International survey of T2* cardiovascular magnetic resonance in β-thalassemia major

Abstract

Accumulation of myocardial iron is the cause of heart failure and early death in most transfused thalassemia major patients. T2* cardiovascular magnetic resonance provides calibrated, reproducible measurements of myocardial iron. However, there are few data regarding myocardial iron loading and its relation to outcome across the world. A survey is reported of 3,095 patients in 27 worldwide centers using T2* cardiovascular magnetic resonance. Data on baseline T2* and numbers of patients with symptoms of heart failure at first scan (defined as symptoms and signs of heart failure with objective evidence of left ventricular dysfunction) were requested together with more detailed information about patients who subsequently developed heart failure or died. At first scan, 20.6% had severe myocardial iron (T2*≤ 10 ms), 22.8% had moderate myocardial iron (T2* 10-20 ms) and 56.6% of patients had no iron loading (T2*>20 ms). There was significant geographical variation in myocardial iron loading (24.8-52.6%; P<0.001). At first scan, 85 (2.9%) of 2,915 patients were reported to have heart failure (81.2% had T2* <10 ms; 98.8% had T2* <20 ms). During follow up, 108 (3.8%) of 2,830 patients developed new heart failure. Of these, T2* at first scan had been less than 10 ms in 96.3% and less than 20 ms in 100%. There were 35 (1.1%) cardiac deaths. Of these patients, myocardial T2* at first scan had been less than 10 ms in 85.7% and less than 20 ms in 97.1%. Therefore, in this worldwide cohort of thalassemia major patients, over 43% had moderate/severe myocardial iron loading with significant geographical differences, and myocardial T2* values less than 10 ms were strongly associated with heart failure and death.

Figure 1.

Myocardial iron loading by region. Percentage of patients with myocardial T2* values <10ms (red), between 10 and 20ms (yellow) and >20ms (green) at baseline scan. Data are presented in Table 2 with regions in order of increasing percentage of iron loading (T2* <20ms).

Figure 2.

World map showing the distribution of the prevalence of severe myocardial iron loading at first CMR scan. The color scale represents the percentage of patients in each region who have severe myocardial iron loading with T2* values <10ms.

Figure 3.

Histograms of the distribution of T2* values. The broken red line represents a T2* value of 10ms. A. Myocardial T2* values for patients with heart failure at first scan. B. Myocardial T2* values for patients who developed new onset heart failure subsequent to their initial CMR scan. C. Myocardial T2* values for patients who died of cardiovascular causes subsequent to their initial CMR scan.