Cardioversion is a

medical procedure A medical procedure is a course of action intended to achieve a result in the delivery of healthcare. A medical procedure with the intention of determining, measuring, or diagnosing a patient condition or parameter is also called a medical test. ...

by which an abnormally fast

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

(

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ( ...

) or other

cardiac arrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...

is converted to a normal rhythm using

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...

or drugs. Synchronized electrical cardioversion uses a therapeutic dose of electric current to the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

at a specific moment in the

cardiac cycle The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...

, restoring the activity of the

electrical conduction system of the heart The cardiac conduction system (CCS) (also called the electrical conduction system of the heart) transmits the signals generated by the sinoatrial node – the heart's pacemaker, to cause the heart muscle to contract, and pump blood through ...

. ( Defibrillation uses a therapeutic dose of electric current to the

at a random moment in the

, and is the most effective resuscitation measure for

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and poss ...

associated with

ventricular fibrillation Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular fibrillation results in cardiac arrest with loss of consciousness and n ...

and pulseless

ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short perio ...

.) Pharmacologic cardioversion, also called chemical cardioversion, uses antiarrhythmia medication instead of an electrical shock.

Electrical

To perform synchronized electrical cardioversion, two

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...

pads are used (or, alternatively, the traditional hand-held "paddles"), each comprising a metallic plate which is faced with a saline based conductive gel. The pads are placed on the chest of the patient, or one is placed on the chest and one on the back. These are connected by cables to a machine which has the combined functions of an

ECG Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...

display screen and the electrical function of a

defibrillator Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current (often called a ''coun ...

. A synchronizing function (either manually operated or automatic) allows the cardioverter to deliver a reversion shock, by way of the pads, of a selected amount of electric current over a predefined number of milliseconds at the optimal moment in the

which corresponds to the R wave of the

QRS complex The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...

on the

. Timing the shock to the R wave prevents the delivery of the shock during the vulnerable period (or relative refractory period) of the

, which could induce

. If the patient is conscious, various drugs are often used to help sedate the patient and make the procedure more tolerable. However, if the patient is hemodynamically unstable or unconscious, the shock is given immediately upon confirmation of the arrhythmia. When synchronized electrical cardioversion is performed as an elective procedure, the shocks can be performed in conjunction with drug therapy until

sinus rhythm A sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node. It is characterised by the presence of correctly oriented P waves on the electrocardiogram (ECG). Sinus rhythm is necessary, but not s ...

is attained. After the procedure, the patient is monitored to ensure stability of the sinus rhythm. Synchronized electrical cardioversion is used to treat hemodynamically unstable supraventricular (or narrow complex)

s, including atrial fibrillation and

atrial flutter Atrial flutter (AFL) is a common abnormal heart rhythm that starts in the atrial chambers of the heart. When it first occurs, it is usually associated with a fast heart rate and is classified as a type of supraventricular tachycardia. Atrial f ...

. It is also used in the emergent treatment of wide complex tachycardias, including

, when a pulse is present. Pulseless

and

are treated with unsynchronized shocks referred to as defibrillation. Electrical therapy is inappropriate for

sinus tachycardia Sinus tachycardia is an elevated sinus rhythm characterized by an increase in the rate of electrical impulses arising from the sinoatrial node. In adults, sinus tachycardia is defined as a heart rate greater than 100 beats per minute (bpm). The ...

, which should always be a part of the differential diagnosis.

Medication

Various

antiarrhythmic agent Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms ( tachycardias), such as atrial fibrillation, supraventricular tachycardia and ventricular ta ...

s can be used to return the heart to normal

. Pharmacological cardioversion is an especially good option in patients with atrial fibrillation of recent onset. Drugs that are effective at maintaining normal rhythm after electric cardioversion can also be used for pharmacological cardioversion. Drugs like

amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia (VT), ventricular fibrillation (VF), and wide complex tachycardia, as well as atrial fibril ...

, diltiazem,

verapamil Verapamil, sold under various trade names, is a calcium channel blocker medication used for the treatment of high blood pressure, angina (chest pain from not enough blood flow to the heart), and supraventricular tachycardia. It may also be ...

and

metoprolol Metoprolol, sold under the brand name Lopressor, among others, is a selective β1 receptor blocker medication. It is used to treat high blood pressure, chest pain due to poor blood flow to the heart, and a number of conditions involving an a ...

are frequently given before electrical cardioversion to decrease the heart rate, stabilize the patient and increase the chance that cardioversion is successful. There are various classes of agents that are most effective for pharmacological cardioversion. Class I agents are sodium (Na) channel blockers (which slow conduction by blocking the Na+ channel) and are divided into 3 subclasses a, b and c. Class Ia slows phase 0 depolarization in the ventricles and increases the absolute refractory period.

Procainamide Procainamide (PCA) is a medication of the antiarrhythmic class used for the treatment of cardiac arrhythmias. It is classified by the Vaughan Williams classification system as class Ia; thus it is a sodium channel blocker of cardiomyocytes. In add ...

quinidine Quinidine is a class I antiarrhythmic agent, class IA antiarrhythmic agent used to treat heart rhythm disturbances. It is the enantiomer of Antimalarial medication, antimalarial agent quinine, originally derived from the bark of the cinchona tre ...

and

disopyramide Disopyramide ( INN, trade names Norpace and Rythmodan) is an antiarrhythmic medication used in the treatment of ventricular tachycardia. It is a sodium channel blocker and therefore classified as a Class 1a anti-arrhythmic agent. Disopyramide has ...

are Class Ia agents. Class 1b drugs lengthen phase 3 repolarization. They include lidocaine,

mexiletine Mexiletine ( INN) (sold under the brand names Mexitil and Namuscla) is a medication used to treat abnormal heart rhythms, chronic pain, and some causes of muscle stiffness. Common side effects include abdominal pain, chest discomfort, drowsiness ...

and

phenytoin Phenytoin (PHT), sold under the brand name Dilantin among others, is an anti-seizure medication. It is useful for the prevention of tonic-clonic seizures (also known as grand mal seizures) and focal seizures, but not absence seizures. The in ...

. Class Ic greatly slow phase 0 depolarization in the ventricles (however unlike 1a have no effect on the refractory period).

Flecainide Flecainide is a medication used to prevent and treat abnormally fast heart rates. This includes ventricular and supraventricular tachycardias. Its use is only recommended in those with dangerous arrhythmias or when significant symptoms cannot ...

moricizine Moracizine or moricizine, sold under the trade name Ethmozine, is an antiarrhythmic of class IC. It was used for the prophylaxis and treatment of serious and life-threatening ventricular arrhythmias, but was withdrawn in 2007 for commercial reaso ...

and

propafenone Propafenone, sold under the brand name Rythmol among others, is a class 1c anti-arrhythmic medication, which is used to treat illnesses associated with rapid heart beat such as atrial and ventricular arrhythmias. Mechanism of action Propafen ...

are Class Ic agents. Class II agents are beta blockers which inhibit SA and AV node depolarization and slow heart rate. They also decrease cardiac oxygen demand and can prevent cardiac remodeling. Not all beta blockers are the same; some are cardio selective (affecting only beta 1 receptors) while others are non-selective (affecting beta 1 and 2 receptors). Beta blockers that target the beta-1 receptor are called cardio selective because beta-1 is responsible for increasing heart rate; hence a beta blocker will slow the heart rate. Class III agents (prolong repolarization by blocking outward K+ current): amiodarone and

sotalol Sotalol, sold under the brand name Betapace among others, is a medication used to treat and prevent abnormal heart rhythms. It is only recommended in those with significant abnormal heart rhythms due to potentially serious side effects. Evidence ...

are effective class III agents.

Ibutilide Ibutilide is a Class III antiarrhythmic agent that is indicated for acute cardioconversion of atrial fibrillation and atrial flutter of a recent onset to sinus rhythm. It exerts its antiarrhythmic effect by induction of slow inward sodium current ...

is another Class III agent but has a different mechanism of action (acts to promote influx of sodium through slow-sodium channels). It has been shown to be effective in acute cardioversion of recent-onset atrial fibrillation and atrial flutter. Class IV drugs are calcium (Ca) channel blockers. They work by inhibiting the action potential of the SA and AV nodes. If the patient is stable, adenosine may be used for restoration of sinus rhythm in patients with macro-reentrant supraventricular tachycardias. It causes a short-lived cessation of conduction through the atrio-ventricular node breaking the circus movement through the node and the macro-reentrant pathway restoring sinus rhythm.

Procedure

Preparation

Cardioversion for restoration of sinus rhythm from an atrial rhythm is largely a scheduled procedure. In addition to cardiology, anesthesiology is also usually involved to ensure comfort of the patient for the duration of the shock therapy. The presence of registered nurses, physician associates, or other medical personnel may also be helpful during the procedure. Before starting the procedure, the patient's chest and back will be prepped for electrode placement. The skin should be free of any oily substances (e.g., lotions) and hair which may otherwise interfere with adhesion of the pads. Once this is complete, the medical team will adhere the pads to the patient using a rolling motion to ensure the absence of air pockets. ''(see details on pad placement below)''. The anesthesiology team will then administer a general anesthetic (e.g., Propofol) in order to ensure patient comfort and amnesia during the procedure. Opioid analgesics (e.g., Fentanyl) may be combined with Propofol, although anesthesiology must weight the benefits against adverse effects including apnea. Bite blocks and extremity restraints are then utilized to prevent self-injury during cardioversion. Once these medications are administered, the

glabellar reflex The glabellar reflex, also known as the "glabellar tap sign", is a primitive reflex elicited by repetitive tapping of the the smooth part of the forehead above the nose and between the eyebrows. Subjects respond to the first several taps by blink ...

or eyelash reflex may be used to determine the patient's level of consciousness. The pads are connected to a machine that can interpret the patient's cardiac rate and rhythm and deliver a shock at the appropriate time. The machine should synchronize ('sync') with the

R wave The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...

of the rhythm strip. Although uncommon, sometimes the machine will unintentionally sync to high amplitude T waves, so it is important to ensure that the machine is synced appropriately to R waves. Interpretation of the patient's rhythm is imperative when using cardioversion to restore sinus rhythm from less emergent arrhythmias where a pulse is present (e.g.,

, atrial fibrillation). However, if a patient is confirmed to be in

pulseless ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a tachycardia, fast heart rate arising from the Ventricle (heart), lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multipl ...

"v-tach" or

"v-fib", then a shock is delivered immediately upon connection of the pads. In this application, electrical cardioversion is more properly termed defibrillation.

Cardioversion

Once the machine is synced with the patient's cardiac rhythm, the machine must be charged. To determine the amount of charge (measured in joules "J") the patient requires, many factors are considered. As a general rule of thumb, recent-onset atrial arrhythmias require less energy compared to persistent atrial arrhythmias. If the cardiologist suspects that the patient may be less respondent to cardioversion, a higher energy may be utilized. Once the machine is synced and charged, a shock can be delivered to the patient.

Recommended Energy Levels

* ''Atrial Flutter and SVT: 50-100 J for biphasic devices; 100 J for monophasic devices'' * ''Atrial Fibrillation: 120-200 J for biphasic devices; 200 J for monophasic devices'' * ''Ventricular Tachycardia (with a pulse): 100 J for biphasic devices; 200 J for monophasic devices'' * ''Pulseless Ventricular Tachycardia and Ventricular Fibrillation: 120-200 J for biphasic devices; 360 J for monophasic devices''

After cardioversion

Following electrical cardioversion, the cardiologist will determine if sinus rhythm has been restored. To confirm sinus rhythm, a distinct

P wave A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...

should be seen preceding each QRS complex. Additionally, each R-R interval should be evenly spaced. If sinus rhythm is restored, the pads may be disconnected, and any other medical equipment is removed from the patients (e.g., bite blocks, restraints, etc.). The patient will regain consciousness soon thereafter (the effects of Propofol generally last for only 3-8 minutes). However, if the arrhythmia is persistent, the machine may be re-charged to a higher energy level, and the cardioversion attempt may be repeated. It is recommended to wait 60 seconds between subsequent cardioversion attempts, but this amount of time may be adjusted based on the patient and/or provider.

Electrode pad placement

Pad placement for electrical cardioversion a cardiac arrhythmia may be either anterior-posterior or anterior-lateral. In an anterior-posterior setup one pad is placed on the chest and the other pad pad is placed on the back. In an anterior-lateral setup, one pad is placed on the chest and the other pad is placed along the left midaxillary line. Choosing the right pad placement can be an important aspect when measuring the success of electrical cardioversion. For example, the anterior-posterior pad positioning is commonly used when attempting to restore an atrial arrhythmia as the vector between the pads predominately runs through the atria. The anterior-lateral pad positioning may be used when attempting to restore pulseless ventricular tachycardia or ventricular fibrillation as there may not be enough time or strength to apply an electrode the patient's back.

Anterior-posterior pad placement

The anterior pad should be placed inferior to the right clavicle while also being vertically centered over at the level of the right 4th intercostal space. The posterior pad should be placed just lateral to the left side of the spine and vertically centered at the level of T7. The inferior angle of the scapula can be used as a reference for the level of T7.

Anterior-Lateral pad placement

The anterior pad should be placed inferior to the right clavicle while also being vertically centered over at the level of the right 4th intercostal space. The lateral pad should be placed along the left midaxillary line at the level of the left 5th intercostal space. The left nipple can be used as a reference for the level of the left 4th intercostal space. From here, the midaxillary 5th intercostal space is identified by moving inferiorly one intercostal space and laterally towards the midaxillary line.

References

External links

''Cardioversion'' from the National Institutes of Health

(1998) * ttps://web.archive.org/web/20081204084601/http://www.emedicine.com/med/topic2968.htm ''Synchronized Electrical Cardioversion'' from eMedicine Online
''Cardioversion'' from the Heart Rhythm Society
{{Cardiac procedures, state = collapsed Cardiac procedures es:Desfibrilación y Cardioversión eléctrica