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Objective: Leadless pacemakers (LPs) were designed to avoid complications associated with transvenous pacing. To minimise risk of perforations, there is preference towards implanting LPs into the septum rather than the apex or free wall. An objective yet feasible way of characterising the LP location is currently lacking. We report a simple radiological method of defining LP position and our analysis of the impact of implantation site on performance of LPs. Methods: The first 100 LPs implanted at our UK centre were reviewed and the devices’ positions in fluoroscopy images and X-rays based on conventional criteria for lead positions and conventional practice for LPs positioning were assessed. The devices’ electrical parameters at implant and at the latest device follow-up were used to compare performance between implantation sites. Results: 35.6% of implants were in the apex. 31.1% in mid-septum, 16.7% in apical septum, 15.5% on the septal right ventricular inflow and 1.1% in the septal RV outflow tract. We had no major complications. Thresholds, R-wave amplitudes, and impedance averaged at 0.67 ± 0.41 V, 10.64 ± 5.30 mV, and 777.67 ± 201.67 Ohms, respectively, at the time of implantation, and 0.66 ± 0.39 V, 14.08 ± 6.14 mV, and 564.29 ± 96.76 Ohms at the last device check. There was no difference in the pacing thresholds or impedance between implant sites. Conclusions: We propose a simple, reproducible way of defining the LP location which can help standardise the assessment of the device location sites across LP implantation centres. Advances in knowledge: Emphasis on the safety and reliability of the leadless pacemakers in a real-world setting. Establishing the variation in the implantation sites for leadless pacemakers and reporting the effect of the implantation sites on the devices’ performance. We propose a simple, reproducible way of defining the LP location which can help standardise the assessment of the device location sites across LP implantation centres.

Guidelines recommend that cardiac pacing should be considered in patients suffering from frequent vasovagal syncopal (VVS) episodes. Studies have demonstrated the safety and efficacy of leadless pacemakers (LP) in cardioinhibitory vasovagal populations specifically, rendering them a reasonable alternative to transvenous pacing in these patients. However, due to the paucity of data on extraction and the number of concomitant LPs that can be safely implanted, there are concerns regarding LPs' battery longevity, especially in younger patients who may require decades of pacing therapy.This is a retrospective analysis of the first 100 LPs implanted at a tertiary cardiac centre in the UK. Demographical data and device parameters at implant and follow-ups were obtained from the hospital's medical records. The battery life of the LPs in the VVS patients was compared to that of patients with other pacing indications.Ninety patients were included in the analysis. 14 patients (15.6%) had VVS, and 76 patients (84.4%) had other indications for pacing. Mean ages were 34 ± 13 years and 62 ± 20 years for the VVS and the other group, respectively. The estimated total battery life was 15.22 ± 0.35 and 13.65 ± 2.97 years in the VVS and the other indications group respectively (p = .04). There were no complications in the VVS group.LPs provide a promising treatment for patients with vasovagal syncope with reassuring battery performance at the short/intermediate term. Further longer-term follow-up data are needed to identify the true battery potential in this patient cohort.

Background A major predictor of eligibility of subcutaneous implantable cardiac defibrillators (S-ICD) is the T:R ratio. The eligibility cut-off of the T:R ratio incorporates a safety margin to accommodate for fluctuations of ECG signal amplitudes. We introduce a deep learning-based tool that accurately measures the degree of T:R ratio fluctuations and explore its role in S-ICD screening. Methods Patients were fitted with Holters for 24 h to record their S-ICD vectors. Our tool was used to assess the T:R ratio over the duration of the recordings. Multiple T:R ratio cut-off values were applied, identifying patients at high risk of T-wave oversensing (TWO) at each of the proposed values. The purpose of our study is to identify the ratio that recognises patients at high risk of TWO while not inappropriately excluding true S-ICD candidates. Results Thirty-seven patients (age 54.5 + / − 21.3 years, 64.8% male) were recruited. Fourteen patients had heart-failure, 7 hypertrophic cardiomyopathy, 7 had normal hearts, 6 had congenital heart disease, and 3 had prior inappropriate S-ICD shocks due to TWO. 54% of patients passed the screening at a T: R of 1:3. All patients passed the screening at a T: R of 1:1. The only subgroup to wholly pass the screening utilising all the proposed ratios are the participants with normal hearts. Conclusion We propose adopting prolonged screening to select patients eligible for S-ICD with low probability of TWO and inappropriate shocks. The appropriate T:R ratio likely lies between 1:3 and 1:1. Further studies are required to identify the optimal screening thresholds.

Background Patients with an existing subcutaneous implantable cardiac defibrillator (S-ICD) may develop a pacing indication. When transvenous pacing is not feasible, combining an S-ICD and a leadless pacemaker (LP) can be a reasonable option. There are reports of concomitant use of both devices. However, the effect of pacing on the S-ICD sensing is not well studied. We hypothesise that pacing changes R and T-wave amplitudes, causing changes in R:T ratios as perceived by a S-ICD, increasing the risk for T wave oversensing (TWO) during paced rhythm with a subsequent risk of inappropriate shocks. Methods This is a prospective study in patients undergoing electrophysiological studies. Participants were fitted with a Holter®, and the leads were placed to correspond to the vectors of an S-ICD. The right ventricle was paced at four positions for 10 beats each at 8 mA/2 ms. The Holter® traces were analysed, using two-way analysis of variance (ANOVA) to assess the effect of pacing on the R:T ratio. Results Forty-seven patients (age 56.02 ± 16.02, 72% male) were enrolled (81% structurally normal heart, 15% dilated cardiomyopathy, 2% ischaemic cardiomyopathy, and 2% adult congenital heart disease). Age, sex, and aetiology had no effect on the R:T ratio. Pacing caused significant changes in the R:T ratio. There was no significant difference in the R:T ratios between the pacing sites (p Conclusions Pacing alters the R:T ratio significantly in most patients, theoretically increasing the risk for TWO and inappropriate shocks. Tailored programming for both devices is important for concomitant use of LPs and S-ICDs.

A major predictor of eligibility of subcutaneous implantable cardiac defibrillators (S-ICD) is the T:R ratio. The eligibility cut-off of the T:R ratio incorporates a safety margin to accommodate for fluctuations of ECG signal amplitudes. We introduce a deep learning-based tool that accurately measures the degree of T:R ratio fluctuations and explore its role in S-ICD screening.Patients were fitted with Holters for 24 h to record their S-ICD vectors. Our tool was used to assess the T:R ratio over the duration of the recordings. Multiple T:R ratio cut-off values were applied, identifying patients at high risk of T-wave oversensing (TWO) at each of the proposed values. The purpose of our study is to identify the ratio that recognises patients at high risk of TWO while not inappropriately excluding true S-ICD candidates.Thirty-seven patients (age 54.5 + / - 21.3 years, 64.8% male) were recruited. Fourteen patients had heart-failure, 7 hypertrophic cardiomyopathy, 7 had normal hearts, 6 had congenital heart disease, and 3 had prior inappropriate S-ICD shocks due to TWO. 54% of patients passed the screening at a T: R of 1:3. All patients passed the screening at a T: R of 1:1. The only subgroup to wholly pass the screening utilising all the proposed ratios are the participants with normal hearts.We propose adopting prolonged screening to select patients eligible for S-ICD with low probability of TWO and inappropriate shocks. The appropriate T:R ratio likely lies between 1:3 and 1:1. Further studies are required to identify the optimal screening thresholds.

Introduction: Patients with an S-ICD may develop a pacing indication. When transvenous pacing is not feasible, the combination of an S-ICD and a leadless pacemaker (LP) might be a sound option. There are increased reports of concomitant use of LPs and S-ICDs. However, the effect of pacing on the S-ICD sensing is not well studied. Hypothesis: We hypothesize that pacing changes R and T waves morphology and amplitudes, causing changes in R:T ratios perceived by an S-ICD, increasing the risk for T wave oversensing (TWO) during paced rhythm with a subsequent risk of inappropriate shocks. Methods: We ran a prospective study in patients undergoing an electrophysiological study on clinical grounds. Participants were fitted with a Holter®, the leads of which placed to correspond to the three vectors of an S-ICD. We used a standard catheter to pace the right ventricle at four positions (figure 1) for 10 beats each at 8mA/2ms. We analysed the Holter® traces and used two-way ANOVA to assess the effect of pacing on the R:T ratio. Results: A total of 47 patients (mean age 56.02 ± 16.02,72% male) were enrolled (81% structurally normal heart, 15% DCM, 2% ICM, and 2% congenital heart disease). Age, sex, and aetiology had no effect on the R:T ratio. Pacing caused significant decrease in the R/T ratio, but there was no significant difference in the R/T ratio between different pacing sites. (P Conclusions: Pacing- regardless of position- causes the S-ICD perceived R:T ratio to fall below the eligibility screening threshold in most patients, increasing the risk of TWO and inappropriate shocks. Caution needs to be exercised and tailored programming of both devices is key for concomitant use of LPs and S-ICDs.