Failure to shock: What is the mechanism?

BACKGROUND The Biotronik DX lead is an attractive option due to its floating atrial bipole and its noninferiority compared to dual-chamber defibrillators. METHODS We describe the case of atrial undersensing by the DX lead resulting in failure of the device to appropriately treat a slow ventricular tachycardia. CONCLUSION This case underlies the importance of understanding the limitations to each lead technology as well as the underlying assumptions inherent to detection enhancement algorithms.