Rheology of the absolute polycythaemias

Hb Levels and Sex Differences in Relation to Short-Term Outcomes in Patients With Acute Myocardial Infarction

Background: Women had worse outcomes after acute myocardial infarction (AMI), and physiologically, women had lower hemoglobin values. We examined whether there were sex-related differences in the relationship between hemoglobin levels and adverse outcomes in patients with acute myocardial infarction.

Method: We conducted a post-hoc analysis of data from the Acute Coronary Syndrome Quality Improvement in Kerala (ACS-QUIK) Study. We explored the relationship between baseline hemoglobin level and 30-days adverse outcomes by logistic regression model, generalized additive model (GAM) and two-piecewise linear regression model. We used multiple imputation, based on five replications and a chained equation approach method in the R multiple imputation procedure, to account for missing data. The primary outcome were 30-day major adverse cardiovascular events (MACEs) defined as death, reinfarction, stroke, and major bleeding. The secondary outcomes were 30-day major bleeding, 30-day stroke and 30-day cardiovascular death (CVD death).

Results: Twenty thousand, five hundred fifty-nine patients with AMI were included in our analysis. Baseline hemoglobin level was associated with major bleeding [OR: 0.74, 95%CI (0.60, 0.92) P < 0.01], CVD death [OR: 0.94, 95%CI (0.90, 0.99) P < 0.01], and MACEs [OR: 0.95, 95%CI (0.92, 0.99) P < 0.01]. There was no significant relationship between baseline hemoglobin level and stroke incidence in both men [OR: 1.02, 95%CI (0.90, 1.14) P = 0.77] and women [OR: 1.15, 95%CI (0.96, 1.37) P = 0.18]. Baseline hemoglobin level was associated with major bleeding [OR: 0.71, 95%CI (0.58, 0.85) P < 0.01] in male patients, however we did not find the same relationship in female patients [OR: 0.89, 95%CI (0.56, 1.41) P = 0.61]. GAM and two-piecewise linear regression model showed the relationships of hemoglobin level with major bleeding, CVD death, and MACEs were non-linear (non-linear P < 0.05), and the threshold value were 13, 14.8, and 14.3 g/dL for MACEs and CVD death, respectively.

Conclusion: Baseline hemoglobin level was one of the independent predictors of prognosis in South Asia patients with acute myocardial infarction. Moreover, its impact on prognosis was largely different depending on the patients' sex.

Relation of Preprocedural Hemoglobin Level to Outcomes After Percutaneous Coronary Intervention

Adverse effects have been reported in patients with preprocedural anemia after percutaneous coronary intervention (PCI), but data regarding the relation between elevated hemoglobin (Hb) level and post-PCI prognosis remain limited. This study assessed the impact of elevated Hb on major adverse cardiac and cerebrovascular event (MACCE) at 12 months, a composite of all-cause mortality, nonfatal myocardial infarction, and ischemic stroke after PCI. We pooled patient-level data from four Korean multicenter drug-eluting stent registries from 2010 to 2016. In total, 5,107 patients were divided into 5 categories according to the baseline Hb level (<10, 10 to 12.9, 13 to 14.9, 15 to 16.9 and ≥17 g/dl). Patients with higher Hb levels were significantly younger, predominantly male, current smokers with higher body mass index, and more frequent dyslipidemia. Hypertension, diabetes, chronic kidney disease, and cerebrovascular accident were more prevalent in lower Hb groups. Categorically, a U-shaped curvilinear relation was observed between baseline Hb and clinical outcomes showing significantly higher MACCE rate in <10g/dl (hazard ratio [HR], 4.62 [2.81 to 7.68]) and ≥17 g/dl (HR, 4.06 [1.57 to 10.5]) groups compared with the reference group (13 to 14.9 g/dl), especially in men. In nonanemic patients (Hb ≥13 g/dl), adjusted HRs of MACCE, mortality, and stroke were significantly higher in ≥17 g/dl group than in the reference group. Furthermore, ≥17 g/dl was an independent predictor for MACCE and all-cause mortality after PCI. In conclusion, not only low Hb but also elevated Hb of ≥17 g/dl was significantly associated with higher MACCE rates and all-cause mortality after PCI. An appropriate treatment strategy for patients with high Hb level should be identified through future studies.

The sex difference in haemoglobin levels in adults - mechanisms, causes, and consequences

Men and women have different mean haemoglobin levels in health in venous blood - women have mean levels approximately 12% lower than men. A similar sex-related difference in haemoglobin levels in adult animals is found in many species of mammals, birds and reptiles, indicating that it is an important physiological phenomenon. It is probably a direct effect of sex hormones, both oestrogen and androgens, on erythropoiesis. However, since there is no difference in erythropoietin levels between the sexes, this effect most likely takes place in the kidney, rather than in the bone marrow. Oestrogens dilate and androgens constrict the renal microvasculature: dilation and vasoconstriction in vessels below 300 μm in diameter respectively increase and decrease the haematocrit in blood in arterioles, capillaries and venules, altering the oxygen delivery per unit red cell mass, and providing a mechanism for varying the red cell mass without compensatory changes in erythropoiesis.

Venesection in haemoglobin Yakima, a high oxygen affinity haemoglobin

High oxygen affinity haemoglobins result in polycythaemia and cardiovascular adaptation to maintain tissue oxygenation. The polycythaemia can cause symptoms of hyperviscosity and vaso-occlusive disease. We report a kindred with a high affinity haemoglobin (Haemoglobin Yakima) one of whose members gave birth to two infants with intra-uterine growth retardation and who suffered with symptoms of hyperviscosity which settled on reduction of the PCV by venesection.

Cyanotic congenital heart disease (CCHD) with symptomatic erythrocytosis

Secondary erythrocytosis of cyanotic congenital heart disease (CCHD) is pathologically different from primary erythrocytosis of polycythemia vera (PV). An association between elevated hematocrit and thrombosis has been established in PV patients, and treatment guidelines recommend maintaining hematocrit <45%. Although an association between elevated hematocrit and thrombosis has not been established in CCHD and secondary erythrocytosis, the current clinical practice is to phlebotomize these patients to hematocrit <65%. We report a 21-year-old woman with CCHD who presented with symptomatic erythrocytosis with numbness and tingling with hemoglobin 25.2 g/dl and hematocrit 75.8%. Her symptoms resolved with IV hydration. Other factors, including dehydration and iron deficiency, may precipitate hyperviscosity symptoms. The treatment is volume replacement and low-dose iron therapy, not phlebotomy. Repeated phlebotomy causes iron deficiency with microcytic erythrocytes, which increases the whole blood viscosity and, therefore, can potentially accentuate rather than decrease the risk for a cerebrovascular accident.

Best practice in primary care pathology: review 3

This best practice review examines four series of common primary care questions in laboratory medicine: (i) "minor" blood platelet count and haemoglobin abnormalities; (ii) diagnosis and monitoring of anaemia caused by iron deficiency; (iii) secondary hyperlipidaemia and hypertriglyceridaemia; and (iv) glycated haemoglobin and microalbumin use in diabetes. The review is presented in question-answer format, referenced for each question series. The recommendations represent a précis of guidance found using a standardised literature search of national and international guidance notes, consensus statements, health policy documents and evidence-based medicine reviews, supplemented by Medline Embase searches to identify relevant primary research documents. They are not standards, but form a guide to be set in the clinical context. Most of the recommendations are based on consensus rather than evidence. They will be updated periodically to take account of new information.

Altered Pulmonary Vascular Reactivity in Mice with Excessive Erythrocytosis

Pulmonary vascular remodeling during chronic hypoxia may be the result of either oxygen deprivation or erythrocytosis. To separate experimentally the effects of hypoxia and erythrocytosis, we analyzed transgenic mice that constitutively overexpress the human erythropoietin gene in an oxygen-independent manner. These mice are characterized by polycythemia but have normal blood pressure, heart rate, and cardiac output. In transgenic mice, pulmonary artery pressure (PAP) was increased in vivo but was reduced in blood-free perfused lungs. The thromboxane receptor agonist U46619 caused a smaller rise in PAP in isolated transgenic lungs than in lungs from wild-type mice. The transgenic pulmonary vasculature was characterized by elevated prostacyclin production, stronger endothelial nitric oxide synthase expression, and reduced pulmonary vascular smooth muscle thickness. The fact that transgenic polycythemic mice have marked pulmonary hypertension in vivo but not in vitro suggests that their pulmonary hypertension is due to the increased blood viscosity, thus supporting an independent role of polycythemia in the development of pulmonary hypertension. In addition, our findings indicate that the lungs of transgenic animals adapt to the high PAP by elevated synthesis of vasodilators and reduced vascular smooth muscle thickness that tend to reduce vascular tone and vascular responsiveness.

Hemostasis and coagulation at a hematocrit level of 0.85: functional consequences of erythrocytosis

We have generated a transgenic mouse line that reaches a hematocrit concentration of 0.85 due to constitutive overexpression of human erythropoietin in an oxygen-independent manner. Unexpectedly, this excessive erythrocytosis did not lead to thrombembolic complications in all investigated organs at any age. Thus, we investigated the mechanisms preventing thrombembolism in this mouse model. Blood analysis revealed an age-dependent elevation of reticulocyte numbers and a marked thrombocytopenia that matched the reduced megakaryocyte numbers in the bone marrow. However, platelet counts were not different from wild-type controls, when calculations were based on the distribution (eg, plasma) volume, thereby explaining why thrombopoietin levels did not increase in transgenic mice. Nevertheless, bleeding time was significantly increased in transgenic animals. A longitudinal investigation using computerized thromboelastography revealed that thrombus formation was reduced with increasing age from 1 to 8 months in transgenic animals. We observed that increasing erythrocyte concentrations inhibited profoundly and reversibly thrombus formation and prolonged the time of clot development, most likely due to mechanical interference of red blood cells with clot-forming platelets. Transgenic animals showed increased nitric oxide levels in the blood that could inhibit vasoconstriction and platelet activation. Finally, we observed that plasmatic coagulation activity in transgenic animals was significantly decreased. Taken together, our findings suggest that prevention of thrombembolic disease in these erythrocytotic transgenic mice was due to functional consequences inherent to increased erythrocyte concentrations and a reduction of plasmatic coagulation activity, the cause of which remains to be elucidated.

Life-threatening thrombotic complications of relative polycythaemia

Relative polycythaemia refers to raised haematocrit with normal red cell mass. Plasma volume may be reduced. This condition is associated with acute hypoxia, smoking, alcohol and diuretics. We describe two life-threatening thrombotic events in two patients with relative polycythaemia under age 40 years. The first had myocardial infarction and on admission haemoglobin was 21.6 g dL-1. The second developed pulmonary embolism and haemoglobin was 19.1 g dL-1. Both patients received antithrombotic measures and isovolumetric venesection. Sixteen patients (age <40 years) who attended our accident and emergency department in 1 year had a haemoglobin level of >18.0 g dL-1. Recognition of relative polycythaemia in at risk-individuals may help reduce thrombotic risk.

Idiopathic erythrocytosis, diagnosis and clinical management

By definition, idiopathic erythrocytosis (IE) applies to a group of patients characterised by having a measured RCM above their predicted normal range (an absolute erythrocytosis) and following investigation do not have a form of primary or secondary erythrocytosis. Patients with IE are heterogenous. The possibilities include physiological variation, 'early' polycythaemia vera (10-15% develop clear features of PV over a few years), unrecognized congenital erythrocytosis, unrecognized or unrecognizable secondary acquired erythrocytosis or a currently undescribed form of primary or secondary erythrocytosis. Patients are more commonly male with a median age at presentation of 55-60 years. Approximately half of the patients present with vascular occlusive complications. Retrospective evidence indicates that vascular occlusion occurs less frequently when the PCV is controlled at normal levels. Venesection is the treatment of choice to lower the PCV. As a general approach to management, all patients with a PCV above 0.54 should be venesected to a PCV less than 0.45. This target PCV should also apply to patients with lesser degrees of raised PCV who have additional other risk factors for vascular occlusion.

Cerebral embolism in a patient with polycythemia rubra vera

Polycythemia rubra vera (PRV) is a rare haematological disorder that has a high risk of stroke, although the pathophysiological origin of the cerebral ischaemia in this disease is not well known. We report a case of a stroke patient with PRV in whom bilateral embolic signals were detected by transcranial Doppler (TCD). Cerebral computed tomography showed a cortical middle cerebral artery infarction, echocardiography was normal, duplex-scan showed moderate left carotid stenosis and digital angiography disclosed right siphon stenosis. TCD examinations in the acute phase repeatedly showed a great number of bilateral microembolic signals (MESs). Four months later magnetic resonance angiography showed no flow signal in the right siphon and a severe stenosis of the proximal right MCA. The detection of bilateral MESs in the absence of cardiac sources of embolism observed in this patient suggests that ischaemic cerebral events in PRV may have an embolic origin favoured by a prothrombotic state.

Rheological influences on thrombosis

Blood flow plays important roles in the localization and morphology of thrombosis within the circulation. Blood flow properties (rheological variables) are associated with thrombotic risk factors and thrombotic risk; conversely their modification may reduce thrombotic risk.

Disorders of blood viscosity

In clinical situations associated with disturbed blood flow, the primary focus is usually on improving cardiovascular performance. However, during recent decades, both basic science and clinical literature reports have presented evidence that the flow properties of blood must also be considered in these situations. Thus, the relatively new fields of haemorheology and clinical haemorheology have evolved; the former deals with the flow and deformation behaviour of blood, plasma and the formed elements of blood, whereas the latter relates to alterations of their behaviour in various pathophysiologic states. This review therefore summarizes some of the salient aspects of clinical haemorheology and of the determinants of blood flow properties (flow rate, haematocrit, plasma viscosity, red cell aggregation, red cell deformability). In addition, it briefly describes several clinical disorders associated with abnormal blood, plasma or cell rheology ('hyperviscosity syndromes' occurring in polycythaemia, leukaemia, sickle cell disease, paraproteinaemias).

Budd-Chiari syndrome and thrombosis of other abdominal vessels in the chronic myeloproliferative diseases

Of 501 patients with chronic myeloproliferative diseases (c-MPD) 18 developed thrombosis of major abdominal vessels including 6 with hepatic vein thrombosis (Budd-Chiari syndrome). The complication was seen in 14 of 140 (10%) patients with polycythemia vera (PV), 3 of 23 (13%) patients with essential thrombocythemia (ET), 1 of 106 (1%) patients with idiopathic myelofibrosis (IMF), and none of 232 patients with chronic myelogenous leukemia (CML). Leading symptoms and signs were abdominal pain, progressive splenomegaly, widening abdominal girth, ascites, venous collaterals, and nausea and vomiting. The diagnostic modalities with highest specificity were angiography and explorative laparotomy. A causal relationship between the thrombotic event and hematocrit, thrombocyte count, or hemostatic abnormalities at the time of diagnosis could not be established. Detailed laboratory tests of platelet function and coagulation and fibrinolytic parameters of 5 surviving patients did not show any specific defect. Despite medical and surgical intervention, 39% of the patients died within 2 months after diagnosis of the thrombosis. The majority of the survivors developed further complications like liver cirrhosis with portal hypertension and esophageal varices or the short bowel syndrome after extensive bowel resection for mesenterial infarction.