QT interval prolongation in asymptomatic anti-SSA/Ro–positive infants without congenital heart block

OBJECTIVE: To analyze the electrocardiograms (EKGs) of infants born to mothers with anti-SSA/Ro antibodies in order to evaluate the QT interval (the time from the beginning of the QRS complex to the end of the T wave). METHODS: Sera from mothers and children were analyzed for anti-Ro and anti-SSB/La antibodies by enzyme-linked immunosorbent assay (ELISA) and by Western blot analysis. Fine specificity of anti-Ro antibodies was evaluated by solid-phase ELISA against recombinant 52- and 60-kd proteins and by Western blot. A retrospective chart review was conducted for EKG analysis. Twenty-eight EKG tracings (21 from anti-Ro-positive and 7 from anti-Ro-negative infants born to mothers with autoimmune diseases) were analyzed by a single investigator who was blinded to the infant's antibody status. The QT interval was measured and corrected for heart rate according to Bazett's formula. RESULTS: The mean QT interval was significantly longer in anti-Ro-positive than in anti-Ro-negative infants, also after correction for heart rate (QTc) (P = 0.001). Nine of 21 anti-Ro-positive infants and 0 of 7 anti-Ro-negative infants had QTc values above the upper normal limit (440 msec). A 24-hour EKG recording was performed on 5 patients and confirmed the QT prolongation. These infants were subsequently treated with a beta-blocker in order to prevent arrhythmias. CONCLUSION: Infants born to mothers who carry anti-Ro autoantibodies may show QT interval prolongation and should be monitored with EKG during the first months of life.