The most common involve either medications pharmacological cardioversion or electricity electrical cardioversion or defibrillation. Electrical cardioversion uses electrodes that are several inches across to conduct electricity through the heart muscle. The electrodes can be placed externally on the chest wall or internally directly on the heart muscle.
There are different types of electrical cardioversion, but they all use the same device known as a defibrillator. Defibrillators come in manual and automated versions. Some of them are capable of being used in either mode.
Defibrillators are used when a patient is in certain cardiac rhythms such as ventricular fibrillation or unstable ventricular tachycardia. These rhythms are life-threatening and require a defibrillator to defribrillate the heart, meaning the defibrillator uses electricity to get the heart back into a regular stable rhythm. Use of the term cardioversion for pharmacological solutions is less common, probably because there is a variety of uses for medications that might cause an immediate change in the heart rhythm —traditionally known as cardioversion—but can also be used chronically to control heart rate or rhythm.
Oftentimes electrical cardioversion is preferred over pharmacologic for many reasons. The types of cardioversion that might be performed by either a medical professional or a lay rescuer depend mainly on the medical condition experienced by the patient and on the severity of the patient's condition.
Electrical and pharmacological are the two most common types of cardioversion. However, within both categories, there are several different types of cardioversion. Ventricular fibrillation is a condition in which the heart no longer beats effectively. Instead, it quivers uncontrollably in a way that cannot conduct blood flow.
This is a primary cause of sudden cardiac arrest. The electrical shock can be monophasic or biphasic and either direct current DC or alternating current AC. Most devices currently manufactured use a biphasic, direct current shock of no more than Joules. Defibrillation causes most of the heart muscle cells to depolarize contract all at the same time. This sudden depolarization provides an opportunity for the natural pacemakers in the heart, located on the right atrium, to regain control of the pace and rate of the heart's rhythm.
This is a form of cardioversion because the patient is being cardioverted from ventricular fibrillation to a cardiac rhythm capable of sustaining life. A second, less common, cause of sudden cardiac arrest that can often be cardioverted using unsynchronized electrical shock defibrillation is pulseless ventricular tachycardia. In this cardiac arrhythmia, the patient's heart is beating in an organized rhythm, but too fast for the heart to fill with blood between beats and keep blood flowing.
This use of cardioversion is also called defibrillation even though the caregiver or the lay rescuer is not removing fibrillation but a different lethal arrhythmia. This is why defibrillation is not always the correct terminology for certain types of emergency cardioversion.
Some forms of tachycardia are still organized cardiac rhythms but are going at too fast of a rate to adequately allow the heart to effectively pump blood. In these cases, the patients are still able to pump blood and therefore will have a pulse and will most likely be conscious. During cases of extremely rapid tachycardia, an electrical shock delivered at just the right moment in the cycle of a heartbeat can result in a higher chance of successful cardioversion.
To deliver an electrical shock at that precise moment requires the shock to be synchronized to the heart's rhythm. Synchronization is done using an electrocardiogram ECG to monitor the rhythm and time of the delivery of the shock using the same electrodes as those used to provide defibrillation.
Medications can be used to speed up or slow down the rate of heart rhythm or to completely change an arrhythmia into a different cardiac rhythm. Pharmacological cardioversion does not require sedation. Electrical cardioversion is preferred in patients who are unstable - that is they have a dangerously abnormal blood pressure or other symptoms.
Used for supraventricular tachycardia SVT that is not atrial fibrillation, adenosine is the newest of the pharmacological cardioversion agents. Adenosine has a transient short-lived , noncurative effect on ventricular tachycardia and on atrial fibrillation.
Certain supraventricular tachycardias can be successfully slowed to a rate that properly conducts blood and reduces symptoms with the use of beta-blockers. Beta-blockers are not always seen as cardioversion agents but might be used for long-term control of tachycardia or hypertension high blood pressure. Factors affecting EEC success Energy is a combination of voltage and current. Electrodes position Defibrillator paddles can be used in different configurations, which affect the success rate of defibrillation.
Thoracic impedance Thoracic impedance is another important factor in treatment by electrical cardioversion. Medications and sedations In a pilot study, Sutton et al demonstrated that atropine administration increased the success rate of direct current cardioversion for atrial fibrillation.
Energy selection Biphasic shock and monophasic shock Transthoracic monophasic defibrillators have been employed for the management of ventricular arrhythmias. Management of patients with failed EEC or resistant patients The risks and benefits of recurrent electrical shock therapy must be taken into account.
Complications and contradictions of cardioversion Complications are minimal. Special conditions Arrhythmias in intensive care patients Atrial and ventricular tachycardias are frequent in patients being treated at intensive care units due to the presence of multiple triggers. Cardioversion in Pregnancy Some investigators have reported that electrical cardioversion is safe during pregnancy. EEC in patients with pacemakers Electrical cardioversion performed in patients with a pacemaker or ICD may lead to dysfunction, namely acute or chronic changes in the pacing or sensitivity threshold.
Termination of ventricular fibrillation in man by externally applied electric counter shock. N Engl J Med. Cardiopulmonary resuscitation: an account of forty five years of research. Hopkins Med J. Jones JL. Waveforms for implantable cardioverter defibrillators ICDs and transchest defibrillation. In: Tacker WA, editor. Defibrillation of the heart.
Louis: Mosby-Year Book; Termination of ventricular fibrillation in dogs by depolarizing a critical amount of myocardium. Am J Cardiol. Defibrillation mechanisms: The parable of the blind men and the elephant.
J Cardiovasc Electrophysiol. Role of prophylactic anticoagulation for direct current cardioversion in patients with atrial fibrillation or atrial flutter. J Am Coll Caridiol. Transesophageal echocardiographically facilitated early cardioversion from atrial fibrillation using short-term anticoagulation: final results of a prospective 4. J Am Coll Cardiol. Direct current cardioversion: indications, techniques, and recent advances. Crit Care Med. Lown B. Defibrillation and cardioversion.
Cardiovasc Res. Ewy GA. The optimal technique for electrical cardioversion of atrial fibrillation. Clin Cardiol. Metabolic determinants of defibrillation. Role of adenosine. Regional hyperkalemia increases ventricular defibrillation energy requirements: role of electrical heterogeneity in defibrillation.
Simultaneous recording of action potentials from endocardium and epicardium during ischemia in the isolated cat ventricle: relation of temporal electrophysiologic heterogeneities to arrhythmias. European Resuscitation Council. Part 6: Advance cardiovascular life support. Section 2: Defibrillation. Effect of electrode position and gel-application technique on predicted transcardiac current during transthoracic defibrillation. Ann Emerg Med. Factors affecting transthoracic impedance during electrical cardioversion.
What is the optimal paddle force during pediatric external defibrillation? How good is your defibrillation technique? J R Soc Med. The use of atropine for facilitation of direct current cardioversion from atrial fibrillation-results of a pilot study. Pretreatment with verapamil in patients with persistent or chronic atrial fibrillation who underwent electrical cardioversion.
Can short-term verapamil therapy reduce the recurrence of atrial fibrillation after successful low energy intracardiac cardioversion? Ital Heart J. How to enhance acute outcome of electrical cardioversion by drug therapy: importance of immediate reinitiation of atrial fibrillation. Your doctor will tell you whether to take any of your regular medications before your procedure.
If you do take medications before your procedure, sip only enough water to swallow your pills. Before cardioversion, you may have a procedure called a transesophageal echocardiogram to check for blood clots in your heart. Blood clots can break free by cardioversion, causing life-threatening complications. Your doctor will decide whether you need a transesophageal echocardiogram before cardioversion. If your doctor finds blood clots, your cardioversion procedure will be delayed for three to four weeks.
During that time, you'll take blood-thinning medications to reduce your risk of complications. You'll be given medications through an IV to make you sleep during the procedure so that you won't feel any pain from the shocks. You may receive other medications through the IV to help restore your heart rhythm. A nurse or technician places several large patches called electrodes on your chest. The electrodes connect to a cardioversion machine defibrillator using wires.
The machine records your heart rhythm and delivers shocks to your heart to restore a normal heart rhythm. This machine can also correct your heart's rhythm if it beats too slowly after cardioversion. Electric cardioversion is done on an outpatient basis, meaning you can go home the same day your procedure is done. You'll spend an hour or so in a recovery room being closely monitored for complications. You'll need someone to drive you home, and your ability to make decisions may be affected for several hours after your procedure.
Even if no clots were found in your heart before your procedure, you'll take blood-thinning medications for at least several weeks after your procedure to prevent new clots from forming. To reduce the risk of aspiration patients should not eat or drink for at least 6 h before elective cardioversion.
Supplemental oxygen should be removed prior to discharge of any electrical energy due to the risk of fire.
Procedural sedation is commonly performed as cardioversion may cause pain, anxiety, and unpleasant memories. Proper electrode placement is important for successful cardioversion as this determines the pathway of current [ 3 ]. Pads are primarily placed in two positions, antero-lateral and antero-posterior Fig.
If an ICD or pacemaker is present pads or paddles should not be placed directly over the device and the antero-posterior position may be favored. Pad placement should also avoid breast tissue.
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