TNNI3 and myotonic dystrophy type 1: The 12-lead ECG currently serves as the cornerstone of cardiac assessment in DM1, with Groh criteria (PR > 240 ms, QRS > 120 ms, rhythm other than sinus, second-degree or third-degree AV block) shown to be predictive of sudden death and cardiac morbidity.[4, 9] Our data suggest that an elevated cTnI does not reliably distinguish patients with severe conduction abnormalities; 31 patients had high-risk ECG changes, among whom only three had elevated cTnI.