Morbid Obesity Lowers In-Hospital Mortality in AMI Patients

Adding more support to the “obesity paradox,” a large, population-based analysis shows that patients with acute myocardial infarction (AMI) who are morbidly obese have a lower risk of in-hospital mortality than their lower-weight counterparts. The study was published online January 28, 2013, ahead of print in the American Journal of Cardiology.

Researchers led by Shaista Malik, MD, PhD, MPH, of the University of California, Irvine (Irvine, CA), looked at 413,673 AMI patients from the Nationwide Inpatient Sample admitted to 1,045 hospitals in 44 states in 2009. Morbid obesity (BMI ≥ 40 kg/m²) was found in 3.7% of patients.

In-hospital mortality was lower for morbidly obese AMI patients than for lower-weight subjects whether they underwent no procedure, diagnostic catheterization, PCI, or CABG (table 1).

Table 1. Associations Between Mortality and Weight After Cardiac Procedures

The lower overall rates of in-hospital mortality were maintained in the subsets of patients with STEMI (4.7% vs. 6.3%; P < 0.0001) and NSTEMI (3.1% vs. 6.3%; P < 0.0001).

After regression analysis adjusting for age, race, sex, income, hospital factors, and comorbidities, morbidly obese patients still showed a reduction in in-hospital mortality (OR 0.86; 95% CI 0.78-0.94; P = 0.0008), driven by differences in patients with NSTEMI, especially those who received no procedures (table 2). Mortality differences disappeared in STEMI patients.

Table 2. Influence of Morbid Obesity After Cardiac Procedures in NSTEMI Patients

Morbidly obese AMI patients were also more likely than their lower-weight counterparts to undergo invasive cardiac procedures when presenting with either STEMI (97.4% vs. 93.8%; P < 0.0001) or NSTEMI (85.5% vs. 80.6%; P < 0.0001). However, regardless of the type of AMI, morbidly obese patients were less likely to undergo PCI (45.1% vs. 52.9%; P < 0.0001) and more likely to undergo CABG (18.6% vs. 10.9%; P < 0.0001). These differences were maintained after multivariable adjustment.

AMI patients with morbid obesity were more likely to be female (45.8% vs. 36.7%; P < 0.0001), younger (age 59.6 vs. 65.3 years; P < 0.0001), and African-American (11.7% vs. 9.2%; P < 0.0001) and had a higher incidence of comorbid conditions such as diabetes (63.4% vs. 33.0%; P < 0.0001), hypertension (77.3% vs. 67.6%; P < 0.0001), and renal failure (21.6% vs. 16.7%; P < 0.0001).

“[Results of] this large, nationwide, contemporary cohort [are] . . . consistent with the phenomenon of the obesity paradox,” Dr. Malik and colleagues write. “Factors that may influence the better survival in morbidly obese patients include presenting at a younger age, the tendency to present with NSTEMI rather than STEMI, and the higher rate of referral for CABG.”

The increased rate of CABG may be explained, they note, by more extensive coronary disease in the morbidly obese, requiring surgical revascularization, and their younger age, making them better surgical candidates.

Underweight May Skew Results

The authors also note that as opposed to previous studies investigating the obesity paradox, which used the lowest risk groups for comparison, the current study compared the morbidly obese with all other patients, including the underweight.

Carl J. Lavie, MD, of Ochsner Medical Center (New Orleans, LA), cited that as an explanation for the results, as well. “It's the morbidly obese against everyone else, including the underweight, who have the worst prognosis. Whereas the overweight may have the best prognosis, the underweight really drag the rest of the group down,” he said in an e-mail communication with TCTMD.

Dr. Lavie’s previous work implicated a so-called lean paradox. “It may not be that the obese do so well but that the leanest patients, who selectively develop cardiovascular disease and specifically in these studies coronary heart disease, actually do so poorly,” he said. “The worst prognosis appears to be in the low fit patients who are also lean, whereas the high fitness patients have a good prognosis and there does not appear to be an obesity paradox.”

Dr. Lavie stressed that while some evidence may suggest that obesity is protective post-AMI, it also may have caused the initial infarction. “It is not good to be morbidly obese. Notice that despite being a lot younger [in the current study], they still showed up with a heart attack,” he said. “I take hospital duty at Ochsner, . . . and it seems that almost every time I have someone in their 30s or even 20s come in with a heart attack, and generally this is with marked, usually class 3, or ‘morbid obesity.’ Nevertheless, once the heart attack occurs, it is not ‘doomsday’ for the obese or morbidly obese, as their [short-term] prognosis appears to be favorable.

“In my opinion, most of these patients would not have developed the heart attack in the first place had obesity or even morbid obesity been prevented,” he concluded.

 

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Source:
Dhoot J, Tariq S, Erande A, et al. Effect of morbid obesity on in-hospital mortality and coronary revascularization outcomes after acute myocardial infarction in the United States. Am J Cardiol. 2013;Epub ahead of print.

 

 

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