Mechanical Circulatory Support in the Morbidly Obese: Laying Out the Facts
When encountering a problem, its nature and scope must be assessed honestly and comprehensively prior to determining what strategic approach(es) ought to be taken, and then what tactical options should be deployed in order to achieve the strategic goals. These preliminary characterizations of a problem's structure are, to use a term in mathematics, the "initial conditions." In this Expert Analysis article, we attempt to outline the initial conditions that we face as a community of cardiovascular surgeons, physicians, and scientists, and from these conditions, to develop strategies and tactics to deal with a particularly challenging problem – how to approach end-stage heart failure (ESHF) in morbidly obese patients.
The first initial condition is one that affects all ESHF patients. This is the severe under-supply of donor hearts for a growing ESHF prospective recipient population.1,2 Historically, this was and has been one of the primary motivators, perhaps the most important, for the development of durable mechanical circulatory support (MCS). Because of the gross imbalance between cardiac allograft supply and recipient needs, the vast majority of ESHF patients as a whole cannot be treated using cardiac transplantation. This is despite ongoing efforts to expand the donor cardiac graft pool via various methods – improved diagnostics for assessing donor organ quality, accepting marginal donor organs, rehabilitating marginal organs, and usage of non-human donor sources: xenotransplantation and tissue-engineered organ constructs.
The second initial condition may be a moving target based on improving outcomes with durable MCS and may not be a totally fair comparison because of differences between patient groups. Cardiac transplantation has markedly superior long-term outcomes to all forms of durable MCS, even the current generation of continuous-flow devices. At present, median survival following cardiac transplantation is approximately 11 years,3 whereas it is approximately 3.5 years following continuous-flow left ventricular assist device (LVAD) implantation.4 Given these substantial differences, any decisions made with respect to cardiac transplantation versus durable MCS ought to be made in the context of maximizing aggregate patient survival and functional capacity. The third initial condition, controversial but difficult to dispute, is that durable MCS with the intent of bridge to transplant (BTT) actually statistically reduces the likelihood that any given ESHF patient receives cardiac transplantation, despite rendering certain patients transplantable. If organ supply is fixed and BTT MCS implantation improves or stabilizes patients such that they are suitable for cardiac transplantation, then a BTT strategy necessarily increases the number of potential recipients competing for a fixed donor organ supply. It ought to come as no surprise that the actual bridge rates observed in LVAD trials have decreased substantially over time: from 50% at one-year post-LVAD implantation in the Thoratec HeartMate II CF LVAD BTT trial5 to only 29% in the HeartWare HVAD CF LVAD BTT trial.6 Thus, most recipients of LVADs or other durable MCS need to be thought of as destination therapy (DT) patients, regardless of their assigned status. The rationale outlined is supported by data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), which demonstrate increasing rates of designation as DT status and decreasing rates of designation as BTT status over time.4
Other initial conditions relate to the specifics of the morbidly obese patient population. In the absence of treatment, morbid obesity is clearly associated with impaired survival. Weight-loss surgery has been shown to improve the morbid complications of obesity.7 In addition, increased patient size necessitates pumps – whether biological or artificial – that are capable of generating higher flow rates. In the context of cardiac transplantation specifically, in which donor organ undersizing negatively impacts recipient survival,8 this limits morbidly obese patients to larger hearts. Thus, only a small subset of an already scarce resource of donor organs are conceptually suitable for morbidly obese recipients. Finally, obesity may cause or exacerbate cardiomyopathy;9 in such patients, permanent cardiac replacement in the form of cardiac transplantation may not be necessary.
Integrating all of these facts, it seems that cardiac transplantation is difficult to justify in the setting of active morbid obesity. If so, only two options exist for most morbidly obese ESHF patients: 1) durable MCS – most commonly LVAD implantation, or 2) palliative medical therapy. Between these two options, however, it seems that there is an obvious superior choice. Palliative medical therapy carries a median survival of less than
Exceptions are always present. Cardiac transplantation may be appropriate for selected patients with morbid obesity. Cardiac transplantation is physiologically superior to MCS for patients with biventricular dysfunction (ideally with normal or low impedance of the pulmonary circulation), and this ought not to be different for patients with morbid obesity. Younger patients have a lesser impact of morbid obesity on intermediate-term survival, and cardiac transplantation may be a better option in selected younger patients. Finally, bariatric surgery may be performed in obese ESHF patients following functional improvement with either LVAD implantation or cardiac transplantation. Furthermore, patients undergoing DT LVAD implantation and bariatric surgery may be able to convert to BTT status, the declining likelihood of successful bridging notwithstanding.
Institutionally, due to a high prevalence of morbid obesity in our patient population, we have employed a strategy of a combined approach of LVAD implantation and bariatric surgery to simultaneously treat ESHF and morbid obesity. These results have been reported recently.10 One of these patients has successfully met criteria for conversion to BTT status and underwent cardiac transplantation, while another is currently listed for cardiac transplantation. A recently published study from Ohio State University11 also supports this approach.
In summary, we think that a close examination of generally agreed-upon facts that frame the problem, or "initial conditions," leads us as a community in one direction with respect to the treatment of morbidly obese ESHF patients – MCS as DT, with bariatric surgery. This strategy provides prompt cardiovascular support and treatment of ESHF, allows safe performance of surgical treatment of obesity, which reduces the comorbid complications of obesity and may facilitate bridging to cardiac transplantation or even cardiac recovery.
- Trivedi JR, Cheng A, Singh R, Williams ML, Slaughter MS. Survival on the heart transplant waiting list: impact of continuous flow left ventricular assist device as bridge to transplant. Ann Thorac Surg 2014;98:830-4.
- Rajagopal K, Lima B, Petersen RP, et al. Infectious complications in extended criteria heart transplantation. J Heart Lung Transplant 2008;27:1217-21.
- Lund LH, Edwards LB, Kucheryavaya AY, et al. The registry of the International Society for Heart and Lung Transplantation: thirtieth official adult heart transplant report; focus theme: age. J Heart Lung Transplant 2013;32:951-64.
- Kirklin JK, Naftel DC, Pagani FD, et al. Sixth INTERMACS annual report: a 10,000-patient database. J Heart Lung Transplant 2014;33:555-64.
- Pagani FD, Miller LW, Russell SD, et al. Extended mechanical circulatory support with a continous-flow rotary left ventricular assist device. J Am Coll Cardiol 2009;54:312-21.
- Aaronson KD, Slaughter MS, Miller LW, et al. Use of an intrapericardial, continuous-flow, centrifugal pump in patients awaiting heart transplantation. Circulation 2012;125:3191-200.
- Gloy VL, Briel M, Bhatt DL, et al. Bariatric surgery versus non-surgical treatment of obesity: a systematic review and meta-analysis of randomised controlled trials. BMJ 2013;347:f5934.
- Reed RM, Netzer G, Hunsicker L, et al. Cardiac size and sex-matching in heart transplantation: size matters in matters of sex and the heart. JACC Heart Fail 2014;2:73-83.
- Turer AT, Hill JA, Elmquist JK, Scherer PE. Adipose tissue biology and cardiomyopathy: translational implications. Circ Res 2012;111:1565-77.
- Shah SK, Gregoric ID, Nathan SS, et al. Simultaneous left ventricular assist device placement and laparoscopic sleeve gastrectomy as a bridge to transplant for morbidly obese patients with heart failure. J Heart Lung Transplant 2015;34:1489-91.
- Chaudhry UI, Kanji A, Sai-Sudhakar CB, Higgins RS, Needleman BJ. Laparoscopic sleeve gastrectomy in morbidly obese patients with end-stage heart failure and left ventricular assist device: medium-term results. Surg Obes Relat Dis 2015;11:88-93.
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