Original Article

Volume 16, Number 11, December 2024, pages 547-553

Possible Risk Factors Contributing to Atrial Fibrillation Occurrence in Heart Failure With Mildly Reduced Ejection Fraction

Heart failure (HF) is a widespread clinical syndrome globally. The number of HF cases doubled from 33.5 million in 1990 to 64.3 million in 2018, and global prevalence remains high [1]. HF is associated with structural and functional abnormalities of the myocardium [2]. The main pathogenic mechanisms contributing to HF include increased hemodynamic overload, ischemia-related dysfunction, contractile protein mutations, ventricular remodeling and altered neurohumoral stimulation [3, 4]. Based on the huge variety of etiology and pathogenesis, HF has multiple causes, which makes precise classification and treatment difficult [5, 6]. Comparison of clinical characteristics, comorbidities, outcomes, and prognosis among patients with HF who have either preserved ejection fraction (EF) (> 50%, HFpEF), or moderately reduced ejection fraction (40-49%, HFmrEF), or reduced ejection fraction (< 40%, HFrEF) leads to consideration of HFmrEF as an intermediate HF phenotype [6, 7]. HFmrEF was first recognized as a new HF phenotype by the European Society of Cardiology in 2016 [8, 9]. Of the more than 6.5 million patients with HF in the United States, 13-24% had HFmrEF [8]. Recent research suggests that patients with HFmrEF benefit from therapies designed to improve outcomes for people with reduced EF [10, 11]. However, the characteristics of HFmrEF and its therapeutic potential remain poorly understood. Atrial fibrillation (AF) is the most common sustained and heterogeneous type of arrhythmia. There is plausible published evidence linking its onset and progression to inflammation and fibrosis [12, 13]. Although AF and HF are distinct diseases, they are increasingly found to overlap and are associated with high morbidity and mortality; in addition, patients with comorbid HF and AF suffer from even more severe symptoms and a worse prognosis [14]. Data from the Framingham Heart Study suggest that AF occurs in more than half of individuals with HF, and that HF occurs in more than one-third of individuals with AF. Thus, HF and AF are commonly encountered together and are closely interrelated with similar risk factors, and each predisposes to the other [15, 16]. However, while HFmrEF is well described, the determinants and outcomes of HFmrEF with concomitant AF remain unclear. In this study, we aimed to identify possible risk factors associated with the onset and progression of AF in patients with HFmrEF.

Blood samples were collected from patients with heart failure (HF) and AF in the Department of Arrhythmia at the Research Institute of Cardiology named after L. Hovhannisyan (Yerevan, Armenia) under protocols approved by the Ethical Committee of the Institute of Cardiology and the Local Ethical Committee (Protocol no. 3 of 05.11.2021). Informed consent was obtained from all patients involved in the study.

The study included 193 patients with non-valvular AF and HFrEF, who were admitted to the Research Institute of Cardiology over a period of 3 years and underwent successful cardioversion. Of these, 103 patients had paroxysmal AF, and 90 had persistent AF. Similar 76 patients with HFmrEF but without AF were examined as the control group. Moreover, the inclusion criteria were the following: HFmrEF 40-49%, N-terminal pro-B-type natriuretic peptide (NT-proBNP) > 125 pg/mL and the presence of ischemic or hypertensive heart disease. Ischemic etiology was defined based on a documented history of myocardial infarction or coronary angiography. Arterial hypertension was diagnosed according to the 2018 European Society of Cardiology/European Society of Hypertension (ESC/ESH) guidelines for the management of arterial hypertension [17]. Furthermore, the exclusion criteria included the following: HF due to valvular heart disease, chronic obstructive pulmonary disease, systemic inflammatory diseases and diabetes. Patients were followed up according to the usual practice of the center. All participants underwent a detailed physical examination that included resting 12-lead electrocardiography (ECG) recording, 24-h blood pressure (BP) monitoring, echocardiography, and 24-h ambulatory Holter monitoring. BP in rest was calculated from the mean of the second and third readings and peak of BP by 24-h BP monitoring. The body mass index (BMI) was calculated as weight divided by height squared and expressed as kg/m². All examined patients were asked to complete a questionnaire about their lifestyle (e.g., smoking, drinking, and nutrition) and the presence of potential comorbidities. Table 1 presents the clinical characteristics of the patients.

Click to view

Table 1. Baseline Demographics and Clinical Characteristics in all Observed HFmrEF Patient With and Without AF

All observed patients with HFmrEF received standard therapy. But patients with AF were prescribed also amiodarone and rivaroxaban in maintenance doses.

Since one of the main electrophysiological factors in the occurrence and maintenance of AF is the inhomogeneity of atrial conduction velocity, the ECG display of this process is the dispersion of the P wave (Pdis), which is defined as the difference between the maximum (Pmax) and minimum (Pmin) duration of the P wave recorded in lead II of the ECG.

To measure left ventricular ejection fraction (LVEF) according to standard criteria, traditional transthoracic echocardiography “Medison SonoAceX6” (Hungary) was used. Echocardiography measurements of chamber sizes, as well as systolic and especially early diastolic cardiac dysfunction were carried out in accordance with established recommendations.

Quantifications were determined using standard laboratory procedures established at the Institute of Cardiology. Plasma levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), and high-sensitivity C-reactive protein (hs-CRP) were measured by enzyme-linked immunosorbent assay (ELISA) kits according to manufacturer’s instructions, using the Stat Fax 303 Plus analyzer (Awareness Technology, Palm City, FL, USA).

Statistically significant differences between parameters were identified using two-step cluster analysis. The findings were modeled using binary logistic regression using the odds ratio (OR). Binary logistic regression was performed for two groups, with the third group selected as a comparison. Using the binary logistic regression method, it is possible to study the dependence of dichotomous variables (binary, having only two possible values) on independent variables of any type of scale. As a rule, in the case of dichotomous variables, we are talking about some event that may or may not occur; binary logistic regression in this case calculates the probability of the event depending on the values of the independent variables. The probability of the event for a certain case is calculated using the formula:

$\text{P}=\frac{1}{\text{1}+{\text{e}}^{-\text{z}}}$

X1 are the values of the independent variables, b1 are the coefficients, the calculation of which is the task of binary logistic regression, and a is some constant. If the value for P is less than 0.05, then it can be assumed that the event will not occur; otherwise, the occurrence of the event is assumed. The significance of the difference of the coefficients from 0 was tested using the Wald statistic, which uses the χ² distribution. This is calculated as the square of the ratio of the corresponding coefficient to its standard error.

OR is one of the most common approaches to describe how the absence or presence of a particular outcome is associated with the presence or absence of a particular factor in a particular statistical group. Thus, the results of using the OR include determining the statistical significance of the relationship between the factor and the result (outcome), as well as its quantitative assessment. It is very important to assess the statistical significance of the identified association between the outcome and the risk factor. If the OR is greater than 1, then the chances of detecting a risk factor in this group are greater, which means that the factor has a direct relationship with the probability of the outcome. Moreover, in each case, the statistical significance of the OR is necessarily assessed based on the values of the 95% confidence interval (CI) (P value < 0.05 was considered significant). This is due to the fact that even with low values of the OR, close to 1, the relationship may nevertheless be significant and should be taken into account in statistical conclusions. Conversely, with large values of the OR, the indicator turns out to be statistically insignificant, and therefore, the identified relationship can be neglected. The studies were conducted using simple randomized protocols using the universal statistical package SPSS 13.0.

Table 1 presents the demographic and clinical characteristics of all studied patients. When analyzing the demographic characteristics of patients, all groups were comparable in terms of gender, age and BMI. The groups were also similar in the proportion of patients who smoked and drinking habits. There were no significant changes in heart rate at rest in the three examined groups. However, peak heart rate in patients with paroxysmal AF was significantly higher than that in patients with persistent AF and patients without AF. There were no significant differences in systolic blood pressure (SBP) and diastolic blood pressure (DBP) at rest between the three groups of patients. However, peak DBP was significantly higher in patients with paroxysmal AF than in patients with persistent AF and the control group (P < 0.05).

An OR method was used to assess the risk of developing paroxysmal AF compared with the control group without AF. Moreover, the indicators associated with an increased risk of developing paroxysmal AF in patients with HFmrEF included the following: age (OR = 1.8; CI = 1.08 - 1.28, P = 0.05), high DBP (OR = 1.09, CI = 1.01 - 1.17, P = 0.017), high frequency of hypertensive crises (HCs, OR = 1.17, CI = 1.07 - 1.43, P = 0.01), and high BMI (OR = 1.13, CI = 0.93 - 1.27, P = 0.031). According to electrocardiographic findings, P-wave maximum (Pmax) and P-wave dispersion (Pdis) were significantly prolonged and associated with increased risk for both paroxysmal AF (Pmax: OR = 3.92, CI = 3.88 - 3.96, P = 0.002; Pdis: OR = 3.91, CI = 3.87 - 3.95, P = 0.002) and persistent AF (Pmax: OR = 4.81, CI = 4.07 - 5.94, P < 0.001; Pdis: OR = 4.90, CI = 4.86 - 5.93, P < 0.001). In addition, based on echocardiographic measurements, it was found that with an increased left atrial volume (LAV), the risk of paroxysmal AF was significantly increased (LAV: OR = 1.76, CI = 1.66 - 1.88, P = 0.002). It is worth noting that an increase in the level of markers of systemic inflammation (hs-CRP: OR = 5.57, CI = 3.38 - 7.87, P = 0.010; IL-6: OR = 4.80, CI = 2.72 - 6.88, P = 0.001; TNF-α: OR = 2.56, CI = 1.43 - 4.73, P = 0.002) contributes to a high risk of developing paroxysmal AF in patients with HFmrEF (Table 2).

Click to view

Table 2. The Analysis of OR Values at a 95% CI of Various Clinical Hemodynamic and Structural-Functional Parameters and Markers of Inflammation and Fibrosis in HFmrEF Patients With Paroxysmal AF Compared to the Control Group

In the analysis of possible risk factors in HFmrEF patients with persistent AF, significant risk factors relative to the control group were the frequency of HCs (OR = 1.56, CI = 1.041 - 1.971, P = 0.001) and increased BMI (OR = 1.97, CI = 0.98 - 2.21, P = 0.044). The OR values for left atrial diameter (LAD) and LAV were also significantly increased (OR = 3.69, CI = 2.58 - 4.82, P = 0.002; OR = 3.80, CI = 2.65 - 4.09, P = 0.040, respectively). An analysis of echocardiological data has revealed that left ventricular (LV) diastolic dysfunction is a possible risk factor in HFmrEF patients with persistent AF, compared to those with paroxysmal AF. Statistically significant increases were observed in interventricular septum thickness (IVST, OR = 1.69, CI = 1.48 - 1.98, P = 0.042), early diastolic filling wave (E peak, OR = 3.05, CI = 3.01 - 3.05, P = 0.012), and isovolumetric relaxation time (IVRT, OR = 3.94, CI = 3.90 - 4.99, P = 0.016). Moreover, in patients with persistent AF, impaired LV systolic function is important. The risk of persistent AF was associated with increased left ventricle end-diastolic diameter (LVEDD, OR = 1.76, CI = 1.58 - 1.99, P = 0.046), left ventricle end-diastolic volume (LVEDV, OR = 1.93, CI = 1.89 - 2.09, P = 0.019), and some reduction in EF (OR = 1.30, CI = 1.08 - 1.57, P = 0.05). A significant increase in the levels of OR markers of inflammation was also revealed (hs-CRP: OR = 6.37, CI = 5.24 - 8.59, P = 0.002; IL-6: OR = 5.58, CI = 4.71 - 7.87, P = 0.001; TNF-α: OR = 2.51, CI = 2.51 - 4.68, P = 0.002), which may also contribute to the high risk of developing persistent AF in patients with HFmrEF. Moreover, an increase in the OR of profibrotic TGF-β1 (OR = 3.84, CI = 2.10 - 6.23, P = 0.005), in contrast to paroxysmal AF, may also be a possible risk factor for the development of persistent AF in patients with HFmrEF (Table 3).

Click to view

Table 3. The Analysis OR Value of Various Clinical Hemodynamic and Structural-Functional Parameters, as Well as Markers of Inflammation and Fibrosis in HFmrEF Patients With Persistent AF Compared With the Control Group

Considering the fact that AF and HF often occur together, much attention is paid to assessing the quality of life, possible risk factors and concomitant diseases that contribute to atrial remodeling, thereby leading to a worsening of the course and prognosis of AF.

It has been demonstrated that left atrial dysfunction, as well as their structural abnormalities, play an important role in the initiation of AF, i.e., electrical and structural remodeling of the atria contributes to the development and progression of AF [16, 18]. Currently, existing data undeniably indicate the participation of inflammation in the pathogenesis of AF. Moreover, AF is known to have a strong association with HF, as many studies have shown that AF and HF often coexist, share common predisposing factors, and may worsen the overall prognosis [19-21]. We examined clinical, structural, and biochemical predictors of paroxysmal/persistent AF in HFmrEF patients and compared them with similar patients without AF. The results of our studies show that the tendency to obesity is one of the possible risk factors for the occurrence of AF in patients with HF. Overweight people have a higher incidence, prevalence, severity and progression of AF than people of normal weight. Obese patients often have multiple risk factors for developing AF, which can improve in response to weight loss; therefore, a consolidated approach to weight loss and management of AF risk factors is preferable [22]. A meta-analysis of 10 studies involving 108,996 patients found that for every 5% increase in weight, the incidence of AF increased by 13% (hazard ratio (HR) = 1.13, 95% CI = 1.04 - 1.23, P < 0.01). The authors of this study concluded that weight gain is associated with an increased risk of AF [23, 24]. Our data suggest that patient BMI is a significant predictor of the occurrence of paroxysmal and persistent AF in patients with HFmrEF.

Recent studies have demonstrated a correlation between changes in the anatomical structure of the atria and the level of inflammatory cytokines [25, 26]. This phenomenon has been accepted as a new insight into the study of the pathogenesis of AF, especially in patients with HF [27].

Comparison of risk factors associated with paroxysmal and persistent AF suggests that predictive factors have different effects on the occurrence and progression of AF in patients with HFpEF. In paroxysmal AF, special attention should be paid to the frequency of HCs, and markers of inflammation (OR). In the persistent form of AF, possible risk factors include inflammatory markers as well as fibrosis markers.

Our comparison of possible risk factors associated with paroxysmal and persistent AF suggests that predictor factors contribute differently to the occurrence and progression of AF. Thus, the OR of indicators of atrial electrical remodeling (Pmax and Pdis) turned out to be quite informative in the analysis, which can emphasize the particular importance of atrial damage in the occurrence of AF.

Based on the study of the relationship between left ventricular diastolic function (peak E, peak A, E/A ratio and IVRT deceleration time) and the risk of AF, it turned out that these parameters do not play an important role in the occurrence of paroxysmal AF but are decisive in persistent AF.

Higher age, BMI, frequency of HCs as well as atrial electrical remodeling play an important role in the occurrence of paroxysmal/persistent AF in patients with HFmrEF.

LV diastolic dysfunction and left atrial geometry changes are possible risk factors of AF occurrence of paroxysmal/persistent AF in patients with HFmrEF.

An increase in the concentration of inflammatory markers contributes to the appearance of paroxysmal/persistent AF in patients with HFmrEF. An increase in the level of a profibrotic marker increases the likelihood of persistent AF in these patients

Acknowledgments

The authors thank the patients who participated in this study and donated their samples, and the staff of the Department of Arrhythmia and Immunological Laboratory of the Research Institute of Cardiology.

Financial Disclosure

Our group of authors did not use any foundation and had no financial support.

Conflict of Interest

The authors declare no conflict of interest.

Informed Consent

All subjects provided written informed consent.

Author Contributions

LH and SG designed and performed the study. PZ, HH, and SG drafted the manuscript and did critical editing. LH, PZ and SG assisted and supported in sample collection and subsequent analysis with statistics. SG and PZ carefully supervised this manuscript preparation and writing.

Data Availability

The authors declare that data supporting the findings of this study are available within the article.

Abbreviations

AF: atrial fibrillation; A peak: late diastolic filling wave; BMI: body mass index; BP: blood pressure; CI: confidence interval; DBP: diastolic blood pressure; DT: deceleration time; E peak: early diastolic filling wave; E/A ratio: the ratio of the E peak to the A peak; EF: ejection fraction; HC: hypertensive crisis; HF: heart failure; HFmrEF: heart failure with mildly reduced ejection fraction; HFpEF: heart failure with preserved ejection fraction; HFrEF: heart failure with educed ejection fraction; HR: heart rate; hs-СRP: high-sensitivity C-reactive protein; IHD: ischemic heart disease; IL-6: interlekine-6; IVRT: isovolumetric relaxation time; IVST: interventricular septum thickness; LAD: left atrial diameter; LAV: left atrial volume; LVEDD: left ventricle end-diastolic diameter; LVEDV: left ventricle end-diastolic volume; LVESD: left ventricle end-systolic diameter; LVESV: left ventricle end-systolic volume; LVPWT: left ventricle posterior wall thickness; OR: odds ratio; Pdis: P-wave dispersion; Pmax: P-wave maximum; SBP: systolic blood pressure; TNF-α: tumor necrosis factor-α; ТGF-β1: transforming growth factor-β1

1. Bragazzi NL, Zhong W, Shu J, Abu Much A, Lotan D, Grupper A, Younis A, et al. Burden of heart failure and underlying causes in 195 countries and territories from 1990 to 2017. Eur J Prev Cardiol. 2021;28(15):1682-1690.
   doi pubmed
2. Shen L, Jhund PS, Petrie MC, Claggett BL, Barlera S, Cleland JGF, Dargie HJ, et al. Declining risk of sudden death in heart failure. N Engl J Med. 2017;377(1):41-51.
   doi pubmed
3. Al-Khatib SM, Benjamin EJ, Albert CM, Alonso A, Chauhan C, Chen PS, Curtis AB, et al. Advancing research on the complex interrelations between atrial fibrillation and heart failure: a report from a us national heart, lung, and blood institute virtual workshop. Circulation. 2020;141(23):1915-1926.
   doi pubmed
4. Carlisle MA, Fudim M, DeVore AD, Piccini JP. Heart failure and atrial fibrillation, like fire and fury. JACC Heart Fail. 2019;7(6):447-456.
   doi pubmed
5. Nso N, Bookani KR, Metzl M, Radparvar F. Role of inflammation in atrial fibrillation: A comprehensive review of current knowledge. J Arrhythm. 2021;37(1):1-10.
   doi pubmed
6. Peters AE, Mentz RJ, Sun JL, Harrington JL, Fudim M, Alhanti B, Hernandez AF, et al. Patient-reported and clinical outcomes among patients hospitalized for heart failure with reduced versus preserved ejection fraction. J Card Fail. 2022;28(12):1652-1660.
   doi pubmed
7. Authors/Task Force M, McDonagh TA, Metra M, Adamo M, Gardner RS, Baumbach A, Bohm M, et al. 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure: Developed by the Task Force for the diagnosis and treatment of acute and chronic heart failure of the European Society of Cardiology (ESC). With the special contribution of the Heart Failure Association (HFA) of the ESC. Eur J Heart Fail. 2022;24(1):4-131.
   doi pubmed
8. Mesquita ET, Barbetta L, Correia ETO. Heart failure with mid-range ejection fraction - state of the art. Arq Bras Cardiol. 2019;112(6):784-790.
   doi pubmed
9. Tsuji K, Sakata Y, Nochioka K, Miura M, Yamauchi T, Onose T, Abe R, et al. Characterization of heart failure patients with mid-range left ventricular ejection fraction-a report from the CHART-2 Study. Eur J Heart Fail. 2017;19(10):1258-1269.
   doi pubmed
10. Koh AS, Tay WT, Teng THK, Vedin O, Benson L, Dahlstrom U, Savarese G, et al. A comprehensive population-based characterization of heart failure with mid-range ejection fraction. Eur J Heart Fail. 2017;19(12):1624-1634.
    doi pubmed
11. Sartipy U, Dahlstrom U, Fu M, Lund LH. Atrial fibrillation in heart failure with preserved, mid-range, and reduced ejection fraction. JACC Heart Fail. 2017;5(8):565-574.
    doi pubmed
12. Bassand JP, Accetta G, Camm AJ, Cools F, Fitzmaurice DA, Fox KA, Goldhaber SZ, et al. Two-year outcomes of patients with newly diagnosed atrial fibrillation: results from GARFIELD-AF. Eur Heart J. 2016;37(38):2882-2889.
    doi pubmed
13. Marrouche NF, Wazni O, McGann C, Greene T, Dean JM, Dagher L, Kholmovski E, et al. Effect of MRI-guided fibrosis ablation vs conventional catheter ablation on atrial arrhythmia recurrence in patients with persistent atrial fibrillation: the DECAAF II randomized clinical trial. JAMA. 2022;327(23):2296-2305.
    doi pubmed
14. Pandey A, Kim S, Moore C, Thomas L, Gersh B, Allen LA, Kowey PR, et al. Predictors and prognostic implications of incident heart failure in patients with prevalent atrial fibrillation. JACC Heart Fail. 2017;5(1):44-52.
    doi pubmed
15. Santhanakrishnan R, Wang N, Larson MG, Magnani JW, McManus DD, Lubitz SA, Ellinor PT, et al. Atrial fibrillation begets heart failure and vice versa: temporal associations and differences in preserved versus reduced ejection fraction. Circulation. 2016;133(5):484-492.
    doi pubmed
16. Kornej J, Borschel CS, Benjamin EJ, Schnabel RB. Epidemiology of atrial fibrillation in the 21st century: novel methods and new insights. Circ Res. 2020;127(1):4-20.
    doi pubmed
17. Williams B, Mancia G, Spiering W, Agabiti Rosei E, Azizi M, Burnier M, Clement DL, et al. 2018 ESC/ESH Guidelines for the management of arterial hypertension. Eur Heart J. 2018;39(33):3021-3104.
    doi pubmed
18. Gopinathannair R, Chen LY, Chung MK, Cornwell WK, Furie KL, Lakkireddy DR, Marrouche NF, et al. Managing atrial fibrillation in patients with heart failure and reduced ejection fraction: a scientific statement from the American Heart Association. Circ Arrhythm Electrophysiol. 2021;14(6):HAE0000000000000078.
    doi pubmed
19. Son MK, Park JJ, Lim NK, Kim WH, Choi DJ. Impact of atrial fibrillation in patients with heart failure and reduced, mid-range or preserved ejection fraction. Heart. 2020;106(15):1160-1168.
    doi pubmed
20. Lippi G, Sanchis-Gomar F, Cervellin G. Global epidemiology of atrial fibrillation: An increasing epidemic and public health challenge. Int J Stroke. 2021;16(2):217-221.
    doi pubmed
21. Hindricks G, Potpara T, Dagres N, Arbelo E, Bax JJ, Blomstrom-Lundqvist C, Boriani G, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS): The Task Force for the diagnosis and management of atrial fibrillation of the European Society of Cardiology (ESC) Developed with the special contribution of the European Heart Rhythm Association (EHRA) of the ESC. Eur Heart J. 2021;42(5):373-498.
    doi pubmed
22. Magnussen C, Niiranen TJ, Ojeda FM, Gianfagna F, Blankenberg S, Njolstad I, Vartiainen E, et al. Sex differences and similarities in atrial fibrillation epidemiology, risk factors, and mortality in community cohorts: results from the BiomarCaRE Consortium (Biomarker for Cardiovascular Risk Assessment in Europe). Circulation. 2017;136(17):1588-1597.
    doi pubmed
23. Vyas V, Lambiase P. Obesity and atrial fibrillation: epidemiology, pathophysiology and novel therapeutic opportunities. Arrhythm Electrophysiol Rev. 2019;8(1):28-36.
    doi pubmed
24. Jones NR, Taylor KS, Taylor CJ, Aveyard P. Weight change and the risk of incident atrial fibrillation: a systematic review and meta-analysis. Heart. 2019;105(23):1799-1805.
    doi pubmed
25. Ihara K, Sasano T. Role of inflammation in the pathogenesis of atrial fibrillation. Front Physiol. 2022;13:862164.
    doi pubmed
26. Saljic A, Grandi E, Dobrev D. TGF-beta1-induced endothelial-mesenchymal transition: a potential contributor to fibrotic remodeling in atrial fibrillation? J Clin Invest. 2022;132(13):e161070.
    doi pubmed
27. Yao Y, Yang M, Liu D, Zhao Q. Immune remodeling and atrial fibrillation. Front Physiol. 2022;13:927221.
    doi pubmed

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial 4.0 International License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Journal of Clinical Medicine Research is published by Elmer Press Inc.