Early detection of left ventricular dysfunction in patients with beta thalassaemia major by dobutamine stress echocardiography

Heart failure in haemoglobinopathies: pathophysiology, clinical phenotypes, and management

Hereditary haemoglobinopathies, mainly beta-thalassemia and sickle cell disease, constitute the most common monogenic disorders in humans, and although once geographically confined, they are currently globally distributed. They are demanding clinical entities that require multidisciplinary medical management. Despite their genotypic and phenotypic heterogeneity, the haemoglobinopathies share several similarities in pathophysiology, clinical manifestations, therapeutic requirements, and complications, among which heart failure (HF) represents a leading cause of mortality and morbidity. However, haemoglobinopathies have generally been addressed in a rather fragmentary manner. A unifying approach focusing on the underlying similarities of HF attributes in the two main entities might contribute to their better understanding, characterization, and management. In the present review, we attempt such an approach to the pathophysiology, clinical phenotypes, and management of HF in haemoglobinopathies.

Combined Iron Chelator and Antioxidant Exerted Greater Efficacy on Cardioprotection Than Monotherapy in Iron-Overloaded Rats

Background

Iron chelators are used to treat iron overload cardiomyopathy patients. However, a direct comparison of the benefits of three common iron chelators (deferoxamine (DFO), deferiprone (DFP) and deferasirox (DFX)) or an antioxidant (N-acetyl cysteine (NAC)) with a combined DFP and NAC treatments on left ventricular (LV) function with iron overload has not been investigated.

Methods and Findings

Male Wistar rats were fed with either a normal diet or a high iron diet (HFe group) for 4 months. After 2 months, the HFe-fed rats were divided into 6 groups to receive either: a vehicle, DFO (25 mg/kg/day), DFP (75 mg/kg/day), DFX (20 mg/kg/day), NAC (100 mg/kg/day) or the combined DFP and NAC for 2 months. Our results demonstrated that HFe rats had increased plasma non-transferrin bound iron (NTBI), malondialdehyde (MDA), cardiac iron and MDA levels and cardiac mitochondrial dysfunction, leading to LV dysfunction. Although DFO, DFP, DFX or NAC improved these parameters, leading to improved LV function, the combined DFP and NAC therapy caused greater improvement, leading to more extensively improved LV function.

Conclusions

The combined DFP and NAC treatment had greater efficacy than monotherapy in cardioprotection through the reduction of cardiac iron deposition and improved cardiac mitochondrial function in iron-overloaded rats.

Left ventricular torsional mechanics and myocardial iron load in beta-thalassaemia major: a potential role of titin degradation

BACKGROUND

Iron may damage sarcomeric proteins through oxidative stress. We explored the left ventricular (LV) torsional mechanics in patients with beta-thalassaemia major and its relationship to myocardial iron load. Using HL-1 cell and B6D2F1 mouse models, we further determined the impact of iron load on proteolysis of the giant sarcomeric protein titin.

METHODS AND RESULTS

In 44 thalassaemia patients aged 25 ± 7 years and 38 healthy subjects, LV torsion and twisting velocities were determined at rest using speckle tracking echocardiography. Changes in LV torsional parameters during submaximal exercise testing were further assessed in 32 patients and 17 controls. Compared with controls, patients had significantly reduced LV apical rotation, torsion, systolic twisting velocity, and diastolic untwisting velocity. T2* cardiac magnetic resonance findings correlated with resting diastolic untwisting velocity. The increments from baseline and resultant LV torsion and systolic and diastolic untwisting velocities during exercise were significantly lower in patients than controls. Significant correlations existed between LV systolic torsion and diastolic untwisting velocities in patients and controls, both at rest and during exercise. In HL-1 cells and ventricular myocardium of B6D2F1 mice overloaded with iron, the titin-stained pattern of sarcomeric structure became disrupted. Gel electrophoresis of iron-overloaded mouse myocardial tissue further showed significant decrease in the amount of titin isoforms and increase in titin degradation products.

CONCLUSIONS

Resting and dynamic LV torsional mechanics is impaired in patients with beta-thalassaemia major. Cell and animal models suggest a potential role of titin degradation in iron overload-induced alteration of LV torsional mechanics.

Cardiac stress testing after surgery for congenital heart disease

PURPOSE OF REVIEW

Heart failure is an important problem after surgical correction of congenital heart disease. Timely recognition may be difficult. Recent developments in exercise testing and stress-imaging may change the management of patients with congenital heart disease.

RECENT FINDINGS

Exercise tests are commonly used in the follow-up of patients with congenital heart disease. Maximal exercise studies are not always feasible in this patient population. Variables of submaximal exercise and ventilator efficiency have shown a good correlation with variables of maximal exercise and have been suggested to relate to long-term cardiac function.For evaluation of submaximal exercise, stress imaging may reveal abnormal responses unrecognized at rest. Both physical exercise as well as pharmacological stress may be used in combination with various imaging modalities. For practical reasons, dobutamine is most widely used to generate and mimic stress and is well tolerated in low doses. Particularly in lesions affecting the right ventricle and with single ventricular physiology after the Fontan operation, magnetic resonance stress imaging has provided additional insight into the cardiac function.

SUMMARY

The abnormal stress responses can potentially be used for risk assessment in the follow-up of patients with congenital cardiac disease. Further studies are required to provide common protocols for stress imaging.

Contractility reserve in children undergoing dialysis by dobutamine stress echocardiography

Left ventricular hypertrophy is an adaptive mechanism in children undergoing chronic dialysis to improve contractility at rest. The aim of this study was to determine the left ventricular performance and contractility reserve by "dobutamine stress echocardiography" in children undergoing chronic dialysis. Thirty-five children undergoing dialysis and 24 healthy subjects were enrolled in this prospective study. We evaluated contractility by means of end-systolic wall stress-velocity of circumferential fiber shortening (VCFc) in 24 healthy subjects and 35 dialysis patients. Dobutamine stress echocardiography was obtained only in children undergoing dialysis. Patients were divided into two groups according to left ventricular mass index. Contractile reserve was estimated by the difference in contractility at rest versus during echocardiography. Significantly higher VCFc (p = 0.008) and VCFc (p = 0.002) differences at rest were observed in the patient group compared to healthy subjects. Children undergoing dialysis had a higher left ventricular mass index compared with controls (42.38 ± 12.41 vs. 17.57 ± 3.66 g/m(2.7), respectively; p = 0.001). Patients with left ventricular hypertrophy had a significantly lower contractile reserve compared with patients without left ventricular hypertrophy (p = 0.013). These findings suggest that children undergoing dialysis have increased left ventricular mass and contractility at rest. However, the contractile reserve during dobutamine stress echocardiography was reduced. Dobutamine stress echocardiography may identify children undergoing dialysis at risk of progressing to systolic dysfunction and heart failure.

Stress imaging in congenital cardiac disease

In patients with coronary arterial disease, stress imaging is able to demonstrate abnormalities in the motion of the ventricular walls, and abnormalities in coronary arterial perfusion not apparent at rest. It can also provide information on prognostic factors. In patients with congenitally malformed hearts, stress imaging is used to determine contractile reserve, abnormalities of mural motion, and global systolic function, but also to assess diastolic and vascular function. In most of these patients, stress is usually induced using pharmacological agents, mainly dobutamine given in varying doses. The clinical usefulness of abnormal responses to the stress induced in such patients has to be addressed in follow-up studies. The abnormal stress might serve as surrogate endpoints, predicting primary endpoints at an early stage, which are useful for stratification of risk in this population of growing patients. We review here the stress imaging studies performed to date in patients with congenitally malformed hearts, with a special emphasis on echocardiography and cardiac magnetic resonance imaging.

Advances in management of thalassemia

Thalassemias represent the most common single-gene disorder causing a major public health problem in India. Thalassemia and hemoglobinopathies probably developed over 7000 years ago as a defense against malaria. In simple terms, thalassemia is caused by a mutation in either the â-globin chain or the á-globin chain which combine equally in red cells to form hemoglobin. These mutations lead to varying degree of anemia resulting into thalassemia minor, intermedia or major. Present write up relates to advances in the management of â-thalassemia major.

Management of pregnancy in a patient with beta thalassaemia major

beta thalassaemia is one of the world's most wide-spread monogenetic disorders. Advances in the management of beta thalassaemia major by extensive blood transfusions and chelation therapy have improved survival of patients into adult life. Due to the prolonged life expectancy and improvements in quality of life, pregnancy has now become an important issue for patients and clinicians. We report a case of a pregnant patient with beta thalassaemia major who underwent a successful caesarean section under spinal anaesthesia. The multidisciplinary approach to management of beta thalassaemia major and pregnancy is discussed.

Ventriculo-vascular interactions in patients with beta thalassaemia major

OBJECTIVES

To determine potential interactions between the heart and arterial system in patients with beta thalassaemia major.

DESIGN AND PATIENTS

Vascular compliance, systemic vascular resistance, and left ventricular (LV) contractility was determined in 34 asymptomatic thalassaemia patients at 2-4 hours after blood transfusion and also in 34 age and sex matched controls using a non-invasive device. The results were compared between groups and inter-relationships between LV contractility and indices of vascular load were explored.

SETTING

Tertiary paediatric cardiac centre.

RESULTS

When compared with controls, patients had greater systemic vascular resistance (1633 (259) v 1377 (276) dynes/s/cm5, p < 0.001) and effective arterial elastance (E(a)) (1.86 (0.25) v 1.65 (0.29) mm Hg/ml, p = 0.001), an index of combined pulsatile and static vascular load. On the other hand, their systolic blood pressure (104 (9) v 112 (13) mm Hg, p = 0.006), pulse pressure (45 (9) v 57 (10) mm Hg, p < 0.001), adjusted systemic vascular compliance (1.21 (0.09) v 1.37 (0.14), p < 0.001), adjusted brachial artery distensibility (21 (0.29) v 7.95 (0.29)%/mm Hg, p < 0.001) and LV+dP/dt (1059 (183) v 1239 (237) mm Hg/s, p = 0.001) were significantly lower. Significant determinants of LV contractility, as reflected by LV+dP/dt, were age (standardised beta = -0.24, p = 0.003), body mass index (standardised beta = -0.34, p = 0.004), systolic blood pressure (standardised beta = 0.90, p < 0.001), and effective E(a) (standardised beta = -0.50, p < 0.001) (model R2 = 0.69). No significant correlation existed between serum ferritin concentration and any of the cardiac or vascular indices.

CONCLUSION

An unfavourable ventriculo-vascular interaction, as characterised by impaired cardiac contractility and increased static and pulsatile vascular load, occurs in patients with beta thalassaemia major.

Early detection of cardiac dysfunction in thalassemic patients by radionuclide angiography and heart rate variability analysis

BACKGROUND

Cardiac dysfunction remains the major cause of death in beta-thalassemia. Aim of this study was to assess early myocardial damage in thalassemic patients with no symptoms or echocardiographic evidence of dysfunction at routine monitoring.

METHODS

Twenty patients (seven females; median 25 yr [first quartile 22,third quartile 28]) with beta-thalassemia underwent radionuclide angiography (RNA) at rest and during low-dose dobutamine infusion (5-10 gamma/kg/min). Right and left ventricular ejection fractions (EF) were determined by first-pass method and gated equilibrium acquisition, respectively. Twenty-four-hour Holter monitoring with time-domain heart rate variability (HRV) assessment and echocardiographic follow-up (21 months [5,27]) were performed.

RESULTS

Eleven patients showed regional wall motion abnormalities at RNA; left ventricular EF, HR and diastolic measurements significantly increased after dobutamine infusion. Patients with abnormal RNA right ventricular EF (n = 8, <0.45) showed lower echocardiographic left ventricular EF at the enrollment (0.54 [0.50,0.61] vs. 0.62 [0.56,0.67], P = 0.02) than those with a normal right ventricular EF. Patients with reduced standard deviation of the averages of RR intervals in all 5-minute periods of entire recording (SDANN) (n = 6, <100 ms), a measure of HRV, had lower echocardiographic left ventricular EF (0.53 [0.49,0.62] vs. 0.62 [0.56,0.66], P = 0.03) and lower fractional shortening (0.28 [0.25,0.32] vs. 0.36 [0.30,0.39], P = 0.003) at the enrollment than those with normal SDANN. No significant association was found between RNA and HRV measurements and follow-up left ventricular function.

CONCLUSIONS

Right ventricular dysfunction and abnormal HRV may represent the early features of cardiac disease in thalassemic patients with no evidence of ventricular dysfunction at routine evaluation.

Assessment of left ventricular function long term after arterial switch operation for transposition of the great arteries by dobutamine stress echocardiography

OBJECTIVES

To use dobutamine stress echocardiography to determine left ventricular (LV) function and wall motion of children long term after arterial switch operation (ASO) for transposition of the great arteries.

DESIGN AND PATIENTS

31 patients (24 boys) with ASO performed at a mean (SD) of 15.5 (4.3) days of life were studied at an age of 9.4 (2.0) years. All had normal coronary angiographic findings. LV echocardiographic indexes, including fractional shortening, ejection fraction, rate corrected velocity of circumferential fibre shortening (VCFc), and wall stress, as well as LV wall motion abnormalities were determined at rest and under dobutamine stress. The results were compared with those of 20 healthy age matched control participants.

SETTING

Tertiary paediatric cardiac centre.

RESULTS

Fractional shortening, ejection fraction, and VCFc were significantly lower in patients than in controls at rest (all with p < 0.001). Stress-velocity index detected impaired LV contractility in 19 (61%) patients at rest. An older age at operation (p = 0.01), longer bypass (p = 0.01) and circulatory arrest times (p = 0.045), and an unusual coronary artery pattern (p = 0.059) were associated with impaired resting LV contractility. Dobutamine stress echocardiography unmasked wall motion abnormalities in 23 (74%) patients. Exercise myocardial perfusion scan, performed in 22 patients, showed reversible myocardial perfusion defects in 17. These defects corresponded to segments of hypokinesia as detected by dobutamine stress echocardiography.

CONCLUSION

A significant proportion of children, albeit asymptomatic, had impaired baseline LV contractility and reversible myocardial perfusion defects and mild wall motion abnormalities on stress after ASO.