Response to Letter Regarding Article, “Continuous Aortic Flow Augmentation: Not Enough MOMENTUM”
I agree with the objection raised by Dr Greenberg about my comment1 that implied that the continuous aortic flow augmentation system had a primary or direct effect on increasing cardiac output. Clearly, any increase in cardiac output would be secondary to a decrease in peripheral resistance associated with the distal aortic perfusion. The study design used in the Multicenter Trial of the Orqis Medical Cancion System for the Enhanced Treatment of Heart Failure Unresponsive to Medical Therapy (MOMENTUM) did in fact include a paired analysis, as noted by Dr Greenberg.
The population of patients who develop worsening heart failure and become progressively unresponsive to standard medical therapy is increasing rapidly. To date, the most effective treatment for such patients has been with the use of ventricular assist devices that can fully support the circulation for extended periods, reduce high cardiac filling pressures, and typically improve a number of comorbidities and end-organ compromise. I also agree with Dr Greenberg that making a comparison of the continuous aortic flow augmentation system to larger left ventricular assist devices, which are capable of supporting the entire circulation, is unfair, as that was never the intent of the device or the study. This field would be greatly helped by the availability of new devices that are designed to provide lower levels of increased cardiac output (primarily or secondarily), especially when implanted at an earlier stage in heart failure progression, before the patient exhibits end-organ compromise. The editorial tried to place that system in the context of other new devices now in clinical trial that are also designed to provide lower levels of support of the circulation. The minimum increase in cardiac output that is not only statistically significant but also clinically meaningful is still unknown; it varies by body size (cardiac index) and the clinical setting, but likely needs to be at least a sustainable 1.5- to 2.0-L increment. These new devices should allow the patient to be ambulatory during this therapy, be minimally invasive to implant (ie, not require a sternotomy), and be shown to be associated with improvement in functional capacity or similar end points, but likely not survival. Whether intermittent therapy that requires the patient to be at bedrest for periods of time will be effective is unknown.
Novel approaches such as continuous aortic flow augmentation are surely needed and should be further evaluated, especially with identification of the mechanism(s) of improvement in cardiac output associated with this therapy, as well as identification of those patients who would be best served by this type of support.
Dr Miller has received research support from Thoratec corporation for both the Heartmate II study and the ongoing Clenbuterol study of LV recovery, and honorarium support from Thoratec for only academic medical center grand rounds lectures during the past year. During the past 2 years, Dr Miller has advised Thoratec, Heartware, and Ventracor corporations on clinical trial design but has received no compensation for any of this advice. Dr Miller has no stock in any medical company and would have no financial gain from this letter or the previous editorial regarding this study.