Pitfalls in programming “LV only” mode in left bundle branch area pacing

A 67‐year old female patient with nonischemic cardiomyopathy and wide (180ms) left bundle branch block (LBBB) and reduced ejection fraction (EF) < 35% despite optimal medical treatment was referred for cardiac resynchronization therapy (CRT). CRT was achieved by left bundle branch area pacing (LBBAP), using a stylet‐driven pacing lead (SoliaS60; Biotronik) in a deep septal position and dedicated delivery sheath (Selectra3D; Biotronik). With LBBAP, unipolar paced QRS revealed a stimulus‐to‐end QRS duration of 145ms with clear R' wave in lead V1 and short left ventricular activation time (Figure 2A). The LBBAP lead was connected to the left ventricular (LV) port of the internal cardioverter defibrillator (ICD) device (Biotronik Acticor 7 HF‐T) and a “LV only” pacing mode was programmed, with a fixed short atrioventricular (AV) delay of 100ms. One month later, interrogation of the device showed the presence of frequent ventricular sensed intervals at ventricular fibrillation (VF) detection rates (Figure 1). In the current report we discuss this particular phenomenon and highlight potential pitfalls when programming devices for LBBAP.