Low BMI May up Complication, Mortality Risk at ICD Implantation

April 03, 2012

April 2, 2012 (Chicago, Illinois) — Being small may be a disadvantage when getting an implantable cardioverter-defibrillator (ICD), according to an analysis of >80 000 cases entered into the National Cardiovascular Data Registry (NCDR) ICD records in 2010 and 2011 [1].

The 1.7% of patients who were underweight, defined as a body-mass index (BMI) <18.5 kg/m2, had significantly more periprocedural complications, longer hospital stays, and higher in-hospital mortality than those who were of normal weight. On the other hand, those who were obese, with a BMI >30 kg/m2, making up 40% of the cohort, fared as well as those of normal weight.

The disadvantage for underweight patients compared with the other two groups was seen "across the spectrum" in a subgroup analysis, lead author Dr Jonathan Hsu (University of California, San Francisco) told heartwire . "Underweight status" remained an independent risk factor for all three end points, he said, regardless of age, sex, whether the patient had diabetes or any of a number of other comorbidities, type of health insurance, or type of ICD implanted: single- or dual-chamber or biventricular pacemaker with or without a defibrillator.

That the findings were independent of device type is particularly noteworthy because they vary in number of implanted leads, implantation procedure length, and other factors that track with procedure risk, according to Hsu, who presented the study in poster form here at the American College of Cardiology 2012 Scientific Sessions.

That underweight patients might fare worse isn't entirely a surprise, he said; it turns out in the surgical literature that patients with low BMI may be at increased risk at coronary bypass and other cardiac surgery. "But we were a little surprised that the obese consistently did not have any significant differences in outcomes in any of the three adverse events."

It may be that underweight isn't getting the attention as a risk factor that it deserves, according to Hsu. "A lot of our efforts have concentrated on obese patients because we know they're at risk for cardiovascular morbidity and mortality, but maybe it takes away from focusing our attention on [other] patients who can certainly be at risk for complications and adverse events at procedures like ICD implantation. Maybe we do need to focus more attention on the underweight population that's clearly at risk."

Outcomes of ICD Implantation by Body-Mass-Index Category

End point BMI <18.5

(underweight)

n=1434 (%)

BMI >18.5 to <30

(normal weight) n=48 539

BMI >30

(obese) n=33 339 (%)

OR (95% CI)a p
Any complication 5.2b 2.3 2.1 2.15 (1.68–2.75) <0.0001
In-hospital death 0.8c 0.3 0.3 2.27 (1.21–4.27) 0.01

a. Underweight vs normal weight, adjusted for demographics, comorbidities (including heart failure, arrhythmias, history of coronary disease events, revascularization history, cerebrovascular disease, chronic lung disease, diabetes, renal function, and echocardiographic and electrocardiographic abnormalities)

b. p<0.001 vs normal or obese

c. p=0.026 vs normal or obese

Hsu cautioned that the analysis didn't adjust for some potential confounders that track with risk and low BMI but weren't captured in the NCDR data set, including cancer, nutritional status, and overall frailty.

Underweight patients also had a significantly longer hospital length of stay (LOS) than normal-weight patients in multivariate analysis (odds ratio for LOS >3 days after implant 1.62; 95% CI 1.38–1.89, p<0.0001).

The most common complications of the implantation procedure for underweight, normal-weight, and obese patients, respectively, were:

  • Pneumothorax at 2.1%, 0.4%, and 0.1%.

  • Hematoma at 1.0%, 0.3%, and 0.2%.

"It's certainly not surprising that underweight patients were more likely than normal-weight and obese patients to have pneumothorax," according to Hsu; it's recognized that vascular access is harder to achieve in smaller or thinner patients, where the risk of lung penetration is higher.

It also "makes sense" that hematomas may be more common in smaller patients, given that dosages of any antiplatelets or anticoagulants they may be taking aren't likely to be adjusted for weight. "And there's always the possibility of detection bias, in that underweight patients find it easier to see or feel the hematoma and therefore it's more commonly diagnosed."

Hsu pointed out that during device and lead implantation procedures, "there are certain approaches to vascular access that reduce the risk of pneumothorax, such as the cephalic approach or axillary approach, compared with the subclavian approach. Knowing in advance that underweight patients are most at risk for pneumothorax, maybe we could use other vascular-access techniques in underweight patients."

And, he proposed, "Maybe we need to be careful about what kind of antiplatelet or anticoagulation medications [underweight patients receiving an ICD] are on. Maybe the dose could be reduced or the medications could be withheld before the procedure."

Hsu said he has no relevant disclosures.

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