Introduction

Coronavirus disease (COVID-19) has emerged as a significant health concern from both short- and long-term perspectives. Individuals with multiple comorbidities exhibit increased susceptibility to complications and experience a more severe course of infection. Patients with cardiac conditions represent a special group1,2,3,4, albeit COVID-19 did not increase the CV risk calculated for primary prevention5. The progression of COVID-19 is more pronounced in these individuals1,6, and even isolated infections, in the absence of multiple comorbidities, markedly influence cardiovascular treatment outcomes. Furthermore, an increased prevalence of cardiovascular disease among COVID-19 patients is evident 12 months following infection3,7.

Based on the available data, men had a greater risk of a more severe course of COVID-19 at the acute stage, a greater risk of hospitalization, admission to the intensive care unit (ICU) and death1,8. The mortality rate among male COVID-19 patients was approximately double that of female patients, even after adjustment for comorbidities, including arterial hypertension, heart failure (HF), and diabetes mellitus (DM), over a few weeks of observation9,10. The estimated 3 months population risk of mortality due to COVID-19 was greater among men with comorbidities, including cardiovascular or pulmonary problems, DM, neoplasms or impaired kidney function11. An elevated risk of in-hospital mortality, ICU admission, requirement for mechanical ventilation, and vasopressor therapy alongside a higher susceptibility to acute cardiac injury and thromboembolism, was observed in men during a 3 months follow-up12.

Currently, the challenges associated with in-hospital care for COVID-19 patients may be less severe compared to those encountered at the peak during the initial pandemic phase in 2020. This is attributed to the accrued knowledge and experience gained during the initial pandemic period, along with a decreased frequency of infections necessitating hospitalization. However, despite this observation, data concerning the prognosis of patients following COVID-19 infection remain insufficient, and there is a significant need for further understanding of risk factors and predictors of mortality. Such knowledge is crucial for the triage of these breakthrough patients to ensure they receive more frequent follow-up care, thereby reducing unexpected mortality. Recent observations of patients admitted to ICU centers have shown that 90 days mortality rates were significantly higher among male patients during a 180 days observation period13. Similar findings have been reported in patients suffering from heart failure or arrhythmias14.

The underlying reasons for this phenomenon remain incompletely elucidated. A prevailing hypothesis suggests that females exhibit a more robust immune response, potentially mitigating the severity of infectious diseases. This conjecture is supported by observations that female patients are more susceptible to autoimmune conditions throughout their lives, indicating that the immune system in females, absent immunosuppression therapy, may be better prepared to mount an effective initial defense15. This observation aligns with the finding that male patients tend to experience COVID-19 infections more frequently.

Moreover, the relationships between gender and various cardiovascular comorbidities, as well as long-term survival following COVID-19 infection, remain inadequately comprehended. Given the substantial number of individuals worldwide impacted by mild to moderate COVID-19 infections, numerous patients may not be effectively assessed to identify pertinent risk factors that could affect mortality outcomes. This study was conceived to address this knowledge gap over a 42 months period (approximately a 3.5 years perspective) of patients post-COVID-19 infection.

Methods

We conducted a retrospective analysis of the medical records of all sequential patients admitted due to SARS-CoV-2 infection to the University Hospital in Krakow from February 13, 2020, to May 10, 2021. The diagnosis of COVID-19 in patients was established in accordance with the WHO and national Polish guidelines, utilizing the RT-PCR method (rhino-oropharyngeal swab positivity for SARS-CoV-2 RNA)16,17,18. The treatment protocol for COVID-19 adhered to the recommendations provided by the Polish Association of Epidemiologists and Infectiologists16,17. Patient data were sourced from the electronic medical records maintained by the University Hospital of Krakow. Cardiovascular risk factors and diseases were ascertained through an examination of antecedent medical history and/or characteristic prior treatment, or diagnoses made during hospitalization, and were defined in accordance with the prevailing guidelines set forth by the European Society of Cardiology19.

Clinical data pertaining to demographics, medical history, inpatient clinical course, laboratory findings, treatment interventions, and in-hospital outcomes were sourced from the electronic medical records utilized by the University Hospital of Krakow. All comorbidities analyzed were diagnosed either prior to hospitalization (as per historical data) or during the hospitalization period. The incidence of mortality within a 42 months timeframe following the initial hospitalization date was evaluated using data procured from the National Electronic Population Registration System in Poland, with the cause of mortality remaining indeterminate. Cases in which patients died during hospitalization or where information regarding death remained inaccessible were excluded from the analysis (Fig. 1). This study constitutes a retrospective analysis of the medical records of patients who had been discharged from the hospital setting. Consequently, it was deemed unnecessary to convey information regarding the study to potential participants. Given that the study’s methodology did not compromise patient safety nor induce potential complications, the acquisition of consent from study participants was considered non-essential and therefore not obtained. The study adhered to the principles of the Declaration of Helsinki, and the aforementioned methodological approach received approval from the Bioethics Committee of Jagiellonian University (decision number 1072.6120.278.2020).

Fig. 1
figure 1

Flowchart of the study.

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Statistical analysis

Categorical variables are reported as numbers and percentages, while continuous variables are detailed through means and standard deviations (SDs) or medians and interquartile ranges (IQRs). Normality was examined using the Shapiro–Wilk test. The study population was stratified into groups according to sex and survival status. Inter-group differences were assessed through the Student’s or Welch’s t-test based on the equality of variances for normally distributed variables. The Mann–Whitney U test was applied for non-normally distributed continuous variables. Receiver operating characteristic (ROC) curve analysis was conducted to define single cutoff points for troponin I, N-terminal pro B-type natriuretic peptide (NT-proBNP), D-dimer, C-reactive protein (CRP), and interleukin-6 (IL-6) as predictors of 42 months mortality. Multivariate Cox proportional hazard analyses were employed to discern independent predictors of mortality. The variables incorporated in the initial analysis were selected as potential risk factors based on their clinical relevance to death at 42 months. These encompass demographic and clinical variables, including sex and age over 65 years, hypertension, hypercholesterolemia, DM, atrial fibrillation (AF), coronary artery disease (CAD), HF, chronic kidney disease (CKD), stroke, and chronic obstructive pulmonary disease (COPD)20,21. The second multivariable Cox model incorporated laboratory markers. The outcomes are reported as hazard ratios (HRs) with 95% confidence intervals (CIs). Additionally, in order to evaluate event-free survival at the 42 months follow-up post hospital admission, Kaplan‒Meier curves were constructed according to sex, focusing on pertinent comorbidities such as hypertension, DM, AF, CAD, HF and CKD in patients discharged from the hospital. In all statistical analyses, a P value of 0.05 or less was deemed statistically significant. Data analysis was conducted using Statistica (data analysis software system), TIBCO Software Inc., version 13 (2017).

Results

A cohort of 4071 COVID-19 patients hospitalized at the University Hospital in Krakow was analyzed during the aforementioned period. Of these, 2183 were male, accounting for 53.6% of the cohort. The demographic and clinical characteristics of the study groups, stratified by sex and survival status, are detailed in Table 1. The mean age of the participants was 59.7 years with a SD of 16.2. The most prevalent comorbidities observed in the entire population included hypertension, DM, hypercholesterolemia, and CAD, as presented in Table 2. Among cardiovascular medications, beta-blockers were the most frequently prescribed, and over 25% of patients received dexamethasone during their hospitalization for COVID-19, as noted in Table 3.

Table 1 Study group characteristics – demographic and clinical data.
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Table 2 Study group characteristics—coexisting diseases.
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Table 3 Study group characteristics – treatment and course of hospitalization.
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In comparison to females, males were younger and presented with more frequent cases of CAD, previous myocardial infarction, HF, and COPD (Tables 1 and 2). Additionally, males required dexamethasone, noninvasive oxygen therapy, and dialysis more frequently during hospitalization for COVID-19 (Table 3). Among both sexes, non-survivors tended to be older. Males demonstrated a lower body mass index (BMI) among non-survivors compared to survivors, a difference not observed in females (Table 1). Most of the analyzed comorbidities were more prevalent in the nonsurvivor group regardless of sex (Table 2).

Angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), statins, and beta-blockers were more prevalently administered during hospitalization among nonsurvivors of both sexes. Noninvasive ventilation was implemented more frequently among survivors irrespective of sex. No significant differences were observed in the administration of dexamethasone or mechanical ventilation between the survival cohorts of both sexes. Vasopressor therapy during hospitalization was more commonly administered to male patients who died during the postdischarge period (Table 3).

Within the male group, no differences in systolic blood pressure were observed between survivors and non-survivors on admission. In contrast to non-survivors, male survivors had lower respiratory rates and higher heart rates on admission (Table 1). Individuals in the non-survivor group, regardless of sex, had longer hospital stays than survivors, possibly indicating a more severe course of COVID-19 (Table 3).

Higher levels of CRP were observed among nonsurvived women compared to those who survived, while elevated levels of D-dimer and IL-6 were noted among nonsurvivors in comparison to survivors, irrespective of sex. Similarly, irrespective of sex, nonsurvivors characterized more pronounced myocardial injury, evidenced by increased levels of NT-proBNP and troponin I, than survivors (Table 4). Additionally, the nonsurvivor group was distinguished by lower eGFR values and a more frequent requirement for dialysis in comparison to the survivor group (Tables 3 and 4).

Table 4 Study group characteristics—laboratory data.
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An analysis of laboratory parameters following stratification by sex disclosed that males had higher CRP and IL-6 concentrations compared to females. In contrast to females, males also demonstrated higher troponin I levels yet lower NT-proBNP concentrations (Table 4).

In the multivariate Cox regression analysis, the presence of comorbidities such as DM, HF, CAD, AF, stroke, CKD, COPD, along with male sex and age above 65 years, were correlated with an increased 42 months mortality rate. Hypercholesterolemia alone was linked with a reduced mortality risk (Fig. 2).

Fig. 2
figure 2

Multiple Cox regressions demonstrating the hazard ratios for the 42 months mortality in model including comorbidities and demographic data. Abbreviations: HR, hazard ratio.

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Male sex was associated with a diminished survival rate among COVID-19 patients younger than 65 years, although this was not observed in the entire study cohort or among those older than 65 years (Fig. 3a–c).

Fig. 3
figure 3

Kaplan‒Meier curves depicting proportional survival rates at the 42 months follow-up stratified by sex in the whole group (a) and in the age subgroups (b, c).

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Utilizing the ROC curve, cutoff thresholds for markers indicative of myocardial injury (troponin I, NT-proBNP), thrombotic state (D-dimer), and inflammation (CRP, IL-6) were established as predictors of 42 months mortality (Fig. 4). The multivariate Cox regression analysis conducted on the entire cohort identified that elevated levels of troponin I, NT-proBNP, and D-dimer beyond these thresholds correlated with an increased risk of mortality (Fig. 5). Furthermore, Kaplan–Meier survival analysis demonstrated heightened mortality rates in patients exhibiting levels of troponin I, NT-proBNP, D-dimer, CRP, and IL-6 exceeding the established thresholds, compared to those with levels below these cutoff points (Fig. 6a–e).

Fig. 4
figure 4

ROC curves to establish cutoff points for troponin I, N-terminal pro-B-type natriuretic peptide, D-dimer, C-reactive protein and interleukin-6 as predictors of 42 months mortality.

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Fig. 5
figure 5

Multiple Cox regressions demonstrating the hazard ratios for 42 months mortality in the model with laboratory tests. Abbreviations: CRP, C-reactive protein; HR, hazard ratio; NT-proBNP, N-terminal pro-B-type natriuretic peptide.

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Fig. 6
figure 6

Kaplan‒Meier curves displaying proportional survival rate at the 42 months follow-up stratified by the levels of troponin I (a), NT-proBNP (b), D-dimer (c), CRP (d), and interleukin-6 (e). Abbreviations: CRP, C-reactive protein; NT-proBNP, N-terminal pro B-type natriuretic peptide; IL-6, interleukin-6; TnI, troponin I.

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Discussion

The principal results of this investigation are as follows:

  1. (1)

    Among patients diagnosed with COVID-19, the independent risk factors associated with mortality at 42 months include age exceeding 65 years, male sex, and the presence of cardiovascular comorbidities;

  2. (2)

    For individuals with COVID-19, elevated maximal levels of troponin I > 11.15 ng/l, NT-proBNP > 1087 pg/ml, D-dimer > 1.09 mg/l, CRP > 82.6 mg/l, and IL-6 > 23.24 pg/ml during hospitalization were correlated with inferior 42 months survival outcomes. It is noteworthy that male sex was linked to a reduced survival rate exclusively in COVID-19 patients under the age of 65;

  3. (3)

    During the period of hospitalization, male patients with COVID-19 exhibited higher levels of CRP, IL-6, and troponin I compared to their female counterparts, despite a younger age profile.

Individuals with cardiovascular disorders appear to have increased susceptibility to infectious diseases. The prognosis for these individuals is generally poorer from the onset of the infectious disease22,23,24,25. Notably, infections of the lower respiratory tract are inclined to manifest with greater severity in patients with a history of cardiac disease22. This phenomenon was also recently observed during pandemic infections attributed to SARS-CoV-21,2,3. Moreover, COVID-19 presents additional non-pulmonary complications, including thromboembolic events and myocarditis26.

In a meta-analysis conducted by Puri et al., it was demonstrated that a higher prevalence of hypertension and cardiovascular disease was observed among patients with severe COVID-19 as compared to those with nonsevere manifestations of the disease27. These conclusions are consistent with the findings of our study, wherein cardiovascular comorbidities were more frequently encountered among nonsurvivors than among survivors.

In large-scale epidemiological studies, males afflicted with COVID-19 exhibited elevated morbidity and mortality rates compared to females28. Such disparities may be attributed to sex-specific responses to viral infections29, a phenomenon observed prior to the COVID-19 era. The expression of genes integral to immunological responses varies between males and females. Several potential factors may account for this disparity. Firstly, the X and Y chromosomes encompass numerous genes pertinent to immune response regulation, which can be impacted by the mosaic loss of the Y chromosome in leukocytes. Conversely, in females, there exists the possibility of escape from inactivation in some cells owing to the presence of two copies of specific genes on the X chromosome30,31. Secondly, males have been observed to express higher levels of angiotensin-converting enzyme 2 (ACE2), including its soluble forms. The coronavirus gains cell entry more readily by binding with ACE2, a receptor present on the surface of the upper respiratory tract. Typically, the ACE2 receptor facilitates anti-inflammatory processes; however, when blocked by the virus, this function is lost30,32. This may elucidate why males have a higher likelihood of encountering cytokine storms than females. This observation is supported by elevated IL-6 levels in males compared to females, a trend also noted in other viral infections30. Consistent findings of elevated IL-6 levels were observed in males over females in our study. Consequently, the significance of estrogenic steroids ought to be considered. Estrogens enhance the expression of toll-like receptor 7 in immune cells, consequently accelerating the elimination of the SARS-CoV-2 virus. Moreover, an increased estradiol concentration, resulting in the rising ratio of CD4 + to CD8 + lymphocytes, is linked with a more robust early response against COVID-19. These hormones, through modulating their effects, also tend to augment the production of IFN alpha. Given the unique characteristics of immune responses between sexes, it is also pertinent to consider findings indicating that females, following a half-dose influenza vaccination, produce comparable antibody levels to males who have received a full dose. Furthermore, antibody levels are correlated with estradiol concentrations33. These mechanisms collectively may elucidate sex-related differences in COVID-19 outcomes.

The potential involvement of estrogen steroids in the course of COVID-19 can also be suspected because sex-dependent differences in mortality were observed in our study only in individuals younger than 65 years of age.

From a short-term perspective, certain studies have demonstrated that elevated levels of CRP, IL-6, D-dimer, and ferritin are associated with increased mortality among both male and female patients34,35,36,37. However, contradictory findings have been reported concerning CRP, ferritin, and D-dimer38. There is a paucity of data regarding the long-term implications of these parameters. Our research identified that males exhibited higher levels of inflammatory markers than females; similarly, nonsurvivors within each sex group showed elevated levels compared to survivors. Nonetheless, results suggests that myocardial damage and prothrombotic processes may be more critical determinants of mortality risk in COVID-19 patients over a 42 months period than inflammation.

An intensified inflammatory state has been identified as a probable mechanism contributing to myocardial injury, facilitating thrombotic processes, including the development of microthrombi that compromise cardiac tissue integrity and lead to vascular dysfunction. ACE2 expression is believed to enhance cardiac involvement by infection, while virus-mediated downregulation of ACE2 might obstruct ACE2-dependent compensatory protective mechanisms36. Myocardial injury is characterized by elevated troponin levels, particularly in men and the elderly population. Among patients with COVID-19, increased levels of both troponin and NT-proBNP possess prognostic importance in both short-term and in-hospital evaluations36,38,39,40,41,42,43,44, as well as in 1 year follow-up assessmets45. Prior investigations have not explored cardiac injury secondary to COVID-19 infection over such an extended follow-up period. Our study validated notably elevated levels of troponin I and NT-proBNP in nonsurvivors, encompassing both sexes. Despite the heightened prevalence of heart failure in males, our study found that the concentration of NT-proBNP was increased in females, aligning with physiological conditions46. Furthermore, within the entire group, levels of troponin I and NT-proBNP were associated with an elevated risk of mortality in long-term follow-up. Patients experiencing more significant myocardial injury also exhibited poorer survival outcomes over a 42 months period.

In COVID-19 patients, acute cardiac injury, both preexisting and newly developed cardiovascular complications, as well as acute kidney injury, have been identified as predictors of mortality in short-term follow-up2,47. Comparable correlations were documented in a cohort of U.S. female veterans with comorbid cardiovascular disease, CKD, COPD, and DM, who required anticoagulation and tested positive for COVID-19 within 60 days48. Conversely, a Danish study demonstrated that, at the 30 days follow-up, only female patients with coexisting AF or HF experienced a more severe progression of COVID-19 and higher mortality, a finding restricted to early-phase COVID-19 cases (prior to 01/05/2020). Among later cases, HF or AF had no impact on outcomes49. No data is available concerning the influence of comorbidities on long-term outcomes in COVID-19 patients with cardiovascular burdens. According to our multivariate analysis, hypercholesterolemia, DM, HF, CAD, AF, stroke, CKD, and COPD were associated with mortality at 42 months. Notably, hypercholesterolemia was observed to exert a protective effect on COVID-19 outcomes. This protective effect may be attributable to the pleiotropic effects, including anti-inflammatory properties, of statins, which are prevalently utilized by patients with hypercholesterolemia50.

A study conducted in Japan identified male sex as a significant predictor of in-hospital mortality51. Numerous studies have consistently demonstrated a higher mortality rate among males with COVID-19 in comparison to females, even when adjusted for cardiovascular comorbidities within a 30–90 days period9,10,11. Our study further substantiates that male sex constitutes an independent risk factor for mortality during long-term follow-up. Nonetheless, no significant differences were observed in survival rates between male and female COVID-19 patients in subgroups with concurrent HF, AH, AF, DM, or CAD. Furthermore, no differences in 42 months mortality were found across the entire study cohort, nonetheless males below the age of 65 exhibited poorer survival outcomes.

Conclusions

In patients with COVID-19, male sex, the presence of cardiovascular comorbidities, and advanced age are determinants that adversely affect survival at the 42 months follow-up. Elevated levels of laboratory indicators of myocardial injury and a thrombotic state are associated with worse outcomes in long-term follow-up. Patients with COVID-19 exhibiting increased levels of D-dimer, troponin I, and NT-proBNP are at a heightened risk of mortality and warrant more rigorous supervision and medical monitoring.

During SARS-CoV-2 infection, female sex over the age of 65 years is no longer a factor improving prognosis; hence, older women with comorbidities should be considered a special medical group.