Electrical Cardioversion

Preparation

• Ensure that there are no contributing factors or illnesses that could be corrected or treated before carrying out the procedure (e.g. hyperthyroidism, heart failure, digitalis toxicity).
• Laboratory investigations (INR, electrolytes, digoxin concentration)
  • Patients on warfarin: ensure that INR has been ≥ 2 for at least 3 weeks.
  • Patients using one of the direct anticoagulants: ensure that the patient has taken the drug according to recommendations for at least 3 weeks.
  • If anticoagulant therapy has not been implemented as instructed, the cardioversion must be postponed or transoesophageal echocardiography (TEE) has to be performed before cardioversion.
  • Electrolyte disturbances, e.g. hypokalaemia, have to be corrected before cardioversion.
  • Digoxin concentration must be checked before cardioversion. The intervention is rescheduled if the concentration is too high (risk of bradycardia and atrial tachycardia with 2:1 block).
• ECG
  • Confirm that the rhythm continues to be abnormal and check the ventricular response rate.
  • Slow ventricular response rate (less than 50-70/min) in a patient not on rate-slowing medication may be a sign of severe atrioventricular conduction disturbance which may be a contraindication to cardioversion.
• Other precautionary measures
  • Ensure that the patient has not had anything to eat or drink for at least 4-6 hours before the procedure.
  • Morning medication may be taken up to 2 hours before the procedure with a small amount of fluid. It is especially important that there are no interruptions in the anticoagulant therapy.

Equipment and medicines

• Equipment
  • Biphasic defibrillator with appropriately sized defibrillator pads
    • Self-adhesive electrodes, one of which is placed on the patient's back, are better than traditional "paddles" (picture 1).
  • Pulse oximeter to monitor oxygenation
  • Blood pressure monitoring equipment
  • Oxygen mask
  • Oral airway, intubation equipment and resuscitator bag and valve
  • Suction
• Medicines
  • Propofol 20 ml ready drawn in a syringe
  • Adrenaline (0.1 mg/ml), atropine (1 mg/ml) and etilefrine (10 mg/ml) easily accessible

The procedure

1. Start an i.v. infusion (e.g. physiological NaCl).
2. Administer oxygen via a mask for at least 5 minutes before the procedure (6-7 l/min).
3. Attach the defibrillator cable leads to the patient and confirm that the ECG trace is of good quality and that the arrhythmia persists.
4. Attach the defibrillator pads in situ (picture 1).
5. The defibrillator must be engaged in the synchronisation mode (press the SYNC button). Confirm from the monitor screen that QRS complexes are correctly recognized (the SYNC light should be lit and each QRS complex must have a visible ”sync” marker). In ventricular fibrillation, it is of utmost importance that the SYNC mode is switched off.
6. Select appropriate initial energy level.
   • In the cardioversion of atrial fibrillation, it is recommended to use from the beginning the maximal debrillation energy (usually 200 J), because it is more effective than treatment with gradually increased defibrillation energy.
   • It is usually easier to succeed in the cardioversion of atrial flutter compared with that of atrial fibrillation, and in atrial flutter, as considered appropriate, a lower initial energy can be used (e.g. 100 J).
7. Check the patient's blood pressure.
8. Inject propofol slowly according to the patient's response (1.0-2.5 mg/kg) until the blink reflex disappears (the patients does not blink when the eyelashes are touched lightly). Depending on the patient, this will take about 30-60 seconds. Short transient cessation of breathing is fairly common during anaesthesia and the patient may require some ventilatory support via a mask.
9. Before the shock is delivered the operator of the defibrillator must give a verbal command: ”All clear!”. The patient or bed must not be touched during defibrillation.
   • If the arrhythmia is not reversed, or is initially reversed but reverts after a few sinus beats, cardioversion can be attempted right away again, but usually it is not worthwhile to perform more than 3 attempts. Before a new attempt, the adhesion of the electrodes should be checked and, if necessary, their position changed.
10. Check the patient's blood pressure immediately after the procedure and record a 12-lead ECG. If the blood pressure is low (less than 90 mmHg), administer fluids and elevate the end of the bed. If necessary, vasopressor agents may be administered (e.g. 5 mg etilefrine as a slow injection).

Unsuccessful electrical cardioversion

• If the attempt at elective cardioversion is unsuccessful, it is usually best to accept atrial fibrillation and optimise ventricular response rate and anticoagulation (see also Treatment Approach for Atrial Fibrillation: Rate Control or Rhythm Control? Rate Control in Permanent Atrial Fibrillation Indications for and Implementation of Anticoagulant Therapy in Atrial Fibrillation).
• If restoration of sinus rhythm is, however, considered necessary:
  • the patient may be given ibutilide (1 mg in an infusion over 10 minutes) after which the cardioversion attempt is repeated during the same anaesthesia. Class 1C drugs have also been tried but the evidence of their efficacy is insufficient
  • the patient may be prescribed oral antiarrhythmic drugs (e.g. amiodarone, flecainide) and the cardioversion attempt repeated after the effect of the medication has stabilised
• Intracardiac cardioversions have been completely abandoned.

Monitoring after electrical cardioversion

• After the procedure, regardless of the result of the cardioversion attempt, the patient should stay at the clinic or ward for at least 4 hours for observation.
  • 2 hours after the procedure the patient may eat and start to mobilise.
  • Driving a car is not allowed on the day of the procedure.

Further treatment after elective cardioversion

• The need for permanent anticoagulation and for preventive antiarrhythmic treatment must always be assessed in association with elective cardioversion.
• Either a direct anticoagulant or warfarin is used for further anticoagulation after cardioversion.
  • Permanent anticoagulation for patients at high risk (CHA₂DS₂-VASc ≥ 2) even if it appears that sinus rhythm were maintained
  • For patients at moderate risk (CHA₂DS₂-VASc = 1), the need for anticoagulant therapy is assessed on the individual basis. Permanent anticoagulation therapy is recommended if the patient has other risk factors (e.g. smoking, dyslipidaemia or renal failure).
  • In low risk patients (CHA₂DS₂-VASc = 0), the benefit from anticoagulation therapy is so minimal that 1-month long anticoagulation is sufficient after elective cardioversion. Direct anticoagulants are to be recommended for these patients.
• Arrhythmia prevention
  • In a patient with atrial fibrillation, either initiation of antiarrhythmic medication, dose increase or drug change should be considered. Another option is to refer the patient for consideration of catheter ablation treatment.
  • As a general principle in frequently recurring atrial fibrillation it is preferable to abstain from cardioversion if it is not possible to simultaneously intensify prophylactic treatment.
  • Patients suffering from recurrent atrial flutter are referred for consideration of catheter ablation treatment Treatment of Atrial Flutter.