We appreciate the interest and comments of Morales Martínez de Tejada and Elduayen Gragera regarding our report.1 The fact that the series described includes 2 patients who, despite being in sinus rhythm at baseline, underwent implantation of a single-chamber pacemaker is not exceptional in clinical practice. In fact, in the 2014 Spanish Pacemaker Registry,2 23.6% of the patients with atrioventricular block and sinus rhythm received a VVI pacemaker, and factors like patient age and comorbidities proved to be determining factors. About the development of atrial fibrillation secondary to VVI pacing, this relationship is not well-established. In fact, data from the United Kingdom Pacing and Cardiovascular Events (UKPACE) trial showed that, in elderly patients with high-grade atrioventricular block, the pacing mode (single-chamber or dual-chamber) did not influence mortality or cardiovascular events during follow-up. Moreover, a higher incidence of atrial fibrillation was observed in the dual-chamber group during the first 18 months after implantation,3 although other authors have reported the opposite.4
Finally, it should be noted that in no patient was biventricular pacing indicated at the time of implantation, and the threshold and R wave were adequate during follow-up in all patients. In view of the known tendency of the threshold and R wave to improve after implantation, as shown by the results of the Micra Transcatheter Pacing trial5 and confirmed during follow-up,1 a somewhat less than ideal threshold or R wave at implantation did not call for the repositioning of the device.
CONFLICTS OF INTERESTM. Pachón is a proctor for the Medtronic Micra system and M.A. Arias is an Associate Editor of Revista Española de Cardiología.