Electrical cardioversion

Electrical conversion is used to convert a tachyarrhythmia to normal sinus rhythm. This may be:

 

• Emergency—when the circulation is absent or severely compromised.

• Semi-elective—when the circulation is compromised to a lesser degree.

• Elective—when synchronised cardioversion is performed to restore sinus rhythm for a non-compromising supraventricular tachycardia.

Synchronisation requires initial connection of ECG leads from the patient to the defibrillator so that the shock is delivered on the R wave to minimise the risk of ventricular fi brillation. Newer, biphasic defibrillators require approximately half the energy setting of monophasic defibrillators.

Indications

Cardiac arrest, e.g. VF.

Compromised circulation, e.g. VT.

Restoration of sinus rhythm and more effective cardiac output.

Lessens risk of cardiac thrombus formation.

Contraindications/cautions

Aware patient.

Severe coagulopathy.

Caution with recent thrombolysis.

Digoxin levels in toxic range.

Complications

Surface burn.

Pericardial tamponade.

Electrocution of bystanders.

Technique

(See algorithm opposite, figure 3.1).

• The chances of maintaining sinus rhythm are increased in elective cardioversion if K+ >4.5mmol/L and plasma Mg

2+ levels are normal.

• Prior to defibrillation, ensure self and onlookers are not in contact with patient, things attached to the patient, or the bed frame.

• To reduce the risk of superficial burns, replace gel/gelled pads after every three shocks.

• Consider resiting paddle position (e.g. anteroposterior) if defibrillation fails.

• The risk of intractable VF following defibrillation in a patient receiving digoxin is small unless the plasma digoxin levels are in the toxic range or the patient is hypovolaemic.

 Fig. 3.1 Algorithm for use of electrical cardioversion.