Weaning of rotary blood pump recipients after myocardial recovery: A computer study of changes in cardiac energetics

Brain Research Institute, University of Vienna, Wien, Vienna, Austria
Journal of Thoracic and Cardiovascular Surgery (Impact Factor: 3.99). 07/2004; 127(6):1743-50. DOI: 10.1016/j.jtcvs.2003.09.029
Source: PubMed

ABSTRACT Weaning of patients from mechanical cardiac support after myocardial recovery has always involved multiple, interacting factors, particularly the training of the myocardium during reduction of pump flow. Rotary pumps offer training advantages when support flow is reduced, even to nearly zero. We report a computer analysis that evaluates the work required of the heart during partial unloading and removal of rotary pumps.
A computer model of the assisted circulation, previously implemented in MATLAB (The MathWorks Inc, Natick, Mass), has been augmented with a model of the MicroMed DeBakey ventricular assist device (MicroMed Technology, Inc, Houston, Tex). Flow, pressure patterns, and external work (pressure-volume area, calculated as the area of the ventricular pressure-volume loop [external work] plus potential energy) were calculated for nonassisted and various continuously assisted patients. Under low-flow conditions, the heart imposes an oscillating forward-backward flow through the non-occlusive rotary pump, causing an increase in ventricular work. Thus, an assist flow of 1 to 1.5 L/min requires work equivalent to that of the unsupported heart. At 60% contractility, the nonassisted pressure-volume area is 1.10 Ws/beat, and the potential energy is 0.38 Ws/beat. At a Qpump of 1 L/min, the pressure-volume area is 1.21 Ws/beat, and the potential energy is 0.37 Ws/beat. At a Qpump of 3 L/min, the pressure-volume area is 0.93 Ws/beat, and the potential energy is 0.29 Ws/beat. These conditions cannot be achieved with pulsatile systems.
During weaning and retraining, an implanted rotary pump can provide a workload to the heart like that in the nonassisted situation, thus increasing the predictability of weaning and reducing the risk of reiterating heart failure.

Download full-text


Available from: Georg Wieselthaler, Mar 24, 2014
  • Wiener klinische Wochenschrift 08/2008; 120:15-20. DOI:10.1007/s00508-008-1043-0 · 0.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mechanical support of the circulation is necessary when heart failure becomes refractory to medical support and is typically applied when organ dysfunction occurs as a result of hypoperfusion. However, in timing the intervention, it is important to apply mechanical support before multiple organ failure occurs. The objective of this work is to review the current strategies for mechanical circulatory support in patients with refractory cardiac failure. A review of the use of mechanical circulatory support is presented for patients with refractory cardiac failure. Data are taken from human studies that were selected to best exemplify the results that may be obtained from various forms of mechanical circulatory support. Commonly applied forms of mechanical support include mechanical ventilatory support, intraaortic balloon counterpulsation, and hemodialysis or ultrafiltration. If these measures fail, mechanical support of the circulation with ventricular assist devices is possible in specialized centers with expertise in the implantation and management of these devices. The decision to pursue mechanical circulatory support in the critically ill patient is based on the cause of acute decompensation, the potential reversibility of the condition, and the possibility for other treatments to improve the underlying condition or, in highly selected cases, heart transplantation. Newer forms of ventricular assistance that require less surgery are becoming available and may allow use in a broader range of critically ill patients. There is a range of means to mechanically support the circulation in patients with advanced heart failure. A variety of means to support the circulation have found application in the treatment of patients with refractory heart failure. More work is required to best identify populations who will benefit from the therapy and to refine the therapy to reduce associated risks.
    Critical Care Medicine 10/2006; 34(9 Suppl):S268-77. DOI:10.1097/01.CCM.0000232490.69771.28 · 6.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Current left ventricular assist devices are designed to provide full hemodynamic support for patients with end-stage failing hearts, but their use has been limited by operative risks, low reliability, and device-related morbidity. Such concerns have resulted in minimum use of left ventricular assist devices for destination therapy. We hypothesize that partial circulatory support, which could be achieved with small pumps implanted with less-invasive procedures, might expand the role of circulatory support devices for treatment of heart failure. We examine the hemodynamic effects of partial left ventricular support using a previously described computational model of the cardiovascular system. Results from simulations were validated by comparison with an in vivo hemodynamic study. Simulations demonstrated that partial support (2-3 L/min) increased total cardiac output (left ventricular assist device output plus native heart output) by more than 1 L/min and decreased left ventricular end-diastolic pressure by 7 to 10 mm Hg with moderate-to-severe heart failure. Analyses showed that the hemodynamic benefits of increased cardiac output and decreased left ventricular end-diastolic pressure are greater in less-dilated and less-dysfunctional hearts. Both the relationships between ventricular assist device flow and cardiac output and ventricular assist device flow and left atrial pressure predicted by the model closely approximated the same relationships obtained during hemodynamic study in a bovine heart failure model. Results suggest that a pump with a flow rate of 2 to 3 L/min could meaningfully affect cardiac output and blood pressure in patients with advanced compensated heart failure. The development of small devices capable of high reliability and minimal complications that can be implanted with less-invasive techniques is supported by these findings.
    The Journal of thoracic and cardiovascular surgery 02/2007; 133(1):21-8. DOI:10.1016/j.jtcvs.2006.07.037 · 3.99 Impact Factor