Pulmonary hypertension in patients with sickle cell disease: a longitudinal study

Sickle cell disease: new opportunities and challenges in Africa

Sickle cell disease (SCD) is one of the most common genetic causes of illness and death in the world. This is a review of SCD in Africa, which bears the highest burden of disease. The first section provides an introduction to the molecular basis of SCD and the pathophysiological mechanism of selected clinical events. The second section discusses the epidemiology of the disease (prevalence, morbidity, and mortality), at global level and within Africa. The third section discusses the laboratory diagnosis and management of SCD, emphasizing strategies that been have proven to be effective in areas with limited resources. Throughout the review, specific activities that require evidence to guide healthcare in Africa, as well as strategic areas for further research, will be highlighted.

Updated role of nitric oxide in disorders of erythrocyte function

Nitric oxide is a potent vasodilator that plays a critical role in disorders of erythrocyte function. Sickle cell disease, paroxysmal nocturnal hemoglobinuria and banked blood preservation are three conditions where nitric oxide is intimately related to dysfunctional erythrocytes. These conditions are accompanied by hemolysis, thrombosis and vasoocclusion. Our understanding of the interaction between nitric oxide, hemoglobin, and the vasculature is constantly evolving, and by defining this role we can better direct trials aimed at improving the treatments of disorders of erythrocyte function. Here we briefly discuss nitric oxide's interaction with hemoglobin through the hypothesis regarding Snitrosohemoglobin, deoxyhemoglobin, and myoglobin as nitrite reductases. We then review the current understanding of the role of nitric oxide in sickle cell disease, paroxysmal nocturnal hemoglobinuria, and banked blood, and discuss therapeutics in development to target nitric oxide in the treatment of some of these disorders.

Pulmonary artery occlusion pressure may overdiagnose pulmonary artery hypertension in sickle cell disease

BACKGROUND

A high prevalence of Pulmonary Hypertension (PH) in sickle cell disease (SCD) has been reported in several studies. However, few studies that describe the hemodynamics have actually measured pulmonary artery occlusive pressure (PAOP). Furthermore, even PAOP has been shown to be unreliable in discriminating pulmonary artery hypertension from pulmonary venous hypertension. We prospectively examined the accuracy of PAOP using simultaneous left ventricular end diastolic pressure (LVEDP) measurement as the gold standard.

HYPOTHESIS

In patients with SCD, PAOP may not reflect LVEDP leading to over-diagnosis of PAH.

METHODS

We prospectively examined hemodynamic data on 26 patients with SCD, at a large academic center, from 2009 through 2011. These patients underwent simultaneous PAOP and LVEDP measurements.

RESULTS

We tested 106 adult SCD patients with 2-D Echocardiography for evaluation of PH. Of the 106 patients, 43 (41%) were found to have a tricuspid regurgitant jet velocity ≥ 2.5 m/sec. Of these 43, 26 patients underwent right heart catheterization (RHC) and simultaneous measurement of LVEDP. Twelve patients among the 106 (11.1%) patients were found to have PH. Eight of these (7.5 %) had PAH by PAOP criteria but only 4/106 (3/7%) had PAH by LVEDP criteria. PAOP significantly underestimated the LVEDP in both the PH group and group with normal hemodynamics (p=0.00004). BNP, and creatinine levels significantly increased in PAH group (p< 0.02, 0.01, 0.03). PAOP misclassified 50% of patients in this sickle cell disease cohort. In conclusion, PAOP may underestimate LVEDP in sickle cell patients with pulmonary hypertension and can lead to misclassification.

Longitudinal study of echocardiography-derived tricuspid regurgitant jet velocity in sickle cell disease

Although echocardiography-derived tricuspid regurgitant jet velocity (TRV) is associated with increased mortality in sickle cell disease (SCD), its rate of increase and predictive markers of its progression are unknown. We evaluated 55 subjects (median age: 38 years, range: 20-65 years) with at least two measurable TRVs, followed for a median of 4·5 years (range: 1·0-10·5 years) in a single-centre, prospective study. Thirty-one subjects (56%) showed an increase in TRV, while 24 subjects (44%) showed no change or a decrease in TRV. A linear mixed effects model indicated an overall rate of increase in the TRV of 0·02 m/s per year (P = 0·023). The model showed that treatment with hydroxycarbamide was associated with an initial TRV that was 0·20 m/s lower than no such treatment (P = 0·033), while treatment with angiotensin converting enzyme inhibitors and angiotensin receptor blockers was associated with an increase in the TRV (P = 0·006). In summary, although some patients have clinically meaningful increases, the overall rate of TRV increase is slow. Treatment with hydroxycarbamide may decrease the progression of TRV. Additional studies are required to determine the optimal frequency of screening echocardiography and the effect of therapeutic interventions on the progression of TRV in SCD.

Prevalence of pulmonary arterial hypertension among sickle cell disease patients in Al Hassa

Background:

The prevalence of pulmonary arterial hypertension (PAH) in Saudi adults with sickle cell disease (SCD), the mechanism of its development, and its prospective prognostic significance are unknown.

Objective:

To assess the prevalence of PAH among sickle cell disease patients attended hematology outpatient clinic at King Fahad Hospital, Al Hassa, Saudi Arabia.

Methods:

Doppler echocardiography was performed for assessments of pulmonary- arterial systolic pressure (PASP) on 203 consecutive patients (102 men and 101 women) aged > 11 years, attending hematology clinic at King Fahad Hospital, Al Hassa, Saudi Arabia. Pulmonary hypertension was prospectively defined as a tricuspid regurgitant jet velocity (TRJV) of at least 2.5 m per second which can be estimate PASP equal or more than 25 mmHg.

Results:

Doppler-defined pulmonary arterial hypertension was diagnosed in 37.1% among 202 patients included in study (after one female patient was excluded) using a cutoff of PASP ≥25 mmHg.

Conclusion:

The prevalence of PAH among adults Saudis with SCD is higher than that reported from the developed countries. Further assessment using invasive techniques is required coupled employing analytical study design to predict the factors that favor the development of PAH among Saudi patients are required.

Hemodynamic predictors of mortality in adults with sickle cell disease

BACKGROUND

Pulmonary hypertension (PH) in adults with sickle cell disease (SCD) is associated with early mortality, but no prior studies have evaluated quantitative relationships of mortality to physiological measures of pre- and postcapillary PH.

OBJECTIVES

To identify risk factors associated with mortality and to estimate the expected survival in a cohort of patients with SCD with PH documented by right heart catheterization.

METHODS

Nine-year follow-up data (median, 4.7 yr) from the National Institutes of Health SCD PH screening study are reported. A total of 529 adults with SCD were screened by echocardiography between 2001 and 2010 with no exclusion criteria. Hemodynamic data were collected from 84 patients. PH was defined as mean pulmonary artery pressure (PAP) ≥ 25 mm Hg. Survival rates were estimated by the Kaplan-Meier method, and mortality risk factors were analyzed by the Cox proportional hazards regression.

MEASUREMENTS AND MAIN RESULTS

Specific hemodynamic variables were independently related to mortality: mean PAP (hazard ratio [HR], 1.61; 95% confidence interval [CI], 1.05-2.45 per 10 mm Hg increase; P = 0.027), diastolic PAP (HR, 1.83; 95% CI, 1.09-3.08 per 10 mm Hg increase; P = 0.022), diastolic PAP - pulmonary capillary wedge pressure (HR, 2.19; 95% CI, 1.23-3.89 per 10 mm Hg increase; P = 0.008), transpulmonary gradient (HR, 1.78; 95% CI, 1.14-2.79 per 10 mm Hg increase; P = 0.011), and pulmonary vascular resistance (HR, 1.44; 95% CI, 1.09-1.89 per Wood unit increase; P = 0.009) as risk factors for mortality.

CONCLUSIONS

Mortality in adults with SCD and PH is proportional to the physiological severity of precapillary PH, demonstrating its prognostic and clinical relevance despite anemia-induced high cardiac output and less severely elevated pulmonary vascular resistance.

Pulmonary hypertension in patients with chronic and end-stage kidney disease

Pulmonary hypertension is defined as a mean pulmonary artery pressure ≥25 mm Hg and is a recently recognized complication of chronic kidney disease and end-stage renal disease. There is significant epidemiological overlap with kidney disease and the underlying causes of World Health Organization group 1-4 pulmonary hypertension (pulmonary arteriopathy, left heart disease, chronic pulmonary disease, and chronic thromboembolic disease, respectively). In addition, an entity of 'unexplained pulmonary hypertension,' group 5, in patients with chronic kidney disease and end-stage renal disease has emerged, with prevalence estimates of 30-50%. The pathogenesis of pulmonary hypertension in this population is due to alterations in endothelial function, increased cardiac output, and myocardial dysfunction leading to elevated left heart filling pressure, with recent data suggesting that left heart dysfunction may account for the vast majority of pulmonary hypertension in patients with kidney disease. Pulmonary hypertension is an independent predictor of increased mortality in patients on dialysis and those undergoing kidney transplantation. This review summarizes what is known about the epidemiology, pathogenesis, transplantation outcomes, mortality, and treatment of pulmonary hypertension in patients with chronic kidney disease and end-stage renal disease.

The association between tricuspid regurgitation velocity and 5-year survival in a North West London population of patients with sickle cell disease in the United Kingdom

Raised tricuspid regurgitant velocity (TRV) occurs in approximately 30% of adults with sickle cell disease (SCD), and has been shown to be an independent risk factor for death. TRV was assessed in 164 SCD patients who were subsequently followed up for survival. Raised pulmonary pressures were defined as a TRV jet ≥2.5 m/s on echocardiography. Elevated TRV was present in 29.1% of patients and it was associated with increased age and left atrial diameter. There were 15 deaths (9.1%) over a median of 68.1 months follow up; seven patients had increased TRV, and eight patients had a TRV<2.5 m/s. Higher TRV values were associated with a greater than 4-fold increased risk of death (Hazard Ratio: 4.48, 99% confidence interval 1.01-19.8), although we found a lower overall mortality rate than has been reported in previous studies. TRV was not an independent risk factor for death. We have confirmed the association between raised TRV and mortality in a UK SCD population whose disease severity appears to be less than that reported in previous studies. Further prospective studies are needed to more clearly characterize which patient factors modify survival in SCD patients with raised TRV.

Genetic modifiers of sickle cell disease

Sickle cell anemia is associated with unusual clinical heterogeneity for a Mendelian disorder. Fetal hemoglobin concentration and coincident α thalassemia, both which directly affect the sickle erythrocyte, are the major modulators of the phenotype of disease. Understanding the genetics underlying the heritable subphenotypes of sickle cell anemia would be prognostically useful, could inform personalized therapeutics, and might help the discovery of new "druggable" pathophysiologic targets. Genotype-phenotype association studies have been used to identify novel genetic modifiers. In the future, whole genome sequencing with its promise of discovering hitherto unsuspected variants could add to our understanding of the genetic modifiers of this disease.

Cardiovascular abnormalities in sickle cell disease

Sickle cell disease is characterized by recurrent episodes of ischemia-reperfusion injury to multiple vital organ systems and a chronic hemolytic anemia, both contributing to progressive organ dysfunction. The introduction of treatments that induce protective fetal hemoglobin and reduce infectious complications has greatly prolonged survival. However, with increased longevity, cardiovascular complications are increasingly evident, with the notable development of a progressive proliferative systemic vasculopathy, pulmonary hypertension (PH), and left ventricular diastolic dysfunction. Pulmonary hypertension is reported in autopsy studies, and numerous clinical studies have shown that increased pulmonary pressures are an important risk marker for mortality in these patients. In epidemiological studies, the development of PH is associated with intravascular hemolysis, cutaneous leg ulceration, renal insufficiency, iron overload, and liver dysfunction. Chronic anemia in sickle cell disease results in cardiac chamber dilation and a compensatory increase in left ventricular mass. This is often accompanied by left ventricular diastolic dysfunction that has also been a strong independent predictor of mortality in patients with sickle cell disease. Both PH and diastolic dysfunction are associated with marked abnormalities in exercise capacity in these patients. Sudden death is an increasingly recognized problem, and further cardiac investigations are necessary to recognize and treat high-risk patients.

Echocardiographic evaluation of left ventricular diastolic and systolic function in Saudi patients with sickle cell disease

BACKGROUND AND OBJECTIVES

Sickle cell disease (SCD) is a chronic, inherited haemoglobin disorder, associated with recurrent vaso-occlusive and haemolytic crises and chronic tissue ischemia which may adversely affect any organ system. Our objectives were to evaluate the left ventricular (LV) systolic and diastolic functions in Saudi patients with SCD originally from the Eastern Province of Saudi Arabia.

DESIGN AND SETTING

Prospective hospital based echocardiography study on adolescent and adult patients with SCD.

METHODS

Forty-five patients with SCD were recruited for echocardiographic study while 45 patients, matched for age and sex, served as controls. Left and right ventricular dimensions and LV wall thicknesses, LV mass index (LVMI) and LV contractility variables were obtained. Left atrial dimension and volume and pulmonary artery systolic pressure (PASP) were also estimated. We also evaluated parameters of LV diastolic function, including early and late mitral flow velocities (E and A wave respectively), E/A ratio, deceleration time (MVDT), A wave duration (MVA D), LV isovolumic relaxation time (IVRT), and tissue Doppler velocities, such as lateral annular e' wave, a' wave, e'/a' ratio and E/e' ratio.

RESULTS

There were increases in the LV dimensions, LV volumes, stroke volume, and LVMI of the SCD patients. The preload was increased (LV diastolic volume) and afterload was decreased (low diastolic blood pressure). The LVEF was equivalent, though there was evidence of LV diastolic dysfunction in 24%, and pulmonary hypertension (PH) in 40% of the SCD patients. The mean left atrial volume (LAV) was also increased in the SCD patients.

CONCLUSION

LV diastolic dysfunction (heart failure with preserved ejection fraction) and PH may complicate cases of the Arab-Indian haplotype of SCD.

Hemodynamic characteristics and predictors of pulmonary hypertension in patients with sickle cell disease

Pulmonary hypertension is a common co-morbidity of sickle cell disease with an associated increased mortality risk, but its etiology is not well-understood. To evaluate the hemodynamic characteristics, clinical predictors, and cardiovascular manifestations of elevated pulmonary arterial pressure in this population, we performed noninvasive hemodynamic assessments of 135 patients with sickle cell disease using Doppler echocardiography. A diagnosis of pulmonary hypertension was determined by gender-, age-, and body mass index-specific normal reference ranges for tricuspid regurgitation jet velocities (TRVs). A high TRV was noted in 34 patients (25%). Pulmonary vascular resistance was elevated in only 2 (6%) of the 34 patients with suspected pulmonary hypertension but was significantly greater than in those with normal TRV. On univariate regression, the TRV correlated with age, body mass index, left atrial pressure, and right ventricular stroke volume and was negatively associated with hemoglobin and glomerular filtration rate. The left atrial pressure, right ventricular stroke volume, and hemoglobin remained independent predictors of TRV in a multivariate model. A greater TRV was also associated with larger right ventricular and right atrial chamber sizes and greater N-terminal probrain natriuretic peptide levels. In conclusion, our results suggest that the mild elevation in TRV often observed in patients with sickle cell disease is rarely associated with a high pulmonary vascular resistance and that multiple factors-including the compensatory high output state associated with anemia, pulmonary venous hypertension, and pulmonary vasculopathy-can contribute to an elevated pulmonary arterial pressure in these patients.

Pulmonary complications of sickle cell disease

Sickle cell disease (SCD) is a common monogenetic disorder with high associated morbidity and mortality. The pulmonary complications of SCD are of particular importance, as acute chest syndrome and pulmonary hypertension have the highest associated mortality rates within this population. This article reviews the pathophysiology, diagnosis, and treatment of clinically significant pulmonary manifestations of SCD, including acute chest syndrome, asthma, and pulmonary hypertension in adult and pediatric patients. Clinicians should be vigilant in screening and treating such comorbidities to improve patient outcomes.

The role of fibrocytes in sickle cell lung disease

Background

Interstitial lung disease is a frequent complication in sickle cell disease and is characterized by vascular remodeling and interstitial fibrosis. Bone marrow-derived fibrocytes have been shown to contribute to the pathogenesis of other interstitial lung diseases. The goal of this study was to define the contribution of fibrocytes to the pathogenesis of sickle cell lung disease.

Methodology/Principal Findings

Fibrocytes were quantified and characterized in subjects with sickle cell disease or healthy controls, and in a model of sickle cell disease, the NY1DD mouse. The role of the chemokine ligand CXCL12 in trafficking of fibrocytes and phenotype of lung disease was examined in the animal model. We found elevated concentration of activated fibrocytes in the peripheral blood of subjects with sickle cell disease, which increased further during vaso-occlusive crises. There was a similar elevations in the numbers and activation phenotype of fibrocytes in the bone marrow, blood, and lungs of the NY1DD mouse, both at baseline and under conditions of hypoxia/re-oxygenation. In both subjects with sickle cell disease and the mouse model, fibrocytes expressed a hierarchy of chemokine receptors, with CXCR4 expressed on most fibrocytes, and CCR2 and CCR7 expressed on a smaller subset of cells. Depletion of the CXCR4 ligand, CXCL12, in the mouse model resulted in a marked reduction of fibrocyte trafficking into the lungs, reduced lung collagen content and improved lung compliance and histology.

Conclusions

These data support the notion that activated fibrocytes play a significant role in the pathogenesis of sickle cell lung disease.

Pathology of sickle cell disease

Sickle cell disease (SCD) is a hereditary chronic hemolytic anemia with numerous clinical consequences. Intravascular sickling of red blood cells leads to multiorgan dysfunction. Although the pathophysiology of SCD has been well studied, there remains a lack of effective treatment. Refinements in overall care have improved quality of life; however, premature death is still not uncommon. SCD usually presents in childhood and is common in areas where malaria is (or was) common. The association with malaria is apparently of benefit to the individual because these individuals tend to contract a milder form of the disease. This review highlights the spectrum of pathology seen in people with SCD, with an emphasis on the pathogenesis of sudden death.

Low micromolar intravascular cell-free hemoglobin concentration affects vascular NO bioavailability in sickle cell disease: a computational analysis

In sickle cell disease, the changes in RBC morphology destabilize the red blood cell (RBC) membrane and lead to hemolysis. Several experimental and clinical studies have associated intravascular hemolysis with pulmonary hypertension in sickle cell disease. Cell-free hemoglobin (Hb) from intravascular hemolysis has high affinity for nitrixc oxide (NO) and can affect the NO bioavailability in the sickle cell disease, which may eventually lead to pulmonary hypertension. To study the effects of intravascular hemolysis related cell-free Hb concentrations on NO bioavailability, we developed a two-dimensional mathematical model of NO biotransport in 50-μm arteriole under steady-state sickle cell disease conditions. We analyzed the effects of flow-dependent NO production and axial and radial transport of NO, a recently reported much lower NO-RBC reaction rate constant, and cell-free layer thickness on NO biotransport. Our results show that the presence of cell-free Hb concentrations as low as 0.5 μM results in an approximately three- to sevenfold reduction in the predicted smooth muscle cell NO concentrations compared with those under physiological conditions. In addition, increasing the diffusional resistance for NO in vascular lumen from cell-free layer or reducing NO-RBC reaction rate did not improve the NO bioavailability at the smooth muscle cell layer significantly for cell-free Hb concentrations ≥1 μM. These results suggest that lower NO bioavailability due to low micromolar cell-free Hb can disturb NO homeostasis and cause insufficient bioavailability at the smooth muscle cell layer. Our results supports the hypothesis that hemolysis-associated reduction in NO bioavailability may play a role in the development of pathophysiological complications like pulmonary hypertension in sickle cell disease that are observed in several clinical and experimental studies.

Risk factors and mortality associated with an elevated tricuspid regurgitant jet velocity measured by Doppler-echocardiography in thalassemia: a Thalassemia Clinical Research Network report

An elevated tricuspid regurgitant jet velocity (TRV) is associated with hemolysis and early mortality in sickle cell disease, yet risk factors, clinical parameters, and mortality associated with this biomarker in thalassemia are poorly defined. This report summarizes the prevalence of an elevated TRV in 325 patients screened by Doppler echocardiography in the Thalassemia Clinical Research Network. A documented TRV was reported in 148 of 325 (46%) of patients. Average age was 25.9 years (range, 5-56 years) and 97% were transfusion-dependent. Mean TRV was 2.3 ± 0.4 m/s (range, 0.2-3.5 m/s). An abnormal TRV ≥ 2.5 m/s was identified in 49 of 148 (33%) of patients with a documented TRV, 5% (8/148), with a TRV ≥ 3.0 m/s, suggesting significant PH risk. Older age was strongly associated with a high TRV; however, 16% of children had a TRV ≥ 2.5 m/s. A history of splenectomy, hepatitis C, smoking, or high white blood cell count was associated with TRV elevation. In summary, an elevated TRV is noted in one-third of transfusion-dependent thalassemia patients with a documented value and develops in both children and adults. Age, splenectomy, hepatitis C, and smoking are significant univariate risk factors, with splenectomy surfacing as the dominant risk factor over time. Mortality was low in this cohort. Prospective longitudinal studies are needed. This study is registered at http://www.clinicaltrials.gov as NCT00661804.

Pulmonary complications of sickle cell disease

The pulmonary complications of sickle cell disease are a major cause of morbidity and mortality in affected patients. The acute chest syndrome (ACS) is a leading cause of death in patients with sickle cell disease and has a multifactorial etiology. Hydroxyurea (HU), stem cell transplantation (SCT) and chronic transfusions are known to prevent the recurrence of ACS. Careful management of patients admitted for pain crises and surgery including use of incentive spirometry is critical in preventing this complication. Pulmonary hypertension is well known to be associated with sickle cell disease and patients with pulmonary hypertension have increased mortality. Asthma is also commonly seen in patients with sickle cell disease and is associated with a more complicated course. Chronic lung disease develops in a significant proportion of patients with sickle cell disease.

Echocardiographic markers of elevated pulmonary pressure and left ventricular diastolic dysfunction are associated with exercise intolerance in adults and adolescents with homozygous sickle cell anemia in the United States and United Kingdom

BACKGROUND

Noninvasively assessed pulmonary pressure elevations and left ventricular (LV) diastolic dysfunction are associated with increased mortality in adults with sickle cell disease, but their relationship to exercise intolerance has not been evaluated prospectively.

METHODS AND RESULTS

Echocardiography, 6-minute walk distance, hemolytic rate, and serum concentrations of ferritin and erythropoietin were evaluated in a cohort of 483 subjects with homozygous hemoglobin S in the U.S. and U.K. Walk-Treatment of Pulmonary Hypertension and Sickle Cell Disease with Sildenafil Therapy (Walk-PHaSST) study. Tricuspid regurgitation velocity, which reflects systolic pulmonary artery pressure, was 2.7 to <3.0 m/s (mean±SD, 2.8±0.1) in 26% of the subjects and ≥3.0 m/s (mean±SD, 3.4±0.4) in 11%. The LV lateral E/e' ratio, which has been shown to reflect LV filling pressure in other conditions but has not been studied in sickle cell disease, was significantly higher in the groups with tricuspid regurgitation velocity ≥2.7 m/s. Increased hemolysis (P<0.0001), LV lateral E/e' ratio (P=0.0001), blood urea nitrogen (P=0.0002), and erythropoietin (P=0.002) were independently associated with an increased tricuspid regurgitation velocity. Furthermore, female sex (P<0.0001), older age (P<0.0001), LV lateral E/e' ratio (P=0.014), and tricuspid regurgitation velocity (P=0.019) were independent predictors of a shorter 6-minute walk distance.

CONCLUSIONS

Echocardiography-estimated elevated pulmonary artery systolic pressure and LV lateral E/e' ratio were independently associated with poor exercise capacity in a large cohort of patients with sickle cell anemia. Controlled trials investigating whether strategies to prevent or delay pulmonary hypertension and/or LV diastolic dysfunction will improve exercise capacity and long-term outcomes in sickle cell anemia should be considered. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00492531.

NT-pro brain natriuretic peptide levels and the risk of death in the cooperative study of sickle cell disease

Epidemiological studies support a hypothesis that pulmonary hypertension (PH) is a common complication of sickle cell disease (SCD) that is associated with a high risk of death and evolves as a complication of haemolytic anaemia. This fundamental hypothesis has been recently challenged and remains controversial. In order to further test this hypothesis in a large and independent cohort of SCD patients we obtained plasma samples from the Cooperative Study of Sickle Cell Disease (CSSCD) for analysis of a biomarker, N-terminal-pro brain natriuretic peptide (NT-proBNP), which is elevated in the setting of pulmonary arterial and venous hypertension. A NT-pro-BNP value previously identified to predict PH in adults with SCD was used to determine the association between the risk of mortality in 758 CSSCD participants (428 children and 330 adults). An abnormally high NT-proBNP level ≥160ng/l was present in 27·6% of adult SCD patients. High levels were associated with markers of haemolytic anaemia, such as low haemoglobin level (P<0·001), high lactate dehydrogenase (P<0·001), and high total bilirubin levels (P<0·007). A NT-proBNP level ≥160ng/l was an independent predictor of mortality (RR 6·24, 95% CI 2·9-13·3, P<0·0001). These findings provide further support for an association between haemolytic anaemia and cardiovascular complications in this patient population.

Hospitalization for pain in patients with sickle cell disease treated with sildenafil for elevated TRV and low exercise capacity

In adults with sickle cell disease (SCD), an increased tricuspid regurgitation velocity (TRV) by Doppler echocardiography is associated with increased morbidity and mortality. Although sildenafil has been shown to improve exercise capacity in patients with pulmonary arterial hypertension, it has not been evaluated in SCD. We therefore sought to determine whether sildenafil could improve exercise capacity in SCD patients with increased TRV and a low exercise capacity. A TRV ≥ 2.7 m/s and a 6-minute walk distance (6MWD) between 150 and 500 m were required for enrollment in this 16-week, double-blind, placebo-controlled sildenafil trial. After 74 of the screened subjects were randomized, the study was stopped early due to a higher percentage of subjects experiencing serious adverse events in the sildenafil arm (45% of sildenafil, 22% of placebo, P = .022). Subject hospitalization for pain was the predominant cause for this difference: 35% with sildenafil compared with 14% with placebo (P = .029). There was no evidence of a treatment effect on 6MWD (placebo-corrected effect -9 m; 95% confidence interval [95% CI] -56-38; P = .703), TRV (P = .503), or N-terminal pro-brain natriuretic peptide (P = .410). Sildenafil appeared to increase hospitalization rates for pain in patients with SCD. This study is registered at www.clinicaltrials.gov as NCT00492531.

Anesthetic management of a patient with sickle β thalassemia

Sickle cell disease is a congenital condition and its most common clinical manifestation is anemia due to chronic hemolysis. Persistent and accelerated hemolysis associated with multiple transfusions is a recognized risk factor for the development of cholelithiasis. The occurrence of gallstones is one of the most important manifestations of sickle cell disease in the digestive tract. Most gallstones are pigmented and characteristically occur at younger ages and the prevalence of cholelithiasis increases progressively with age, affecting 50% of young adults. Cholecystectomy is the most common surgical procedure performed in sickle cell disease patients. Anesthesia in this population of patients for major surgeries deserves special attention due to various complications particularly silent infarctions of end organs are common. We are reporting a 14-year-old girl diagnosed with sickle cell anemia and β⁺ thalassemia with cholelithiasis went for cholecystectomy under general anesthesia. Although the patient has both β⁺ thalassemia and sickle cell disease component, the latter is of more concern for anesthesia.

A hemodynamic study of pulmonary hypertension in sickle cell disease

BACKGROUND

The prevalence and characteristics of pulmonary hypertension in adults with sickle cell disease have not been clearly established.

METHODS

In this prospective study, we evaluated 398 outpatients with sickle cell disease (mean age, 34 years) at referral centers in France. All patients underwent Doppler echocardiography, with measurement of tricuspid-valve regurgitant jet velocity. Right heart catheterization was performed in 96 patients in whom pulmonary hypertension was suspected on the basis of a tricuspid regurgitant jet velocity of at least 2.5 m per second. Pulmonary hypertension was defined as a mean pulmonary arterial pressure of at least 25 mm Hg.

RESULTS

The prevalence of a tricuspid regurgitant jet velocity of at least 2.5 m per second was 27%. In contrast, the prevalence of pulmonary hypertension as confirmed on catheterization was 6%. The positive predictive value of echocardiography for the detection of pulmonary hypertension was 25%. Among the 24 patients with confirmed pulmonary hypertension, the pulmonary-capillary wedge pressure was 15 mm Hg or less (indicating precapillary pulmonary hypertension) in 11 patients. Patients with confirmed pulmonary hypertension were older and had poorer functional capacity and higher levels of N-terminal pro-brain natriuretic peptide than other patients. In contrast, patients who had a tricuspid regurgitant jet velocity of at least 2.5 m per second without pulmonary hypertension and patients with a tricuspid regurgitant jet velocity of less than 2.5 m per second had similar clinical characteristics.

CONCLUSIONS

In this study of adults with sickle cell disease, the prevalence of pulmonary hypertension as confirmed on right heart catheterization was 6%. Echocardiographic evaluation alone had a low positive predictive value for pulmonary hypertension. (Funded by the French Ministry of Health and Assistance Publique-Hôpitaux de Paris; ClinicalTrials.gov number, NCT00434902.).

Leukocytosis is a risk factor for lung function deterioration in children with sickle cell disease

BACKGROUND

The decline in lung volumes associated with sickle cell disease (SCD) may begin in childhood. Risk factors for early restrictive lung disease may include SCD severity markers such as leukocytosis.

OBJECTIVE

We examined the relationship between early alteration of lung function and extra-pulmonary markers of SCD severity.

METHODS

We analyzed pulmonary function test results for 184 SCD children (mean age 12.6 y) enrolled in a pediatric cohort.

MAIN RESULTS

Total lung capacity (TLC) and vital capacity (VC) were not associated with a history of acute chest syndrome. Lower TLC values were significantly associated with three independent factors: older age, previous acute episodes of anemia <6 g/dl, and higher baseline white blood cell counts. Only the baseline WBC count and age were independent risk factors for lower VC. Relative risks to have a TLC or a VC lower than the mediane value in our population were significantly associated to the baseline leukocytosis (per 10(9) G/L), after adjustment on age, sex, genotype, baseline Hb, and treatment (RR (95% CI) =1.16 (1.04-1.29) p<0.009, and 1.17 (1.06-1.29) p<0.002, respectively). The obstructive pattern, defined by FEV1/FVC ratio, was not significantly associated to biological parameters.

CONCLUSIONS

Hemolysis and leukocytosis were independent risk factors for an early decline in lung volumes in this pediatric SCD cohort.

Reconstructing sickle cell disease: a data-based analysis of the "hyperhemolysis paradigm" for pulmonary hypertension from the perspective of evidence-based medicine

The "hyperhemolytic paradigm" (HHP) posits that hemolysis in sickle disease sequentially and causally establishes increased cell-free plasma Hb, consumption of NO, a state of NO biodeficiency, endothelial dysfunction, and a high prevalence of pulmonary hypertension. The basic science underpinning this concept has added an important facet to the complexity of vascular pathobiology in sickle disease, and clinical research has identified worrisome clinical issues. However, this critique identifies and explains a number of significant concerns about the various HHP component tenets. In addressing these issues, this report presents: a very brief history of the HHP, an integrated synthesis of mechanisms underlying sickle hemolysis, a review of the evidentiary value of hemolysis biomarkers, an examination of evidence bearing on existence of a hyperhemolytic subgroup, and a series of questions that should naturally be applied to the HHP if it is examined using critical thinking skills, the fundamental basis of evidence-based medicine. The veracity of different HHP tenets is found to vary from true, to weakly supported, to demonstrably false. The thesis is developed that the HHP has misidentified the mechanism and clinical significance of its findings. The extant research questions identified by these analyses are delineated, and a conservative, evidence-based approach is suggested for application in clinical medicine.

Association of soluble fms-like tyrosine kinase-1 with pulmonary hypertension and haemolysis in sickle cell disease

The pathophysiology of pulmonary hypertension (PHT) in sickle cell disease (SCD) is probably multifactorial. Soluble fms-like tyrosine kinase-1 (sFLT-1) is a member of the vascular endothelial growth factor receptor (VEGFR) family. By adhering to and inhibiting VEGF and placenta growth factor, it induces endothelial dysfunction. We sought to evaluate the association of sFLT-1 with clinical complications of SCD. We confirmed that sFLT-1 was significantly elevated in SCD patients compared to healthy, race-matched control subjects. The level of sFLT-1 was significantly higher in patients with PHT, but no association was observed between sFLT-1 and the frequency of acute pain episodes or history of acute chest syndrome. sFLT-1 was correlated with various measures of haemolysis, erythropoietin and soluble vascular cell adhesion molecule-1. By inducing endothelial dysfunction, sFLT-1 may contribute to the pathogenesis of SCD-associated PHT, although this effect does not appear to be independent of haemolysis.

Elevated tricuspid regurgitation velocity and decline in exercise capacity over 22 months of follow up in children and adolescents with sickle cell anemia

BACKGROUND

While in adults with sickle cell disease an elevation of tricuspid regurgitation velocity is associated with increased mortality, the importance of this finding in children has not been established. The role of intravascular hemolysis in the development of this complication is controversial.

DESIGN AND METHODS

We conducted a prospective, longitudinal, multi-center study of 160 individuals aged 3-20 years with hemoglobin SS, performing baseline and follow-up determinations of clinical markers, six-minute walk distance less than tricuspid regurgitation velocity and E/Etdi ratio by echocardiography.

RESULTS

At baseline, 14.1% had tricuspid regurgitation velocity of 2.60 m/sec or over, which suggests elevated systolic pulmonary artery pressure, and 7.7% had increased E/Etdi, which suggests elevated left ventricular filling pressure. Over a median of 22 months, baseline elevation in tricuspid regurgitation velocity was associated with an estimated 4.4-fold increase in the odds of a 10% or more decline in age-standardized six-minute-walk distance (P = 0.015). During this interval, baseline values above the median for a hemolytic component derived from four markers of hemolysis were associated with a 9.0-fold increase in the odds of the new onset of elevated tricuspid regurgitation velocity (P = 0.008) and baseline E/Etdi elevation was associated with an estimated 6.1-fold increase in the odds (P = 0.039). In pathway analysis, higher baseline hemolytic component and E/Etdi predicted elevated tricuspid regurgitation velocity at both baseline and follow up, and these elevations in turn predicted decline in six-minute-walk distance.

CONCLUSIONS

Further studies should define the long-term risks of elevated tricuspid regurgitation velocity in childhood and identify potential interventions to prevent increased pulmonary artery pressure and preserve function.

Sickle-cell disease

Sickle-cell disease is one of the most common severe monogenic disorders in the world. Haemoglobin polymerisation, leading to erythrocyte rigidity and vaso-occlusion, is central to the pathophysiology of this disease, although the importance of chronic anaemia, haemolysis, and vasculopathy has been established. Clinical management is basic and few treatments have a robust evidence base. One of the main problems of sickle-cell disease in children is the development of cerebrovascular disease and cognitive impairment, and the role of blood transfusion and hydroxycarbamide for prevention of these complications is starting to be understood. Recurrent episodes of vaso-occlusion and inflammation result in progressive damage to most organs, including the brain, kidneys, lungs, bones, and cardiovascular system, which becomes apparent with increasing age. Most people with sickle-cell disease live in Africa, where little is known about this disease; however, we do know that the disorder follows a more severe clinical course in Africa than for the rest of the world and that infectious diseases have a role in causing this increased severity of sickle-cell disease. More work is needed to develop effective treatments that specifically target pathophysiological changes and clinical complications of sickle-cell disease.

Pulmonary complications of hemoglobinopathies

Hemoglobinopathies are diseases caused by genetic mutations that result in abnormal, dysfunctional hemoglobin molecules or lower levels of normal hemoglobin molecules. The most common hemoglobinopathies are sickle cell disease (SCD) and the thalassemias. In SCD, an abnormal hemoglobin alters the erythrocyte, causing a chronic hemolytic anemia, which can lead to pulmonary parenchymal damage and impaired vascular function. Pulmonary complications of SCD include the acute chest syndrome (ACS), reactive airways disease, pulmonary hypertension (PH), and pulmonary fibrosis. Episodes of ACS and the development of PH both increase the risk of death in patients with SCD. Both α and β thalassemia are characterized by impaired production of hemoglobin subunits, and severity of disease varies widely. Although screening studies suggest that PH is a common complication for patients with thalassemia, its impact on survival is unknown. Understanding the pathogenesis, diagnostic options, and prevention and treatment strategies for such complications is critical for clinicians who care for these patients. In this review, we discuss the mechanisms and clinical presentation of pulmonary complications associated with hemoglobinopathies, with a focus on recent advances in pathogenesis and treatment.

Reproducibility of tricuspid regurgitant jet velocity measurements in children and young adults with sickle cell disease undergoing screening for pulmonary hypertension

The reproducibility of tricuspid regurgitant jet velocity (TRJV) measurements by Doppler echocardiography has not been subjected to systematic evaluation among individuals with sickle cell disease (SCD) undergoing screening for pulmonary hypertension. We examined sources of disagreement associated with peak TRJV in children and young adults with SCD. Peak TRJV was independently measured and interpreted a week apart by separate sonographers and readers, respectively, in 30 subjects (mean age, 15.8 ± 3.3 years) who provided 120 observations. We assessed intra-/inter-reader, intra-/inter-sonographer, sonographer-reader, and within subject agreement using Intraclass Correlation Coefficient (ICC) and Cohen's kappa (κ). Agreement was examined graphically using Bland-Altman plots. Although sonographers could estimate and measure peak TRJV in all subjects, readers designated tricuspid regurgitation nonquantifiable in 10-17% of their final interpretations. Intra-reader agreement was highest (ICC = 0.93 [95% CI 0.86, 0.97], P = 0.0001) and within subject agreement lowest (ICC = 0.36 [95% CI 0.02, 0.64], P = 0.021) for single TRJV measurements. Similarly, intra-reader agreement was highest (κ = 0.74 [95% CI 0.53, 0.95], P = 0.0001) and within subject lowest (κ = 0.14 [95% CI -0.17, 0.46], P = 0.38) when sonographers and readers categorized TRJV measurements. On Bland-Altman plots, absolute differences in observations increased with higher mean TRJV readings for intra-/inter-reader agreement. Peak TRJV measurements in individual children and young adults with SCD are affected by several sources of disagreement, underscoring the need for methodological improvements that ensure reproducibility of this screening modality for making clinical decisions in this population.

Urinary albumin excretion is associated with pulmonary hypertension in sickle cell disease: potential role of soluble fms-like tyrosine kinase-1

BACKGROUND

Pulmonary hypertension (PHT) is reported to be associated with measures of renal function in patients with sickle cell disease (SCD). The purpose of this exploratory study was to determine the relationship between albuminuria and both clinical and laboratory variables in SCD.

DESIGN AND METHODS

This cross-sectional study was performed using a cohort of adult patients with SCD and control subjects without SCD. Spot urine for microalbumin/creatinine ratio, measures of hemolysis, inflammation and other laboratory studies were obtained. Pulmonary artery systolic pressure was determined by Doppler echocardiography, and the diagnosis of PHT was defined using age-, sex- and body mass index-adjusted reference ranges.

RESULTS

Seventy-three patients with SCD and 21 healthy, race-matched control subjects were evaluated. In patients with SCD, normoalbuminuria was observed in 34 patients (46.6%), microalbuminuria in 24 patients (32.9%) and macroalbuminuria in 15 patients (20.5%). There was a significant correlation between urine albumin excretion and age. In patients with HbSS and Sbeta(0) thalassemia, the levels of sFLT-1, soluble VCAM and NT pro-BNP were significantly higher in those with macroalbuminuria, compared to patients with microalbuminuria and normoalbuminura, but no significant differences were observed in the levels of laboratory measures of hemolysis. Urine albumin excretion was associated with PHT and a history of stroke.

CONCLUSIONS

Our study confirms the high prevalence of albuminuria in SCD. The association of urine albumin excretion with sFLT-1 suggests that this vascular endothelial growth factor receptor family member may contribute to the development of albuminuria in SCD. By inducing endothelial activation and endothelial dysfunction, sFLT-1 appears to be a link between glomerulopathy and PHT in SCD.

Adenosine A2A receptors induced on iNKT and NK cells reduce pulmonary inflammation and injury in mice with sickle cell disease

We showed previously that pulmonary function and arterial oxygen saturation in NY1DD mice with sickle cell disease (SCD) are improved by depletion of invariant natural killer T (iNKT) cells or blockade of their activation. Here we demonstrate that SCD causes a 9- and 6-fold induction of adenosine A(2A) receptor (A(2A)R) mRNA in mouse pulmonary iNKT and natural killer (NK) cells, respectively. Treating SCD mice with the A(2A)R agonist ATL146e produced a dose-dependent reversal of pulmonary dysfunction with maximal efficacy at 10 ng/kg/minute that peaked within 3 days and persisted throughout 7 days of continuous infusion. Crossing NY1DD mice with Rag1(-/-) mice reduced pulmonary injury that was restored by adoptive transfer of 10(6) purified iNKT cells. Reconstituted injury was reversed by ATL146e unless the adoptively transferred iNKT cells were pretreated with the A(2A)R alkylating antagonist, FSPTP (5-amino-7-[2-(4-fluorosulfonyl)phenylethyl]-2-(2-furyl)-pryazolo[4,3-ε]-1,2,4-triazolo[1,5-c]pyrimidine), which completely prevented pro-tection. In NY1DD mice exposed to hypoxia-reoxygenation, treatment with ATL146e at the start of reoxygenation prevented further lung injury. Together, these data indicate that activation of induced A(2A)Rs on iNKT and NK cells in SCD mice is sufficient to improve baseline pulmonary function and prevent hypoxia-reoxygenation-induced exacerbation of pulmonary injury. A(2A) agonists have promise for treating diseases associated with iNKT or NK cell activation.

Pulmonary hypertension in hemolytic disorders: pulmonary vascular disease: the global perspective

The inherited hemoglobin disorders sickle cell disease and thalassemia are the most common monogenetic disorders worldwide. Pulmonary hypertension is one of the leading causes of morbidity and mortality in adult patients with sickle cell disease and thalassemia, and hemolytic disorders are potentially among the most common causes of pulmonary hypertension. The pathogenesis of pulmonary hypertension in hemolytic disorders is likely multifactorial, including hemolysis, impaired nitric oxide (NO) bioavailability, chronic hypoxemia, chronic thromboembolic disease, chronic liver disease, and asplenia. In contrast to patients with traditional forms of pulmonary arterial hypertension, patients with hemolytic disorders have a mild-to-moderate degree of elevation in mean pulmonary pressures, with mild elevations in pulmonary vascular resistance. The hemodynamic etiology of pulmonary hypertension in these patients is multifactorial and includes pulmonary arterial hypertension, pulmonary venous hypertension, and pulmonary hypertension secondary to a hyperdynamic state. Currently, there are limited data on the effects of any specific treatment modality for pulmonary hypertension in patients with hemolytic disorders. It is likely that maximization of treatment of the primary hemoglobinopathy in all patients and treatment with selective pulmonary vasodilators and antiproliferative agents in patients with pulmonary arterial hypertension would be beneficial. However, there is still a major need for large multinational trials of novel therapies for this patient population.

The risks and benefits of long-term use of hydroxyurea in sickle cell anemia: A 17.5 year follow-up

A randomized, controlled clinical trial established the efficacy and safety of short-term use of hydroxyurea in adult sickle cell anemia. To examine the risks and benefits of long-term hydroxyurea usage, patients in this trial were followed for 17.5 years during which they could start or stop hydroxyurea. The purpose of this follow-up was to search for adverse outcomes and estimate mortality. For each outcome and for mortality, exact 95% confidence intervals were calculated, or tests were conducted at alpha = 0.05 level (P-value <0.05 for statistical significance). Although the death rate in the overall study cohort was high (43.1%; 4.4 per 100 person-years), mortality was reduced in individuals with long-term exposure to hydroxyurea. Survival curves demonstrated a significant reduction in deaths with long-term exposure. Twenty-four percent of deaths were due to pulmonary complications; 87.1% occurred in patients who never took hydroxyurea or took it for <5 years. Stroke, organ dysfunction, infection, and malignancy were similar in all groups. Our results, while no longer the product of a randomized study because of the ethical concerns of withholding an efficacious treatment, suggest that long-term use of hydroxyurea is safe and might decrease mortality.