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J Thorac Cardiovasc Surg 2004;127:1743-1750
© 2004 The American Association for Thoracic Surgery

Cardiopulmonary support and physiology

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

^a Departments of Cardio-Thoracic Surgery and LBI of Cardio-Surgical Research, , Vienna, Austria
^b Biomedical Engineering and Physics,, Vienna, Austria
^c Biomedical Research,, Vienna, Austria
^d Cardiovascular Anesthesiology, University of Vienna, Austria

Received for publication May 26, 2003; revisions received July 7, 2003; accepted for publication September 9, 2003.

^* Address for reprints: Heinrich Schima, PhD, Institute of Biomedical Research, University of Vienna, Waehringer Guertel 18-1Q, A-1090 Vienna, Austria
heinrich.schima{at}akh-wien.ac.at

BACKGROUND: 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.

METHODS AND RESULTS: 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.

CONCLUSION: 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.

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