Letter by Greenberg Regarding Article, “Continuous Aortic Flow Augmentation: Not Enough MOMENTUM”
To the Editor:
I appreciate Dr Miller’s commentary regarding the Multicenter Trial of the Orqis Medical Cancion System for the Enhanced Treatment of Heart Failure Unresponsive to Medical Therapy (MOMENTUM) results.1,2 However, there are some inaccuracies in his editorial, and I respectfully disagree with a number of his points and conclusions. He indicates that the continuous aortic flow augmentation (CAFA) device generates cardiac output. In fact, the arterial-to-arterial flow loop used to produce CAFA does not directly generate cardiac output. Rather, the hemodynamic findings of this trial confirmed that increasing flow exclusively in the descending aorta progressively reduces systemic vascular resistance, presumably through an arterial signaling effect, thereby secondarily improving cardiac function, as evidenced by the simultaneous progressive increase in cardiac output and reduction in pulmonary capillary wedge pressure.
I disagree with Dr Miller’s statement that, “A modest goal of the study was that the device could provide improvement in cardiac index or at least 1 L/min over baseline” (p 1223). He is misinterpreting the technical component of our composite primary efficacy success criteria, stated in the article to entail “insertion and attainment of flow ≥1 L/min” within the pump circuit. As we explain, “Unlike a ventricular assist device, the artery-to-artery circuit does not directly replace or augment CI [cardiac index], so the CI increase does not occur instantaneously. Rather, it occurs progressively, associated with reduced systemic vascular resistance.”
Dr Miller repeatedly compares the Cancion device to ventricular assist devices, designed to provide support to patients with cardiogenic shock. These latter devices directly augment cardiac output by driving blood into the arterial circulation, without an arterial-to-arterial flow circuit. We studied “patients hospitalized with an exacerbation of chronic HF and persistent hemodynamic and renal compromise” but excluded patients with cardiogenic shock, who required cardiac mechanical support. We postulated that the improvement in cardiac function achieved would translate into sustained clinical benefit.
Dr Miller contrasts earlier time points in which there was little or no between-group difference in mean cardiac index (ignoring the slightly greater control-group baseline value) with later time points at which this difference emerges and increases. It is therefore surprising that he later states that the augmentation in systemic vascular resistance “did not lead to further improvement in cardiac index” (p 1223). In fact, it most certainly did.
Dr Miller criticizes the fact that our data were not “broken out by paired analysis for each patient” (p 1223). In fact, our primary analysis did just that, comparing success rates within the 2 groups, although we predefined hemodynamic effect based on change in pulmonary capillary wedge pressure, an indicator that has been more closely linked to clinical improvement.3–5 We will soon be reporting factors that predicted both hemodynamic and clinical responses within our population.
The CAFA device is not a ventricular assist device. The observed increment in cardiac index carries a quite different implication as a reflection of true improvement in cardiac performance, rather than a direct consequence of ventricular assist device flow. Although the hemodynamic changes did not translate into a statistically significant benefit in the composite primary efficacy end point, the progressive improvement in cardiac function in MOMENTUM confirms the novel biological effect of CAFA and provides guidance for future investigation of both this device and other CAFA devices under development.
Dr Greenberg served as an investigator for the MOMENTUM study and have received consulting fees from Orqis Medical.
Greenberg B, Czerska B, Delgado RM, Bourge R, Zile MR, Silver M, Klapholz M, Haeusslein E, Mehra MR, Mather P, Abraham WT, Neaton JD, Brown BS, Parker IC, Konstam MA; MOMENTUM Investigators and Coordinators. Effects of continuous aortic flow augmentation in patients with exacerbation of heart failure inadequately responsive to medical therapy: results of the Multicenter Trial of the Orqis Medical Cancion System for the Enhanced Treatment of Heart Failure Unresponsive to Medical Therapy (MOMENTUM). Circulation. 2008; 118: 1241–1249.
Miller LW. Continuous aortic flow augmentation: not enough MOMENTUM. Circulation. 2008; 118: 1223–1224.
Steimle AE, Stevenson LW, Chelimsky-Fallick C, Fonarow GC, Hamilton MA, Moriguchi JD, Kartashov A, Tillisch JH. Sustained hemodynamic efficacy of therapy tailored to reduce filling pressures in survivors with advanced heart failure. Circulation. 1997; 96: 1165–1172.