{'fraction_non_alphanumeric': 0.03545491788015344, 'fraction_numerical': 0.037875684332054675, 'mean_word_length': 4.800820911643983, 'pattern_counts': {'":': 0, '<': 10, '<?xml version=': 0, '>': 2, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Cardiac T2* magnetic resonance for prediction of cardiac complications in thalassemia major

BACKGROUND
The goal of this study was to determine the predictive value of cardiac T2* magnetic resonance for heart failure and arrhythmia in thalassemia major.


METHODS AND RESULTS
We analyzed cardiac and liver T2* magnetic resonance and serum ferritin in 652 thalassemia major patients from 21 UK centers with 1442 magnetic resonance scans. The relative risk for heart failure with cardiac T2* values <10 ms (compared with >10 ms) was 160 (95% confidence interval, 39 to 653). Heart failure occurred in 47% of patients within 1 year of a cardiac T2* <6 ms with a relative risk of 270 (95% confidence interval, 64 to 1129). The area under the receiver-operating characteristic curve for predicting heart failure was significantly greater for cardiac T2* (0.948) than for liver T2* (0.589; P<0.001) or serum ferritin (0.629; P<0.001). Cardiac T2* was <10 ms in 98% of scans in patients who developed heart failure. The relative risk for arrhythmia with cardiac T2* values <20 ms (compared with >20 ms) was 4.6 (95% confidence interval, 2.66 to 7.95). Arrhythmia occurred in 14% of patients within 1 year of a cardiac T2* of <6 ms. The area under the receiver-operating characteristic curve for predicting arrhythmia was significantly greater for cardiac T2* (0.747) than for liver T2* (0.514; P<0.001) or serum ferritin (0.518; P<0.001). The cardiac T2* was <20 ms in 83% of scans in patients who developed arrhythmia.


CONCLUSIONS
Cardiac T2* magnetic resonance identifies patients at high risk of heart failure and arrhythmia from myocardial siderosis in thalassemia major and is superior to serum ferritin and liver iron. Using cardiac T2* for the early identification and treatment of patients at risk is a logical means of reducing the high burden of cardiac mortality in myocardial siderosis. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00520559.

T halassemia is the most common single-gene disorder worldwide, with Ϸ94 million heterozygotes for ␤-thalassemia and 60 000 homozygotes born each year. 1 Although survival is improving in cohorts of patients in whom deferoxamine was introduced at a younger age, 2 myocardial siderosis resulting in heart failure remains the major cause of death (50% to 70%) in thalassemia major patients. 2,3 This occurs at a strikingly young age, with between 15% to 50% of patients dying by 35 years of age. 2,3

Editorial see p 1937 Clinical Perspective on p 1968
Severe myocardial siderosis causes a toxic dilated cardiomyopathy that can be reversed if aggressive chelation is begun early, 4 but clinical diagnosis is often delayed because of the typically late onset of symptoms. Catastrophic deterioration in cardiac function resulting in death may occur rapidly once clinically obvious heart failure is present. Methods for predicting heart failure have been developed that are based on established measures of iron loading, most importantly, time-averaged serum ferritin Ͼ2500 g/L 2,5 and liver iron concentration Ͼ15 mg/kg dry weight. 6 However, the persistently high mortality rate from heart failure indicates that high-risk patients are not being identified in time for effective intervention. Measurement of ventricular function such as alteration over time in ejection fraction has also been proposed in thalassemia, but it identifies patients at a relatively late stage, 7 and dysfunction may be masked because of supranormal left ventricular function in thalassemia patients in the absence of myocardial iron loading. 8 Most recently, direct assessment of myocardial iron with magnetic resonance (MR) relaxation has been used because iron deposits shorten T1, T2, and T2*. Of these, the measurement of T2* has become the most widely used in the heart because it is easily combined with cardiac gating, is fast and robust, and is the most sensitive to iron deposition. 9 The cardiac T2* technique is transferrable with good interscanner agreement 10 and has been implemented in at least 50 centers worldwide on 1.5T scanners from the 3 largest scanner manufacturers. Direct calibration of the cardiac T2* value to the myocardial iron concentration has been reported in animals 11 and humans. 12 However, although this work is important for complete scientific understanding, the relationship between cardiac T2* and prediction of cardiac events can be made independently of these data and, in terms of patient care, is the more important. Here, we report the value of cardiac T2* MR for predicting cardiac events from a large prospective database of thalassemia major patients compared with the established predictors of outcome, liver iron and serum ferritin.

Patient Population
A total of 652 patients (1442 scans) with ␤-thalassemia major were included in this study. Their clinical care was undertaken at 21 hematology centers throughout the United Kingdom, and they were scanned at the Cardiovascular MR Unit of Royal Brompton Hospital, London, UK, between 1999 and 2006. This is a substantial majority of the UK thalassemia major patients (Ϸ800 patients) and therefore represents a multicenter national sample. Patients were referred for clinical evaluation according to local practice at each caring center and were unselected. All patients were included in the database, but 17 were excluded from the predictive analysis reported in this study because of clinical heart failure (nϭ11) or arrhythmia (nϭ6) at the time of their first MR scan. Of these patients, 319 were male and 333 female, with a mean age at time of their first scan of 27.1Ϯ9.6 years. Detailed patient demographics are shown in Table 1. The prospective database of all patients was maintained from local patient records, and follow-up was completed by local case note review by a single researcher using a standard case record form. At the time of analysis, the follow-up was complete (100%) for a total of 1285 patient-years. At the time of the first scan, 22 patients were receiving no chelation, having had bone marrow transplantation. Of those patients who were treated with chelation, 433 patients were receiving deferoxamine, 72 patients were on deferiprone, 105 patients were taking deferoxamine combined with deferiprone, 19 patients were receiving deferasirox only, and 1 patient was taking deferasirox combined with deferoxamine. Ferritin levels were recorded within 22.5Ϯ22.4 days of all MR scans. The mean number of blood units transfused per year per patient was 32.6Ϯ11.5. The prediction of heart failure and arrhythmia in the year after each scan was predefined as the primary end point of this study. The holding, follow-up, and reporting of the results of this database were fully approved by Trent National Health Service Research Ethics Committee.

Diagnostic Criteria
A diagnosis of heart failure was made only if the patient complained of worsening dyspnea at rest or during exercise, objective left ventricular dysfunction was present with an ejection fraction of Ͻ56%, 9,13 and the caring clinician made the clinical diagnosis of heart failure. A diagnosis of arrhythmia was made only if the patient complained of palpitations and arrhythmia was objectively demonstrated by ECG with 24-hour monitoring or a standard 12-lead recording. Arrhythmias were categorized according to American Heart Association/American College of Cardiology guidelines 14 and included atrial fibrillation, defined as a cardiac arrhythmia arising from the atrium with an atrial rate Ͼ300 bpm and an irregular ventricular response in the presence of conduction (Ͼ10 minutes of sustained arrhythmia); supraventricular tachycardia, defined as a tachycardia that emanates from or requires participation of supraventricular tissue other than atrial fibrillation/flutter (Ͼ10 minutes of sustained arrhythmia); ventricular tachycardia, defined as Ն3 con- secutive complexes in duration emanating from the ventricles at a rate of Ͼ100 per minute; and ventricular fibrillation, defined as rapid, usually Ͼ300 per minute, grossly irregular ventricular rhythm with marked variability in QRS cycle length, morphology, and amplitude. Cardiac T2* values Ͼ20 ms were considered normal. 9 A liver T2* value ofϽ0.96 ms is calibrated to a dry weight equivalent of Ͼ15 mg/g dry weight. 9

Magnetic Resonance
Patients were scanned with a 1.5T scanner (Sonata, Siemens Medical Solutions, Erlangen, Germany) using previously reported techniques. 15 In brief, cardiovascular MR was performed with a cardiacgated, single-breath-hold, 8-echo sequence (2.6 to 16.7 ms, increasing in 2.02-ms increments) of a single midventricular short-axis slice. A single-breath-hold, 20-echo sequence (1.07 to 0.21 ms) of a transaxial slice of the liver was also acquired. Long-axis cines and a contiguous stack of short-axis cines were also acquired to assess left ventricular dimensions and function using standard techniques. 16 Data analysis was performed using CMRtools and its plug-in ThalassemiaTools (Cardiovascular Imaging Solutions, London, UK) for the liver T2* (a large region of interest excluding vascular structures) and heart T2* (a large region of the interventricular septum excluding regions in proximity to the coronary veins), as well as left ventricular ejection fraction using semiautomated planimetry of endocardial borders. 16 All scans were reported at the time of acquisition by multiple operators, and a clinical report was generated for the referring physician.

Statistics
All statistical analyses were performed by the Medical Statistics Department at our institution (M.R.). Because many patients in this study had multiple scans, we used a mixed-model Poisson regression with nested values (nϭ1442 scans) to produce univariate and multivariate analyses of cardiac T2*, liver T2*, and serum ferritin for cardiac outcomes and presented as relative risk (RR; with 95% confidence intervals [CIs]). Nesting incorporates all data from all scans in the predictive model for cardiac outcomes, and all repeated scans from any patient are modeled as nonindependent. Therefore, the unit of analysis is each individual scan with the 1 year of follow-up that follows it. Scans from the same patient are then nested within that patient. Each scan is assessed with regard to the outcomes following that individual scan, with the patient entered as a random effect to account for within-patient correlation. For purposes of comparison only, the RRs were also calculated per scan (nonnested analysis in which all scans are considered to be independent; nϭ1442 scans) and for patient first scans only (nonnested analysis considering each patient's first scan only, with any repeated scans ignored; nϭ652 scans). These data are given in tables in the online-only Data Supplement because they show results similar to the main analysis. Patients were censored from further analysis after a first outcome. All patient demographics are presented according to the first scan for each patient. The distributions of liver T2*, cardiac T2*, ferritin, and ejection fraction were not significantly deviated from normal by Kolmogorov-Smirnov testing and therefore are presented using mean and SD and per scan. Receiver-operating characteristic graphs were produced for cardiac T2*, liver T2*, and serum ferritin to compare predictive accuracy for cardiac outcomes across the full range of measured values using the area under the curve. Kaplan-Meier curves for time to heart failure and arrhythmia were generated. Data with a normal distribution are presented as meanϮSD; those with nonnormal distributions are presented as median and interquartile range. Statistical significance was set at PϽ0.05, and all P values are 2 tailed. All analyses were performed with STATA 10.2 (StataCorp, College Station, Tex).

Summary of Primary End-Point Events
At 1 year of follow-up, there were 80 episodes of heart failure and 98 episodes of arrhythmia. There were 4 deaths: 3 patients died of sepsis after bone marrow transplantation, and 1 patient died after an episode of ventricular tachycardia. There were 32 instances in which a patient was recorded as having both a heart failure event and an arrhythmia event within 1 year of a scan.

Heart Failure
For the 80 heart failure episodes, 60 presented in New York Heart Association class II, 16 were class III, and 4 were class IV. The mean ejection fraction of these 80 patients at the time of diagnosis of heart failure was 43.1Ϯ7.2%. The median time of onset from the time of the T2* MR scan to an episode of heart failure was 158 days (quartiles 1 and 3, 52 and 342 days). In these heart failure patients, the preceding cardiac T2* was 6.7Ϯ1.8 ms, liver was T2* 3.9Ϯ3.7 ms, and ferritin was 2713Ϯ1686 g/L. The distribution of cardiac T2* values in those patients who went on to develop heart failure compared with the T2* values of those patients who remained free of heart failure is shown in Figure 1A. The RRs associated with cardiac T2*, liver T2*, and ferritin are given in Table 2. The cardiac T2* was Ͻ10 ms in 98% of patients who developed heart failure. The 1-year incidence of heart failure in patients with the lowest cardiac T2* of Ͻ6 ms was 47%. Compared with cardiac T2* values Ͼ10 ms, there was a significantly increased risk of heart failure associated with cardiac T2* values Ͻ10 ms, with an RR of 160 (95% CI, 39 and 653) in the nested analysis. The RR for cardiac T2* Ͻ6 ms was 270 (95% CI, 64 and 1129). Serum ferritin using the conventional threshold (Ͼ2500 g/L) was a significant but weaker predictor of heart failure, with an RR of 0.56 (95% CI, 0.34 and 0.91) versus ferritin Ͻ2500 g/L ( Table 2). Liver T2* Ͻ0.96 ms (equivalent to the conventional threshold of Ͼ15 mg/g dry weight iron) was not a significant predictor of heart failure, with an RR of 0.81 (95% CI, 0.23 and 2.80) versus liver T2* Ͼ0.96 ms. Receiver-operating characteristic curves for the prediction of heart failure by cardiac T2*, liver T2*, and serum ferritin are shown in Figure  1B. The areas under the curve for serum ferritin (0.629) and liver T2* (0.589) were similar (Pϭ0.21), but the area under the curve for cardiac T2* (0.948) was substantially and significantly greater (PϽ0.001 versus liver T2*; PϽ0.001 versus serum ferritin). The RRs for the first scan only (nonnested) and per scan (nonnested) groups gave similar conclusions (Table I of the online-only Data Supplement). The Kaplan-Meier curves for the occurrence of heart failure stratified into 4 levels of cardiac T2* shown in Figure 1C illustrate a significant increase in risk with increasing cardiac iron loading (PϽ0.001). Overall, the T2* threshold of 10 ms predicted heart failure with a sensitivity of 97.5% (95% CI, 91.3 to 99.7) and specificity of 85.3% (95% CI, 83.3 to 87.2). The data were also analyzed for prediction of asymptomatic left ventricular dysfunction at the time of the scan and showed significant incremental RR for each level of cardiac T2* Ͻ10 ms (T2* 8 to 10 ms, 2.97; T2* 6 to 8 ms, 3.48; T2* Ͻ6 ms, 4.51; all PϽ0.001).

Arrhythmia
For the 98 patients who developed arrhythmias within 1 year of MR scanning, 78 patients had atrial fibrillation, 14 patients had supraventricular tachycardia, 5 patients had ventricular tachycardia, and 1 patient had ventricular fibrillation. In these patients, at the time of first MR scan, the mean cardiac T2* was 13.5Ϯ9 ms, mean liver T2* was 6.0Ϯ6.4 ms, mean serum ferritin was 2140Ϯ1540 g/L, and mean ejection fraction was 60.7Ϯ9.3%. The median time to developing arrhythmia was 133 days. The distribution of cardiac T2* values in the patients who went on to develop arrhythmia compared with those who remained free of arrhythmia is shown in Figure 2A. The RRs associated with cardiac T2*, liver T2*, and ferritin are given in Table 3. A cardiac T2* Ͻ20 ms was present in 83% of patients who developed arrhythmia. The incidence of arrhythmia at 1 year in patients with the lowest cardiac T2* of Ͻ6 ms was 14%. The mean cardiac T2* in the arrhythmia patients was as follows: atrial fibrillation, 13.6Ϯ9.9 ms; supraventricular tachycardia, 11.9Ϯ7.1 ms; ventricular tachycardia, 16.5Ϯ9.3 ms; and ventricular fibrillation, 9.0 ms. There was no significant difference between the cardiac T2* values for atrial and ventricular arrhythmias (Pϭ0.28). Compared with cardiac T2* values Ͼ20 ms, there was a significantly increased risk of arrhythmia associated with cardiac T2* values Ͻ20 ms, with an RR of 4.60 (95% CI, 2.66 to 7.95). The RR for a cardiac T2* Ͻ6 ms was 8.79 (95% CI, 4.03 to 19.2). There was no significant predictive value using the conventional thresholds of ferritin (Ͼ2500 g/L), with an RR of 0.90 (95% CI, 0.55 to 1.45) versus ferritin Ͻ2500 g/L, or liver T2* (Ͻ0.96 ms), with an RR of 0.81 (95% CI, 0.24 to 2.74) versus   Heart failure RRs for increments in cardiac T2* from Ͻ6 to 10 ms vs reference value of T2* Ͼ10 ms. Heart failure RRs for increments in liver T2* from Ͻ0.96 ms vs reference value of Ͼ6.3 ms. Heart failure RRs for serum ferritin Ͼ2500 and Ͻ2500 g/L. T2* Ͼ0.96 ms. Receiver-operating characteristic curves for the prediction of arrhythmia by cardiac T2*, liver T2*, and serum ferritin are shown in Figure 2B. The areas under the curve for serum ferritin (0.518) and liver T2* (0.514) were similar (Pϭ0.99), but the area under the curve for cardiac T2* (0.747) was substantially and significantly greater (PϽ0.001 versus liver T2*; PϽ0.001 versus serum ferritin). The RRs for the first scan only (nonnested) and per scan (nonnested) groups give similar conclusions and are shown in Table II of the online-only Data Supplement. The Kaplan-Meier curves for the occurrence of arrhythmia stratified into 3 levels of cardiac T2* shown in Figure 2C illustrate a significant increase in risk with increasing cardiac iron loading (PϽ0.001). Overall, the T2* threshold of 20 ms predicted arrhythmia with a sensitivity of 82.7% (95% CI, 73.7 to 89.6) and specificity of 53.5% (95% CI, 50.8 to 56.2).

Effect of MR Result on Risk
The reporting of the cardiac T2* value may have caused alterations in treatment that could have affected the outcome events. Therefore, we analyzed the RRs for an increase or decrease in each chelator (relative to not changing dose) and   Arrhythmia RRs for increments in cardiac T2* from Ͻ6 to 10 ms vs reference value of T2* Ͼ10 ms. Arrhythmia RRs for increments in liver T2* from Ͻ0.96 ms vs reference value of Ͼ6.3 ms. Arrhythmia RRs for serum ferritin Ͼ2500 and Ͻ2500 g/L.
included these in an adjusted analysis examining heart T2* for the prediction of heart failure or arrhythmia. There was no statistically significant effect of changing dose, except that an increased dose of deferoxamine was associated with a small increased RR of arrhythmia and the adjusted RR relating heart T2* to outcomes remained very similar to the unadjusted ones. Therefore, there is little statistical evidence from the database that short-term changes in chelation dose after scans altered the ability of T2* to predict outcomes over the period of collection of data.

Effect of Prior History of Heart Failure or Arrhythmia on Outcomes
All patients reported in this study did not have heart failure or arrhythmia at the time of first MR scan, but 9 patients had a prior (and resolved) history of heart failure, and 1 patient had a prior (and resolved) history of arrhythmia. Therefore, we reanalyzed the predictive power of cardiac T2* using prior history of heart failure or arrhythmia as covariates and including in the analysis those patients who developed end points within 1 year of follow-up who had additional MR scans. The RR of prior heart failure predicting future heart failure was 1.93 (95% CI, 1.19 to 3.13), and the RR of prior heart failure or arrhythmia predicting future heart failure was 1.60 (95% CI, 0.92 to 2.81) and 1.59 (95% CI, 0.84 to 3.02), respectively. The RR of prior arrhythmia predicting future arrhythmia was 2.67 (95% CI, 1.41 to 5.09), and the RR of prior arrhythmia or heart failure predicting future arrhythmia was 1.84 (95% CI, 0.86 to 3.94) and 2.08 (95% CI, 1.07 to 4.02), respectively. There was no significant interaction between heart T2* and prior heart failure in analyses of heart failure and no significant interaction between heart T2* and prior arrhythmia in analyses of arrhythmia. Overall, therefore, these results show that there were significant associations between prior disease and new disease, but they were independent of the predictive ability of T2*, and T2* was still a much more powerful predictor.

Regression Between Iron Parameters
There were significant relationships between all 3 iron variables (cardiac T2* versus liver T2*: R 2 ϭ0.003, Pϭ0.040; cardiac T2* versus ferritin: R 2 ϭ0.003, Pϭ0.041; liver T2* versus ferritin: R 2 ϭ0.37, PϽ0.001). These results should be interpreted in the context of the large sample size (nϭ1442), which was highly powered to find significant results for regression analysis, and on data inspection, only the relationship between liver T2* and ferritin is meaningful.

Effect of Age, Gender, and Baseline Medication on Heart Failure
Neither age nor gender was significantly associated with either study outcome (PϾ0.3 for all). There was no association between baseline treatment and heart failure events when assessed either as a single variable (PϾ0.2 for all) or in conjunction with T2* (PϾ0.4 for all).

Discussion
Failure to control serum ferritin and liver iron over sustained periods has been linked to increased risk of heart disease 2,5,6,7 and other complications of iron overload. 17 However, low values of liver iron or serum ferritin do not necessarily signify low risk of iron-induced cardiomyopathy. 9 This may arise because iron chelation therapy can remove iron more rapidly from the liver than from the heart, which may normalize liver iron while myocardial iron remains high. 9,18,19 Other mechanisms may be involved, including potential genetic variations in function of cardiac iron transport channels such as the L-type calcium channel and the divalent metal transporter 1. 20,21 Therefore, there is often a need to identify those patients most at risk of cardiomyopathy even when serum ferritin and liver iron values are currently well controlled. Although sequential quantification of heart function identifies a patient group at increased risk of cardiac mortality, 7 it would be preferable to identify high-risk patients early before cardiomyopathy develops and use targeted treatment. 22,23 The estimation of heart iron by MR offers this possibility. We have used the MR relaxation parameter T2*, which is sensitive to the presence of storage iron microaggregates, which disturb the homogeneity of the magnetic microenvironment. Evidence has been accumulating that low values of cardiac T2*, which reflect high cardiac iron levels, are associated with heart failure. In a cross-sectional study of 28 patients presenting with heart failure, 89% of cases had a cardiac T2* Ͻ10 ms. 24 Limited other data have supported this experience. 25 Therefore, in the present study, we analyzed our prospective database on all thalassemia major patients living in the United Kingdom who had a cardiac T2* scan since 1999. The data unequivocally demonstrate that cardiac T2* is a powerful predictor of the subsequent development of heart failure. The RR was substantial at 270 for the highest-risk group with a cardiac T2* Ͻ6 ms compared with a cardiac T2* of Ͼ10 ms. Analysis of the incidence of heart failure following the finding of a cardiac T2* of Ͻ6 ms was impressive, with 47% of such patients developing this ominous complication within 12 months. The receiver-operating characteristic analysis showed that the predictive value of cardiac T2* for heart failure was significantly and substantially greater than for conventional iron measures for the prediction of cardiac complications (liver iron, serum ferritin).
The results for the prediction of arrhythmia by cardiac T2* are also significant but of lower magnitude than for the prediction of heart failure. In addition, the distribution of cardiac T2* in patients presenting with arrhythmia had a greater spread with higher cardiac T2* values. However, 83% of cases occurred in patients with cardiac T2* values Ͻ20 ms, indicating myocardial siderosis as the primary cause. The majority of the arrhythmias were atrial in origin and were not dependent on failing ventricular function because they were observed at higher (although still abnormal) T2* levels than those seen with heart failure. The atrial myocardium might be more sensitive to iron deposition than the ventricle in the causation of arrhythmias; this hypothesis is supported somewhat by historical data before the use of iron chelators, which suggested that iron deposition is greater in the ventricles than in the atria. 26 Unfortunately, T2* measurements of the thin atrial myocardium are limited by partial volume effects and are unlikely to be robust; therefore, this issue is not easy to address with current noninvasive MR techniques. Thalasse-mia patients are also susceptible to non-iron-dependent causation of atrial arrhythmia because of chronically raised cardiac output and atrial dilation.
Our study has some limitations. We have not formally validated our results in a different cohort. However, we did not attempt to build a multivariate model from a number of available factors but looked at a small number of prespecified iron measures and prospectively showed their relation to the outcomes of interest. However, it would still be of interest to reproduce these results in another cohort. We used the widely accepted normal cardiovascular MR threshold for the lower limit of normality of left ventricular ejection fraction of 56% to categorize ventricular dysfunction, although data from a single center, which have not been reproduced, suggest that slightly higher threshold values may pertain to thalassemia major patients in the absence of cardiac siderosis. 27

Conclusions
This study shows that cardiac T2* is highly predictive over 1 year for the development of heart failure and arrhythmia and is significantly more predictive than contemporaneous measures of liver iron and serum ferritin. This indicates that the inclusion of cardiac T2* assessment, in concert with conventional long-term assessments of tissue iron loading, is mandatory for the comprehensive evaluation of iron loading. A widespread program using cardiac T2* in ␤-thalassemia major has considerable potential for reducing mortality from heart failure by the early identification and treatment of patients at risk. 28 These data will also be of direct value in the management of different iron loading conditions such as hemochromatosis and other transfusion-dependent anemias.