Discussion
We reported an anecdotal case of pararrhythmia with LFVT and ss AVNRT. Co-existence of LPFVT and AVNRT in one patient is rare. They can occur spontaneously at different times or be induced separately by atrial or ventricular stimulation [2]. Extremely limited literatures reported simultaneous LPFVT and slow-fast AVNRT after intravenous administration of atropine [3]. The mechanism of the pararrhythmia was attributed to two coexisting reentrant circuits with similar cycle lengths by chance. During the procedure, it could be seen that the QRS complex morphology alternately transformed among wide, narrow and fusive, accompanied by change of HV interval that shortened or lengthened following QRS complex widened or narrowed. This phenomenon indicated a concurrent attack of two tachycardias, which should be distinguished from supraventricular tachycardia with intermittent bundle branch block. In the latter case, there shouldn’t be obvious shortening of HV interval. Considering that both LPFVT and AVNRT were originated from the AV conduction system, maybe there is an unconfirmed interaction between the two kinds of arrhythmias.