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Ann Thorac Surg 2005;79:1383
© 2005 The Society of Thoracic Surgeons

New technology

INVITED COMMENTARY

William L. Holman, MD

Department of Surgery, University of Alabama at Birmingham, 1530 3rd Ave S, ZRB 719, Birmingham, AL 35294–0007, USA

wholman{at}its.uab.edu

Recent Food and Drug Administration approval for the CardioWest total artificial heart (TAH) (SynCardia Systems, Tucson, AZ) and ongoing investigational use of the AbioCor TAH (Abiomed, Danvers, MA) are important developmental milestones for this type of mechanical circulatory support. There are advantages that TAHs have over ventricular assist devices (VADs), but there are also two important challenges that are inherent to the TAH concept. First, a TAH must be highly reliable, as the patient's native heart is removed; and second, it must fit within the relatively confined space (especially the anteriorposterior dimension) of the human chest. Schenk and associates address the second of these problems with a novel TAH that is smaller than previous designs, but is able to deliver relatively high flows by rapid cycling.

Rapid cycling to achieve adequate flow is an intriguing concept that raises several questions. First, what is the rate of pressure change over time (dP/dt) for this pump, which uses bioprosthetic valves? Figure 8 indicates that the pump's dP/dt is high relative to the native bovine heart. Prior experience with the HeartMate vented electrical left VAD (Thoratec, Pleasanton, CA) showed the vulnerability of bioprosthetic valves to premature failure as a result of high dP/dt, and suggests that valve durability in the MagScrew TAH may be limited. Second, the cycling of this pump is anywhere from 2 to 3 times more rapid than in previous TAHs, and rapid cycling may produce wear that is worse than expected because of increased velocity of movement in pump components. Are there any special design considerations to ensure that the durability of this device is similar to devices that operate at a slower rate? The trade-off between size and durability is an especially important consideration in a TAH, as device failure typically equates with patient death. Have there been any computational fluid dynamic or flow visualization studies of this pump when it is run at a rapid rate? The patterns of flow may be considerably different than those for a pump cycled at a slower rate, which may favorably or adversely affect thrombus formation depending on the changes produced by rapid cycling.

The pump designers chose to have a static compensation mechanism for left to right shunting, and it worked well in these bovine implants. However, there is presumably a maximum shunt flow beyond which there is net accumulation of blood volume in the pulmonary circulation. If this occurs, is there any way to deal with the problem? Will it be possible to modify this pump to account for left to right shunting in a dynamic rather than static fashion?

Finally, does the rapid cycling of the pump increase power requirements? If that is the case, the time that the pump will run without changing batteries will be diminished or heavier batteries will be needed. Both of these solutions decrease patient mobility. In summary, the authors have taken the first step toward solving an important problem with the use of the TAH in humans. The small pump they have designed has impressive capacity for generating flow and pulse pressure. There are challenges inherent in their approach, but if this group is able to successfully address the problems associated with a rapidly cycling artificial heart, they will have substantially broadened the range of patients who can be considered for circulatory support using a TAH.




This article has been cited by other articles:


Home page
 Ann. Thorac. Surg.Home page
S. Schenk, S. Weber, W. A. Smith, and K. Fukamachi
MagScrew Total Artificial Heart
Ann. Thorac. Surg., June 1, 2006; 81(6): 2338 - 2339.
[Full Text] [PDF]

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