Defibrillator Settings For Cardioversion
Bran Cardello
When tachycardic rhythms fail to respond to pharmacologic treatment or present with or deteriorate into unstable manifestations, synchronized cardioversion is the treatment of choice. This activity reviews the guidelines for the provision of emergency synchronized cardioversion to victims of sudden cardiac arrest.
Objectives:
- Explain the approach to the management of tachycardic rhythms.Identify the difference between defibrillation and synchronized cardioversion.Describe the technique of synchronized cardioversion in treating unstable tachycardic rhythms.Explain the importance of improving care coordination among the interprofessional team in performing synchronized electrical cardioversion.
Synchronized cardioversion is a procedure similar to electrical defibrillation in that a transthoracic electrical current is applied to the anterior chest to terminate a life-threatening or unstable tachycardic arrhythmia. Unlike defibrillation, which is used in cardiac arrest patients, synchronized cardioversion is performed on patients that still have a pulse but are hemodynamically unstable. It is used to treat both hemodynamically unstable ventricular and supraventricular rhythms.
Each year almost 350,000 Americans die from heart disease. Half of these will die suddenly, outside of a hospital, because of the sudden cessation of spontaneous, organized cardiac function. The most common cause of sudden cardiac arrest in adults is pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF). VT can also occur in the presence of a pulse; often, it is the precursor to VF. VT is characterized by rapid, wide (greater than 0.12 seconds) QRS complexes.
Supraventricular Tachycardia (SVT) refers to a cardiac rhythm greater than 100 beats per minute, which originates above the bundle of His. SVT is characterized by rapid, narrow (less than 0.12 seconds wide) QRS complexes. Any tachycardic rhythm that does not originate in the ventricles is referred to as SVT. This includes sinus tachycardia, junctional tachycardia, reentrant tachycardias, multiple atrial tachycardia (MAT), atrial fibrillation, and atrial flutter. Although various supraventricular rhythms can cause SVT, clinically, they are treated with the same approach.[1]
Under the American Heart Association's advanced cardiovascular life support (ACLS) guidelines, the identification and treatment strategies for all tachycardic rhythms involve three simple, rapid decision points.[3] First is the identification of the rhythm as tachycardic.
Next, the tachycardic rhythm is divided into one of two categories depending on the width of the QRS complex: (1) wide-complex tachycardia (QRS width greater than 0.12 seconds) or (2) narrow-complex tachycardia (QRS width less than 0.12 seconds). All narrow-complex tachycardias are considered to be supraventricular in origin and are referred to as SVTs. Although wide-complex tachycardic rhythms can occur from sites above the ventricles (such as in supraventricular rhythms with a bundle branch block or other aberrant conduction), clinically, especially during emergent situations, wide-complex tachycardia is usually treated as ventricular in origin, as it is the most potentially life-threatening condition.
The treatment of all emergent tachycardic rhythms, whether narrow-complex or wide-complex, depends on the third and final clinical determination: the presence or absence of a pulse. Pulseless rhythms are treated under the ACLS cardiac arrest algorithms: a wide-complex tachycardia would be considered to be pulseless ventricular tachycardia, which is treated the same as VF under the VF algorithm. A narrow-complex tachycardia would be considered to be a pulseless SVT and is treated under the PEA (Pulseless Electrical Activity) algorithm.
In the presence of a pulse, the specific treatment for all tachycardic rhythms depends on one final determination: whether the pulse being generated is allowing the patient to be considered stable or unstable. In stable patients, the treatment for the underlying arrhythmia is usually medication.[4] For the unstable patient, the treatment of choice is electricity. All tachycardic rhythms, whether wide or narrow complex, are considered to be unstable if the patient also has chest pain, dyspnea, altered mental status, hypotension, pulmonary edema, or ischemic changes on the EKG. The treatment for all unstable tachycardic rhythms is synchronized cardioversion.
Synchronized cardioversion differs from defibrillation in two aspects: (1) the amount of energy needed to convert the rhythm is usually less than that required for defibrillation, and (2) the shock is delivered in a different part of the cardiac cycle.
The appropriate energy level is then selected, and the discharge/shock button is pressed and held. The defibrillator does not release the shock immediately. Instead, it waits for the next R-wave to appear and delivers the shock at the time of the R-wave. This allows the shock to be provided safely away from the T wave, avoiding the R-on-T phenomenon.
The recommended energy levels used to perform synchronized cardioversion vary from 50 to 200 joules. Recalling the specific energy level for a particular sub-type of unstable tachycardia is difficult, especially in an emergent situation. The safest and easiest recommendation is to start at the lowest energy level (50 joules), and if the shock is unsuccessful, double the amount of energy used. In a refractory case, you will be at 200 joules after just three shocks.
Cardioversion is performed both inside and outside the hospital, and it is one technique that all healthcare professionals, including nurses, pharmacists, and EMS, should be familiar with. It has been shown to save lives, and hence it is important to know how the device works and its indications. To ensure proficiency with cardioversion, regular updating of ATLS protocols is necessary. Education by an interprofessional team of specialty-trained nurses and clinicians will provide the best results. [Level V]
Cardioversion and defibrillation are both treatments which treat abnormal heart rhythms, called arrhythmias. Arrhythmias can occur in healthy hearts and, most of the time, they are both short-lived and harmless. However, serious arrhythmias that are prolonged and significantly disrupt heart function are very dangerous. Certain types of arrhythmia can even lead to Sudden Cardiac Arrest (SCA).
Defibrillation is used to treat patients in cardiac arrest who do not have a pulse, as well as patients with certain types of arrhythmias. A defibrillation shock from an AED is a more powerful shock than those delivered during cardioversion, resetting scrambled signals and enabling the heart to beat normally.
In a normal, healthy heart, electrical impulses trigger a coordinated sequence of muscle contractions that enable the heart to pump blood. When the heart is in ventricular fibrillation or ventricular tachycardia, the electrical signals that control the heart are scrambled. Therefore, the heart muscle is not contracting in an organized fashion.
After the heart has been defibrillated, it goes back into a normal sinus rhythm wherein it starts recirculating oxygen-rich blood throughout the body. Skin color may return to normal and, in some cases, the person will start breathing on their own.
Unsynchronized cardioversion is not as nuanced, uses more energy, and delivers a shock at any point during the cardiac cycle, when the machine has reached full charge. For all intents and purposes, unsynchronized cardioversion is the same thing as defibrillation, and is used when the patient does not have a pulse.
Typically set at 100 joules, the first shock may be enough to restore a regular rhythm. If the first shock is unsuccessful, the clinician may ramp up the energy incrementally, delivering shocks until the abnormal rhythm ceases. The precise amount of energy delivered typically varies from 100 to 300 joules, with most arrhythmias stopping after an application of 120 joules.
Biphasic defibrillators can tailor their energy level to the patient by measuring their impedance (electrical resistance) using an internal mechanism to dampen the energy delivered when appropriate. Biphasic defibrillator devices vary by manufacturer but typically release between 120 to 200 joules of energy with each shock.
Every minute that a person in Sudden Cardiac Arrest does not receive defibrillation, their chances of survival drop by 7-10%, making rapid defibrillation imperative for survival and one of the key steps in saving a life from Sudden Cardiac Arrest. Therefore, the benefits of using a defibrillator far outweigh the risks.
Understanding cardiac arrhythmia is essential for treating it properly. Even minor atrial flutter or fibrillation could require treatment to avoid potential blood clotting and the development of more severe arrhythmias. If you have severe tachycardia or atrial fibrillation, your healthcare provider may talk with you about cardioversion.
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