Bispidine compounds useful in the treatment of cardiac arrythmias

There is provided compounds of formula I, ##STR1##

wherein R¹, R², R³, R⁴, R^5a, R^5b, R⁶, X, A, B and D have meanings given in the description, which are useful in the prophylaxis and in the treatment of arrhythmias, in particular atrial and ventricular arrhythmias.