MECHANISM OF TACHYCARDIA-DEPENDENT APPEARANCE OF VENTRICULAR EXTRASYSTOLES IN CONCEALED BIGEMINY

A case of concealed ventricular bigeminy is reported in which the numb er of sinus QRS complexes intervening between two successive noninterp olated extrasystoles was always uneven. Coupling intervals of manifest extrasystoles to the preceding sinus QRS complexes were almost fixed and much longer than sinus QT intervals. Bradycardia-dependent disappe arance of manifest bigeminy and tachycardia-dependent appearance of ex trasystoles occurred in this case. Apparently, 2:1 block of sinus impu lses occurred in the reentrant pathway, with markedly depressed conduc tivity. Concealed electrotonic conduction of blocked sinus impulses in the pathway of extrasystoles may have favored the appearance of the s ubsequent manifest extrasystoles without concealed conduction owing to two-level block. A possible explanation for the mechanism of such con cealed bigeminy is presented, which uses the concepts of longitudinal dissociation and electrotonic inhibition in the reentrant pathway with markedly depressed conductivity.