Prolonged QTc in Sickle Cell Disease: A Potential Risk Factor for Early Death?

Background: Sudden unexplained death is one of the leading causes of mortality in sickle cell disease (SCD). Prolonged QTc has been associated with sudden death in older patients and in those with cardiac disease. Sudden death due to cardiac arrhythmias occurs in thalassemia (Thal) patients from cardiac iron toxicity, and recently, QTc prolongation has also been identified in this transfusion-dependent population. Chronic transfusion and iron overload have become more frequent in patients with SCD due to treatment regimens aimed at stroke prevention and treatment of stroke, pulmonary hypertension (PH) and recurrent vaso-occlusive crisis. Cardiac iron toxicity is thought to be rare in SCD but other factors such as anemia, PH, and hemolysis-associated nitric oxide dysregulation may predispose SCD to prolongation of the QTc interval. The purpose of this study was to examine the prevalence of QTc prolongation in chronically transfused and iron-overloaded SCD (txSCD) patients compared to a control group of non-transfused SCD patients.

Methods: In this study, electrocardiograms (EKGs) were reviewed from SCD patients participating in the MCSIO, a five-year prospective study of the complications of iron toxicity in SCD and Thal. Using Bazett’s formula, a subset of 96 EKGs were analyzed for QTc prolongation, defined as ≥ 0.45 seconds and borderline as 0.44 to 0.449 seconds. Echocardiograms (ECHOs) obtained within an average of seven months were analyzed for left ventricular dysfunction (LVD) --which was defined as an ejection fraction < 55% or shortening fraction < 28% --and the presence of PH, defined as a tricuspid regurgitant jet velocity (TRJV) of ≥ 2.5 m/second.

Results: There was no difference in mean age (25.3 ± 13.6) or gender (64% female) between the 65 txSCD and 31 control SCD patients. The txSCD group had been transfused 10 ± 6.2 years and their baseline ferritin was 3107 compared to 116 in the controls. QTc prolongation was present in 32% of the txSCD and 29% of the control group (n.s.); borderline prolongation was seen in an additional 17% and 13%, respectively. Mean QTc in txSCD was also not significantly different from the SCD controls: 0.45±.04 vs. 43±.03 (n.s.). None of the 68 patients with ECHOs had LVD. 36 patients had TRJV measured during the study: 50% of the txSCD had PH compared to 30% of non-transfused SCD (n.s.). The average QTc in PH patients was 0.45 ± .04 compared to 0.43 ± .04 in those without PH (p=.09). However, the frequency of either prolonged or borderline QTc was significantly higher in patients with PH (72% vs. 22%, p= .007). No correlations between QTc and age, gender, or baseline laboratory values (hemoglobin, white blood count, or platelets) were found. In the txSCD, QTc was not correlated to ferritin or years of transfusion.

Conclusions: Overall, QTc prolongation was found in 31 % of SCD patients and borderline prolongation in an additional 16%. QTc intervals ≥ 0.44 were more common in patients with PH. Transfusion exposure and iron overload were not associated with QTc prolongation in this group of txSCD patients. The frequency of QTc prolongation is concerning in SCD patients, who often have pulmonary hypertension and are treated with medications known to contribute to QTc prolongation. Routine screening for QTc prolongation appears warranted with treatment of high-risk SCD patients.