Magnetic Resonance T2* Measurement of Myocardial Iron Deposition in Sickle Cell Disease: Risk Factors and Relationship with Cardiac Function.

Children with thalassemia major (TM) and sickle cell disease (SCD) receiving chronic blood transfusion are at risk of developing cardiac iron overload. Magnetic resonance imaging (MRI) has emerged as a non invasive tool for the direct measurement of myocardial iron deposition in these patients. Previous studies have shown that patients with TM develop significant myocardial iron deposition that correlates with transfusion burden and cardiac function. However, the prevalence of myocardial iron overload, the risk factors and its relationship with cardiac function in patients with SCD are not well known.

To review the patterns of cardiac iron overload using cardiac MRI in our cohort of children with SCD.

Cardiac MRI studies performed in children with SCD at a steady state from January 2009 to June 2009 at our institution were reviewed. We abstracted demographic and laboratory data and reviewed their transfusion history. These patients were receiving chronic blood transfusion every 3-4 weeks. All patients had been on chelation therapy desferrioxamine and/or deferasirox. In each patient, MR (1.5T Avanto™, Siemens) T2* measurements were performed in the interventricular septum, as well as in the paravertebral muscles as an internal control. Cardiac T2* value of 25-46 was considered normal as previously published.

A total of 20 patients with Hb SS (50 % male), with a mean age of 14 years were studied. The mean duration of blood transfusion was 9.5 ± 5.3 years. Seventeen patients (85%) were on chronic transfusion for stroke or abnormal TCD and three (15%) for other reasons such as recurrent pain crises and priapism. Overall, the mean cardiac T2* was 31.2 ± 6.6 ms in our patients. Mean T2* values in the myocardium were significantly lower than T2* values measured in the paravertebral muscles in the same patients (31.2 ± 6.6 versus 48.2 ± 5.1, p<0.05). Two patients (10%) had low cardiac T2* (17 and 22) indicating significant myocardial iron deposition. In addition, borderline low T2* values (26 each) were noted in two additional patients (10%) suggesting high myocardial iron deposition. There was a weak but not significant correlation between cardiac T2* and left ventricular end-diastolic volume (r=0.17), left ventricular ejection fraction (r=0.21) and right ventricular end-diastolic volume (r=0.37). Also, there was no statistically significant correlation between myocardial T2* and transfusional burden (r= -0.26), duration of transfusion (r= -0.35), serum ferritin (r= -0.4) and liver iron concentration by biopsy (r= -0.33) and liver T2* (r=0.04).

Our study shows that patients with SCD develop significant cardiac iron overload (low cardiac T2*) than previously reported. However, there was no significant correlation between cardiac T2* and parameters of ventricular function even in patients with high myocardial iron content. The lack of correlation between cardiac T2* and serum ferritin, liver iron content and transfusion burden in our cohort concurs with previous studies. Thus the risk factors for cardiac iron accumulation and its correlation with cardiac function in this patient population remain unclear. Further prospective studies are needed to understand the pathogenesis and the consequences of cardiac iron overload in patients with SCD.

No relevant conflicts of interest to declare.