Myocardial tissue characterization and the role of chronic anemia in sickle cell cardiomyopathy

Safe and Informed Use of Gadolinium-Based Contrast Agent in Body Magnetic Resonance Imaging: Where We Were and Where We Are

Gadolinium-based contrast agents (GBCAs) have helped to improve the role of magnetic resonance imaging (MRI) for the diagnosis and treatment of diseases. There are currently nine different commercially available gadolinium-based contrast agents (GBCAs) that can be used for body MRI cases, and which are classifiable according to their structures (cyclic or linear) or biodistribution (extracellular-space agents, target/specific-agents, and blood-pool agents). The aim of this review is to illustrate the commercially available MRI contrast agents, their effect on imaging, and adverse reaction on the body, with the goal to lead to their proper selection in different clinical contexts. When we have to choose between the different GBCAs, we have to consider several factors: (1) safety and clinical impact; (2) biodistribution and diagnostic application; (3) higher relaxivity and better lesion detection; (4) higher stability and lower tissue deposit; (5) gadolinium dose/concentration and lower volume injection; (6) pulse sequences and protocol optimization; (7) higher contrast-to-noise ratio at 3.0 T than at 1.5 T. Knowing the patient's clinical information, the relevant GBCAs properties and their effect on body MRI sequences are the key features to perform efficient and high-quality MRI examination.

Evaluation of left ventricular systolic function in children with sickle cell anemia: contribution of 2D strain

BACKGROUND

Children with sickle cell anemia (SCA) are at an increased risk of cardiovascular complications. The aim of this study was to assess the role of speckle tracking echocardiography in detecting subclinical myocardial damage in children with SCA.

METHODS

A cross-sectional case-control study was conducted at the echocardiography laboratory of the military hospital of Tunis between July and December 2018. Thirty patients with SCA were included. A control(C) group including 30 normally developing children was selected and matched to the SCA group by sex and age. We compared between the two groups: conventional echocardiographic parameters including cardiac output, left ventricular ejection fraction (LVEF), thickness and the global longitudinal strain (GLS). The echocardiographic measurements were indexed according to body surface area. The left ventricular (LV) GLS association with clinical characteristics and echocardiographic parameters were also evaluated.

RESULTS

Patients and controls were matched for age and sex: the mean age was (11± 2years) in SCA group versus (12± 1 years) in C group with a sex ratio of (1.31 versus 1.27, respectively). Body surface area was comparable. LV hypertrophy and dilation were revealed in the SCA group, whereas measurements were normal in the C group. No significant differences were observed for cardiac output (p=0.4). LVEF were preserved in both groups. However, two-dimensional (2D) LVGLS was impaired in 46% of SCA group (n=14) with mean value of (-21%±3.07 vs -25%±2.98; p<0.01).In SCA group, impaired LVGLS was significantly associated with LV mass (r = - 0.399, p<0.01), LV tele diastolic diameter(r= -0.419, p<0.01) and left atrial volume (r= - 0.399, p< 0.04). In multivariate analysis, LV mass was the only independent factor.

CONCLUSIONS

In the present study, LVGLS measurement revealed subclinical LV systolic impairment in patients with SCA. Therefore, 2D strain could be beneficial to detect the natural history of LV dysfunction in SCA.

Early initiation of disease-modifying therapy can impede or prevent diffuse myocardial fibrosis in sickle cell anemia

Cardiovascular disease is a major cause of mortality in patients with sickle cell disease (SCD). Niss et al previously reported that cardiac magnetic resonance in 25 patients showed universal myocardial fibrosis, which they correlated with increased extracellular volume fraction (ECV). In the current study, they compared patients with SCD who were treated with hydroxyurea or transfusion at age &lt;6 years to a group of patients with SCD without therapy. They documented that patients treated early had ECV levels comparable to normal controls, potentially preventing subsequent myocardial fibrosis.

Cardiomyopathy in Sickle Cell Disease

Sickle cell disease (SCD) is an inherited disorder that occurs due to point mutation in the beta-globin chain resulting in the production of hemoglobin S that tends to become rigid and sickle-shaped under low oxygen concentration. These sickle-shaped red blood cells (RBCs) obstruct the blood vessels leading to reduced blood flow to the organs, causing ischemia and tissue fibrosis. These sickle RBCs being abnormal in shape are frequently sequestered by the spleen, creating a state of chronic anemia in the body. This chronic anemia leads to a high cardiac output state causing cardiac remodeling. To tackle chronic anemia, patients are frequently treated with blood transfusions that makes them more prone to the risk of iron overload (from newly transfused RBCs and iron release from the RBCs that just got sequestered as well as from volume overload) and volume overload causing left ventricular (LV) dilation. The above-mentioned mechanism of cardiac hypertrophy, along with LV dilation together, makes SCD-related cardiomyopathy unique cardiomyopathy with features of restrictive cardiomyopathy with LV dilation. It is interesting to note here that even though there is a presence of LV dilatation, Systolic dysfunction is very uncommon in SCD-related cardiomyopathy.

Cardiovascular manifestations of sickle cell disease

Sickle cell disease (SCD) is the most frequent genetic haemoglobinopathy worldwide. Early childhood mortality has dramatically decreased in high-income countries, and most patients now survive beyond the 5th decade. However, in the aging SCD population, the morbidity related to chronic organ damage, especially kidney and heart, has become a major concern. While pulmonary hypertension has attracted most attention, it appears that this condition is frequently linked to left heart failure (HF). Accordingly, SCD-associated cardiomyopathy is emerging as a major cause of reduced quality of life and early mortality in these patients. The diagnosis of this particular phenotype of high-output HF is challenging. Exercise intolerance and dyspnoea in SCD patients are linked to multiple causes including chronic anaemia. Moreover, echocardiographic features are unusual and can be misinterpreted. The classical diagnosis algorithm for HF is generally not suitable in SCD patients, and HF is poorly recognized and mostly diagnosed at a late congestive stage in routine practice. Such patients need to be identified at an earlier stage of myocardial dysfunction via improved phenotyping. This constitutes the first step towards further investigations in SCD needed to improve the prognosis and the quality of life. This article provides an updated review of the recent advances in the pathophysiology and diagnosis, and in addition, perspectives of new therapeutic approaches in SCD-related cardiac manifestations.

A reappraisal of the mechanisms underlying the cardiac complications of sickle cell anemia

Anemia, hemolysis-driven vasculopathy, and intrinsic myocardial injury have been proposed as predisposing factors to cardiac disease in sickle cell anemia (SCA). The individual impact of these mechanisms on the cardiac features of SCA and the way they influence complications such as sudden death and dysrhythmias have been unclear. Recent findings of an acquired restrictive SCA-related cardiomyopathy, driven by myocardial fibrosis, may explain some of these cardiac features. Given the complexity of cardiac pathology in SCA, using additional parameters to tricuspid regurgitant jet velocity (left atrial volume, diastolic parameters, NT-proBNP) may improve the accuracy of noninvasive screening for cardiopulmonary complications in SCA.

Applications of cardiac magnetic resonance imaging in sickle cell disease

Cardiac magnetic resonance imaging (CMR) has evolved from an effective research tool to a non-invasive clinical modality with versatile applications. The accuracy of volume measurements and functional assessment and the ability to identify unique myocardial tissue characteristics non-invasively are the primary advantages of CMR. The use of CMR in sickle cell disease (SCD) has been limited clinically to myocardial iron assessment. The use of other CMR applications to characterize the cardiac pathology in SCD is slowly emerging but remains limited to research level. In this review, we discuss some of the applications of CMR in studying cardiovascular diseases and its potential uses in SCD for research and clinical purposes.

Association between diffuse myocardial fibrosis and diastolic dysfunction in sickle cell anemia

Sickle cell anemia (SCA)-related cardiomyopathy is characterized by diastolic dysfunction and hyperdynamic features. Diastolic dysfunction portends early mortality in SCA. Diastolic dysfunction is associated with microscopic myocardial fibrosis in SCA mice, but the cause of diastolic dysfunction in humans with SCA is unknown. We used cardiac magnetic resonance measurements of extracellular volume fraction (ECV) to discover and quantify diffuse myocardial fibrosis in 25 individuals with SCA (mean age, 23 ± 13 years) and determine the association between diffuse myocardial fibrosis and diastolic dysfunction. ECV was calculated from pre- and post-gadolinium T1 measurements of blood and myocardium, and diastolic function was assessed by echocardiography. ECV was markedly increased in all participants compared with controls (0.44 ± 0.08 vs 0.26 ± 0.02, P < .0001), indicating the presence of diffuse myocardial fibrosis. Seventeen patients (71%) had diastolic abnormalities, and 7 patients (29%) met the definition of diastolic dysfunction. Participants with diastolic dysfunction had higher ECV (0.49 ± 0.07 vs 0.37 ± 0.04, P = .01) and N-terminal pro-brain natriuretic peptide (NT-proBNP; 191 ± 261 vs 33 ± 33 pg/mL, P = .04) but lower hemoglobin (8.4 ± 0.3 vs 10.9 ± 1.4 g/dL, P = .004) compared with participants with normal diastolic function. Participants with the highest ECV values (≥0.40) were more likely to have diastolic dysfunction (P = .003) and increased left atrial volume (57 ± 11 vs 46 ± 12 mL/m², P = .04) compared with those with ECV <0.4. ECV correlated with hemoglobin (r = -0.46, P = .03) and NT-proBNP (r = 0.62, P = .001). In conclusion, diffuse myocardial fibrosis, determined by ECV, is a common and previously underappreciated feature of SCA that is associated with diastolic dysfunction, anemia, and high NT-proBNP. Diffuse myocardial fibrosis is a novel mechanism that appears to underlie diastolic dysfunction in SCA.

Severe cardiac iron toxicity in two adults with sickle cell disease

BACKGROUND

Use of chronic blood transfusions as a treatment modality in patients with blood disorders places them at risk for iron overload. Since patients with β-thalassemia major (TM) are transfusion-dependent, most studies on iron overload and chelation have been conducted in this population. While available data suggest that compared to TM, patients with sickle cell disease (SCD) have a lower risk of extrahepatic iron overload, significant iron overload can develop. Further, previous studies have demonstrated a direct relationship between iron overload and morbidity and mortality rates in SCD. However, reports describing the outcome for patients with SCD and cardiac iron overload are rare.

STUDY DESIGN AND METHODS

We performed a retrospective analysis and identified two SCD patients with cardiac iron overload. We provide detailed descriptions of both cases and their outcomes.

RESULTS

Serum ferritin levels ranged between 17,000 and 19,000 μg/L. Both had liver iron concentrations in excess of 35 mg of iron per gram of dried tissue as well as evidence of cardiac iron deposition on magnetic resonance imaging. One patient died of an arrhythmia and had evidence of severe multiorgan iron overload via autopsy. On the other hand, after appropriate therapy, a second patient had improvement in cardiac function.

CONCLUSION

Improper treatment of iron overload in SCD can lead to a fatal outcome. Alternatively, iron overload may potentially be prevented or reversed with judicious use of blood transfusions and early use of chelation therapy, respectively.

Sickle cell anemia mice develop a unique cardiomyopathy with restrictive physiology

Cardiopulmonary complications are the leading cause of mortality in sickle cell anemia (SCA). Elevated tricuspid regurgitant jet velocity, pulmonary hypertension, diastolic, and autonomic dysfunction have all been described, but a unifying pathophysiology and mechanism explaining the poor prognosis and propensity to sudden death has been elusive. Herein, SCA mice underwent a longitudinal comprehensive cardiac analysis, combining state-of-the-art cardiac imaging with electrocardiography, histopathology, and molecular analysis to determine the basis of cardiac dysfunction. We show that in SCA mice, anemia-induced hyperdynamic physiology was gradually superimposed with restrictive physiology, characterized by progressive left atrial enlargement and diastolic dysfunction with preserved systolic function. This phenomenon was absent in WT mice with experimentally induced chronic anemia of similar degree and duration. Restrictive physiology was associated with microscopic cardiomyocyte loss and secondary fibrosis detectable as increased extracellular volume by cardiac-MRI. Ultrastructural mitochondrial changes were consistent with severe chronic hypoxia/ischemia and sarcomere diastolic-length was shortened. Transcriptome analysis revealed up-regulation of genes involving angiogenesis, extracellular-matrix, circadian-rhythm, oxidative stress, and hypoxia, whereas ion-channel transport and cardiac conduction were down-regulated. Indeed, progressive corrected QT prolongation, arrhythmias, and ischemic changes were noted in SCA mice before sudden death. Sudden cardiac death is common in humans with restrictive cardiomyopathies and long QT syndromes. Our findings may thus provide a unifying cardiac pathophysiology that explains the reported cardiac abnormalities and sudden death seen in humans with SCA.

Magnetic resonance safety

Magnetic resonance imaging (MRI) has a superior soft-tissue contrast compared to other radiological imaging modalities and its physiological and functional applications have led to a significant increase in MRI scans worldwide. A comprehensive MRI safety training to protect patients and other healthcare workers from potential bio-effects and risks of the magnetic fields in an MRI suite is therefore essential. The knowledge of the purpose of safety zones in an MRI suite as well as MRI appropriateness criteria is important for all healthcare professionals who will work in the MRI environment or refer patients for MRI scans. The purpose of this article is to give an overview of current magnetic resonance safety guidelines and discuss the safety risks of magnetic fields in an MRI suite including forces and torque of ferromagnetic objects, tissue heating, peripheral nerve stimulation, and hearing damages. MRI safety and compatibility of implanted devices, MRI scans during pregnancy, and the potential risks of MRI contrast agents will also be discussed, and a comprehensive MRI safety training to avoid fatal accidents in an MRI suite will be presented.

Abnormalities in aortic properties: a potential link between left ventricular diastolic function and ventricular-aortic coupling in sickle cell disease

Left ventricular (LV) diastolic dysfunction in patients with sickle cell disease (SCD) is associated with increased mortality. However, its mechanisms are not well known, preventing the development of effective therapies. We hypothesized that patients with SCD have altered aortic properties despite normal blood pressure, which may contribute towards the development of diastolic dysfunction. We studied 31 stable adult patients with SCD (32 ± 7 years) and 12 healthy controls of similar age (29 ± 10 years) who underwent echocardiography and cardiovascular magnetic resonance (CMR) imaging on the same day. Echocardiographic measurements of mitral inflow and mitral annulus velocities were used to evaluate LV diastolic function. CMR imaging included standard LV function evaluation and myocardial tissue characterization as well as velocity-encoded images of the ascending aorta to measure aortic diastolic cross-sectional area, distensibility, as well as peaks and volumes of the global, forward and backward blood flow rate. Compared to controls, SCD patients had increased aortic diastolic area, global stroke volume, and both forward and backward flow, while aortic distensibility and peripheral blood pressure were similar. Furthermore, peak backward flow rate and volume were able to discriminate between patients with and without diastolic dysfunction. Our findings show that some aortic properties are altered in SCD patients and may be associated with diastolic dysfunction despite normal systolic blood pressure. If confirmed in larger studies, these aortic changes could be a novel therapeutic target to prevent or delay the development of LV diastolic dysfunction in SCD and thus potentially improve outcomes in these patients.

New insights into transfusion-related iron toxicity: Implications for the oncologist

Iron overload is a potentially life-threatening consequence of multiple red-blood-cell transfusions. Here, we review factors affecting excess iron distribution and its damage to specific tissues, as well as mechanisms of oncogenesis by iron. Although consequences of transfusional iron overload are best described in thalassemia major and related inherited anemias, they are increasingly recognized in acquired conditions, such as myelodysplastic syndromes (MDS). Iron overload in MDS not only impacts on certain tissues, but may affect the clonal evolution of MDS through generation of reactive oxygen species. Iron overload may also influence hematopoietic-stem-cell-transplantation outcomes. Novel MRI methods for assessing body iron have impacted significantly on outcome in inherited anemias by allowing monitoring of iron burden and iron chelation therapy. This approach is increasingly being used in MDS and stem-cell-transplant procedures. Knowledge gained from managing transfusional iron overload in inherited anemias may be translated to general oncology, with potential for improved patient outcomes.

The pathophysiology of transfusional iron overload

The pathophysiologic consequences of transfusional iron overload (TIO) as well as the benefits of iron chelation therapy are best described in thalassemia major, although TIO is increasingly seen in other clinical settings. These consequences broadly reflect the levels and distribution of excess storage iron in the heart, endocrine tissues, and liver. TIO also increases the risk of infection, due to increased availability of labile iron to microorganisms. The authors suggest that extrahepatic iron distribution, and hence toxicity, is influenced by balance between generation of nontransferrin-bound iron from red cell catabolism and the utilization of transferrin iron by the erythron.

Cardiac iron overload in sickle-cell disease

Chronically transfused sickle cell disease (SCD) patients have lower risk of myocardial iron overload (MIO) than comparably transfused thalassemia major (TM) patients. However, cardioprotection is incomplete. We present the clinical characteristics of six patients who have prospectively developed MIO, to identify potential risk factors for cardiac iron accumulation. From 2002 to 2011, cardiac, hepatic, and pancreatic iron overload were assessed by R2 and R2 * magnetic resonance imaging techniques in 201 chronic transfused SCD patients as part of their clinical care. At the time, they developed MIO, five of six patients had been on chronic transfusion for more than 11 years; only one was on exchange transfusion. The time to MIO was correlated with reticulocyte and hemoglobin S percentages. All patients had qualitatively poor chelation compliance (<50%). All patients had serum ferritin levels >4600 ng/ml and liver iron concentration >22 mg/g. Pancreatic R2 * was >100 Hz in every patient studied (5/6). Cardiac iron rose proportionally to pancreas R2 *, with all patients having pancreas R2 *>100 Hz when cardiac iron was present. MIO had a threshold relationship with liver iron that was higher than observed in TM patients. In conclusion, MIO occurs in a small percentage of chronically transfused SCD patients and is only associated with exceptionally poor control of total body iron stores. Duration of chronic transfusion is clearly important but other factors, such as levels of effective erythropoiesis, appear to contribute to cardiac risk. Pancreas R2 * can serve as a valuable screening tool for cardiac iron in SCD patients.

Mechanistic insights and characterization of sickle cell disease-associated cardiomyopathy

BACKGROUND

Cardiovascular disease is an important cause of morbidity and mortality in sickle cell disease (SCD). We sought to characterize sickle cell cardiomyopathy using multimodality noninvasive cardiovascular testing and identify potential causative mechanisms.

METHODS AND RESULTS

Stable adults with SCD (n=38) and healthy controls (n=13) prospectively underwent same day multiparametric cardiovascular magnetic resonance (cine, T2* iron, vasodilator first pass myocardial perfusion, and late gadolinium enhancement imaging), transthoracic echocardiography, and applanation tonometry. Compared with controls, patients with SCD had severe dilation of the left ventricle (124±27 vs 79±12 mL/m(2)), right ventricle (127±28 vs 83±14 mL/m(2)), left atrium (65±16 vs 41±9 mL/m(2)), and right atrium (78±17 vs 56±17 mL/m(2); P<0.01 for all). Patients with SCD also had a 21% lower myocardial perfusion reserve index than control subjects (1.47±0.34 vs 1.87±0.37; P=0.034). A significant subset of patients with SCD (25%) had evidence of late gadolinium enhancement, whereas only 1 patient had evidence of myocardial iron overload. Diastolic dysfunction was present in 26% of patients with SCD compared with 8% in controls. Estimated filling pressures (E/e', 9.3±2.7 vs 7.3±2.0; P=0.0288) were higher in patients with SCD. Left ventricular dilation and the presence of late gadolinium enhancement were inversely correlated to hepatic T2* times (ie, hepatic iron overload because of frequent blood transfusions; P<0.05 for both), whereas diastolic dysfunction and increased filling pressures were correlated to aortic stiffness (augmentation pressure and index, P<0.05 for all).

CONCLUSIONS

Sickle cell cardiomyopathy is characterized by 4-chamber dilation and in some patients myocardial fibrosis, abnormal perfusion reserve, diastolic dysfunction, and only rarely myocardial iron overload. Left ventricular dilation and myocardial fibrosis are associated with increased blood transfusion requirements, whereas left ventricular diastolic dysfunction is predominantly correlated with increased aortic stiffness.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01044901.

Left ventricular systolic function in sickle cell anemia: a meta-analysis

BACKGROUND

We sought to evaluate whether patients with sickle cell anemia (SCA) have left ventricular (LV) systolic dysfunction.

METHODS AND RESULTS

We conducted a Medline, Embase, Ebscohost, and Google scholar literature search articles published before April 2010. All studies that compared any measure of LV function (eg, ejection fraction [EF], fractional shortening [FS], or cardiac index [CI]) between normal control subjects and SCA (hemoglobin SS) patients were included. Among 57 studies that qualified for review, 19 studies including 841 SCA patients and 554 control subjects met the inclusion criteria. There were no significant differences in either LVEF (Hedge g = 0.15; 95% confidence interval -0.84 to 1.14; P = .76) or FS (P = .28) between SCA patients and control subjects. CI was significantly higher (P < .001) and LV end-systolic stress-volume index (load independent) was significantly lower (P < .001) in SCA patients. All LV systolic measures inversely correlated with age (all P < .001). LV end-systolic and -diastolic dimensions were significantly higher in SCA patients and increased with age.

CONCLUSIONS

SCA patients have similar load-dependent but lower load-independent measures of LV systolic function than control subjects. SCA is associated with LV dilation. LV structural and functional abnormalities appear to be age dependent with progressive LV dilation and impairment over time.

Right and left ventricular function and myocardial scarring in adult patients with sickle cell disease: a comprehensive magnetic resonance assessment of hepatic and myocardial iron overload

BACKGROUND

Patients with Sickle cell disease (SCD) who receive regular transfusions are at risk for developing cardiac toxicity from iron overload. The aim of this study was to assess right and left cardiac volumes and function, late gadolinium enhancement (LGE) and iron deposits in patients with SCD using CMR, correlating these values with transfusion burden, ferritin and hemoglobin levels.

METHODS

Thirty patients with SCD older than 20 years of age were studied in a 1.5 T scanner and compared to age- and sex-matched normal controls. Patients underwent analysis of biventricular volumes and function, LGE and T2* assessment of the liver and heart.

RESULTS

When compared to controls, patients with SCD presented higher left ventricular (LV) volumes with decreased ejection fraction (EF) with an increase in stroke volume (SV) and LV hypertrophy. The right ventricle (RV) also presented with a decreased EF and hypertrophy, with an increased end-systolic volume. Although twenty-six patients had increased liver iron concentrations (median liver iron concentration value was 11.83 ± 9.66 mg/g), only one patient demonstrated an abnormal heart T2* < 20 msec. Only four patients (13%) LGE, with only one patient with an ischemic pattern.

CONCLUSIONS

Abnormal heart iron levels and myocardial scars are not a common finding in SCD despite increased liver iron overload. The significantly different ventricular function seen in SCD compared to normal suggests the changes in RV and LV function may not be due to the anemia alone. Future studies are necessary to confirm this association.

Comparison of biventricular dimensions and function between pediatric sickle-cell disease and thalassemia major patients without cardiac iron

Patients with chronic anemia develop compensatory ventricular dilation, even when maintained on chronic transfusion regimens. It is important to characterize these effects to interpret pathological changes in cardiac dimensions and function introduced by iron overload and sickle cell vasculopathy. Our primary goal was to compare biventricular dimensions and function assessed by cardiovascular magnetic resonance (CMR) in pediatric, chronically-transfused sickle-cell disease (SCD) and thalassemia major (TM) patients who had normal cardiac iron levels. Moreover, we explored systematic sex differences in ventricular dimensions in both populations. We identified 261 studies suitable for analysis from 64 patients with SCD (34 females) and 49 patients with TM (20 females). All demographic and CMR parameters were inversely weighted by the number of exams. In both populations, males had larger left and right ventricular dimensions than females, with a more marked effect observed in patients with SCD. Compared to patients with TM, patients with SCD showed significantly greater biventricular dilation and left ventricular hypertrophy. This difference could not be explained by different hemoglobin levels, cardiac iron overload, and systolic blood pressure. The left ventricular (LV) ejection fraction (EF) for the males and the right ventricular (RV) EF for both the sexes were comparable between SCD and TM groups, while females with SCD had significantly lower LV EF than females with TM. Our results represent important baseline findings that place changes introduced by iron overload as well as systemic and pulmonary vasculopathy in proper context.

Evaluation of myocardial deformation in patients with sickle cell disease and preserved ejection fraction using three-dimensional speckle tracking echocardiography

BACKGROUND

Sickle cell disease (SCD) is a hemoglobinopathy that affects one in 500 African Americans. Although it is well established that patients with SCD have left ventricular (LV) diastolic dysfunction, it is not clear whether they have subtle LV systolic dysfunction despite preserved ejection fraction (EF). We used three-dimensional speckle tracking echocardiography (3DSTE) to assess changes in both systolic and diastolic LV function in SCD.

METHODS

Transthoracic real time 3D images were obtained (Philips iE33) in 56 subjects, including 28 stable outpatients with SCD (age 33 ± 7 years) and 28 normal controls (age 35 ± 9 years). 3DSTE was performed using prototype software (4DLV Analysis, TomTec) to obtain LV volume and deformation time curves, from which indices of systolic and diastolic LV function were calculated.

RESULTS

In SCD patients, 3DSTE-derived LV filling parameters were significantly different from normal controls, reflecting an increase in both rapid and atrial filling volumes and prolonged active relaxation, depicted by a decrease in filling volume fractions at fixed times and an increase in rapid filling duration. Global LV systolic function was not only preserved but increased compared to controls, as reflected by significantly increased global longitudinal strain. Importantly, twist angle and torsion as well as radial and circumferential components of 3D strain were similar in both groups.

CONCLUSIONS

3DSTE was able to confirm diastolic dysfunction, as expected in some patients with SCD. However, 3DSTE strain analysis did not reveal any changes in LV systolic function. These findings provide novel insight into the pathophysiology of the cardiovascular complications of SCD.

Assessment of cardiac iron deposition in sickle cell disease using 3.0 Tesla cardiovascular magnetic resonance

Many patients with sickle cell disease receive blood transfusions as a life-saving treatment. However, excess transfusions may lead to increased body iron burden. Specifically, heart failure due to cardiac iron overload is the leading cause of death in these patients. The purpose of this study was to investigate the potential role of high-field 3.0-Tesla (T) cardiovascular magnetic resonance (CMR) for assessment of cardiac iron content by measuring the transverse relaxivity rate R2*. The R2* was measured in calibrated phantoms with different iron concentrations at 3.0T and 1.5T using optimized pulse sequences. Myocardial R2* was measured at 3.0T in a group of sickle cell disease patients with different disease stages, and the results were compared to the serum ferritin levels and hepatic R2*. The phantom R2* measurements at 3.0T were double those at 1.5T, and the measurements of both systems showed linear relationships with iron concentration. The 3.0T R2* was more sensitive than 1.5T in detecting low iron concentration. In patients, myocardial R2* had weak and good correlations with hepatic R2* and serum ferritin levels, respectively. Bland-Altman analysis showed low inter- and intra-observer variabilities. In conclusion, measuring myocardial R2* at 3.0T is a promising technique with high sensitivity and reproducibility for evaluating cardiac iron overload in sickle cell disease patients.

Evaluation of the acute effects of distal coronary microembolization using multidetector computed tomography and magnetic resonance imaging

The purpose of this study was to test the potential of clinical imaging modalities, 64-slice multidetector computed tomography (MDCT) and 1.5T magnetic resonance imaging (MRI) for qualitative and quantitative evaluation of acute microinfarcts and to determine the effects of <120 μm microemboli on left ventricular function, perfusion, cardiac injury biomarkers, arrhythmia, and cellular and vascular structures. Under X-ray fluoroscopy, 40-120 μm (16 mm(3) ) microemboli were delivered to embolize the left anterior descending (LAD) coronary artery of nine pigs. MDCT/MRI were performed at 72 h in a single session. Microinfarcts were visible in six of nine animals on delayed contrast-enhanced MDCT/MR images but measurable in all animals using semiautomated threshold methods. Other MDCT and MRI sequences demonstrated decline in left ventricular ejection fraction, regional strain and perfusion in visible and invisible microinfarcted regions. Microemboli caused significant elevation in cardiac injury enzymes and arrhythmias. Various sizes of microinfarcts appeared microscopically as distinct aggregates of macrophages replacing myocardium. Semiautomated threshold methods are necessary to measure and confirm/deny the presence of myocardial microinfarcts. This study offers support for alternative applications of MDCT/MRI in assessing clinical cases in which microemboli <120 μm escape protective devices during percutaneous coronary interventions. Although microembolization resulted in no mortality, it caused left ventricular dysfunction, perfusion deficit, cellular damage increase in cardiac injury enzymes, and arrhythmias.

Safety of gadolinium-based contrast material in sickle cell disease

PURPOSE

To assess the safety of intravenously administered gadolinium-based contrast material in sickle cell disease (SCD) patients.

MATERIALS AND METHODS

All pediatric and adult SCD patients evaluated by magnetic resonance imaging (MRI) at our institution between January 1995 and July 2009 were identified. The medical records of SCD patients who underwent contrast-enhanced MRI as well as an equal-sized cohort of SCD patients who underwent unenhanced MRI were reviewed for adverse (vaso-occlusive and hemolytic) events within 1 week following imaging.

RESULTS

Eight (five mild and three moderate) adverse events were documented within 1 week following contrast-enhanced MRI (38 patients and 61 contrast injections), while six (five mild and one moderate) similar events occurred within 1 week following unenhanced MRI (61 patients and 61 unenhanced MRI examinations). This difference in the number of adverse events was not statistically significant (odds ratio = 1.4; 95% confidence interval [CI] 0.4, 5.2). No severe adverse event occurred in either patient cohort.

CONCLUSION

Gadolinium-based contrast materials do not appear to be associated with increased risk of vaso-occlusive or hemolytic adverse events when administered to SCD patients. Larger, prospective studies using multiple gadolinium-based contrast materials would be useful to confirm the results of our investigation.

Iron overload in thalassemia and related conditions: therapeutic goals and assessment of response to chelation therapies

Transfusional iron loading inevitably results in hepatic iron accumulation, with variable extrahepatic distribution that is typically less pronounced in sickle cell disease than in thalassemia disorders. Iron chelation therapy has the goal of preventing iron-mediated tissue damage through controlling tissue iron levels, without incurring chelator-mediated toxicity. Historically, target levels for tissue iron control have been limited by the increased frequency of deferoxamine-mediated toxicity and low levels of iron loading. With newer chelation regimes, these limitations are less evident. The reporting of responses to chelation therapies has typically focused on average changes in serum ferritin in patient populations. This approach has three limitations. First, changes in serum ferritin may not reflect trends in iron balance equally in all patients or for all chelation regimens. Second, this provides no information about the proportion of patients likely respond. Third, this gives insufficient information about iron trends in tissues such as the heart. Monitoring of iron overload has advanced with the increasing use of MRI techniques to estimate iron balance (changes in liver iron concentration) and extrahepatic iron distribution (myocardial T2*). The term nonresponder has been increasingly used to describe individuals who fail to show a downward trend in one or more of these variables. Lack of a response of an individual may result from inadequate dosing, high transfusion requirement, poor treatment adherence, or unfavorable pharmacology of the chelation regime. This article scrutinizes evidence for response rates to deferoxamine, deferiprone (and combinations), and deferasirox.

Ventricular diastolic dysfunction in sickle cell anemia is common but not associated with myocardial iron deposition

BACKGROUND

Cardiac failure from myocardial iron deposition is a severe complication in patients with transfusion-related iron overload. Progressive heart damage from iron overload can cause left ventricular systolic and diastolic dysfunction in patients with hematologic disorders. Since nontransfused patients with sickle cell anemia (SCA) have a high incidence of diastolic dysfunction, we investigated the relationships among transfusional iron burden, myocardial iron deposition, and diastolic ventricular dysfunction by T2*-MRI and tissue Doppler echocardiography in iron-overloaded children with SCA.

PROCEDURE

Children (> or =7 years) with SCA and iron overload (serum ferritin >1,000 ng/ml or > or =18 lifetime transfusions) were eligible. Serum ferritin and hepatic iron content (HIC) were measured and participants underwent nonsedated T2*-MRI of the heart, echocardiogram, electrocardiogram, and multi-uptake gated acquisition (MUGA) scan. Age-matched normative echocardiographic data were used for comparison.

RESULTS

Among 30 children with SCA (median age, 13 years) and iron overload, mean (+/-SD) HIC and serum ferritin were 10.8 mg Fe/g (+/-5.9 mg Fe/g) and 3,089 ng/ml (+/-2,167 ng/ml), respectively. Mean T2*-MRI was 33 msec (+/-7 msec, range, 22-49). Echocardiography showed a high prevalence of diastolic dysfunction (77% and 45% abnormally low mean mitral annular velocity and mean tricuspid annular velocity, respectively); however, echocardiogram and MUGA scan findings were not significantly associated with HIC or T2*-MRI.

CONCLUSIONS

Diastolic dysfunction is not associated with transfusional iron burden or myocardial iron deposition among children with SCA. Diastolic dysfunction likely results from disease pathophysiology and severity rather than iron overload.

Heterogeneous microinfarcts caused by coronary microemboli: evaluation with multidetector CT and MR imaging in a swine model

PURPOSE

To directly compare the sensitivity of 64-section multidetector computed tomography (CT) with that of 1.5-T magnetic resonance (MR) imaging in the depiction and measurement of heterogeneous 7-8-week-old microinfarcts and the quantification of regional left ventricular (LV) function and perfusion in the territory of coronary intervention in a swine model.

MATERIALS AND METHODS

Approval was obtained from the institutional animal committee. An x-ray/MR system was used to catheterize the left anterior descending (LAD) coronary artery with x-ray guidance and to delineate the perfusion territory. The vessel was selectively microembolized in six pigs with small-diameter embolic material (40-120 microm, 250000 count). At 7-8 weeks after microembolization, multidetector CT and MR imaging were used to assess LV function, first-pass perfusion, and delayed contrast enhancement in remote myocardium and microinfarct scars. Histochemical staining with triphenyltetrazolium chloride (TTC) was used to confirm and quantify heterogeneous microinfarct scars. The two-tailed Wilcoxon signed rank test was used to detect differences between modalities and myocardial regions.

RESULTS

The LAD territory was 32.4% +/- 3.8(stadard error of the mean) of the LV mass. Multidetector CT and MR imaging have similar sensitivity in the detection of regional and global LV dysfunction and extent of microinfarct. The mean LV end-diastolic volume, end-systolic volume, and ejection fraction were 93 mL +/- 8, 46 mL +/- 4, and 50% +/- 3, respectively, on multidetector CT images and 92 mL +/- 8, 48 mL +/- 5, and 48% +/- 3, respectively, on MR images (P > or = .05). The extent of heterogeneous microinfarct was not significantly different between multidetector CT (6.3% +/- 0.8 of the LV mass), MR imaging (6.6% +/- 0.5 of the LV mass), and TTC staining (7.0% +/- 0.6 of the LV mass). First-pass multidetector CT and MR imaging demonstrated significant regional differences (P < .05) in time to peak between the heterogeneous microinfarct and remote myocardium (17.0 seconds +/- 0.3 and 12.4 seconds +/- 0.6, respectively, for multidetector CT and 17.2 seconds +/- 0.8 and 12.5 seconds +/- 1.0, respectively, for MR imaging).

CONCLUSION

Modern multidetector CT and MR imaging are sensitive modalities with which to depict heterogeneous microinfarcts and determine regional LV dysfunction and decreased perfusion in the territory of intervention. (c) RSNA, 2010.

Clinical practice: heart failure in children. Part I: clinical evaluation, diagnostic testing, and initial medical management

Current evidence suggests that almost half of all children with cardiomyopathy and symptomatic heart failure will die or require a cardiac transplant within 5 years of diagnosis. The recognition, diagnostic assessment, and treatment of heart failure in children are therefore challenging undertakings, to say the least. It involves an assessment of cardiac appearance and function, adaptation of the child as a whole, and a diagnostic approach that evaluates many possible root causes. This review is intended to assist the practicing pediatrician and cardiologist by providing a framework for this diagnostic assessment and to give an overview of the treatment options available for children with heart failure. In this first part, we will focus on clinical evaluation, diagnostic testing, and initial medical management. In the second part of this series, the maintenance treatment and treatment options applicable when medical treatment is insufficient will be addressed.

Reperfusion injury components and manifestations determined by cardiovascular MR and MDCT imaging

Advances in magnetic resonance (MR) and computed tomography (CT) imaging have improved visualization of acute and scar infarct. Over the past decade, there have been and continues to be many significant technical advancements in cardiac MR and multi-detector computed tomography (MDCT) technologies. The strength of MR imaging relies on a variety of pulse sequences and the ability to noninvasively provide information on myocardial structure, function and perfusion in a single imaging session. The recent technical developments may also allow CT technologies to rise to the forefront for evaluating clinical ischemic heart disease. Components of reperfusion injury including myocardial edema, hemorrhage, calcium deposition and microvascular obstruction (MO) have been demonstrated using MR and CT technologies. MR imaging can be used serially and noninvasively in assessing acute and chronic consequences of reperfusion injury because there is no radiation exposure or administration of radioactive materials. MDCT is better suited for assessing coronary artery stenosis and as an alternative technique for assessing viability in patients where MR imaging is contraindicated. Changes in left ventricular (LV) volumes and function measured on cine MR are directly related to infarct size measured on delayed contrast enhanced images. Recent MR studies found that transmural infarct, MO and peri-infarct zone are excellent predictors of poor post-infarct recovery and mortality. Recent MR studies provided ample evidence that growth factor genes and stem cells delivered locally have beneficial effects on myocardial viability, perfusion and function. The significance of deposited calcium in acute infarct detected on MDCT requires further studies. Cardiac MR and MDCT imaging have the potential for assessing reperfusion injury components and manifestations.

Cardiac iron across different transfusion-dependent diseases

Iron overload occurs in patients who require regular blood transfusions to correct genetic and acquired anaemias, such as beta-thalassaemia major, sickle cell disease, and myelodysplastic syndromes. Although iron overload causes damage in many organs, accumulation of cardiac iron is a leading cause of death in transfused patients with beta-thalassaemia major. The symptoms of cardiac iron overload will occur long after the first cardiac iron accumulation, at a point when treatment is more complex than primary prevention would have been. Direct measurement of cardiac iron using T2* magnetic resonance imaging, rather than indirect methods such as measuring serum ferritin levels or liver iron concentration have contributed to earlier recognition of myocardial iron loading and prevention of cardiac toxicity. Cardiac siderosis occurs in all transfusional anaemias, but the relative risk depends upon the underlying disease state, transfusional load, and chelation history. All three available iron chelators can be used to remove cardiac iron, but each has unique physical properties that influence their cardiac efficacy. More prospective trials are needed to assess the effects of single-agent or combination iron chelation therapy on the levels of cardiac iron and cardiac function. Ultimately, iron chelation therapies should be tailored to meet individual patient needs and lifestyle demands.

Practical implications of liver and heart iron load assessment by T2*-MRI in children and adults with transfusion-dependent anemias

This study examined the relationship between hepatic and myocardial iron concentration, assessed by T2*-MRI in 66 patients (3-82 years) with transfusion-dependent anemias and thalassemia intermedia, to determine whether hepatic iron levels alone suffice for chelation adjustments. We found a poor correlation between hepatic and myocardial iron (r = 0.10, P = 0.43) and identified a subgroup (14%) with increased myocardial iron without a matched degree of hepatic hemosiderosis. Left ventricular ejection fraction was insensitive for detecting elevated myocardial iron. These findings were present in both adult and pediatric patients. We recommend therapeutic monitoring of iron burden by evaluation of both liver and myocardial iron with T2*-MRI.