acls-algorithms.com/rhythms/other-tachycardias/
You will notice that the Polymorphic VT waves above are not symmetrical. This means that the ventricular impulses are from multiple locations. Some QRS complexes may be narrower, taller, or wider. Sometimes Polymorphic VT is caused by an underlying condition, and is often presented as Torsades de Pointes, often just called Torsade’s. Treatment of Torsade’s can be difficult, however if the patient is unstable, defibrillation is always used as soon as possible.
The following rhythm strip shows VT which rapidly deteriorates into Ventricular Fibrillation (VF).
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Image source: http://floatnurse-mike.blogspot.com/2012/03/identify-appropriate-electrical_30.html
Called VFib, V-Fib, or VT, this rhythm is one of the most lethal. It is often accompanied by:
It then quickly deteriorates into:
Without immediate treatment, VF causes death within minutes. The abrupt stoppage of blood supply to the body shuts down vital processes and quickly damages organs.
The following is a strip of a patient in VF that was quickly defibrillated and restored to a perfusing rhythm (although notice it is still wide and bradycardic)
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Image Source: http://floatnurse-mike.blogspot.com/2012/01/pediatric-pulseless-ventricular_27.html
After a productive heart rhythm is established, the patient’s condition may still be fragile until the underlying causes of arrhythmia are corrected. The patient may need surgery, to have electrolyte imbalances corrected, or a cardiac cath lab procedure to clear a coronary blockage.
The patient may go back into a lethal rhythm at any time. It is advisable to leave a set of new defibrillation patches and defibrillator attached to the patient or immediately available at the bedside.
Meanwhile, the patient should be transported to an intensive care or emergency environment so that the following can be continuously monitored and stabilized:
It is also to be expected that the patient will have labs drawn, a chest X-ray, and will probably need to be prepared for cardiac catheterization. The patient may be intubated by this point and will need ventilator settings monitored. Medications to support blood pressure and prevent additional arrhythmias may need to be administered and titrated.
Skin burns from defibrillator paddles or patches are a common occurrence after defibrillation. These burns should be assessed and treated with the appropriate skin care to promote healing. Patients are also at risk for blood clots after defibrillation, which can result in deep vein thrombosis, stroke, or pulmonary embolism.
Now that we know what rhythms are shockable, which ones are not?
Pulseless Electrical Activity (PEA) and Asystole (flatline) both represent no heart muscle activity at all. Therefore, delivering shocks to these rhythms would do no good since there is nothing to “reset.” The best treatment for these rhythms is continued CPR, medications, and trying to correct any underlying identified causes (see the “H’s and T’s”).
Other rhythms, such as atrial or junctional arrhythmias have specific treatments as well, none of which require unsynchronized shocks. In these rhythms, the electrical signal is still originating in the upper part of the heart, making a “reset” unnecessary and potentially very dangerous. Any electrical current delivered in these situations is likely to be synchronized, such as with pacing or a planned cardioversion.
In the heat of the moment, it is easy to forget some of the basics of defibrillation. Always keep in mind the following tips to make sure you deliver effective and safe defibrillation:
Although fast defibrillation is the goal, it doesn’t pay to ignore proper safety precautions. This can lead to injury to yourself, bystanders, and further delays in treatment of the patient.
Remember, rapid defibrillation makes all the difference for patients in VT or VF. Your fast thinking and actions can mean saving precious neurological function and lead to complete recovery. ACLS-prepared clinicians are equipped with the skills and knowledge to save lives in clinical settings and in their communities.
If you would like to learn more about the drugs, ECG rhythms, clinical scenarios, and other topics related to ACLS, AMRI has study materials that can help you develop your understanding. Accredited by the National Board of Emergency Care Certifications (NBECC), AMRI has helped more than one million medical professionals earn their ACLS, BLS, and PALS certifications or recertifications since 1983.
Are you ready to take your skillset to the next level? Many clinical areas such as intensive care, emergency, and surgery require ACLS. Obtaining this certification lets employers and colleagues know that you are knowledgeable and prepared to respond. Additional study materials by AMRI give you details you don’t always get - such as deep dives into medications, protocols, and understanding the “why” behind ACLS treatment.
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