CARDIOVERSION AND DEFIBRILLATION
Cardioversion and defibrillation are treatments for tachydysrhythmias. They are used to deliver an electrical current to depolarize a critical mass of myocardial cells. When the cells repolarize, the sinus node is usually able to recapture its role as the heart’s pacemaker. One major difference between cardioversion and defibrillation has to do with the timing of the delivery of electrical current.Another major difference concerns the circumstance: defibrillation is usually performed as an emergency treatment, whereas cardioversion is usually, but not always, a planned procedure.
Electrical current may be delivered through paddles or conductor pads. Both paddles may be placed on the front of the chest (Fig. 27-29), which is the standard paddle placement, or one paddle may be placed on the front of the chest and the other connected to an adapter with a long handle and placed under the patient’s back, which is called an anteroposterior placement (Fig. 27-30).
Instead of paddles, defibrillator multifunction conductor pads may be used (Fig. 27-31). The pads, which contain a conductive medium, are placed in the same position as the paddles. They are connected to the defibrillator and allow for hands-off defibrilla-tion. This method reduces the risks of touching the patient dur-ing the procedure and increases electrical safety. AEDs use this type of delivery for the electrical current.
Whether using pads or paddles, the nurse must observe two safety measures. First, maintain good contact between the pads or paddles (with a conductive medium) and the patient’s skin to prevent electrical current from leaking into the air (arcing) when the defibrillator is discharged. Second, ensure that no one is in contact with the patient or with anything that is touching the pa-tient when the defibrillator is discharged, to minimize the chance that electrical current will be conducted to anyone other than the patient.
When performing defibrillation or cardioversion, the nurse should remember these key points:
· Use multifunction conductor pads or paddles with a con-ducting agent between the paddles and the skin (the con-ducting agent is available as a sheet, gel, or paste).
· Place paddles or pads so that they do not touch the patient’s clothing or bed linen and are not near medication patches or direct oxygen flow.
· If cardioverting, ensure that the monitor leads are attached to the patient and that the defibrillator is in sync mode. If defibrillating, ensure that the defibrillator is not in sync mode (most machines default to the “not-sync” mode).
· Do not charge the device until ready to shock; then keep thumbs and fingers off the discharge buttons until paddles or pads are on the chest and ready to deliver the electrical charge.
· Exert 20 to 25 pounds of pressure on the paddles to ensure good skin contact.
· Before pressing the discharge button, call “Clear!” three times: As “Clear” is called the first time, ensure that you are not touching the patient, bed or equipment; as “Clear” is called the second time, ensure that no one is touching the bed, the patient, or equipment, including the endotracheal tube or adjuncts; and as “Clear” is called the third time, per-form a final visual check to ensure you and everyone else are clear of the patient and anything touching the patient.
· Record the delivered energy and the results (cardiac rhythm, pulse).
· After the event is complete, inspect the skin under the pads or paddles for burns; if any are detected, consult with the physician or a wound care nurse about treatment.
Cardioversion involves the delivery of a “timed” electrical cur-rent to terminate a tachydysrhythmia. In cardioversion, the de-fibrillator is set to synchronize with the ECG on a cardiac monitor so that the electrical impulse discharges during ventricular depo-larization (QRS complex). Because there may be a short delay until recognition of the QRS, the discharge buttons must be held down until the shock has been delivered. The synchronization prevents the discharge from occurring during the vulnerable pe-riod of repolarization (T wave), which could result in VT or ven-tricular fibrillation. When the synchronizer is on, no electrical current will be delivered if the defibrillator does not discern a QRS complex. Sometimes the lead and the electrodes must be changed for the monitor to recognize the patient’s QRS complex.
If the cardioversion is elective, anticoagulation for a few weeks before cardioversion may be indicated. Digoxin is usually with-held for 48 hours before cardioversion to ensure the resumption of sinus rhythm with normal conduction. The patient is in-structed not to eat or drink for at least 8 hours before the proce-dure. Gel-covered paddles or conductor pads are positioned front and back (anteroposteriorly) for cardioversion. Before cardioversion, the patient receives intravenous sedation as well as an analgesic medication or anesthesia. Respiration is then supported with supplemental oxygen delivered by a bag-mask-valve device with suction equipment readily available. Although patients rarely require intubation, equipment is nearby if it is needed. The amount of voltage used varies from 25 to 360 joules, depending on the defibrillator’s technology and the type of dysrhythmia. If ventricular fibrillation occurs after cardioversion, the defibrillator is used to defibrillate the patient (sync mode is not used).
Indications of a successful response are conversion to sinus rhythm, adequate peripheral pulses, and adequate blood pressure. Because of the sedation, airway patency must be maintained and the patient’s state of consciousness assessed. Vital signs and oxy-gen saturation are monitored and recorded until the patient is stable and recovered from sedation and the effects of analgesic medications or anesthesia. ECG monitoring is required during and after cardioversion.
Defibrillation is used in emergency situations as the treatmentof choice for ventricular fibrillation and pulseless VT. Defibrilla-tion depolarizes a critical mass of myocardial cells at once; when they repolarize, the sinus node usually recaptures its role as the pacemaker. The electrical voltage required to defibrillate the heart is usually greater than that required for cardioversion. If three de-fibrillations of increasing voltage have been unsuccessful, cardio-pulmonary resuscitation is initiated and advanced life support treatments are begun.
The use of epinephrine or vasopressin may make it easier to convert the dysrhythmia to a normal rhythm with defibrillation. These drugs may also increase cerebral and coronary artery blood flow. After the medication is administered and 1 minute of cardio-pulmonary resuscitation is performed, defibrillation is again administered. Antiarrhythmic medications such as amiodarone (Cordarone, Pacerone), lidocaine (Xylocaine), magnesium, or pro-cainamide (Pronestyl) are given if ventricular dysrhythmia persists (see Table 27-1). This treatment continues until a stable rhythm resumes or until it is determined that the patient cannot be revived.
The implantable cardioverter defibrillator (ICD) is a device that detects and terminates life-threatening episodes of VT or ventricular fibrillation in high-risk patients. Patients at high risk are those who have survived sudden cardiac death syndrome, usu-ally caused by ventricular fibrillation, or have experienced symp-tomatic VT (syncope secondary to VT). In addition, an ICD may be indicated for patients who have survived an MI but are at high risk for cardiac arrest.
An ICD consists of a generator and at least one lead that can sense intrinsic electrical activity and deliver an electrical impulse. The device is usually implanted much like a pacemaker (Fig. 27-32). ICDs are designed to respond to two criteria: a rate that exceeds a predetermined level, and a change in the isoelectric line seg-ments. When a dysrhythmia occurs, rate sensors take 5 to 10 sec-onds to sense the dysrhythmia. Then the device takes several seconds to charge and deliver the programmed charge through the lead to the heart. Battery life is about 5 years but varies de-pending on use of the ICD over time. The battery is checked dur-ing follow-up visits.
Antiarrhythmic medication usually is administered with this technology to minimize the occurrence of the tachydysrhythmia and to reduce the frequency of ICD discharge.
The first defibrillator, which was implanted in 1980 at Johns Hopkins University, simply defibrillated the heart. Today, how-ever, several devices are available, and many are programmed for multiple treatments (Atlee & Bernstein, 2001). Each device of-fers a different delivery sequence, but all are capable of delivering high-energy (high-intensity) defibrillation to treat a tachycardia (atrial or ventricular). The device may deliver up to six shocks if necessary. Some ICDs can respond with antitachycardia pacing, in which the device delivers electrical impulses at a fast rate in an attempt to disrupt the tachycardia, by low-energy (low-intensity) cardioversion, by defibrillation, or all three (Atlee & Bernstein, 2001). Some also have pacemaker capability if the patient devel-ops bradycardia, which sometimes occurs after treatment of the tachycardia. Usually the mode is VVI (V, paces the ventricle; V, senses ventricular activity; I, paces only if the ventricles do not de-polarize) (Atlee & Bernstein, 2001). Some ICDs also deliver low-energy cardioversion, and some also treat atrial fibrillation (Bubien & Sanchez, 2001; Daoud et al., 2000). Which device is used and how it is programmed depends on the patient’s dysrhythmia.
Complications are similar to those associated with pacemaker insertion. The primary complication associated with the ICD is surgery-related infection. There are a few complications associ-ated with the technical aspects of the equipment, such as prema-ture battery depletion and dislodged or fractured leads. Despite the possible complications, the consensus among clinicians is that the benefits of ICD therapy exceed the risks.
Nursing interventions for the patient with an ICD are pro-vided throughout the preoperative, perioperative, and postoper-ative phases. In addition to providing the patient and family with explanations regarding implantation of the ICD in the preoper-ative phase, the nurse may need to manage acute episodes of life-threatening dysrhythmias. In the perioperative and postoperative phases, the nurse carefully observes the patient’s responses to the ICD and provides the patient and family with further teaching as needed (White, 2000) (Chart 27-4). The nurse can also assist the patient and family in making lifestyle changes necessitated by the dysrhythmia and resulting ICD implantation (Dougherty, Benoliel, & Bellin, 2000).