Left atrial far-field sensing by left ventricular leads: a potential hazard in cardiac resynchronisation therapy.

Background: Cardiac resynchronisation therapy (CRT) requires a lead advanced through the coronary sinus (CS) to pace the left ventricle (LV). Left atrial far-field signals (LAFFS) may be sensed by the LV lead at the time of implant or after lead dislodgement, and may inhibit ventricular pacing.
Objective: To assess the incidence of detection of LAFFS > 2 mV and its correlation with the CS lead position.
Methods: Data from the first 75 consecutive patients enrolled in the InSync III multicentre study were analysed. The position of the LV lead was recorded at implant. During follow-up, pacing was temporarily inhibited and the LV channel electrogram was recorded. The amplitude of LAFFS observed before discharge from the hospital and at 1 month of follow-up was retrospectively analysed. A LAFFS > 2 mV was considered clinically significant.
Results: CRT systems were successfully implanted in 71 of 75 patients. A LAFFS > 2 mV was recorded by the LV lead channel in six of 71 patients (8.5%). This phenomenon developed between hospital discharge and 1 month of follow-up in two of these patients and in one case disappeared within 1 month. It was observed in all CS tributaries except the anterior and mid-cardiac veins.
Conclusions: Left atrial far-field signals sensed by the LV lead were not rare. Implanting physicians should be aware of this phenomenon in order to prevent potentially serious complications.