HCM is commonly inherited primary cardiac disorder and associated with an increased incidence of WPW syndrome and 10–40% of AF [1,2,3]. However, a delta-like wide QRS morphology could be observed in the hypertrophied myocardium due to the intraventricular conduction delay. To the best of our knowledge, there is no electrocardiogram interpretation method for the differentiation of wide QRS due to HCM or WPW syndrome.
Although QRS morphologies and axis in some limb leads were slightly changed by the catheter ablation, the delta-like wide QRS was persisted in this case. The changing of QRS morphologies in the lead III (from Rs to rS) and aVF (from Rs to RS) might be related to changing of the intraventricular conduction rather than ablation of the BT, suggesting that the hypertrophied myocardium causes the delta-like QRS widening. When considering the rarity of paraseptal BT, the normal QRS axis could be a clue of HCM cause. In such a case, further detailed evaluation including electrophysiology study will be required, and selection of the catheter ablation should be prudent. Furthermore, differential diagnosis for septal BT should be performed before the catheter ablation. We tried to evaluate decremental property from the RV pacing, but decremental conduction was not observed due to early AV conduction block and HRA pacing showed persistent wide QRS morphology, which might suggest septal BT. However, PR interval was prolonged by the catheter ablation mainly due to prolongation of AH interval and partially HV interval combined some QRS morphologic changes. This finding is compatible with AV conduction delay rather than the ablation of septal BT for the prolongation of PR interval. Para-Hisian pacing could be helpful for differentiation between septal BT and delay conduction by HCM. Additionally, atriofascicular, nodofascicular/ventricular or fasciculoventricular BT should be differentiated [4].