[Antidromic reciprocating rhythm in Wolff-Parkinson-White syndrome precipitated by a ventricular extrasystole arising at the emergence of the preexcitation pathway].

A 9 year old child was investigated for attacks of wide QRS complex tachycardia occurring exclusively during the daytime and favoured by exercise or stress, with ventricular extrasystoles of the same form occurring between attacks. Endocavitary investigation showed a concealed atrioventricular accessory pathway during sinus rhythm with anterograde 1/1 conduction up to 270/min; retrograde conduction was not so good with block occurring at 175/min. The spontaneous tachycardia was reproduced by catecholamine infusion: it was an antidromic reciprocating rhythm triggered by a ventricular extrasystole of identical form to that of a pure preexcitation complex and to that of the tachycardia complexes. Spontaneous termination of attacks always occurred when conduction from the ventricle to the atria stopped. The attacks could be induced by ventricular extrastimuli when they caused an increment in retrograde conduction time resulting from retrograde conduction up the nodohisian pathway and not the Kent bundle. The tachycardia could also be initiated by atrial extrastimuli providing pure pre-excitation could be obtained. In both cases, retrograde conduction of the nodohisian pathway had to be improved by catecholamines. When the patient was given betablocker therapy the attacks of tachycardia completely disappeared. The association of ventricular extrasystoles and antidromic reciprocating rhythm and their morphological identity suggest that these extrasystoles were in fact automatic activity of the Kent bundle. Escape phenomena as signs of passive automatism have been described in this conditions but, to our knowledge, extrasystoles suggesting an active automatic process have not been previously reported.