Acute pacing threshold elevation during simultaneous l0eadless pacemaker implantation and atrioventricular node ablation

BACKGROUND In patients with refractory atrial fibrillation (AF) rate control strategy, atrioventricular node (AVN) ablation and permanent pacemaker implantation is recommended. The Micra Transcatheter Pacing System (TPS) is a single chamber leadless pacemaker implanted from the femoral vein and thus offers the possibility of AVN ablation in the same procedure. Here, we describe two cases of acute Micra TPS ventricular pacing threshold elevation immediately following radiofrequency AVN ablation at distance from the TPS requiring device retrieval and re-implantation of new Micra systems. METHODS AND RESULTS All consecutive patients with a Micra TPS implantation, at a single center, from November 2014 to March 2020, were analyzed retrospectively (n=56). Among them, 36% had a prior complication from a transvenous implant and in 16% lead extraction was performed concurrently with the TPS implantation. A total of ten patients (18%) underwent AVN ablation within the same procedure. Among them, two (20%) presented acute increase in the right ventricular pacing threshold after radiofrequency delivery requiring retrieval of the initial TPS and deployment of a new device. The first case was a 48 years-old man with previous heart transplantation. A Micra TPS was implanted in a mid-septal position (threshold 0,5 Volts x 0,24 milliseconds; impedance 800 Ohms; correct pull and hold test). To obtain a complete atrioventricular block, a retrograde arterial approach with an 8 mm nonirrigated catheter (60 degrees Celsius for 294 seconds) was required. After RF delivery, a loss of capture was observed. The second case included a 69 years-old woman. The TPS was implanted at an apico-septal position (Threshold 0,75 Volts x 0,24 milliseconds; impedance 720 Ohms; correct pull and hold test). The AVN ablation was achieved (52 degrees Celsius for 136 seconds) with a 4 mm nonirrigated catheter. Immediately, a threshold elevation >2 Volts x 0,24 milliseconds was observed. In both cases, continuous fluoroscopic control confirmed no direct interaction between the ablation catheter and the TPS. The device was successfully recaptured, and a new leadless PPM was immediately implanted with good results in these two cases. CONCLUSION We described two cases of acute threshold elevation during a combined procedure of TPS implantation and AVN ablation. This complication was not reported in series assessing safety of combining AVN ablation and Micra TPS implantation. We hypothesize a possible shunt of current to the distal electrode. An in vitro study is currently underway to explain the mechanism of indirect interaction between radiofrequency delivery and Micra TPS dysfunction.