A 34-year longitudinal study on long-term cardiac outcomes in DM1 patients with normal ECG at baseline at an Italian clinical centre.

Cardiac conduction and/or rhythm abnormalities (CCRA) are the most frequent and life-threatening complications in DM1. In order to determine prevalence, incidence, characteristics, age of onset and predictors of CCRA, CCRA progression and sudden cardiac death (SCD) in DM1, we collected ECG/24hECG-Holter data from a yearly updated 34-year database of a cohort of 103 DM1 patients without cardiac abnormalities at baseline, followed for at least 1 year. Fifty-five patients developed CCRA [39 developed conduction abnormalities (CCA) and 16 rhythm abnormalities (CRA)], which progressed in 22. Nine had SCD. Risk and incidence of CCRA amounted to 53.4 and 6.83% person-years (CCA: 37.9 and 4.8%; CRA 15.5 and 2%), respectively; risk and incidence of SCD amounted to 8.74 and 0.67% person-years, respectively. CTG expansion represented a predictor of CCRA incidence (HR 1.10, p = 0.04), CCRA progression (HR 1.28, p = 0.001) and SCD (HR 1.39, p = 0.002). MIRS progression during follow-up was associated with CCRA prevalence (OR 5.82, p = 0.004); older age and larger CTG expansion to SCD prevalence (OR 2.67, p = 0.012; OR 1.54, p = 0.005). Age of CCRA onset and CCRA progression was significantly lower in patients with larger CTG expansion and in those with MIRS progression. Age when SCD occurred was significantly lower in patients with larger CTG expansion. Amongst recorded cardiac abnormalities, both atrial flutter (OR 8.70; p = 0.031) and paroxysmal supraventricular tachycardia (OR 8.67; p = 0.040) were associated with SCD. Although all DM1patients may develop cardiac abnormalities at any time in their life, patients older than 30 years with larger CTG expansion and MIRS progression in particular should be carefully monitored via periodical ECG.