Underweight Patients Fare Worse After Heart Catheterization

Marlene Busko

August 27, 2017

BARCELONA, SPAIN — Among patients undergoing left heart catheterization, those with a body-mass index (BMI) below 20 were most likely to die or be readmitted soon after the procedure, in a large US registry study[1].

The findings, which were presented here at the European Society of Cardiology (ESC) 2017 Congress, draw attention to an overlooked group—underweight, mainly female patients undergoing cardiac catheterization.

Dr Afnan Tariq

This research also reinforces the concept of an "obesity paradox," since obese patients were less likely to have poor outcomes than normal-weight patients, Dr Afnan Tariq (Lenox Hill Hospital, New York, New York) told theheart.org | Medscape Cardiology.

It was "really striking how poorly underweight patients do," Tariq said. A larger proportion of underweight patients were women, and underweight patients were also less likely to have PCI.

Among the patients who did have PCI, underweight patients had a fivefold greater risk of dying after the procedure than obese patients, and they were 18% more likely to be readmitted at 30 days than normal-weight patients.

Thus, "obesity does not necessarily portend a worse outcome in patients undergoing cardiac catheterization," Tariq summarized in a press briefing. "We really as clinicians need to be cognizant that the underweight patient can be very sick, and they tend to do worse."

It is difficult to interpret this study, press briefing cochair Dr Rosa Ana Hernandez Antolin (Universidad de Alcalá de Henares, Madrid, Spain) cautioned during the briefing. The registry data don't provide information on why the patients were undergoing coronary catheterization, and it was probably a very heterogeneous population, she noted.

Dr Josepa Mauri Ferré (Hospital Germans Trias I Pujol, Badalona, Spain), a spokesperson for the ESC, echoed these comments. "I think these are different [types of] patients," she said. It is "dangerous" to misinterpret the study as saying that obesity is not harmful, "because the main killer is coronary artery disease, and the main risks are obesity, diabetes," and other well-known factors.

Session cochair Dr Manel Sabaté Tenas (Autonomous University of Barcelona, Spain) concurred, adding: "One thing is clear. Obesity is a risk factor for developing coronary artery disease. Once you have the disease maybe, it's better to be a little bit overweight than underweight, in case you need surgery, for instance."

Tariq conceded that "we don't have a good measure for frailty for coronary disease and this is something we need to look into."

Does BMI Predict Outcome After PCI?

The impact of BMI on cardiovascular outcomes after cardiac catheterization are unclear, Tariq said. Thus, the researchers aimed to examine mortality, cost of care, and impact on readmission among patients grouped into five BMI categories.

They retrospectively analyzed discharge data for index admission and 30-day and 6-month readmissions for patients undergoing cardiac catheterization in 2013, for patients who were part of the National Readmission Database (NRD) and Nationwide Inpatient Sample (NIS) Databases.

These all-payer inpatient databases maintained by the Healthcare Cost and Utilization Project (HCUP) look at 15 million hospitalizations a year, which are weighted to represent more than 35 million hospitalizations.

Patients were classed as underweight (BMI <20), normal weight (BMI 20–25), overweight (BMI 25–30), obese (BMI 30–40), or morbidly obese (BMI >40).

The researchers identified 1,035,727 left heart catheterizations (LHC) that were performed in 2013, of which 435,434 (42.0%) received PCI during the index admission.

Of these patients, 0.3% were underweight, 11.4% were obese, and 8.0% were morbidly obese.

Of the underweight patients, 55% were female, vs 31% to 35% of the normal-weight to obese patients, and 46% of morbidly obese patients.

Only a quarter of the underweight patients (26%) underwent PCI as opposed to 33% of the morbidly obese patients, 41% of the overweight or obese patients, and 43% of the normal-weight patients (P<0.001 for all).

Among the patients who had PCI, 6% of underweight patients but only 1.2% to 1.9% of the overweight to morbidly obese patients and 2.3% of normal-weight patients died after the procedure (P<0.001 for all).

Similarly, 21% of underweight patients but only 13% to 15%% of the overweight to morbidly obese patients and 13% of normal-weight patients were readmitted to the hospital 30 days after the procedure (P<0.001 for all).

Compared with the morbidly obese patients, normal-weight patients stayed in hospital for fewer days (5.1 vs 6.2 days, P<0.01) and their care cost less ($22,581 vs $23,889, P<0.01).

Underweight patients stayed in hospital the longest compared with all other BMI groups (10.5 days vs 5 to 6.2 days) and, in parallel, their care cost the most ($33,540).

After controlling for age, gender, insurance, and number of comorbidities (Elixhauser score), the researchers found that, compared with patients of normal weight, underweight patients had an 18% higher risk of being readmitted (odds ratio 1.18), whereas patients who were overweight, obese, or morbidly obese all had about a 10% lower risk of being readmitted (odds ratio 0.89 to 0.92, P<0.05).

Patients in the underweight category who underwent left heart catheterization in this study were "skinny and sicker, and there's also the possibility that we may not be treating them as aggressively," Tariq said. "People have posited that perhaps underweight patients smoke, which suppresses the appetite, but it can't be that simple," he noted.

"We've seen this relationship, and we haven't been able to find a causality—but it is an important relationship that we really need to delineate," he added. "We need to set up a prospective study to look at these populations."

The authors have no relevant financial relationships. 

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