NEW HAVEN, CT — Being underweight (ie, with a body-mass index (BMI) <18.5 kg/m2) was significantly and independently associated with increased short- and long-term mortality following an acute MI, in an analysis based on Medicare patients. It adjusted for markers of frailty and cachexia that had long been supposed as confounding factors in such analyses.
"To our knowledge, this is the first study to report differences in the effect of underweight on mortality after acute MI by age and sex," write the authors, led by Dr Emily Bucholz (Yale University, New Haven, CT). Their report was published online April 19, 2016 in PLOS Medicine.
The authors offer several potential explanations for their findings. "First, patients with low BMI have decreased physiologic reserve and fat stores, which may lower their ability to withstand insults to health over time."
Also, they write, "We observed that underweight patients were significantly less likely to receive guideline-recommended therapies for acute MI, including primary reperfusion and revascularization procedures. These lower treatment rates in underweight patients may be due to either physician bias or poorer clinical presentations on arrival."
Another possibility is that acute MI "may be a fundamentally different process in underweight patients than in normal-weight and overweight patients." Given the role of adiposity and dyslipidemia in CAD development, it may be that genetic predisposition played a more-than-average role in their disease, worsening their prognosis, the group observes.
Their data came from the Cooperative Cardiovascular Project, in which 57,574 patients aged 65 or older were hospitalized for acute MI in the 1990s. Subjects were followed for 17 years, and short- and long-term mortality rates were compared in subjects who were underweight and those who were normal weight. Slightly under 10% of the cohort were underweight at baseline.
Short- and Long-term Overall Hazard Ratios for Mortality: Underweight vs Normal-Weight Patients
|Time||Adjusted* underweight HR (95% CI)||Adjusted* underweight HR (95% CI) among patients with no significant comorbidity|
|30 d||1.13 (1.07–1.20)||1.08 (0.93–1.26)|
|1 y||1.25 (1.20–1.30)||1.18 (1.05–1.32)|
|5 y||1.27 (1.23–1.31)||1.22 (1.12–1.33)|
|17 y||1.26 (1.23–1.30)||1.21 (1.14–1.29)|
The primary outcomes were mortality rates at 30 days post-AMI and again at 1 year, 5 years, and 17 years from the day of hospital admission. "Underweight patients had a 61% to 73% higher crude risk of death than normal-weight patients at all follow-up time points," according to the group.
After adjustment for measures of cachexia, frailty, and nutritional status, the short- and long-term mortality risk among the underweight was somewhat attenuated, but underweight patients still had a significant 13% to 27% higher risk of mortality than their normal-weight counterparts.
Restricted to the subset of patients who did not have significant comorbidity or frailty, "underweight patients continued to have a [significant] 8% to 22% higher risk of death than normal-weight patients."
The negative consequences of being underweight were most apparent in subjects with very low BMI, the group observed.
"Understanding how low BMI relates to post-MI mortality has implications for the care and management of underweight patients in the hospital and after discharge," Bucholz and associates point out. For example, nutritional supplementation by itself is often not effective in helping to reverse cachexia, they note.
Thus, other ways to promote weight gain, including the use of agents such as megestrol acetate, medroxyprogesterone, ghrelin, and omega-3 fatty acids, may be more successful in improving survival odds among the elderly who have an AMI, the authors write.
Bucholz et al had no relevant financial relationships.
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Cite this: 'Underweight' Predicts Post-MI Mortality in Elderly Independently of Frailty, Cachexia - Medscape - May 04, 2016.