Page 109 - Biomedical Engineering and Design Handbook Volume 2, Applications

88 MEDICAL DEVICE DESIGN

3.7.5 Future Trends
Improvements in catheter design are likely to be evolutionary, representing progress in materials,
surface treatments, and functional monitoring as catheters are expected to perform for increasingly
extended periods. Surfaces with active antithrombotic and antimicrobial activity will continue to be
developed and evaluated as will surfaces designed to minimize protein and cellular adhesion. The
risk of reduced reimbursement in light of the Center for Medicare and Medicaid’s new policies
regarding hospital-acquired infections will spur and accelerate development of low-cost, low-risk
catheter designs.

3.8 CIRCULATORY SUPPORT DEVICES

3.8.1 Market Size
Heart disease remains the leading cause of death in the United States (Rosamond et al., 2008) and
worldwide (Mathers and Loncar, 2006). The devices discussed in the current section provide cardiac
support for a spectrum of indications and durations, spanning damage due to an acute myocardial
infarction to the long-term decline that accompanies chronic congestive heart failure. The section
excludes therapies such as extracorporeal membrane oxygenation and the use of cardiopulmonary
bypass pumps as a support method since these are described in the following section on artificial
lungs.
The most commonly used means of mechanical circulatory support is the intra-aortic balloon
pump (IABP). In 1990, it was estimated that IABP therapy was provided to 70,000 patients annually
(Kantrowitz, 1990); recent CDC data indicate at least 40,000 patients were supported via IABP in
the United States in 2005 (DeFrances et al., 2007). As described below, the IABP can provide only
limited cardiovascular support as its effects are limited to pressure unloading of the ventricle, in con-
trast to artificial hearts and ventricular assist devices, which provide volume unloading (Mehlhorn
et al., 1999). To be effective, the IABP requires that the patient maintains some native pumping
capacity as the movement of blood due to the balloon is minimal.
Unlike the IABP, ventricular assist devices (VADs) and total artificial hearts (TAHs) aid or
replace the function of the native organ for an extended period of time. A cardiac transplant is the
last resort for many patients who fail other medical and surgical therapy. Unfortunately, donor organs
remain limited, creating the market for both temporary and extended cardiac support. It has been
estimated that up to 100,000 patients in the United States alone would benefit from the implantation
of a long-term cardiac support device, with between 5000 and 10,000 requiring biventricular support
(Willman et al., 1999). However, existing designs are imperfect due to mechanical and biocompati-
bility limitations, falling far short of meeting the clinical need for mechanical support. These inher-
ent limitations continue to spur development of novel approaches to chronic cardiac support.

3.8.2 Indications
The indications for IABP placement have changed over the years, as has the insertion method
(Torchiana et al., 1997; Mehlhorn et al., 1999). Current indications can be divided into hemodynamic
indications, due to cardiogenic shock, congestive heart failure, and hypotension, which are charac-
terized by low cardiac output and systemic perfusion, or ischemic indications such as those caused
by coronary artery disease, which result in poor cardiac perfusion and dysfunction (Torchiana et al.,
1997). Current trends indicate an increased use of IABP support for ischemia in patients undergoing
percutaneous cardiac therapies such as balloon angioplasty, with a dramatic shift from almost 100 percent
surgical implantation to percutaneous implantation in 95 percent of cases (Torchiana et al., 1997;
Ferguson et al., 2001). The number of IABPs placed for ischemic indications now exceeds those
placed for hemodynamic concerns, with the trend for hemodynamic causes staying relatively flat
(Torchiana et al., 1997).