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Underweight patients are at higher risk of death following an acute myocardial infarct as compared to normal weight patients. This was found to be true even when other comorbidities were excluded.

The association between being underweight and death after an acute myocardial infarction (AMI) has been known previously, but it wasn't clear whether the risk was connected to just having a low body mass index (BMI), or whether medical conditions causing the patient to be underweight was the actual problem

Researchers at Yale University conducted a study on elderly patients who were hospitalized for an AMI. This study was done to compare the short- and long-term mortality risk in both underweight and normal weight patients. This was done while also considering other important factors such as the presence of other comorbid conditions and frailty of the patient.

The questions that this study sought out to answer were the following:

  1. Does comprehensive risk adjustment for comorbidities and frailty measures explain the increased mortality in underweight patients, after an AMI, as compared to normal weight patients?
  2. In patients with AMI who do not have any chronic illness and who are assumed to not be cachexic, is the relationship between being underweight and mortality also observed?

The research

Over 55,000 patients' data was analyzed over a 17 year period. Comparisons of the mortality rate amongst these patients were done at 30 days, 1 year, 5 years and 17 years after the initial AMI. 

When other comorbidities, such as chronic illnesses and cancer, that caused cachexia (severe wasting) and frailty were included, it was discovered that underweight patients had a 13% increased risk of dying at 30 days post-AMI and a 26% increased mortality risk over 17 years as compared to normal weight patients. With comorbidities excluded, the mortality risk was increased by 21% in underweight patients as compared to normal weight patients over the 17 year period.

The data showed that the survival curves for the underweight patients and normal weight patients had separated early and then remained that way over the 17 year period. This suggested that the underweight patients had remained at am increased survival disadvantage over that time. Similar findings were found among the group of underweight patients who had no comorbidities, as they had a 30 day adjusted mortality similar to that of normal weight patients, but with an increased mortality risk over the long term.

The importance of this study

The researchers weren't able to accurately measure cachexia and were also not able to determine the initial cause of the low BMI in the involved patients.

Even though this was the case, the findings in the study suggest that, while comorbid conditions which cause cachexia do contribute an additional risk to the patient's mortality, a low BMI on its own is an important independent risk factor for death after an AMI, even after many years.

Conclusive message of the study

The researchers of this study noted that their findings warranted additional research to be done in underweight patients, as they were frequently excluded from studies that evaluated the BMI in patients with coronary artery disease (CAD). 

From a clinical point of view, it was also suggested that strategies to promote weight gain in underweight patients who had suffered an AMI would be worthy of further testing.

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