HORIZONS-AMI Substudy Examines Effects of Obesity on STEMI Outcomes

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In patients with ST-segment elevation myocardial infarction (STEMI), higher body mass index (BMI) is linked with a more extensive adjusted cardiovascular risk profile and disease burden but similar acute and long-term outcomes, according to a substudy of the HORIZONS-AMI trial published online April 17, 2014, ahead of print in the American Journal of Cardiology.

Roxana Mehran, MD, of Mount Sinai School of Medicine (New York, NY), and colleagues stratified 3,579 STEMI patients enrolled in the HORIZONS-AMI trial by BMI quartile, each with slightly fewer than 900 patients:

• Cohort 1: < 24.5 kg/m²
• Cohort 2: 24.5-27.08 kg/m²
• Cohort 3: 27.08-30.12 kg/m²
• Cohort 4: > 30.12 kg/m²

In-hospital rates of CABG, reinfarction, and stroke did not differ among the cohorts, but major bleeding was most common in the lowest BMI group (P < .05 for trend). There was an inverse relationship between BMI and in-hospital mortality, driven primarily by cardiac mortality (table 1).

Table 1. In-hospital Mortality

After adjusting for confounders, this relationship was maintained only when comparing the highest and lowest BMI quartiles (OR 0.48; 95% CI 0.22-1.02; P = .055).

Thirteen-month follow-up was available in 1,202 patients with 1,409 lesions, and no difference was seen in the overall incidence of in-stent restenosis among the original quartiles (P = .27). MACE from 30 days to 3 years was higher in the lowest BMI group (20.7%) than in cohorts 2 (15.4%; P < .05), 3 (17.7%; P = .1), and 4 (16.5%; P < .05). A slight inverse trend was seen in net adverse clinical events across the cohorts (21.4%, 16.8%, 18.4%, and 17.3%, respectively; P = .06). The only difference observed among individual endpoints across the cohorts was a slightly higher prevalence of mortality with lower BMI (P = .0534), but this was driven by noncardiac mortality (P = .0161) rather than cardiac mortality (P = .7353).

Patients were then restratified according to a priori definitions of the World Health Organization (WHO) for underweight/normal weight (BMI < 25 kg/m²; n = 1,056), overweight/mild obesity (BMI 25-35 kg/m²; n = 2,300), and moderate/severe obesity (BMI > 35 kg/m²; n = 223). In this case, in-hospital cardiac mortality was higher in the low/normal BMI group (2.8%) compared with the high (1.3%; P = .2) and medium (1.5%; P < .05) BMI groups. However, when BMI was included as a continuous variable on multivariate analysis, there was no association with cardiac mortality.

At 13 months, patients in both the low/average (2.3%) and high (3.0%) BMI groups by WHO definition had higher cardiac mortality compared with the middle group (1.2%; P < .05 for both).

There was no interaction between age and BMI with regard to overall, cardiac, or noncardiac mortality.

No ‘Cardioprotective Effect’ From Obesity

Since there was no difference in peripheral arterial disease across BMI quartiles, Dr. Mehran and colleagues observe, “This may indicate that obesity affects the coronary circulation differently than other arterial regions, possibly related to an increased extent of epicardial fat. Indeed, the volume of the pericardial adipose tissue has been noted to be significantly higher in patients with CAD, particularly in those with high-risk lesions.

“Moreover,” they write, “consistent with a prior report of an inverse relationship between BMI and coronary artery calcification, we found a lower level of calcification in lesions in patients with a high BMI.  Whether this represents a higher prevalence of soft, vulnerable plaques in patients with a high BMI remains unknown at this point.”

Although obesity escalates other comorbidities, “and accelerates the development of coronary atherosclerosis, it did not adversely affect the dynamics and characteristics of an evolving STEMI in this analysis,” the authors comment.

Dr. Mehran and colleagues write, “There is no direct ‘cardioprotective’ effect of obesity itself. In fact, recent data from the National Cardiovascular Data Registry ACTION Registry [‘Get With the Guidelines’]… would suggest that the in-hospital STEMI mortality risk does increase with extreme obesity, and similar dynamics were noted for non-ST segment myocardial infarction.”

Age is the telltale predictor of in-hospital mortality, they explain, since prior studies “already suggested that the relationship between BMI and mortality was age-dependent and was most prominent in the elderly (over 65 years of age). In the current study, we found that the association between BMI and in-hospital mortality was lost after adjusting for age, similar to the findings of a prior study in a Japanese population.”

Fitness Over ‘Fatness’

In an email with TCTMD, Carl J. Lavie, MD, of Ochsner Medical Center (New Orleans, LA), said that although “not every study shows exactly the same finding, [the] general idea is consistent with much prior research.”

Most importantly, “these patients need cardiac rehab and [to improve] their fitness,” he said, adding that the study was lacking this patient information. In the long term, Dr. Lavie continued, “fitness is more important than fatness” with the worst prognoses seen in thin patients with low muscle, low physical activity, and low fitness.

Study Details

Patients in the highest BMI quartile were younger and had a higher prevalence of systemic hypertension, hyperlipidemia, and diabetes compared with patients in the lower BMI quartiles. Smoking prevalence decreased with increasing BMI, as did anemia.

D2B times did not differ among the quartiles and radial access was used equally across the groups. Most patients underwent coronary artery stenting with 71% receiving DES. Reference vessel diameter increased with increasing BMI, as did final minimal lumen diameter and acute gain in stent area. Procedural complications and success rates did not differ nor did postprocedural TIMI 3 flow or myocardial blush grade 3.

Note: Several coauthors are faculty members of the Cardiovascular Research Foundation, which owns and operates TCTMD.

 

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Source:
Herrmann J, Gersh BJ, Goldfinger JZ, et al. Body mass index and acute long-term outcomes after acute myocardial infarction (from the Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction [HORIZONS-AMI] trial). Am J Cardiol. 2014;Epub ahead of print.

 

 

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