What is Electrical Cardioversion

Electrical cardioversion is a procedure where a device called a defibrillator is used to give electric shock to the heart with some abnormal rhythm to restore normal (sinus) rhythm.
Electrical cardioversion is usually used to treat atrial fibrillation. If rhythm control drugs fail to work or cause side effects or they stop working then Electrical cardioversion may be necessary. It is also used to treat atrial flutter, supraventricular tachycardia (SVT), ventricular tachycardia with pulse.
(the same device defibrillator is also used for another procedure named Defibrillation used to treat ventricular fibrillation and pulseless ventricular tachycardia).
Rule out if there is any serious secondary cause of hemodynamic instability such as sepsis, COPD, CHF. In these cases  rapid ventricular rate may be compensatory and atrial fibrillation is incidental. So try to correct these conditions first because rate control drugs, rhythm control Drugs even electrical cardioversion may have serious adverse effects. Rule out any digitalis toxicity and electrolyte imbalance. 
It is a good practice to perform a TEE  ( transesophageal echocardiography)  to see if there is a thrombus (blood clot) in the left atrium, especially if the duration of atrial fibrillation is >24 hours. If there is a thrombus in the left atrium, cardioversion may be deferred. Not observing a thrombus in TEE does not exclude the risk of embolism.
If duration of atrial fibrillation is >12 hours but there is high risk of thromboembolism (CHA2DS2 VASC score is ≥2 in men and ≥ 3 in women) anticoagulant treatment may be continued for at least 4 weeks (INR 2- 3) before cardioversion. (CHA2DS2 VASC is a scoring system to evaluate risk of ischemic stroke in a patient with atrial fibrillation).
If duration of atrial fibrillation is < 48hours and if there is no thrombus in the left atrium in TEE, start heparin or LMWH ( low molecular weight heparin) simultaneously with cardioversion followed by administration of warfarin. Continue heparin/ LMWH until the INR 1.8 with the administration of warfarin. Then continue  oral anticoagulant for at least 30 days after cardioversion. Thereafter anticoagulants may be continued according to CHA2DS2 VASC score.
If duration of atrial fibrillation is > 48 hours, rate control drug + anticoagulant may be used. After a period of minimum four weeks on anticoagulation and when INR ( International normalized ratio) is greater than 2 in two separate occasions cardioversion may be tried.
Electrical cardioversion is life saving in emergency situations. If the patient is hemodynamically unstable, urgent electrical cardioversion may be necessary.
Electrical cardioversion is of two varieties external and internal. When the shock is delivered from a device outside the body it is called external electrical cardioversion first performed in 1950. When shock is applied inside the heart from a catheter introduced through a leg vessel it is called internal electric cardioversion.

Mechanism how Electrical cardioversion Works- 

When electric shock is applied outside of the heart in chest and back with abnormal rhythm such as atrial fibrillation the heart is stunned for a moment, by this time it’s normal pacemaker restores the normal sinus rhythm.

Procedure of external Electrical cardioversion

1 Food or drinks to be stopped for 8 hours prior to cardioversion, only medicines can be taken with sips of water if advised by doctor.
2 All jewellery to be removed and kept at home
3 Any powder, ointment or lotion not to be applied on the chest or back 24 hours before the procedure
4 Chest may need to be saved
5 An intravenous line in the forearm is done through which drugs may be given.
6 The patient is given General anesthesia or sedation as per need so that he cannot feel pain during the procedure
7 Electrodes/ paddles  attached with a defibrillator machine are placed on the anterior portion of the chest over the sternum a little bit to the right and the second electrode is placed at the posterior part of chest a little bit left to midline at the level of the heart. ( the paddles or electrodes may be placed in different configurations, both may be applied in the anterior chest wall)
8 ECG (Electrocardiography) electrodes are placed on the chest to monitor ECG using specially lead II
9 Sync button is pressed and a synchronized marker line appears on the monitor marking each R wave of electrocardiogram. By synchronization electric current is applied for a few milliseconds and the time of shock corresponds with the R wave of ECG, thus allowing the system to determine when the shock will be delivered so that it is not delivered during other time which may cause ventricular fibrillation ( a more dangerous cardiac arrhythmia)
10 Energy level is chosen, usually 200 joules biphasic shock wave
11 Charge button is pressed. 
12 It is ensured that all is clear around the bed, no one is touching or connected with the patient to prevent accidental electrocution of anybody. The shock button is pressed and hold. There may be 1-2 second delay as the machine ensures synchronization. Shock is delivered when the next R wave is detected. There will be a brief contraction of the patient’s chest wall muscles. Rhythm is checked, if sinus rhythm is restored then the procedure is stopped otherwise the patient may need another shock at higher energy level. Higher energy may be needed in overweight or obese patient.
This whole procedure takes about 30 minutes. Patient is closely watched for a few hours for any complication. If all is correct, the patient may go home the same day but driving is not allowed as he or she may feel sleepy. Patient have to take medicines as advised by his doctor.

Complications of cardioversion-

1 Ventricular fibrillation due to general anesthesia
2 Thromboembolism- Stasis of blood due to abnormal rhythm may cause blood clot in the heart that may dislodge during cardioversion and move to other parts of the body causing stroke etc.
3 Other abnormal heart rhythm such as non sustained ventricular tachycardia 
4 Heart block 
5 Bradycardia ( slow heartbeat)
6 Transient LBBB ( left bundle branch block)
7 Myocardial necrosis ( death of heart muscle cells)
8 Myocardial dysfunction
9 Transient hypotension (low blood pressure)
10 Pulmonary edema 
11 Skin Burn
12 Electrical cardioversion in a patient with a pacemaker or ICD (implantable cardioverter-defibrillator) may lead to dysfunction of the device, changes in the pacing or sensitivity threshold.

Success of electrical cardioversion

Success rate of Atrial fibrillation by electrical cardioversion is around 90% (75-93%), though there may be recurrence. In case of large atrium and constant atrial fibrillation for more than one or two years it may not work. Success of EEC depends on careful patient selection, paddle size and position, transthoracic impedance, left atrial size, presence of any conductive material such as gel between skin and paddles.
If gel is applied then gel between two paddles should not touch each other. Shock wave should be applied during expiration. Antiarrhythmic medicine therapy before, during and after cardioversion may prevent shock failure, maintain sinus rhythm and prevent recurrence of  atrial fibrillation. 
Here the procedure time is short, higher success rate and it is less proarrhythmogenic than chemical cardioversion. It is indicated in hemodynamically unstable patient and may be tried in case of failure with chemical cardioversion. 
Patients with implanted pacemaker or cardioverter-defibrillator needs special precaution during performing external electrical cardioversion, low energy to be tried, paddle position should be anteroposterior, and distance of paddle from pacemaker battery should be more than 8 cm. After the procedure, devices to be checked whether they are working properly or not.