On the basis of some accumulating evidence of dose dependent QT prolongation with citalopram the manufacturer Lundbeck has issued new guidance on its use. The long and the short of it is that they advise the maximum dose is now 40mg (20mg in the elderly), that it shouldn't be used concomitantly with drugs that also prolong the QT interval (e.g. methadone, tricyclic antidepressants, amiodarone and sotalol), and that it should only be used with caution in those at risk of Torsade de Pointes (CCF, recent MI, bradyarrhythmias, predisposition to hypokalaemia or hpomagnesaemia, including due to medication). This risk also likely applies to escitalopram.
Citalopram is probably the first-line antidepressant in medical practice, partly due to the lower rates of interactions, but give recent evidence that sertraline is more effective, at least compared with straight citalopram (rather than escitalopram), I think sertraline is going to become the go to SSRI of choice now, particularly in the elderly (the maximum dose of 20mg is also the minimum therapeutic dose - so not much scope for increasing it).