@article {Lillo-Castellano1662, author = {J M Lillo-Castellano and Manuel Marina-Breysse and Alfonso G{\'o}mez-Gallanti and J B Mart{\'\i}nez-Ferrer and Javier Alzueta and Luisa P{\'e}rez-{\'A}lvarez and Arcadi Alberola and Ignacio Fern{\'a}ndez-Lozano and Anibal Rodr{\'\i}guez and Rosa Porro and Ignacio Anguera and Adolfo Fontenla and J J Gonz{\'a}lez-Ferrer and Victoria Ca{\~n}adas-Godoy and Nicasio P{\'e}rez-Castellano and Daniel Gar{\'o}falo and {\'O}scar Salvador-Monta{\~n}{\'e}s and Conrado J Calvo and Jorge G Quintanilla and Rafael Peinado and Inmaculada Mora-Jim{\'e}nez and Juli{\'a}n P{\'e}rez-Villacast{\'\i}n and J L Rojo-{\'A}lvarez and David Filgueiras-Rama}, title = {Safety threshold of R-wave amplitudes in patients with implantable cardioverter defibrillator}, volume = {102}, number = {20}, pages = {1662--1670}, year = {2016}, doi = {10.1136/heartjnl-2016-309295}, publisher = {BMJ Publishing Group Ltd}, abstract = {Objective A safety threshold for baseline rhythm R-wave amplitudes during follow-up of implantable cardioverter defibrillators (ICD) has not been established. We aimed to analyse the amplitude distribution and undersensing rate during spontaneous episodes of ventricular fibrillation (VF), and define a safety amplitude threshold for baseline R-waves.Methods Data were obtained from an observational multicentre registry conducted at 48 centres in Spain. Baseline R-wave amplitudes and VF events were prospectively registered by remote monitoring. Signal processing algorithms were used to compare amplitudes of baseline R-waves with VF R-waves. All undersensed R-waves after the blanking period (120 ms) were manually marked.Results We studied 2507 patients from August 2011 to September 2014, which yielded 229 VF episodes (cycle length 189.6{\textpm}29.1 ms) from 83 patients that were suitable for R-wave comparisons (follow-up 2.7{\textpm}2.6 years). The majority (77.6\%) of VF R-waves (n=13953) showed lower amplitudes than the reference baseline R-wave. The decrease in VF amplitude was progressively attenuated among subgroups of baseline R-wave amplitude (>=17; >=12 to \<17; >=7 to \<12; >=2.2 to \<7 mV) from the highest to the lowest: median deviations -51.2\% to +22.4\%, respectively (p=0.027). There were no significant differences in undersensing rates of VF R-waves among subgroups. Both the normalised histogram distribution and the undersensing risk function obtained from the >=2.2 to \<7 mV subgroup enabled the prediction that baseline R-wave amplitudes <=2.5 mV (interquartile range: 2.3{\textendash}2.8 mV) may lead to >=25\% of undersensed VF R-waves.Conclusions Baseline R-wave amplitudes <=2.5 mV during follow-up of patients with ICDs may lead to high risk of delayed detection of VF.Trial registration number NCT01561144; results.}, issn = {1355-6037}, URL = {https://heart.bmj.com/content/102/20/1662}, eprint = {https://heart.bmj.com/content/102/20/1662.full.pdf}, journal = {Heart} }