Figure 1 Panel A - Recordings of 4 surface leads and intracardiac electrograms from the distal poles of an irrigated tip ablation catheter (Coolflex, St Jude's Medical, MN, USA) placed at the right ventricular apex (RVA). The predominant RBBB-like escape beats were interspaced with intermittent LBBBlike beats. Over a period of 2 minutes recording the coupling interval between RBBB-like to LBBB-like beats varied closely from 698-801ms. No fusion beats were observed. Panel B – the ablation catheter has been moved to a right ventricular septal position. In this position the intermittent LBBB-like beats were completely suppressed but a local non-propagating deflection was recorded (arrow). Over a period of 2 minutes recording the coupling interval between RBBB-like to the non-propagating signal varied from 660-773ms.