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AP-517-01 THE LIKELIHOOD OF CLINICALLY SIGNIFICANT QTC PROLONGATION DURING LONG-TERM FOLLOW UP IN PATIENTS WITH CONCEALED LONG QT SYNDROME AND NORMAL QTC AT INITIAL PRESENTATION

      Background

      Patients carrying genetic variants associated with long QT syndrome (LQTS) who initially present with normal QTc is a large and growing group of patients who are commonly diagnosed during genetic cascade family screening. Long-term progression of QTc interval in this patient group remains poorly described.

      Objective

      To assess the risk of QTc prolongation during long-term follow-up in LQTS patients who have normal QTc at first presentation.

      Methods

      ECGs from adult patients with LQTS followed up at three tertiary care hospitals in Sweden and Denmark were retrieved from regional ECG archives thaht contain ECGs recorded for any reason both in-hospital and in outpatient settings. Patients who had ECGs recorded after 16 years of age with at least two years apart were included. QTc (Bazett) was automatically calculated. Patients with QTc under 450 ms in men or 460 ms in women (upper limits of normal, ULN) at their first presentation were considered as patients with concealed LQTS. The likelihood of observing prolonged QTc above ULN, 480 ms and 490 ms thresholds at any time during follow-up was calculated. Data presented as median [interquartile range].

      Results

      Out of 207 patients meeting the inclusion criteria, 65 had concealed LQTS at first presentation (LQT1: n=32, age 36 [22-55]; LQT2: n=26, age 29 [18-45]; LQT3: n=7, age 36 [24-44]). In total, 1082 ECGs recorded from patients with concealed LQTS were available for analysis with time between the first and the latest ECGs 6 [3-10] years. Median number of ECGs was 10 [6-20] per patient. During follow up, 35 patients (54%) had QTc remaining under ULN and only 10 (15%) demonstrated QTc prolongation in the interval 480-499 ms (Figure). No significant differences between LQTS genotypes were observed.