Body mass index effect on long-term survival after coronary artery bypass surgery: a competing risk analysis

Q: What is the clinical evidence from this study?

Study design: Cohort. Population: Coronary artery disease undergoing primary isolated coronary artery bypass surgery (n=5242). Intervention: Preoperative body mass index (overweight, obesity, severe obesity, and morbid obesity categories, as well as continuous BMI) vs. Normal weight (18.50 < BMI < 24.99 kg/m2). Primary outcome: Long-term (15-year) all-cause mortality (p=0.400).

Q: What does this research mean for the field?

Preoperative body mass index categories do not significantly affect 15-year all-cause or cause-specific mortality following isolated coronary artery bypass grafting, showing no evidence of an obesity paradox. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

Armando Abreu; José Máximo; Francisca Saraiva; Adelino Leite‐Moreira

doi:10.1093/icvts/ivad161

September 1, 2023Interdisciplinary CardioVascular and Thoracic SurgeryOpen Access

Body mass index effect on long-term survival after coronary artery bypass surgery: a competing risk analysis

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Key result

Preoperative body mass index categories showed no significant difference in 15-year all-cause mortality after isolated coronary artery bypass grafting (log-rank P = 0.400).

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Why the study?

The study investigated whether an obesity paradox exists for long-term mortality after primary isolated coronary artery bypass surgery, and if any discrepancy is attributable to cardiovascular versus noncardiovascular causes.

Does elevated preoperative body mass index (overweight or obesity) confer a protective effect on long-term all-cause and cause-specific mortality in patients undergoing primary isolated coronary artery bypass grafting?

Key Points

To evaluate whether an obesity paradox influences long-term survival in patients undergoing primary isolated coronary artery bypass grafting and determine whether outcomes differ by cardiovascular versus noncardiovascular mortality.
Retrospective analysis of 5242 consecutive patients with a body mass index over 18.5 kg/m2 undergoing primary isolated coronary artery bypass surgery between 2000 and 2015 at a Portuguese level III hospital.
Categorized patients by World Health Organization body mass index cutoffs and evaluated body mass index continuously.
Assessed long-term all-cause, cardiovascular, and noncardiovascular mortality with a median follow-up of 12.79 years (interquartile range, 9.51-16.61; 99.7% complete) using cumulative incidence functions, Cox regression, and cause-specific hazard models.
Fifteen-year all-cause mortality did not differ significantly across body mass index categories (log-rank test, P=0.400): 47.3% (95% CI, 43.7-50.7%) in normal weight, 45.7% (95% CI, 43.3-48.1%) in overweight, 45.1% (95% CI, 41.0-49.0%) in obese, 42.5% (95% CI, 33.5-51.3%) in severely obese, and 45.2% (95% CI, 22.5-61.3%) in morbidly obese patients.
In competing risk analyses, 15-year cardiovascular mortality showed no difference across categories (Gray's test, P=0.996; rates ranging from 18% in normal weight to 26% in morbidly obese), nor did 15-year noncardiovascular mortality (Gray's test, P=0.305; rates ranging from 14% to 18%).
Multivariable-adjusted Cox regression and cause-specific hazard models confirmed no categorical survival differences, although continuous modeling indicated an optimal body mass index between 25.8 and 30.3 kg/m2 (nadir around 28.9 kg/m2) depending on reference value definitions.

Study Design

Type

Cohort (n=5,242)

Multicenter

No

Structured PICO

Does elevated preoperative body mass index (overweight or obesity) confer a protective effect on long-term all-cause and cause-specific mortality in patients undergoing primary isolated coronary artery bypass grafting?

P

Population

5,242 consecutive patients with BMI > 18.5 kg/m2 undergoing primary isolated coronary artery bypass grafting at a Portuguese level III hospital between 2000 and 2015, followed for a median of 12.79 years.

E

Exposure

Elevated preoperative body mass index (BMI), analyzed both as WHO predefined categories—overweight (25.00 < BMI < 29.99 kg/m2), obesity (30.00 < BMI < 34.99 kg/m2), severe obesity (35.00 < BMI < 39.99 kg/m2), and morbid obesity (BMI >= 40.00 kg/m2)—and as a continuous variable.

C

Comparator

Normal weight category (18.50 < BMI < 24.99 kg/m2; median 23.4 kg/m2 used as reference for continuous spline analysis).

O

Outcome

Long-term all-cause mortality (assessed up to 15 years, median follow-up 12.79 years, via linkage to the National Patient Registry).hard clinical

Main Result

Absolute Event Rate: 45.1% vs 47.3%

p-value: p=0.400

This large, long-term competing risk analysis refutes the 'obesity paradox' in primary isolated CABG patients, showing no survival advantage for obesity and reinforcing the need for weight management in secondary coronary prevention.

Limitations

BMI was used as a surrogate measure of obesity and cannot discriminate between fat and lean mass
BMI was only measured once on the day of surgery, not accounting for dynamic weight changes over the long follow-up
Reliance on death certificate data to determine cause of death, which can be unreliable
Treating BMI as a categorical variable created unbalanced groups with small numbers in specific categories, potentially limiting statistical power
BMI was used as a surrogate measure of obesity, which is an imperfect measure of bodily adiposity and cannot discriminate between fat and lean mass.
Analyses focused only on weight and height at the day of surgery and did not account for dynamic changes in BMI over the follow-up period.
Use of death certificate data to disclose the cause of death is highly unreliable.
Treating BMI as a categorical variable created unbalanced groups with small numbers of patients in extreme categories, potentially limiting power for time-to-event analysis.

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Implication

Challenges obesity paradox after CABG; leaves open whether weight management improves long-term survival in secondary prevention.

Abstract

OBJECTIVES: The aim of this sudy was to investigate the presence of an obesity paradox on the long-term mortality of patients undergoing primary isolated coronary artery bypass surgery and to uncover whether any discrepancy found could be attributable to cardiovascular or noncardiovascular causes. METHODS: Retrospective analysis of 5242 consecutive patients with body mass index (BMI) over 18.5 kg/m2 undergoing primary isolated coronary artery bypass surgery, performed from 2000 to 2015, in a Portuguese level III Hospital. The primary end point was long-term all-cause mortality. Secondary outcomes were long-term cause-specific mortality (cardiovascular and noncardiovascular). We fitted overall, and cause-specific hazard models, with BMI forced both as a categorical (using World Health Organization predefined cutoffs) and as a continuous variable. RESULTS: Follow-up was 99.7% complete. The median follow-up time was 12.79 years (interquartile range, 9.51-16.61). The cumulative incidence functions failed to uncover any difference in 15-year all-cause (log-rank test, P = 0.400), cardiovascular (Gray's test, P = 0.996) and noncardiovascular mortality (Gray's test, P = 0.305) between BMI categories. Likewise, extensive multivariable-adjusted Cox regression and cause-specific hazards models failed to demonstrate in-between category differences, with BMI forced as a categorical variable. On the other hand, using BMI as a continuous variable, the model identified the optimal BMI as between 25.8 and 30.3 kg/m2 (nadir around 28.9 kg/m2), albeit this was dependent on the definition of the reference value. CONCLUSIONS: In this longitudinal, population-level analysis of patients undergoing isolated primary coronary artery bypass grafting, we could not attest to any protective effect of obesity on long-term survival.

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Cite This Study

Abreu et al. (2023) conducted a cohort in Coronary artery disease undergoing primary isolated coronary artery bypass surgery (n=5,242). Preoperative body mass index (overweight, obesity, severe obesity, and morbid obesity categories, as well as continuous BMI) vs. Normal weight (18.50 < BMI < 24.99 kg/m2) was evaluated on Long-term (15-year) all-cause mortality (p=0.400). Preoperative body mass index categories showed no significant difference in 15-year all-cause mortality after isolated coronary artery bypass grafting (log-rank P = 0.400).

synapsesocial.com/papers/6a7856f9a0847c3df1ecd5b6 https://doi.org/10.1093/icvts/ivad161

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Body mass index effect on long-term survival after coronary artery bypass surgery: a competing risk analysis

Figures

Key Points

Study Design

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

Body mass index effect on long-term survival after coronary artery bypass surgery: a competing risk analysis

Figures

Key Points

Study Design

Structured PICO

Main Result

Limitations

Ask about this paper

Implication

Abstract

Discussion

Cite This Study

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