Underweight, Markers of Cachexia, and Mortality in Acute Myocardial Infarction: A Prospective Cohort Study of Elderly Medicare Beneficiaries

Emily M Bucholz, Hannah A Krumholz and Harlan M Krumholz

PLOS Medicine, 2016, vol. 13, issue 4, 1-18

Abstract: Background: Underweight patients are at higher risk of death after acute myocardial infarction (AMI) than normal weight patients; however, it is unclear whether this relationship is explained by confounding due to cachexia or other factors associated with low body mass index (BMI). This study aimed to answer two questions: (1) does comprehensive risk adjustment for comorbid illness and frailty measures explain the higher mortality after AMI in underweight patients, and (2) is the relationship between underweight and mortality also observed in patients with AMI who are otherwise without significant chronic illness and are presumably free of cachexia? Methods and Findings: We analyzed data from the Cooperative Cardiovascular Project, a cohort-based study of Medicare beneficiaries hospitalized for AMI between January 1994 and February 1996 with 17 y of follow-up and detailed clinical information to compare short- and long-term mortality in underweight and normal weight patients (n = 57,574). We used Cox proportional hazards regression to investigate the association of low BMI with 30-d, 1-y, 5-y, and 17-y mortality after AMI while adjusting for patient comorbidities, frailty measures, and laboratory markers of nutritional status. We also repeated the analyses in a subset of patients without significant comorbidity or frailty. Conclusions: Underweight BMI is an important risk factor for mortality after AMI, independent of confounding by comorbidities, frailty measures, and laboratory markers of nutritional status. Strategies to promote weight gain in underweight patients after AMI are worthy of testing. In this prospective cohort study of elderly medicare beneficiaries, Harlan Krumholz and colleagues investigate the association between underweight and mortality after acute myocardial infarction independent of cachexia and frailty.Background: A heart attack, or acute myocardial infarction (AMI), is a potentially fatal medical emergency that occurs when part of the heart muscle dies because the blood supply to the heart becomes blocked, usually by a blood clot. Every year in the US alone, more than three-quarters of a million people have a heart attack—more than one person every minute. Heart attacks are usually caused by coronary artery disease. With age, fatty deposits (atherosclerotic plaque) coat the walls of arteries, the vessels that supply the organs of the body with oxygen and nutrients. Coronary artery disease develops when plaques form in the arteries that supply the heart. A heart attack occurs when a blood clot forms in the narrowed vessel or when a plaque ruptures and triggers clot formation. Symptoms of a heart attack include chest pain, shortness of breath, and feeling lightheaded. Treatments for AMI include dissolving the blood clot with drugs and surgically opening up or bypassing the blocked artery. Why Was This Study Done?: Underweight people are at a higher risk of death after AMI than normal weight people, but is being underweight a direct risk factor for death after AMI? “Confounding” by cachexia—unintentional weight loss, muscle wasting, and fatigue that occur in the setting of chronic disease—could explain excess mortality (death) among underweight patients. That is, people who are underweight may have a higher risk of death post-AMI than normal weight people because they have another underlying disease that has caused them to lose weight. If the relationship between being underweight and post-AMI mortality is largely explained by a comorbid (coexisting) illness, managing this underlying condition may improve outcomes, whereas if being underweight is an independent risk factor for death after AMI, promoting weight gain may improve outcomes. In this prospective cohort study, the researchers investigate whether comprehensive risk adjustment for comorbid illness and frailty measures explains the higher mortality after AMI in underweight patients, and they ask whether the relationship between being underweight and mortality is also observed post-AMI in patients who have no other significant chronic illness. What Did the Researchers Do and Find?: The researchers used data from the Cooperative Cardiovascular Project, a US quality improvement initiative in which a cohort (group) of Medicare beneficiaries hospitalized for AMI were followed for many years (Medicare is a government-run program that funds healthcare for people aged ≥65 years in the US). Specifically, they analyzed short- and long-term mortality among 57,574 underweight and normal weight patients (individuals with a body mass index [BMI] of

Date: 2016
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Persistent link: https://EconPapers.repec.org/RePEc:plo:pmed00:1001998

DOI: 10.1371/journal.pmed.1001998

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