Coronary microvascular dysfunction (CMD) identified with cardiac stress PET testing was a better predictor of adverse events among obese patients than body mass index (BMI) and other traditional risk factors, researchers reported in the Journal of the American College of Cardiology.
Although BMI is easy to calculate and widely used in clinical practice, it is far from a perfect risk marker, the authors noted.
“BMI may not distinguish between patients with more metabolically malignant versus benign body fat profiles and distribution (or even between excess body fat vs. lean mass), which may vary substantially by geographical region and sex,” wrote lead researcher Navkaranbir S. Bajaj, MD, MPH, with the cardiovascular imaging program at Brigham and Women’s Hospital in Boston, and colleagues.
Bajaj et al. studied outcomes from 827 patients in the single-center study, which only included individuals without obstructive coronary artery disease. However, CMD was defined as impaired coronary flow reserve (CFR) in the absence of flow-limiting coronary artery disease.
After the threshold for obesity, as BMI went up CFR went down. But when adjusting for multiple risk factors, only CFR remained independently associated with the primary composite endpoint of death and hospitalizations for heart failure and myocardial infarction.
Over a median follow-up of 5.6 years, each one-unit decrease in CFR signaled a 95 percent increased risk of meeting that endpoint, while each 10-unit increase in BMI boosted odds by 20 percent—a statistically insignificant difference. Among obese patients, CFR below 1.7 was associated with an adjusted event rate of 5.7 percent, compared to a rate of 2.6 percent for participants above that cutoff.
In adding CFR to a prediction model that already included BMI, the researchers found the c-statistic improved from 0.71 to 0.74.
“BMI and CFR both appeared to be prognostically important in unadjusted and partially adjusted models, but only CFR improved model discrimination and remained independently associated with events in fully adjusted analyses,” Bajaj and colleagues wrote. “Indeed, in obese patients, only those with impaired CFR demonstrated a significantly increased risk of events; this was particularly evident in patients without extreme obesity (BMI 30 to 39 kg/m2), in whom impaired CFR was associated with a significant ≥2.5-fold increased adjusted rate of events.”
In addition to bariatric surgery, the authors said therapies targeting cholesterol, inflammation and glucose handling in the kidneys may improve CMD among obese patients and move them to a lower-risk category. But further research is needed to validate these suggestions, they added, and to determine whether CMD can guide interventions resulting in better clinical outcomes.
“When stratified by CFR, it became apparent that obese patients in this cohort represent a heterogeneous group with varying levels of risk (i.e., some patients have severe CMD and may potentially benefit from aggressive management strategies, including bariatric surgery), whereas others may be closer to representing a ‘metabolically healthy’ phenotype in which close patient monitoring and less invasive approaches may be reasonable,” Bajaj and coauthors wrote.
Daniel joined TriMed’s Chicago editorial team in 2017 as a Cardiovascular Business writer. He previously worked as a writer for daily newspapers in North Dakota and Indiana.