A 32-year-old woman presented with a history of palpitations over the prior 7 days. Twelve-lead ECG indicated an irregular, wide QRS complex tachycardia with a left bundle branch block (LBBB) morphology and a late precordial R/S transition. Two attempts of electrical cardioversion of 200 J failed to restore sinus rhythm, and the administration of intravenous amiodarone slowed but failed to terminate the arrhythmia. Because the tachycardia was incessant, urgent catheter ablation was planned. Using a three-dimensional electroanatomic mapping system (CARTO 3), the site of the earliest local ventricular activation was found in mid-anteroseptal region of the right ventricle. Here, the right bundle branch (RBB) potentials were slightly earlier than the ventricular activation. Intra-cardiac electrocardiograms demonstrated that the RBB potentials precede the earliest ventricular activation, and the His potentials lag behind the right ventricle apical activation during tachycardia. This activation sequence of RBB–V–His ruled out the possibility of BBR or junctional rhythm with LBBB because these rhythms should have a His–RBB–V activation pattern. Ablation at the site of the earliest RBB potential activation terminated the tachycardia with subsequent sinus rhythm and complete RBB block morphology, supporting that this arrhythmia was of RBB origin.
The full-length version of this report can be viewed at: http://www.escardio.org/Guidelines-&-Education/E-learning/Clinical-cases/Electrophysiology/EP-Case-Reports.
Author notes
The first two authors contributed equally to the study.
