Red blood cell count and risk of adverse outcomes in patients with mildly reduced left ventricular ejection fraction

Abstract Background Anemia is associated with increased rates of heart failure (HF)‐related mortality and hospitalization. No studies have focused on the association between the red blood cell (RBC) count and the prognosis of patients with HF with mildly reduced left ventricular ejection fraction (HFmrEF). We retrospectively analyzed the effect of the RBC count on outcome events in patients with HFmrEF. Methods We investigated the association of the RBC count with outcome events in 1691 patients with HFmrEF (mean age: 68 years; 35% female) in Xiangtan Central Hospital. Using Cox proportional hazards models, the RBC count was assessed as both a continuous and categorical variable. Results During follow‐up (median: 33 months), cardiovascular death occurred in 168 patients (114 men and 54 women). After adjusting for established risk factors, each 1.0 × 1012 cell/L increase in the RBC count was associated with a 28% lower risk of cardiovascular death in men and a 43% lower risk in women. Patients with low RBC counts had a 0.5‐fold higher risk of cardiovascular death than those with normal RBC counts. The hazard ratio for men was 1.42 (95% confidence interval [CI]: 1.07–1.89), and the hazard ratio for women was 1.79 (95% CI: 1.20–2.67). The RBC count was not significantly associated with the composite endpoint of cardiovascular death and HF readmission (cardiovascular events) (p > .05). Conclusions A decreased RBC count is associated with increased cardiovascular mortality in patients with HFmrEF. Correcting a low RBC count might potentially reduce the risk of cardiovascular death in patients with HFmrEF.

Significant progress has been made in the pathogenesis of heart failure (HF), and reasonable treatment has improved patients' prognoses. 1However, the prognosis of HF remains unsatisfactory. 2,3emia is common in patients with HF, 3 and the pathogenesis of anemia in HF is multifactorial. 4,5Patients are classified as having HF with reduced ejection fraction [HFrEF; left ventricular ejection fraction (LVEF) of ≤40%], HF with mildly reduced ejection fraction (HFmrEF; LVEF of 41%-49%), or HF with preserved ejection fraction (HFpEF; LVEF of ≥50%). 1 Furthermore, studies have shown that anemia is an independent predictor of mortality and morbidity in patients with HFrEF or HFpEF. 5,6Few studies have examined the relationship between anemia and HFmrEF or between the red blood cell (RBC) count and HFmrEF; therefore, whether changes in the RBC count impact the prognosis of patients with HFmrEF remains unclear.
In the present study, we retrospectively analyzed the effect of the RBC count on outcome events in patients with HFmrEF.At the same time, we conducted a stratified analysis of men and women with HFmrEF to determine whether changes in the RBC count result in differences in outcome events in men and women with HFmrEF.The aim of this study is to increase the overall understanding of the characteristics of patients with HFmrEF and formulate more reasonable treatment for these patients.

| RBC count
According to the definition of the standard RBC count in routine blood testing at our hospital, the reference range for men is 4.0 to 5.5 × 10 12 /L and that for women is 3.5 to 5.0 × 10 12 /L.After excluding patients with elevated RBC counts (>5.5 × 10 12 /L in men and >5.0 × 10 12 /L in women), the patients were divided into those with reduced RBC counts (<4.0 × 10 12 /L in men and <3.5 × 10 12 /L in women) and normal RBC counts (≥4.0 × 10 12 /L in men and ≥3.5 × 10 12 /L in women).We chose to evaluate RBC count as our primary parameter rather than hemoglobin or RBC specific volume (hematocrit), because RBC count is less affected by hypoxia, dehydration, and volume status, which can be confounding clinical factors within this patient population.

| Participants
The study protocol was approved by the Ethics Committee of Xiangtan Central Hospital (Xiangtan, China) and conformed to the principles outlined in the Declaration of Helsinki. 7Informed consent was obtained from all patients or their guardians before the study protocol was initiated.The requirement for written informed consent was waived because of the study's retrospective nature; consent was only obtained verbally in person or by telephone.This study was based on the Outcome of Discharged HFmrEF Patients study (OUDI-HF study; ClinicalTrials.govnumber NCT05240118).The OUDI-HF study included 1691 patients with HFmrEF who were admitted to our hospital from January 1, 2015 to August 31, 2020.The inclusion criteria were HF with an LVEF of 41%-49% and a New York Heart Association HF score of II-IV.The exclusion criteria were malignancies or other non-cardiac diseases with expected survival of less than 1 year.After excluding 52 patients with increased RBC counts, 1149 patients with normal RBC counts and 490 patients with decreased RBC counts were included in the study (Figure 1).

| Outcomes
Demographic and procedural data were collected from the patients' hospital charts or the hospital database.All study participants were followed up on August 31, 2021.A panel of seven experienced physicians reviewed suspected cardiovascular (CV) events by examining the information obtained from hospital records and follow-ups, including clinical telephone interviews and community visits.The primary outcome of interest was CV death after discharge, and the secondary outcome was the composite of CV death and HF readmissions (CV events).CV death was defined as death from any CV mechanism, including acute myocardial infarction, sudden cardiac death, HF, stroke, CV surgery, CV hemorrhage, and other CV causes.

| Statistical analysis
We used Cox proportional hazards regression models stratified by cohort to examine the association of the RBC count with the rate of outcome events.We performed a sex-stratified analysis.The RBC count was assessed as a continuous variable (increased risk was calculated for each 1.0 × 10 12 cell/L increase) and as a categorical variable.We adjusted for the following baseline covariates: age, body Clinical characteristics were compared between the groups using the t-test for continuous variables and the Chi-square test for categorical variables.The Kaplan-Meier method was used to estimate the incidence of cumulative events.All p values were obtained using the Kruskal-Wallis rank-sum test for continuous variables and Fisher's exact probability test for count variables.The results were considered significant when the p value was <.05.All analyses were performed using R (http://www.R-project.org) and EmpowerStats (www.empowerstats.net,X&Y Solutions, Inc.).

F I G U R E 1 Flow diagram for participant screening, eligibility and analysis.
T A B L E 1 Baseline characteristics according to whether the RBC count decreases (n = 1639).| 1279

| Baseline characteristics
More than half of the 1639 patients included in this study were male (n = 1067).The patients' mean age was 68.5 ± 12.3 years, their mean body mass index was 25.1 ± 4.1 kg/m 2 , their mean LVEF was 44.4% ± 2.7%, and more than half of the patients had been hospitalized for myocardial infarction (51.8%) (Table 1).
The mean RBC count was 4.2 ± 0.7 × 10 12 /L in men and 3.8 ± 0.6 × 10 12 /L in women.Men with reduced RBC counts had higher rates of hypertension, diabetes, and renal insufficiency but lower rates of hyperlipidemia and myocardial infarction.Women with reduced RBC counts had higher rates of diabetes and renal insufficiency but lower rates of myocardial infarction (Table 1).However, the incidence of CV events was not significantly correlated between the two groups (HR: 1.10; 95% CI: 0.83-1.47;p = .506).

| DISCUSSION
This study showed that reduced RBC counts were associated with increased CV mortality in patients with HFmrEF after adjusting for covariates.However, there was little correlation between changes in RBC counts and the incidence of CV events in patients with HFmrEF.
[8][9][10] In a metaanalysis involving more than 150 000 patients with HF from 33 studies, anemia doubled the risk of death. 11Compared with patients without anemia, those with anemia are older, more likely to be female, and more likely to have diabetes, chronic kidney disease (CKD), and severe HF with a worse functional status. 4,6,12,13In addition, patients with HF and anemia have several comorbidities, including CKD, malnutrition associated with cardiac cachexia, and a low albumin concentration, all of which may worsen the prognosis. 9,12,14rthermore, anemia and CKD often coexist in patients with HF.
One study showed that although anemia doubled the risk of death in patients with HF, the adjusted risk of death was further increased by 1.5fold in the presence of CKD. 14 The above-mentioned studies and ours have demonstrated the association between HF and anemia.However, the difference is that unlike our study, previous studies failed to focus specifically on patients with HFmrEF.Our study demonstrates a relationship between RBC count and prognosis in patients with HFmrEF.T A B L E 2 Univariate analysis was performed on the cumulative incidence of outcome events according to RBC count grouping Severe anemia may progress to HF syndrome, which disappears when the anemia is corrected. 15The erythropoietin concentration increases in proportion to the severity of HF. 13,16 The relationship between renal blood flow and erythropoietin secretion in patients with HF is complex and not fully understood. 17For many years, correction of anemia in patients with HF was thought to improve symptoms, quality of life, and clinical outcomes.However, research has shown that treating anemia with erythropoiesis-stimulating agents does not improve clinical outcomes but is associated with higher rates of thromboembolic events. 39][20][21][22] Iron deficiency is also a significant cause of anemia.A meta-analysis of randomized controlled trials comparing ferric carboxymaltose versus placebo showed that ferric carboxymaltose administration was associated with reduced mortality and HF hospitalization in iron-deficient patients with HFrEF. 23 been demonstrated, the long-term (>1 year) clinical benefit is uncertain. 24rthermore, studies have also shown that an increased hemoglobin concentration in patients with HFrEF increases systemic vascular resistance and decreases the LVEF. 6,9,13These findings may also explain why some patients with HF exhibited correction of anemia but not a reduction in adverse outcome events.Some patients who have HF with anemia can experience a spontaneous increase in hemoglobin, and the prognosis of these patients is similar to that of patients who have HF without anemia. 25No studies have focused on the correction of anemia in patients with HFmrEF.
Therefore, whether using drugs to correct anemia in patients with HFmrEF will lead to adverse outcomes remains unclear.

| Limitations
This study had several limitations.First, this was designed as a retrospective study to minimize bias in patient selection; however, unobserved confounders remained.Second, we exclusively recruited patients from an isolated population at a local heart center in China, and the study population thereby lacked adequate diversity to justify the uniformity of the findings.Finally, because of the study's retrospective nature, some test results could not collected; the most important of these was the absence of data on the B-type natriuretic peptide concentration.

| CONCLUSIONS
Our findings suggest that reduced RBC counts are associated with increased CV mortality in patients with HFmrEF.Women with HFmrEF are more sensitive to changes in RBC counts than are men.Compared with men with HFmrEF, women with reduced RBC counts had a greater risk of CV death, and an increased RBC count was associated with a more significant reduction in the risk of CV death in women.Correcting a decreased RBC count can potentially reduce the risk of CV death in patients with HFmrEF.However, there is no clear conclusion regarding the need for medication to correct anemia in patients with HFmrEF.
Further research is needed to understand the risk associated with anemia in patients with HFmrEF.A better understanding of risk factors for anemia in patients with HFmrEF may help to develop strategies to improve outcomes of patients with this severe disease.

2 | METHODS 2 . 1 |
Three critical parameters related to RBCs RBC count: This denotes the concentration of RBCs per microliter of blood, typically enumerated in millions.Integral to oxygen transportation, diminished counts may indicate conditions such as anemia, while elevated counts could signal disorders like polycythemia vera.Hemoglobin: This intracellular protein is responsible for transporting oxygen to tissues and returning carbon dioxide to the lungs.Hemoglobin concentrations, quantified in grams per deciliter, can reflect various health conditions, with lower levels potentially indicative of anemia and higher levels suggestive of polycythemia vera or chronic hypoxia.Red blood cell specific volume (RBCSV): This parameter represents the volume fraction of RBCs in the blood, also called hematocrit.Normal hematocrit ranges differ by sex.Deviations from normal ranges can indicate various conditions-low levels may suggest anemia, and high levels could indicate dehydration or other disorders.
mass index，smoking status, alcohol use, hypertension, hyperlipidemia, diabetes, coronary heart disease, atrial fibrillation, previous stroke, chronic obstructive pulmonary disease, renal insufficiency, New York Heart Association functional class, myocardial infarction, percutaneous coronary intervention, uric acid concentration, estimated glomerular filtration rate, potassium concentration and LVEF.The credibility of the Cox proportional risk regression model was verified using propensity score matching analysis.Propensity score matching analysis based on a multivariate logistic regression model with the following factors: age, body mass index, gender, smoking status, alcohol use, hypertension, hyperlipidemia, diabetes, coronary heart disease, atrial fibrillation, previous stroke, chronic obstructive pulmonary disease, renal insufficiency, New York Heart Association functional class, myocardial infarction, percutaneous coronary intervention, uric acid concentration, estimated glomerular filtration rate, potassium concentration and LVEF.Propensity scores were calculated by the dichotomous variable of whether the patient's RBC count was reduced, and then the scores were matched 1:1, allowing for a difference in scores of 0.01.This strategy results in 389 matching pairs per group.

Table S3
(p < .0001for both), and 0.97 for males and 0.95 for females in the Adjust II model (p = .0033for males, p = .0006for females).These findings underscore the clinical significance of Hemoglobin and RBCSV as potential indicators for prognosis and management in patients with HFmrEF.
Although the clinical benefit of intravenous iron in anemic patients with HF has T A B L E 3 Results of a multivariate Cox proportional hazards model for the effect of RBC count on outcome events in patients with HFmrEF.The population was classified according to whether the male RBC count was ≥4.0 × 10 12 /L and whether the female RBC count was ≥3.5 × 10 12 /L.Bold represent significant values (p < .05).Adjust I, adjusted for age and body mass index.Adjust II, adjusted for age, body mass index, coronary heart disease, hypertension, hyperlipidemia, atrial fibrillation, diabetes mellitus, previous stroke, previous myocardial infarction, percutaneous coronary intervention, chronic obstructive pulmoriary disease, renal insufficiency, New York Heart Association functional class, uric acid, estimated glomerular filtration rate, potassium, left-ventricular ejection fraction, current smoker and current drinker at baseline.