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Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): BIOTRONIK, Berlin, Germany Introduction A single-lead implantable cardioverter-defibrillator (ICD) with atrial sensing dipole (the DX ICD system) can potentially give additive information concerning atrial diagnostics in patients requiring only a single-chamber ICD. We therefore report the real-world experience from large DX registry on implantation, atrial signal quality and detection and the long-term stability of the atrial signal. Methods The prospective, single-arm MATRIX (Management and Detection of Atrial Tachyarrhythmias in Patients Implanted With BIOTRONIK DX Systems, NCT01774357) registry study effectively enrolled 2041 patients at 119 sites in 24 countries. All patients had a DX system implanted for a single-chamber ICD indication for primary or secondary prevention of sudden cardiac death. Patients were followed for 24 months including remote monitoring. Implantation and follow-up data are reported for the whole patient set. For the analyses on atrial sensing amplitude values, remotely transmitted device measurements of patients without history of long-standing persistent or permanent AF at baseline were used. Results The mean follow-up period was 677±173 days. Implantation took place at 15±22 days before enrollment. Baseline and implantation data are shown in the table. Implantation procedure and lead insertion were rated as "easy" or "very easy" in 91.0% and 96.3% of assessments, respectively. At implantation, the investigators rated the quality of the atrial sensing amplitude as "sufficient" in 97% of the assessed cases. At enrollment (12-month/24-month follow-up), the atrial signal quality and detection were rated as "good" or "excellent" in 92.3% (89.8%/89.9%) and 92.4% (90.1%/91.3%) of assessments, respectively. For 1841 patients (90.2%), remotely transmitted device information was received. The median (mean ± SD, IQR) transmission rate was 92.5% (85.4±18.2%, 81.4-97.3%). 1746 patients (85.5%) matched the inclusion criteria for the quantitative analyses on atrial sensing. 95.6% of available RA sensing amplitude values were ≥1 mV. Based on each patient’s overall median value, the median (mean ± SD, IQR) RA sensing amplitude was 4.6 mV (4.4±2.0 mV, 2.8-6.2 mV). The time course of patient median values stratified by month is shown in the figure. Conclusion The study followed 2041 patients implanted with the DX ICD system for two years. In the vast majority of cases, investigators rated implantation as (very) easy and the atrial signal over 24 months as good/excellent. According to daily, automatic Home Monitoring data, the overall mean P-wave amplitude remained stable throughout the whole follow-up. The MATRIX study demonstrated functionality and clinical utility of the DX concept in an unselected, real-life setting.

Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): BIOTRONIK, Berlin, Germany Introduction Device-detected atrial high-rate episodes (AHRE) and their burden progression are associated with an increased risk for thromboembolic events in correlation with CHA2DS2-VASc score and AHRE burden. To allow timely initiation of anticoagulation therapy for the prevention of stroke, the European guidelines on atrial fibrillation (AF) recommend the monitoring of AHRE progression along pre-specified strata (6min… Methods From the MATRIX (Management and Detection of Atrial Tachyarrhythmias in Patients Implanted With BIOTRONIK DX Systems) registry, we analyzed remotely transmitted, and electrogram (IEGM) AHREs in a subset of patients with remote transmissions and without history of long-standing AF at baseline. For each patient, we selected the first occurring episode per duration stratum and the first subsequent occurrence when progressing to a stratum of any longer duration. After episode adjudication by an independent electrophysiologist, we assessed the classification performance of the device (positive predictive value [PPV]) and analyzed AHRE onset and progression pathways. Results Of the MATRIX cohort, 1,746 patients matched the inclusions criteria (see table for patient characteristics) and 1,451 had no AF history. Of the 258 patients with AHREs (14.8%), 450 out of 465 evaluated episodes were correctly classified as AHRE. Reasons for misclassification were artifact (13) and R-wave oversensing (2). PPV was 96.8% (95% confidence interval 94.7%-98.2%). Grouped by stratum, PPV was 93.9%, 99.5% and 100% for 6min… Discussion and Conclusion: The single-chamber ICD with atrial sensing capabilities correctly classified ≈97% of all adjudicated AHREs ≥6min. About 7% of patients had device-detected AHRE onset and/or progression and a mid to high stroke risk. These patients would potentially benefit the most from a guideline-conform AF monitoring strategy to timely initiate anticoagulation medication for stroke prevention.

Funding Acknowledgements Type of funding sources: None. Background Arrhythmias in elderly patients (pat) are common. In this subset of pat, atrial fibrillation is by far the most frequent sustained arrhythmia but not the only one. Clinical, ECG and electrophysiological (EP) features of AV-nodal reentrant tachycardia (AVNRT) have rarely been described in the elderly, and this represents the aim of the current study. Methods At 2 EP-centres in Germany, data from all pat undergoing an EP-study (EPS) and diagnosed with AVNRT between January 2018 and May 2021 were collected and analysed. Pat > 65 years constituted the study population. Results During the study period AVNRT was diagnosed in a total of 329 pat. 93 pat (28%) were > 65 years and represent the study population [median age 74 (65-89) years, 48% female]. In the majority (85%), the duration of symptoms was short (< 1 year), 14 pat had symptoms of paroxysmal tachycardia for longer than 10 years. Most of the pat (n=88, 94%) had at least one ECG-documentation. In SR, the PR interval was relatively long [median 180 (120-380) ms)]. In 84% of pat, sustained AVNRT [median cycle length (CL) 400 (270-800) ms] was induced during EPS. In the remaining pat, at least 2 typical AV-nodal-echo beats were induced. Slow pathway (SP) ablation/modification was performed in all but one patient presenting with a very long baseline PR-interval, low antegrade Wenckebach-point (WP) and very slow AVNRT. In this case, the pat was treated with ß-blocker after pacemaker (PM) implantation. In 3 additional pat, PM implantation was necessary after ablation due to intermittent high-degree AV-block. In comparison to the rest of the study population, these four pat had a longer baseline PQ interval [median 275 (IQR 248- 303) ms vs. 180 (IQR 160- 192) ms], a longer baseline AH interval [median 207ms (IQR 185- 234) ms vs. 95 (IQR 80- 107) ms], a lower baseline antegrade WP CL [median 510 (IQR 435- 645) vs. 390ms (IQR 355- 470) ms], and a longer tachycardia CL [TCL 557 (IQR 454- 661) ms vs. 400 (IQR 364- 443) ms; p value Discussion Elderly pat also have AVNRT, there are a slight differences in physiology (i.e. relatively long baseline PR-interval and TCL, likely due to changes of the conduction system with aging), and as in young pat, ablation is curative treatment with similar (low) complication rate. A subset of pat, characterized by longer PR- and AH-intervals, lower WP and longer TCL may be at higher risk for AV-block after SP modification. Whether this is due to pre-existing damage or to posterior location of the FP remains unknown. SP ablation is safe and effective even in elderly pat. In pat presenting with EP characteristics presumptive of a baseline impairment of the conduction properties of the FP, ablation of the FP could be attempted to avoid postprocedural high degree AV block.