Atrial pacing may prevent the onset of atrial fibrillation through the following mechanisms: a) prevention of the relative bradycardia that triggers paroxysmal AF; b) prevention of the bradycardia-induced dispersion of refractoriness; c) suppression or reduction of premature atrial contractions

that initiate the re-entry and predispose to AF; and d) preservation of atrio-ventricular synchrony, which may prevent switch-induced changes in atrial repolarization, predisposing to AF (40, 41). APP algorithm adapts the atrial pacing rate to a value slightly higher than the intrinsic Inhibitors,research,lifescience,medical sinus rate; this can result in suppression and/or prevention of atrial ectopy favorably modifying the arrhythmogenic substrate. Previous studies, though based on short term follow- up data, have shown that APP is an efficacy algorithm for preventing paroxysmal Inhibitors,research,lifescience,medical AF in DM1 patients implanted with dual-chamber PM for atrioventricular VEGFR inhibitor conduction disorders (12, 13). Our study further

shows that APP may significantly reduce the atrial fibrillation Inhibitors,research,lifescience,medical burden in DM1 patients, regardless of the site of atrial stimulation (Backmann’s bundle or right atrial appendage). This effect can be explained by the high percentage of atrial pacing, warranted by atrial overdrive algorithm, that may prevent the relative bradycardia and reduce the number of premature atrial contractions, causing the reentry and predisposing Inhibitors,research,lifescience,medical to AF. However a more extensive study, including a greater number of patients will confirm these preliminary data. Conclusions Heart blocks and supraventricular arrhythmias are an integral part of the clinical picture of myotonic dystrophies. Implantation of a pacemaker (PM) is the only possibility to prevent cardiac sudden death, while atrial Inhibitors,research,lifescience,medical pacing seems to prevent the onset of atrial fibrillation. Therefore we recommend that

all patients with Myotonic Dystrophy type 1, once molecularly diagnosed, are carefully monitored for the development of conduction defects and arrhythmias, even in the absence of cardiac signs/symptoms and in the early stages of the disease. Furthermore we suggest to implant APP as it significantly Adenylyl cyclase reduces the AT/AF burden over a long-term follow-up in DM1 patients implanted with dual chamber pacemaker, compared with those implanted with conventional DDD/R pacing alone. Acknowledgements The work was in part supported by Telethon grants (GUP07013A and GTB12001H) to LP. DNA samples from patients with DM1 derive from the NHMGB bank, that is partner of Eurobiobank and Telethon Network of Genetic Biobanks.