TSRA Content:
Author: J. Lee West, MD
Mechanism
Defibrillation is defined as the delivery of an electrical shock in order to terminate an arrhythmia, primarily ventricular fibrillation.
Cardioversion relates to the synchronized delivery of an electrical impulse in order to depolarize myocardium in a reentrant circuit, so that it may return to sinus rhythm. Cardioversion is primarily used for atrial fibrillation/flutter, AV reentrant tachycardia and ventricular tachycardia.
The defibrillator, when activated, charges a capacitor to the selected energy level in joules and then delivers it to the patient. The energy delivered can be in the form of a monophasic or biphasic waveform. Biphasic defibrillators are now considered the standard of care. Biphasic defibrillation delivers an electrical current in one direction from one pad to the second pad and then reverses direction and delivers current from the second pad through the heart to the first pad. Biphasic defibrillators deliver less current, thereby decreasing chances of burns to the skin and injury to myocardium. They are also lighter and more portable than monophasic defibrillators.
On a cellular level, the electrical impulse from defibrillation alters the transmembrane potentials and produces a refractory state. Therefore, the reentrant circuit causing the arrhythmia can no longer propagate and sinus rhythm resumes.
Technique
It is important for every provider to become familiar with the model of defibrillator at their institution.
Setup
Remember to use defibrillation/cardioversion at the appropriate time and for the appropriate clinical situation as dictated by the ACLS guidelines. Check to ensure that the patient has the appropriate monitoring equipment and intravenous access. The code cart should be at bedside with all anticipated medications stocked. Assure that necessary personnel (RN, respiratory therapist, etc.) are present and aware of the plan.
During a code event if the patient is not intubated, then it is the clinician's decision whether to intubate or perform bag-mask ventilation. In the case of cardioversion, if the patient is alert, then adequate sedation must be given.
The electrodes on the defibrillator will be either handheld paddles or self-adhesive pads. Handheld paddles have been shown to be slightly more effective due to improved contact surface; however self-adhesive pads are more efficient by allowing continuous telemetry monitoring.
Each provider must become familiar with the type of pads at their institution and know where the recommended location is per the manufacturer. The most common locations are anterior-posterior, right upper parasternal-left lateral (over cardiac apex), and right infrascapular - left lateral. On women, the electrode should be placed lateral to or under the breast. It is suggested that if the initial shock is unsuccessful, one should attempt moving the electrodes to a different location. However, during a cardiac arrest this is often difficult to do.
If using a gel for paddles, use only enough to coat the paddle, as excessive gel will dissipate the energy delivered. Finally, check the telemetry monitor and determine the specific arrhythmia present.
Shock
After determining the specific arrhythmia, adjust the initial energy level to be delivered according to the following guidelines from the American Heart Association:
Atrial fibrillation: 120 to 200 joules for biphasic devices
Atrial flutter: 50 to 100 joules for biphasic devices
Ventricular tachycardia with a pulse: 100 joules for biphasic devices
Ventricular fibrillation or pulseless ventricular tachycardia: 120 to 200 joules for biphasic devices
Obese patients may need higher initial levels due to increased electrode-to-electrode distance.
If performing cardioversion for atrial fibrillation, atrial flutter, SVT, or ventricular tachycardia with a pulse, then press the corresponding sync button on the console. You will notice a marker (dot, dash, etc.) above the R on the QRS complex on the defibrillator monitor. This means that the defibrillator has synced. Be aware, if the console has synced to another point in the QRS complex, a shock may induce ventricular fibrillation.
Press the charge or equivalent button on the console. Most defibrillators have a visual or auditory signal that indicates fully charged.
If using handheld paddles, place them in the appropriate location.
Announce to all present that a shock is to be delivered
Press the shock or equivalent button (If possible, defibrillation after exhalation is preferred and more effective).
Immediately after the shock, assess the patient's clinical status and resume CPR, if applicable. Follow the ACLS guidelines to determine the next appropriate step or necessary medications.
If the initial shock was unsuccessful, then increase the energy level (biphasic 50-70-120-150-170-200 J) and re-shock.
Remember to be aware of the synchronization of the device and the energy being delivered. You may have to switch from sync to unsync and/or adjust the energy level quickly depending on the clinical scenario.
Remember after every shock (successful or unsuccessful), immediately assess the clinical status of the patient. A patient rarely emerges from defibrillation in a hemodynamically stable state. Be ready to continue to treat the patient according to critical care guidelines.
Defibrillation During Cardiac Surgery
Ventricular fibrillation is common intraoperatively immediately after the cross clamp has been released. Defibrillation can be performed directly on the heart with internal paddles, most commonly with 10 to 20 joules of energy. When placing paddles directly on the heart make sure to watch out for and avoid distal coronary anastomoses, if present.
If the first attempt at internal defibrillation is unsuccessful then repeat attempts can be performed at higher energy. In addition, for persistent or recurrent fibrillation it is important to correct all electrolyte abnormalities post cardiopulmonary bypass, especially hyperkalemia, and ensure adequate rewarming. Intravenous lidocaine or amiodarone can be given for persistent or recurrent fibrillation.
Defibrillation Post Cardiac Surgery
Ventricular fibrillation is seen in 25-50% of cardiac arrests post cardiac surgery. It is paramount to diagnose ventricular fibrillation and defibrillate early in this patient population. Patients with ventricular fibrillation or pulseless ventricular tachycardia that have recently had cardiac surgery are often not treated by ACLS guidelines. It is common to give repeated shocks in a post op patient prior to starting chest compressions. Practices vary and it is important to have a protocol in place at each institution. The Society of Thoracic Surgeons’ “Expert Consensus for the Resuscitation of Patients Who Arrest After Cardiac Surgery” recommends that “for patients with VF or pulseless VT, three sequential shocks should be given without intervening ECM (external cardiac massage or CPR). (Class I, Level B)”