Background: The QT interval a marker of ventricular depolarization and repolarization is reported to be prolonged in some proportion of patients with systemic lupus erythematosus (SLE). We studied electrocardiographic (ECG) abnormalities, in particular QT interval and its relationship with anti-Ro antibodies, disease activity, and serum interleukin 1β (IL-1β), interleukin 6 (IL-6) in SLE.
Methods: A 12-lead resting ECG was performed on 140 adult SLE patients fulflling SLICC/ACR classification criteria. All patients received hydroxychloroquine and prednisolone. Corrected QT (QTc) °440 milliseconds (ms) was defined as prolonged QTc. QT dispersion (QTd) °60 ms was defined as increased QTd.
Results: Eighty-four patients had some form of ECG abnormality. Prolongation of QTc and QTd was present in 24 (17.1%) and 50 (35.7%) respectively. Anti-Ro/SSA antibodies were present in 63 (45%). Prolongation of QTc in anti-Ro positive versus anti-Ro negative was 17.5% and 17% respectively, p=0.98. Prolongation of QTd in anti-Ro-positive versus anti-Ro-negative was 32% and 39% respectively, p=0.37. Prolonged QTc was observed in 15% patients with SLEDAI ˛4 compared to 17.5% patients with SLEDAI °5, p=0.78. The median serum concentrations of IL-1β and IL-6 were similar in the groups with and without prolonged QTc, with and without prolonged QTd. On binary logistic regression analyses neither clinical nor laboratory factors were predictors of prolonged QTc. However, having valvular regurgitation and hypercholesterolemia was associated with significantly reduced odds of having prolonged QTd, adjusted OR 0.33 (CI 0.14-0.83), p=0.018 and 0.19 (CI 0.05-0.80), p=0.023 respectively. Those with high LDL cholesterol and hypertriglyceridemia had a significantly higher odds of having a normal QTd with adjusted OR of 4.34 (1.31-14.46) p=0.017and 5.59 (1.62-19.38) p=0.007respectively.
Conclusion: Though 17% and 35% SLE patients have QTc and QTd prolongation, association with anti-Ro antibodies or disease activity was absent. A large proportion has other asymptomatic ECG abnormalities that may reflect subclinical cardiac involvement.
Keywords: QT dispersion; QT interval; interleukin 1β; interleukin 6; lupus.