Corrected QT Interval Is Related to Markers of Hemolysis and Tricuspid Regurgitant Jet Velocity in a Young Cohort with Sickle Cell Disease.

Recent evidence suggests that prolongation in QT interval may be a frequent finding in patients with sickle cell disease (SCD). Few studies, however, have examined the relationship between conduction abnormalities and other cardiac complications, such as left ventricular hypertrophy (LVH) and tricuspid regurgitant jet velocity (TRJV) elevation, in this population. Moreover, long QT may be a marker of increased mortality in conditions, other than SCD, associated with LVH. We therefore sought to evaluate QT interval and its relationship to echocardiographic findings, laboratory parameters and disease severity in a cohort of children and young adults with SCD.

Methods We prospectively evaluated the corrected QT interval (QTc) on standard 12-lead ECG in a cross-sectional, convenience sample of 73 subjects (41 males, mean age 14.2±3 years, range 10 to 24) with Hb SS, SC and S-β⁰ thalassemia undergoing screening for TRJV elevation. Subjects on chronic transfusions were excluded and all studies were performed at baseline on the same day. A review of available medical records was also performed.

Results In our cohort, QTc (mean 436±24 ms, range 387 to 531) was prolonged > 440 ms in 30/73 (41%) of subjects at steady state. We also found TRJV elevation ≥ 2.5 m/s in 24/73 (33%) and LVH by ECG or echocardiographic criteria in 32/73 (44%) subjects. Using Pearson’s correlation coefficient, we observed significant correlations between QTc and TRJV (r=0.38, p=0.002), WBC (r=0.37, p=0.001) and several markers of hemolysis, including LDH (r=0.46, p=0001), Hb (r=-0.32, p=0.005), retic (r=0.29, p=0.013), plasma Hb (r=0.27, p=0.03) and AST (r=0.38, p=0.001). Using Student’s t-test for independent samples, only TRJV (2.55±0.33 vs. 2.34±0.26 m/s, p=0.006), LDH (450±166 vs. 329±143 U/L, p=0.001), WBC (10.6±4.7 vs. 8.6±3.3×10⁹/L, p=0.048), retic (14.4±9.2 vs. 10.6±6.1%, p=0.039) and AST (50±22 vs. 38±15 U/L, p=0.009) were significantly higher and Hb (9.1±1.3 vs. 9.9±1.7 g/dL, p=0.04) lower in subjects with QTc > 440 ms compared to those with QTc ≤ 440 ms. We found no significant relationship between QTc and age, LV mass, platelet count or fetal Hb. By χ² analysis, a larger proportion of subjects with QTc > 440 ms also had a history of acute chest syndrome (p=0.007), gallstones (p=0.047), exchange transfusion (p=0.04) and to a less significant degree, TRJV elevation (p=0.112). Prolonged QTc was not affected by sex, hydroxyurea use or a history of LVH, frequent pain, asthma, splenectomy, priapism and tonsilloadenoidectomy. Given sample size limitations and data reduction methods, we found by logistic regression analysis that the combination of TRJV and history of acute chest syndrome best predicted QTc prolongation, correctly identifying 80% of cases and resulting in positive and negative predictive values of 76% and 81%, respectively.

Conclusions We conclude that QTc prolongation is common in a prospectively screened cohort of young sickle cell patients at baseline and is associated with evidence of hemolysis and to a lesser degree, TRJV elevation. Our results contrast with findings in other conditions that link QTc prolongation primarily to LVH. Future studies will be critical to further define QTc variability, pathophysiologic determinants as well as the clinical consequences of conduction abnormalities, which may or may not relate to TRJV elevation, in the sickle cell population.