Despite technologic improvement in lead manufacturing, long-term increase of the RVPT occurs in about 13% of patients, possibly representing a serious safety issue in 3.7% when 2.5 V at 0.4 ms is exceeded. AVC algorithms can improve patients' safety by automatic tailoring of the pacing output to threshold fluctuations, while maximizing device longevity.

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Funding Acknowledgements Type of funding sources: None. Background Implantable cardioverter defibrillator (ICD) is an effective therapy for sudden cardiac death (SCD). 2015 HRS/EHRA/APHRS/SOLAECE expert consensus document suggests long VT detection, above 185 bpm, as optimal ICD programming to reduce unnecessary therapies in primary prevention (PP). Purpose The aim of our study is to evaluate incidence, safety and efficacy of ICD treatment for VT arrhythmias below 185 bpm, in a contemporary population of PP ICD recipients with long detection intervals (LDI), morphological discrimination algorithm and antitachycardia pacing therapies (ATP) before shock. Methods We conducted a single centre retrospective study enrolling 236 patients implanted with a primary-prevention indication from January 2013 to June 2019. Patients were implanted with single or dual chamber single-lead transvenous ICD. All patients had standard device setting with long (at least 20 s in VT and 7 s in VF) VT/VF detection above 150 bpm and therapies starting from 171 with up to 5 ATP and multiple shocks. PainFREE-like bursts and Schaumann-like ramps ATP were always set in VT zone. Of each patient we collected a detailed report of up to five appropriate events and three inappropriate events. Arrhythmia diagnosis was confirmed from 3 independent expert physicians.  Date of the event, cycle length, type of morphology (polymorphic or monomorphic), therapies with their effect were collected. Results During a mean follow-up of 42 months, 47 (20 %) and 18 (8%) patients had at least one appropriate and inappropriate activation, respectively. The detailed-events analysis shows that 16 (7%) patients had 38 (30%) appropriate events with rate <188 bpm. At these rate ATP were 97% effective. 14 (38%) of inappropriate activations were caused by arrythmias with ventricular rate below 188 bpm and half of these received a shock; 30% of inappropriate shocks were due to arrhythmia with rate <188 bpm. 73% of treated events, with rate <188 bpm, were appropriate. Only 5.6% (n = 10) of ATP attempts cause arrhythmia acceleration. Conclusions One third of detected arrhythmias had a rate below 188 bpm and 73% were true VT. In this slow VT zone, ATP had a high success rate with low percentage of acceleration.

Funding Acknowledgements Type of funding sources: None. Background Arrhythmogenic Cardiomyopathy (ACM) is an inherited cardiomyopathy characterized by ventricular arrhythmias and sudden cardiac death. Implantable cardioverter defibrillator (ICD) remains the only proven therapy to reduce mortality in ACM. Purpose The objective of this study was to identify characteristics of ventricular arrhythmias and treatment in patients with ACM. Method Retrospective analysis of the data of consecutives patients with confirmed diagnosis of ACM based on the proposed Padua Criteria, who underwent implantation of transvenous ICD from January 1992 and October 2021. The clinical data and information about appropriate and inappropriate ICD therapies were obtained from medical records with the review of the available intra-cardiac electrograms (EGMs). Results We enrolled 52 patients (69% males, mean age at implant 48.9 ±14.8 years), 27 (52%) were implanted for primary prevention, 25 (48%) for secondary prevention. After a median follow-up of 7.52 years [IQR: 4.37 - 12.0], 32 patients (61.5%) had 914 sustained episodes of ventricular arrhythmias (VA). 25 patients (48%) had 309 episodes of life-threatening arrhythmias (LT-VA), defined as sustained ventricular tachycardia ≥200 beats/min. In 29/32 patients (91%) ATP treated at least one episode of VA and in 14/25 (56%) at least one episode of LT-VA. Ventricular tachycardia (VT) detection was programmed at least 20 seconds, while VF detection was at least 7 seconds. Among patients with appropriate ICD activation, the first treated episode was a LT-VA in 50% of cases. Out of 914 VA episodes, 735 (80.4%) were treated with ATP and 179 (19.6%) with shocks. Considering LT-VA (cycle length 248 ± 25 ms), 201/309 (65%) and 108/309 (35%) episodes were treated with ATP and shocks, respectively. In 13 patients (25%) there was an inappropriate ICD activation, mostly caused by atrial fibrillation, while in 8 patients (15%) there was a complication needing reintervention (in 3 cases there was a loss of ventricular sensing dictating lead revision). Conclusions ACM patients are at risk of VA and LT-VA. The majority of VA at follow-up are monomorphic at rate <200 beats/minute, however the first treated VA episode is a LT-VA in half of cases. ATP is highly successful in terminating VT and even LT-VA, which questions the use of non-transvenous ICD in this young patient population. Nevertheless, transvenous ICDs are burdened by a relevant rate of lead complications which should be weighed in the choice of the ICD type.