Very high pacing thresholds during long‐term follow‐up predicted by a combination of implant pacing threshold and impedance in leadless transcatheter pacemakers

Abstract

Background Micra transcatheter pacemaker system (TPS) usually achieves low implant pacing threshold (IPT). However, IPT may increase in some patients during follow‐up. Aim To apply implant parameters in predicting long‐term occurrence of very high pacing threshold (VHPT) in patients with Micra‐TPS. Methods A cohort of 110 consecutive patients implanted with a Micra‐TPS from 2014 to 2018 was evaluated at discharge and at 1, 12, 24, 36, and 48 months follow‐up. VHPT was defined as greater than 2 V/0.24 ms. VHPT predictors were identified. Results Micra‐TPS was implanted successfully in 108 patients (98.2%). During a mean follow‐up of 24 ± 16 months, 18 patients (16.7%) died of causes nonpacemaker‐related, and 4 (3.8%) developed VHPT. Patients with VHPT had higher IPT and lower implant impedance than patients with non‐VHPT: 1 ± 0.31 vs 0.55 ± 0.29 V/0.24 ms (P = .003) and 580 ± 59 vs 837 ± 232 Ω (P = .03), respectively. IPT and impedance had excellent discriminative power to predict VHPT (area under the curve: 0.85 ± 0.07 and 0.91 ± 0.05, respectively). Negative predictive value (NPV) of IPT ≤ 0.5 V/0.24 ms was 100%; positive predictive value (PPV) was 8% throughout follow‐up. Implant impedance ≤ 600 Ω had NPV of 99% throughout follow‐up, whereas PPV varied: 16%, 21%, 16%, and 28% at 1, 12, 24, and 36 months, respectively. Sequential combination of IPT greater than 0.5 V/0.24 ms and impedance ≤ 600 Ω improved PPV to 25%, 35%, 27%, and 44%, respectively, whereas NPV remained 99% throughout follow‐up. Conclusion Despite favorable long‐term electrical performance of Micra‐TPS, a small percent of patients developed VHPT during follow‐up. A sequential combination of IPT and impedance could allow the implanter to identify patients who will develop VHPT during long‐term follow‐up.

Predictors of increase in pacing threshold after transcatheter pacing system implantation due to micro‐dislodgement

“…While it was expected that impedance at the time of implantation would function as a predictive factor for the altered threshold status, it was also observed that the pacing threshold at the time of implantation served as a predictor in which it tended to be low if the device was well anchored. This finding is similar to a report by Tolosana et al, who showed that impedance and threshold at the time of implantation play important roles in achieving a pacing threshold of ≤2.0 V/0.24 ms 7 …”

“…This finding is similar to a report by Tolosana et al, who showed that impedance and threshold at the time of implantation play important roles in achieving a pacing threshold of ≤2.0 V/0.24 ms. 7 We observed that the pacing threshold improved in the majority of cases in the IPT group, while a higher threshold was maintained in a few cases. This may be due to fixation and adhesion of the dislodged device.…”

“…Most of the rapid increases in pacing threshold occur within 1 month of implantation, but there are few cases where the threshold increases in the medium-to-long term. [7][8][9] Therefore, we hypothesized that it is possible to obtain an SPT in the long term if increase in threshold is prevented in the short term.…”

“…Predictors that require long‐term high pacing thresholds have been reported, 6 but the cause of increased thresholds after implantation has not been clarified. Most of the rapid increases in pacing threshold occur within 1 month of implantation, but there are few cases where the threshold increases in the medium‐to‐long term 7–9 . Therefore, we hypothesized that it is possible to obtain an SPT in the long term if increase in threshold is prevented in the short term.…”

Leadless pacemaker: State of the art and incoming developments to broaden indications

“…In Micra patients with an IPT of >1 to 2 V, approximately three‐quarters or more had an optimal threshold (≤1 V) by 6 months. However, if the IPT is ≥2 V, clinicians should strongly consider recapturing and redeploying the device, since an IPT of >2V was associated with VHPT in almost half of the patients at 6 months 49 . IPT ≤0.5 V/0.24 ms ensured a stable threshold during follow‐up.…”