Body Composition Estimated by Bioelectrical Impedance Analysis in Patients with Acute Coronary Syndrome.

1. Introduction

It is indisputable that obesity is a global epidemic. According to the latest data from the World Health Organization (WHO), the prevalence of obesity has tripled since 1975. In 2016, there were 650 million obese people worldwide, representing 13% of those over 18 years of age. Its definition is simple: a body mass index greater than 30. Moreover, it is a preventable condition.

In developing countries, its prevalence is steadily increasing. According to data from the Permanent Household Survey conducted in Argentina, the prevalence of obesity in 2013 was 20.8%; this represented an increase of 15.6% compared to the 2009 edition (prevalence of 18.0%) and 42.5% compared to the 2005 edition (prevalence of 14.6%). The obesity indicator was higher among men (22.9%) than among women (18.8%) and higher among older people (with a maximum of 29.6% in the 50 to 64 age group) compared to younger individuals (7.7%).

The health importance of obesity is mainly due to its relationship with cardiovascular disease. In a classic study analyzing 457,785 men and 588,369 women published in 1999, it was found that the total mortality risk due to obesity was 2.58 and 2.0 times higher, respectively. The relative risk of cardiovascular death in obese men was 2.9, with a 95% confidence interval (CI95%) of 2.37 to 3.56. Obesity increases the metabolism of free fatty acids, reduces insulin sensitivity, increases sympathetic activity, promotes inflammation, and causes a state of higher coagulability: all of these factors can contribute to the development of coronary disease.

Despite the well-known predisposition to cardiovascular disease caused by obesity, once established, its relationship with body weight is more complex. In 2002, a study analyzing the impact of obesity in patients undergoing percutaneous coronary intervention (PCI) was published. Gruber et al. analyzed data from 9,633 patients and observed that obese individuals were generally younger but had more cardiovascular risk factors (hypertension, diabetes, hypercholesterolemia, and smoking). Although angiographic success rates were similar in all groups, the presence of normal BMI was associated with higher cardiovascular mortality. For long-term death, BMI presented in multivariable analysis an odds ratio (OR) of 0.94, with a CI95% of 0.94 - 0.98, showing to be a protective factor. This effect was named the "obesity paradox," which could be formulated as follows: obese individuals have a higher risk of coronary disease, but obese coronary patients have a lower risk of mortality. This was confirmed in a more recent study in patients with ST-elevation acute coronary syndrome (STEMI), where after analyzing data from 50,149 patients, hospital mortality rates of 7.7% were observed for individuals with normal weight and 4.3%, 4.4%, and 6.1% for subjects with class I, II, and III obesity, respectively.