Entrainment mapping of a concealed nodoventricular accessory pathway in a man with complete heart block and tachycardia-induced cardiomyopathy

True nodoventricular (NV) accessory connections, as originally described by Mahaim, are rare entities, with the majority of previously reported cases now recognized as being due to decremental atriofascicular pathways. Here, we present a patient with incessant narrow and wide QRS complex tachycardia occurring in the setting of prior complete heart block. Entrainment mapping proved useful in diagnosing orthodromic reentry utilizing a concealed right septal NV pathway. The patient was successfully treated with radiofrequency ablation, resulting in a marked improvement in left ventricular function.