To the Editor:
With great interest, we read the article by Akay et al.,1 which concluded that higher body mass index (BMI) was associated with driveline infection (DLI) in left ventricular assist device (LVAD) patients.
There has been still controversy in the association of BMI and DLI. Forest et al.2 reported similar results, which included approximately 9,000 patients from interagency registry for mechanically assisted circulatory support database. They divided patients into four groups: underweight (BMI < 18.5 kg/m2); nonobese (BMI > 18.5 to < 30 kg/m2); obese (BMI> 30 to < 40 kg/m2); and morbidly obese (BMI > 40 kg/m2), and concluded that morbidly obese was associated with ventricular assist device-related infection.2 Contrary to that, our group previously reported the relationship between lower BMI and DLI related readmission.3 Nowadays, we may better consider the limitation of BMI.
Body mass index is a simple index for the evaluation of obesity, whereas it has no any other data including fat distribution, muscle volume, or metabolic disorder. The authors hypothesized that high BMI may have negative impact on the immune function and pro-inflammatory state, resulting in the development of DLI. However, the adiposity-related metabolic and immune effect may vary between central obesity and noncentral obesity,4 and the absolute value of BMI have less metabolic/nutritional information. In the current article, the No-DLI group had relatively higher white blood cell count and higher incidence of repeat sternotomy, which may result in more inflammatory condition. Further studies may be required to address the relationship between BMI and metabolic/inflammatory markers including insulin-resistance, high-sensitivity C-reactive protein, and other adipocytokines
Local fat distribution may also have deep association with DLI. Some studies reported that the thickness of subcutaneous fat was associated with postoperative surgical site infection.5 The local surgical site’s thickness of subcutaneous fat may vary irrespective of the absolute value of BMI. Malnutrition may also be a significant predictor for DLI in LVAD patients. Malnutrition causes impaired immune status and an extremely thin subcutaneous tissue is vulnerable to infection from outside. In the present article, they did not analyze the DLI incidence among extremely lower BMI patients. Patients with cardiac cachexia may not be enrolled in this study. Recently some nutritional status indices were advocated as useful markers like Controlling Nutrition Status score and Prognostic Nutritional Index.6 Such markers may be more beneficial to evaluate nutritional status than just using the single value of BMI.
In conclusion, the interpretation of BMI may better be with caution when considering the risk of DLI. Optimal risk stratification for future DLI and therapeutic strategy for the high-risk populations is warranted.
Division of Cardiology
Department of Medicine
The University of Chicago Medicine
1. Akay MH, Nathan SS, Radovancevic R, et al. Obesity is associated with driveline infection of left ventricular assist devices. ASAIO J 2018. doi: 10.1097/MAT.0000000000000916.
2. Forest SJ, Xie R, Kirklin JK, et al. Impact of body mass index on adverse events after implantation of left ventricular assist devices: An IMACS registry analysis. J Heart Lung Transplant 2018.37: 1207–1217.
3. Imamura T, Kinugawa K, Nitta D, et al. Readmission due to driveline infection can be predicted by new score by using serum albumin and body mass index during long-term left ventricular assist device support. J Artif Organs 2015.18: 120–127.
4. Sahakyan KR, Somers VK, Rodriguez-Escudero JP, et al. Normal-weight central obesity: Implications for total and cardiovascular mortality. Ann Intern Med 2015.163: 827–835.
5. Watts CD, Houdek MT, Wagner ER, Taunton MJ. Subcutaneous fat thickness is associated with early reoperation and infection after total knee arthroplasty in morbidly obese patients. J Arthroplasty 2016.31: 1788–1791.
6. Yost G, Tatooles A, Bhat G. Preoperative nutritional assessment with the prognostic nutrition index in patients undergoing left ventricular assist device implantation. ASAIO J 2018.64: 52–55.