[Pre-excitation syndrome in monozygotic twins].

A family group of seven members is presented, two of which have pre-excitation syndrome. These subjects are identical twin brothers. One of them has the W-P-W syndrome tipe B, and the other has L-G-L syndrome. The latter had an associated atrial-septal defect, and the other twin had no associated cardiovascular lesions. Both underwent electrocardiographic and vectorcardiographic studies, as well as His bundle electrograms. In the case with W-P-W, the diagnosis was made by electrocardiography, and was confirmed by vertocardiography. The His bundle electrogram showed the habitual findings in this type of pre-excitation. The His bundle potential was preceded by the beginning of the delta wave. The patient with W-P-W had episodes of supraventricular paroxysmal tachycardia, some of these with antegrade conduction through the normal pathway, and others with conduction through the anomalous pathway. The other had a L-G-L syndrome, demonstrated by electrocardiography and vectorcardiography. During the register of the His bundle electrogram, he did not present pre-excitation, the tracings in basal conditions as well as during atrial stimulation were normal. The conclusion is that many factors exist which back up the hypothesis that the pre-excitation syndromes occur because of anomalous pathways, and that this type of alteration might have a sex linked genetic basis. This presumption appears to be confirmed by the presence of pre-excitation in identical twin brothers. Other possibilities are also discussed.