Functional bundle branch block and orthodromic reciprocating tachycardia cycle length: do not bet on accessory pathway location.

AIMS

To show 2 examples in which the analysis of the effect of bundle branch block on orthodromic reciprocating tachycardia cycle length was misleading.

METHODS AND RESULTS

We performed an electrophysiological study in two patients with orthodromic reciprocating tachycardia showing a transition from wide to narrow QRS during tachycardia. Our two cases of left bundle branch block during reciprocating tachycardia using infero-septal pathways show that ventricular to atrial conduction time prolongation may be larger than 30 ms and may be concealed by a shortening of atrial to ventricular conduction time. In the 2 cases, the atrial insertion of the accessory pathway could be successfully ablated from the right atria at the ostium of the coronary sinus.

CONCLUSIONS

The observation of the association between left bundle branch block and cycle length prolongation during reciprocating tachycardia may be associated with a successful ablation at the ostium of the coronary sinus.