Abnormalities of cardiac repolarization in Williams syndrome.

Williams syndrome (WS) affects 1 in 8,000 live births and has a high risk of sudden death. No previous studies have evaluated corrected QT (QTc) prolongation in WS. Retrospective review of all patients with WS evaluated at our institution from January 1, 1980 to December 31, 2007 was performed. WS was diagnosed by a medical geneticist and/or by fluorescence in situ hybridization. Patients with ≥1 electrocardiogram (ECG) with sinus rhythm and measurable intervals were included. Normal control ECGs were identified from a large clinical database. Corrected JT (JTc) interval was calculated when QRS and QTc intervals were prolonged. QTc interval ≥460 ms and JTc interval >340 ms were defined as prolonged. Prevalence comparisons were made using Fisher's exact test. Statistical probability of <0.05 was considered significant. Of 270 patients identified, 188 had ECGs for review. Complete data were present in 499 of 517 ECGs (patients' mean age 10.3 ± 9.9 years); 1,522 normal ECGs of age-similar patients composed the control group. QTc prolongation prevalences were 2.0% in controls and 13.6% in WS (p <0.0001); in those, JTc prolongation prevalences were 1.8% in controls and 11.7% in WS (p <0.0001). Four patients died during follow-up; 2 had QTc prolongation and 1 died during noncardiac surgery. Another patient with QTc prolongation sustained cardiac arrest during a procedure. In conclusion, cardiac repolarization is prolonged in WS. Presence of prolonged cardiac repolarization may contribute to the high incidence of periprocedural mortality in these patients. All patients with WS should be screened for cardiac repolarization abnormalities, especially before surgery.