Page 97 - Biomedical Engineering and Design Handbook Volume 2, Applications

76 MEDICAL DEVICE DESIGN

suffer from electrical interference due to extracardiac muscle activity or electromagnetic interference
(EMI), which can cause pacemaker malfunction (Morley-Davies and Cobbe, 1997; Mitrani et al.,
1999). Because of this shortcoming, unipolar pacemaker leads are incompatible with implantable
defibrillator devices (Mitrani et al., 1999).
Among common lead-insulation materials, polyurethane 80A, a polyetherurethane (PEU), is known
to suffer from higher rates of degradation and failure and is responsible for a large proportion of lead
malfunctions (Tyers et al., 1997; Crossley, 2000). The PEU 80A degrades via three mechanisms:
environmental stress cracking, metal-ion–catalyzed oxidation, and calcification (Schmidt and Stotts,
1998; Crossley, 2000). The use of alternate polymers such as ETFE, polycarbonateurethanes, and
more durable formulations of PEU are being used to overcome the limitations of PEU 80A (Schmidt
and Stotts, 1998). These materials do not suffer from the same mechanisms of failure, or at least
exhibit increased resilience to degradation via those pathways (Schmidt and Stotts, 1998).

3.4.5 Future Developments
Up to a fifth of all patients with implanted cardioverter-defibrillators have also demonstrated a pace-
maker requirement (Pinski and Trohman, 2000). The dual requirement for pacemakers and ICDs has led
to the development of units combining the two technologies on an advanced level, complete with dual
chamber activity (Morris et al., 1999; Pinski and Trohman, 2000). The benefits of a combined EP device
is the elimination of separate costs for each system and potential harmful interactions between pacemakers
and ICDs, including a reduction in the number of leads (Morris et al., 1999; Pinski and Trohman, 2000).
Steady improvements in microelectronics and software will further expand the capabilities of EP
devices toward the analysis and treatment of other pathologic heart conditions currently on the fringe
of electrophysiology, such as atrial arrhythmias (Morris et al., 1999; Boriani et al., 2007). These
enhanced units will monitor a wide variety of patient and system data to optimize performance to a
greater extent than current systems. There is room for improvement in power technology and lead
design, as well as improved algorithms able to perform advanced rhythm discrimination (Morris et al.,
1999). As suggested in the literature, the development of a universal programmer capable of interfac-
ing with any EP device would be a significant advance both in cost and ease of use for providers now
faced with a multitude of different programming units (Kusumoto and Goldschlager, 1996). Improved
and simplified programmer interfaces would also benefit the implanting physicians, who are now
overwhelmed with feature-heavy and highly adjustable systems (Morris et al., 1999).

3.5 ARTIFICIAL VASCULAR GRAFTS

3.5.1 Market Size
The market for artificial vascular grafts is in a state of transition due to technological and clinical
advancements. The advent of successful endovascular therapies (angioplasty, stenting, stent-grafting,
etc.) has led to a shift toward less-invasive interventions for vascular repair and reconstruction, with
a concomitant reduction in traditional open excision and replacement. Although changes in proce-
dure classification limit direct comparison, data from nonfederal acute-care hospitals estimate that
the total number of blood vessel resections with graft placement declined from at least 66,000 in
1997 (Owings and Lawrence, 1999) to 35,000 in 2005 (DeFrances et al., 2007), with an even greater
shift toward endovascular repair of the abdominal aorta, once the dominant area for artificial graft
usage. When less invasive approaches are unsuccessful or impractical, the limited availability of bio-
logic tissues with the proper size and length for the replacement of large vessels often necessitates
the use of an artificial vascular prostheses (Brewster, 2000).
In contrast to the technological changes identified above, prioritization of arteriovenous fistula
(AVF) creation through various clinical initiatives is reducing the need for vascular access grafts in
hemodialysis (HD) treatment, a major area for the use of artificial vascular prosthesis. Since 1991,
the percentage of prevalent (existing) HD patients receiving treatment through an artificial graft has
fallen more than half to around 35 percent in 2004 (US Renal Data System, 2007). Through the