100 QUESTIONS IN CARDIOLOGY

68 What factors determine the chances of

successful elective cardioversion from atrial

fibrillation?

Suzanna Hardman and Martin Cowie

Elective cardioversion should only be undertaken when the

precipitant (e.g. hypoxia, ischaemia, thyrotoxicosis, hypokalaemia

and hypoglycaemia) has been treated and the patient is

metabolically stable. With this proviso, the success of

cardioversion depends not so much on the ability to restoresinus

rhythm (success rates of 70–90% are usual), but rather on the

capacity to sustainsinus rhythm.

Cardioversion of unselected patients will result in consistently

high rates of relapse: at one year 40 to 80% of patients will have

reverted to atrial fibrillation. Early cardioversion, particularly in

those patients in whom a clear trigger of atrial fibrillation has been

effectively treated and in whom there is little or no evidence of

concomitant cardiac disease, is associated with the best long term

outcome. This may reflect the finding (well described in animal

models) that sustained atrial fibrillation modifies atrial electro-

physiology so that, with time, there is a predisposition to continued

and recurrent AF. If early cardioversion is not feasible, then the

extent of underlying cardiac disease may be a more important

determinant of long term outcome than the duration of AF.

The presence of severe structural cardiac disease is associated

with a high relapse rate and sometimes an inability to achieve

cardioversion, e.g. severe ventricular dysfunction, markedly

enlarged atria and valvular disease.

Certain categories of patients justify specific mention:

• Obese patients may be especially resistant to cardioversion

from the external route but not necessarily using electrodes

positioned within the heart.

• A proportion of patients with paroxysmal atrial fibrillation

will eventually develop chronic atrial fibrillation: for many

this provides a paradoxical reprieve from their symptoms. If

cardioverted their propensity to atrial fibrillation remains and

they are likely to relapse.

• The prognosis of patients with structurally normal hearts who

develop atrial fibrillation as a result of thyrotoxicosis is