Cardiovascular disease is the leading cause of death worldwide¹ and the second leading cause of death in Brazil.² Despite continuous efforts by health services with actions to prevent risk factors, promote health and develop technological care, hospital mortality in patients with acute myocardial infarction (AMI) remains high.³

Risk stratification upon admission of patients with AMI is considered an effective strategy as it enables early intervention, more effective treatment and, consequently, longer patient survival.⁴ In this context, different factors have been proposed as risks for cardiovascular mortality, including advanced age, high Killip class, hyperglycemia, tachycardia, renal dysfunction, atypical chest pain,^5,6 and admission systolic blood pressure (SBP).

Studies involving millions of patients with AMI have shown that the mortality rate from cardiovascular causes within one year after AMI was significantly lower among patients with SBP ≤108mmHg⁷ or <120mmHg^8,9 on admission compared to those with SBP greater than 108mmHg⁷ or 125mmHg.^8,9 On the other hand, in another study involving 13,104 participants with AMI, a significant association was shown between admission SBP <90mmHg and higher in-hospital mortality.¹⁰

It is understood that the identification of risk factors can support the planning of care to reduce morbidity and mortality in patients with AMI. In this context, the following question was formulated: what are the contributing factors for in-hospital mortality from cardiac causes in patients with AMI? The aim of the present study was to determine the risk factors of in-hospital death from cardiac causes after AMI with STEMI.

Characteristics of participants (n = 459) are described in Table 1.

Considering the mortality from cardiac causes in the first 30 days after STEMI, it was observed that 55 (12.0%) patients died. Mortality rate was higher in women, patients with hypertension and elderly (Table 2).

Mean (±SD) SBP on admission was 109.08 ± 28.21mmHg in patients who died and 127.96 ± 24.87mmHg among survivors. A positive and significant correlation (r = 0.25; p<0.001) was observed between SBP on admission and survival time up to 30 days after STEMI.

Using Cox regression analysis, of the variables evaluated (gender, age, SBP on admission, and obesity), age and sex influenced the occurrence of death. The elderly had 3.54 times greater risk of dying when compared to adults. In addition, females had a 2.55 times greater risk of progressing to death when compared to males. Admission SBP acted as a protective factor, that is, for each additional point on SBP, the risk of the patient progressing to death was reduced by 3% (Table 3).

In a prospective study¹² involving 2369 post-STEMI individuals, the authors analyzed the prevalence and the accumulated number of cardiovascular risk factors, such as SAH, hypercholesterolemia, smoking, diabetes, and obesity, and found that most participants had multiple concomitant factors.¹² This is in line with the findings of the present study, which highlights the high prevalence of SAH in this population; although there was no significant association between SAH and mortality (p = 0.07), there was a higher prevalence of this comorbidity in patients who died after STEMI than those who survived. The high prevalence of SAH may be at least in part justified by the aging of the population and the increase in obesity.¹³ It is noteworthy that SAH, especially in the elderly, can be related to severe adverse cardiovascular outcomes, such as AMI and death.¹³

In this study, post-STEMI mortality rates were higher among females and older people, corroborating other studies.^14–18 In addition, previous reports^18–20 have shown that, when suffering from AMI, women were older and had a higher prevalence of cardiovascular risk factors, such as diabetes mellitus, hypercholesterolemia and SAH, when compared to men. A survey carried out with 31,698 patients who suffered STEMI showed that, although women had a higher in-hospital mortality rate than men, this difference did not seem to be caused by sex itself, but due to comorbidities and age differences.¹⁵

As the population ages and the prevalence of risk factors associated with lifestyle increases, the incidence of AMI in women will likely be more similar to that of men.²¹ Gender differences in cardiovascular risk have become more evident, indicating the importance of addressing risk factors for preventive strategies and policies.

It is evident that increasing age is an important influencing factor in the mortality of post-AMI patients.¹⁹ In a study that evaluated the impact of age on the patient's prognosis after the event, a worse prognosis was observed for those with more advanced age.²² At 60 years of age, men are at greater risk of suffering an AMI, but after 70 years of age both sexes have the same chance.⁸ Aging results in several structural and functional changes in the arterial vasculature. A study investigated the effects of arterial stiffness on left ventricular (LV) function in a period from three and six months after AMI and observed that arterial stiffening can result in a less effective recovery of LV function.²³ Increased wave velocity pulse rate and age are associated with changes in metabolic syndrome components, inflammatory markers and oxidative stress.²⁴ However, each of these components has a different and specific impact on arterial stiffness according to age. In particular, oxidative stress may be independently associated with arterial stiffness in individuals over 45 years of age.²⁵

In risk stratification of patients with AMI on admission, BP has been an important prognostic factor. In our study, we observed that admission SBP values influenced the post-STEMI mortality. Similar results were demonstrated in other studies that indicated admission SBP <106 mmHg as an independent predictor of hospital mortality after STEMI, and admission SBP <125mmHg as an independent predictor of cardiovascular mortality one year after STEMI.^8,26 These results suggest that high admission SBP can be considered an important protective factor in post-STEMI mortality.

A study conducted with 1475 patients with STEMI showed that an admission SBP between 141-158mmHg could be correlated with a better in-hospital prognosis, while an admission SBP <105mmHg was associated with in-hospital death.²⁶ In this study, as the sample was not homogeneous, we chose to investigate mean admission SBP values of individuals who progressed to death instead of determining a cutoff for admission SBP that would predict mortality. A prospective study with 167 patients found that an admission SBP lower than 95mmHg was a significant predictor of 30-day mortality in patients with STEMI.²⁷

The impact of BP on STEMI prognosis is still a matter of debate. Researchers have found that increased admission SBP values in the acute phase of AMI indicate that the heart still responds to stress, suggesting that the use of drug classes such as nitrates, beta blockers and angiotensin-converting enzyme inhibitor would be safe in this context.⁷ Therefore, admission BP values after AMI should be interpreted in contrast with the conventional, preventive point of view, and low admission BP values should serve, therefore, as a warning sign in these patients.²⁸

Results of the present study add evidence to the clinical practice of health professionals, by demonstrating that female gender, advanced age, and admission BP influence post-STEMI mortality. This is an important finding considering that the professional's decision-making, when based on risk assessment, results in the prevention of cardiovascular complications, better quality of care and patient safety.