Prognostic value of rubidium 82 cardiac PET not influenced by BMI

Rubidium 82 cardiac PET has prognostic utility for myocardial perfusion imaging regardless of BMI, whereas other modalities may have decreased accuracy among the obese, according to recent results.

Researchers enrolled 7,061 patients who underwent cardiac rubidium 82 PET for myocardial perfusion imaging into a multicenter observational registry, with a median follow-up of 2.2 years for incidence of cardiac death and all-cause mortality. Patients were classified according to BMI as normal (<25), overweight (25-29.9) or obese (≥30). Obese patients were further subdivided as moderately (BMI, 30-34.9) or severely obese (BMI, ≥35). The researchers calculated summed stress, rest and summed difference scores utilizing a 17-segment model and a 5-point scoring system. The percentage of atypical myocardium was measured at three sites and classified as normal (0%), mild (0.1%-9.9%), moderate (10%-19.9%) or severe (≥20%).

The primary outcome of cardiac death was measurable in 6,037 patients, and all-cause mortality was evaluable in all 7,061 patients. The mean BMI of the population evaluated for the primary outcome was 30.5, and patients were classified as normal in 21.6% of cases, overweight in 33.9% and obese in 44.5%. Among the obese participants, 50% were classified as moderately obese and 50% were severely obese.

During the course of the study, 169 cardiac deaths and 570 all-cause deaths occurred. Factors associated with both cardiac and all-cause deaths on univariable analysis included all three summed scores from PET myocardial perfusion imaging, as well as age, sex, BMI, symptoms, cardiac risk factors and a history of revascularization.

Researchers observed an association between normal PET imaging results and excellent prognosis among normal, overweight, and moderately and severely obese patients, whereas those with abnormal imaging results had poorer outcomes. Analysis according to all-cause mortality yielded similar results.

The addition of PET imaging results to a model predicting cardiac or all-cause mortality via clinical predictors and summed stress score resulted in a net reclassification improvement (NRI) of 0.46 (95% CI, 0.31-0.61) for cardiac death and 0.2 (95% CI, 0.11-0.28) for all-cause mortality. Results were similar among moderately and severely obese patients specifically, both for cardiac death (NRI=0.44; 95% CI, 0.12-0.76 for moderately obese; NRI=0.63; 95% CI, 0.27-0.98 for severely obese patients) and all-cause mortality (NRI=0.2; 95% CI, 0-0.41 for moderately obese; NRI=0.28; 95% CI, 0.06-0.51 for severely obese patients).

The researchers wrote that additional studies are necessary to determine whether the prognostic utility of PET is superior to that of other modalities in obese patients.

“[Rubidium 82] PET has incremental prognostic value in all patients, irrespective of BMI,” the researchers concluded. “In the obese population, where other modalities may have reduced diagnostic accuracy, cardiac PET appears to be a promising noninvasive modality with prognostic value.”

Disclosure: See the full study for a list of relevant disclosures.