DC cardioversion requires a light general anaesthetic or sedation with intravenous diazepam; intubation is not usually required.
- the DC shock is synchronized with an R wave on the electrocardiogram in order to reduce the chance of ventricular fibrillation
- presence of two or more consecutive P waves after shock delivery is usually considered as an indication of successful DCC (1)
DC cardioversion may precipitate systemic emboli from intracardiac thrombus. To avoid thromboembolic events:
- formal anticoagulation is required for at least three weeks before and four weeks after the cardioversion since
- thrombi may form as soon as 48 hours after the onset of AF(2)
- co-ordinated atrial activity may not resume for 2 weeks following cardioversion even if sinus rhythm is apparent on the ECG
- prolonged anticoagulation is not needed when the arrhythmia has existed for less than 48 hours
- no intracardiac thrombus is apparent on trans-oesophageal echocardiography (3)
The use of DC cardioversion is
- recommended acutely in patients who are haemodynamically unstable
- considered electively in order to initiate a long-term rhythm control management strategy (1)
In patients who are haemodynamically stable and do not have severe underlying heart disease, outpatient/ambulatory DCC can be carried out (1)
The results of DC cardioversion in patients with chronic atrial fibrillation indicate a high initial effectiveness but poor long-term effectiveness:
- 70-90% patients with chronic atrial fibrillation will be converted to sinus rhythm by DC cardioversion
- 60-75% of successfully cardioverted patients will revert to atrial fibrillation within one year
NICE state with respect to cardioversion (6)
- for people having cardioversion for atrial fibrillation that has persisted for longer than 48 hours, offer electrical (rather than pharmacological) cardioversion
- consider amiodarone therapy starting 4 weeks before and continuing for up to 12 months after electrical cardioversion to maintain sinus rhythm, and discuss the benefits and risks of amiodarone with the person.
- for people with atrial fibrillation of greater than 48 hours' duration, in whom elective cardioversion is indicated
- both transoesophageal echocardiography (TOE)-guided cardioversion and conventional cardioversion should be considered equally effective
- a TOE-guided cardioversion strategy should be considered:
- where experienced staff and appropriate facilities are available and
- where a minimal period of precardioversion anticoagulation is indicated due to the person's choice or bleeding risks
- in people with atrial fibrillation in whom the duration of the arrhythmia is greater than 48 hours or uncertain and considered for long-term rhythm control, delay cardioversion until they have been maintained on therapeutic anticoagulation for a minimum of 3 weeks
- during this period offer rate control as appropriate
Notes:
- DCC is contraindicated in patients with digitalis toxicity (1)
- maintaining sinus rhythm after cardioversion
- several class IA, IC and III drugs are effective in maintaining sinus rhythm but increase adverse events, including pro-arrhythmia, and disopyramide and quinidine are associated with increased mortality. The authors of a systematic review concluded that (5) any benefit on clinically relevant outcomes (embolisms, heart failure, mortality) remains to be established
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