Underweight BMI is an independent risk factor for mortality post-AMI
Underweight, Markers of Cachexia, and Mortality in Acute Myocardial Infarction: A prospective cohort study of elderly Medicare beneficiaries
Bucholz EM, Krumholz HA, Krumholz HM.
PLoS Med 2016;13(4): e1001998
BackgroundUnderweight patients are at significantly higher risk of death after an acute myocardial infarction (AMI) compared to patients with normal weight [1–4]. Cachexia is considered to be the underlying cause of the increased mortality observed in these patients [5-8]. Cachexia in AMI patients can derive from comorbidities. It is mediated by neuroendocrine, metabolic, and inflammatory pathways [9,10], however criteria to define cachexia vary widely. Diagnosis is usually based on a combination of parameters; current BMI or recent weight loss, symptoms of fatigue or anorexia, and biochemical markers .
Understanding how a low BMI relates to post-AMI mortality is important because:
- if low BMI is associated with mortality after AMI independent of other conditions, then the control of caloric intake to increase body weight may improve outcome
- if the relationship between underweight and post-AMI mortality can be explained by cachexia or other comorbidities, then managing the underlying conditions is equally important as the optimisation of the nutritional status
- Does comprehensive risk adjustment for comorbid illness and frailty measures explain the higher mortality rate after AMI in underweight patients?
- Is the relationship between underweight and mortality also observed in patients with AMI but without other significant chronic illness or cachexia?
- At baseline, 5678 (9.8%) of 57574 patients with AMI included in this cohort were underweight (BMI < 18.5 kg/m). Underweight patients were older on average, than normal weight patients and had a higher prevalence of most comorbidities and measures of frailty
- Crude mortality was significantly higher for underweight patients than for normal weight patients at: 30 days: 25.2% versus 16.4%; P < 0.001, 1 year: 51.3% versus 33.8%; P < 0.001, 5 years: 79.2% versus 59.4%; P < 0.001 and 17 years: 98.3% versus 94.0%; P < 0.001.
- Findings were independent of markers for cachexia: After adjustment for comorbidity, signs of frailty or abnormal laboratory nutritional marker levels at baseline, underweight patients compared with normal weight patients still had a 13% higher death risk at day 30 (HR: 1.13; 95% CI: 1.07–1.20) and 26% at 17 years (HR: 1.26; 95% CI: 1.23–1.30).
- Survival curves for underweight and normal weight patients separated early and remained separate over 17 years, suggesting that underweight patients remained at a significant survival disadvantage over time
- Similar findings were observed among the subset of patients without comorbidity at baseline. Underweight patients had a 21% higher risk of death over the long-term compared with normal weight patients (30-days HR: 1.08; 95% CI: 0.93–1.26, 17-years HR: 1.21; 95% CI: 1.14–1.29)
ConclusionIn a large cohort of AMI patients, underweight BMI was an important risk factor for mortality. This was independent of cachexia markers; comorbidities, frailty, and laboratory markers of nutritional status. These data suggest that therapeutic strategies to increase body weight in underweight patients after AMI are worth testing to reduce the mortality in AMI patients with low BMI.
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