Pacemaker upgrade causing new-onset heart failure in a patient with complete congenital atrioventricular block.

For infants with congenital complete atrioventricular block (CCAVB), the choice of pacing modalities is limited. Due to their size and surgical limitations, neonates typically start with an epicardial right ventricular pacing system, then upgrade to right-sided dual-chamber pacing once appropriate size is achieved. These modes are generally well tolerated. However, the reported case involved a patient with CCAVB who paradoxically experienced congestive heart failure after upgrading to a dual-chamber system, a theoretically superior pacing modality. With conversion to biventricular pacing, a relatively new modality for adults with very little pediatric experience to date, the patient's symptoms dramatically improved.