Editor,—Staniforth et al’s paper comparing exercise capacity in VVIR and VVI pacing modes in 12 patients with complete AV block showed that rate responsive pacing improved some but not all measures of exercise capacity.1 They conclude that the best investigation for assessing exercise capacity remains unclear.

On the contrary, we feel that what is at fault is the pacing mode rather than the investigation. It is widely accepted that the preservation of AV synchrony is optimal for patients with sinus rhythm and complete AV block and is indeed recommended by the British Pacing and Electrophysiology Group.2 Maintaining AV synchrony …