San Francisco, CA - Although recent guidelines consider obesity a relative contraindication to heart transplantation, the postoperative survival of many "obese" patients is nearly as good as those who are merely "overweight," according to a retrospective study of more than 18 000 patients that used accepted body habitus categories based on body-mass index (BMI) [1].

The analysis, presented here at the International Society for Heart and Lung Transplantation (ISHLT) 2007 Annual Meeting, also highlighted the increased morbidity and mortality risk of patients who are "underweight" at transplantation, defined as a BMI <18.5, and the need for greater attention to poor nutritional status as a modifiable risk factor in wait-listed patients, according to its investigators.

The main contention, however, is with the ISHLT's recently published guidelines for listing patients for heart transplantation, which discourage the procedure in those with a BMI of 30 or more [2]. Some in that group, those who are "obese" with a BMI of 30 to <35, have a median survival "approaching or exceeding 10 years," comparable to that of "overweight" patients, those with a BMI of 25 to <30, observed Dr Faisal H Cheema (Columbia University, New York, NY) when presenting the results. In contrast to what the ISHLT guidelines recommend, "transplant should be considered in patients with a body-mass index of less than 35," he said.

Dr Randall Starling (Cleveland Clinic Foundation, Ohio), a coauthor of the ISHLT guidelines and a member of the society's board of directors, said the transplant community understands that posttransplant risk climbs for patients with either an extremely low or extremely high BMI. "The 30-to-35 range, in my practice I don't consider that a contraindication to transplantation, but I certainly start to scrutinize patients very carefully from a composite view when their BMI is over 30," he told heartwire.

Moreover, according to Starling, the ISHLT guidelines, which were based on international data and consider varying needs and practices around the world, were meant only as "guidance." BMI is one of many important variables to consider, and decisions are tailored to each patient. "They have to be put in the context of individual centers' practices, experience, outcomes, and comfort level," he said. "It's hard to be dogmatic with a specific BMI."

Cheema and his colleagues based their conclusions on outcomes data for 18 662 adults undergoing first-time heart transplantation from 1995 to 2005, supplied by the United Network for Organ Sharing (UNOS) and arranged by BMI categories defined by the National Heart, Lung, and Blood Institute.

Mortality outcomes for 18 662 patients undergoing heart transplantation, by obesity category

Parameter	Underweight (BMI<18.5)	Normal (BMI 18.5 to <25)	Overweight (BMI 25 to <30)	Obese (BMI 30 to <35)	Severely obese (BMI 35 to <40)	Morbidly obese (BMI >40)
% of total	4	40	37	15	3	<1
Median survival (y)	9.8	10.5	10.0	9.7	8.4	7.0
Mortality (incidence per 100 patient-years)	8.36	6.74	7.37	7.81	9.51	10.7
1-year actuarial survival (%)	82	87	87	86	85	83
10-year actuarial survival (%)	47	53	51	49	31	32

The relevant ISHLT guidelines appear under the heading "Caution should be exercised in considering obese patients for transplantation" and include a distillation of available data on obesity and heart-transplantation outcomes. It then states, "Overall, it appears that pretransplant BMI >30 kg/m² or PIBW [percent ideal body weight] >140% is associated with poor outcome after cardiac transplantation. Therefore, for severely obese patients, weight loss should be mandatory to achieve a BMI <30 kg/m² or PIBW <140% before listing for cardiac transplantation."

But the analysis of UNOS data challenge the recommendations for patients with BMI 30 to <35, according to coauthor Dr Mark J Russo (Columbia University, New York, NY). "There is not a clinically important difference in survival between the obese group and the overweight group," he told heartwire. Their long-term survival, he said, "is good considering that, in the absence of a heart transplant, their expected survival would probably be about 250 days." On the other hand, he noted, patients with a BMI of 35 or higher have a decrease in survival that's significant as well as clinically important.

Morbidity outcomes for 18 662 patients undergoing heart transplantation, by obesity category

Parameter	Underweight (BMI<18.5)	Normal (BMI 18.5-<25)	Overweight (BMI 25- <30)	Obese (BMI 30- <35)	Severely obese (BMI 35 to <40)	Morbidly obese (BMI >40)
Infection (%)	26.8	22.5	22.5	23.3	25.8	29.2
Stroke (%)	3.2	2.6	2.5	2.0	3.1	1.7

The obesity categories appeared to have an effect on nonmortality outcomes as well. Cheema observed that the rates of infection and stroke tended to parallel mortality, in that the risks were lowest for normal, overweight, and obese patients and higher for underweight and severely obese patients.

It's another limitation of the guidelines that they don't discuss "underweight" patients or their management in the listing criteria, according to Russo. Chronic muscle wasting is a marker of heart-failure severity, and the data suggest that patients transplanted with a BMI <18.5 have a significantly worse one-year survival as well as an increased risk of infection and stroke compared with overweight or obese patients. But their survival was comparable at 10 years.