Page 115 - Biomedical Engineering and Design Handbook Volume 2, Applications

94 MEDICAL DEVICE DESIGN

common complications seen during balloon pump support are vascular in nature, with limb
ischemia remaining the dominant problem (Busch et al., 1997). Other vascular complications
include bleeding and hematoma formation (Busch et al., 1997), aortic dissection (Busch et al.,
1997), embolism (Kumbasar et al., 1999), and rare events such as paraplegia due to spinal infarc-
tion (Hurle et al., 1997). Nonvascular complications include infection and mechanical or device-
related failures such as balloon rupture (Stavarski, 1996; Scholz et a1., 1998). Factors increasing
the risk of complications vary among different studies, but generally include peripheral vascular
disease, diabetes, female sex (Busch et al., 1997; Arafa et al., 1999; Cohen et al., 2000), small
patient size (BSA <l.65 m ) and advanced age (*75 years) (Ferguson et al., 2001). Results have
2
been mixed as to whether smaller catheter sizes and shorter periods of support can limit complica-
tion rates (Scholz et al., 1998; Arafa et al., 1999; Cohen et al., 2000) but a recent comparison of
8 Fr to 9.5 Fr IAB catheters revealed a lower rate of limb ischemia with smaller catheters (Cohen
et al., 2002).
Complications associated with TAH and VAD use can be divided into those experienced shortly
after implantation and events occurring later in the implant period. Postoperatively, the major con-
cerns include hemorrhage, and in the case of isolated left ventricular VAD support, right heart
failure or dysfunction, resulting in low pump outputs (Heath and Dickstein, 2000). Bleeding
management can include infusion of blood products, but in some cases surgical intervention may be
required. Right heart performance can often be improved through reduction of the pulmonary vas-
cular resistance with various drug infusions and inhalants (Heath and Dickstein, 2000). Long-term
VAD complications include infection, thromboembolism, and device failure (Kasirajan et al., 2000);
the latter was found to be the second most common cause of death during the REMATCH trial and
led to design changes and improvements (Rose et al., 2001). Infection can involve the percutaneous
connections of the pump, the pump interior or exterior surfaces, or can be systemic in nature
(Holman et al.,1999). Management includes antibiotics, debridement, and in severe cases involving
the pump pocket, removal or replacement of the pump (Holman et a1., 1999; Kasirajan et al., 2000).
Thromboembolism is limited through the use of anticoagulant medications such as heparin periop-
eratively and warfarin in the long term, although not all pumps require such therapy (Kasirajan
et al., 2000). Antiplatelet regimens, such as aspirin, are also used to prevent emboli (Kasirajan et al.,
2000).

3.8.5 Future Trends

Improvements in electronics and software development will undoubtedly be incorporated into future
IABP designs. Closed loop designs requiring minimal operator intervention have been investigated
(Kantrowitz et al., 1992) and results suggest that independent device control could be achieved.
Catheters coated with antithrombotic agents have been shown to reduce thrombosis and thrombotic
deposition even in immobile (noninflating) balloons when compared to similar uncoated designs
(Lazar et al., 1999; Mueller et al., 1999). Hydrophilic coatings have also been placed on balloon
catheters, providing a 72 percent reduction in ischemic vascular complications when modified
devices are used (Winters et al., 1999). Antibiotic coatings for indwelling catheters could be used to
coat intra-aortic balloons if such treatment is proven to be efficacious.
Recent animal data suggest a combination of percutaneous cardiac therapies (VAD and IABP)
could produce better outcomes (Sauren et al., 2007) and eliminate the need for a surgical implanta-
tion in critical patients. As cardiac support becomes more mainstream, combination products such as
the iPulse console (Abiomed Inc., Danvers, MA) are being developed, which can provide cardiac
support through either an IAB or artificial external ventricles.
In contrast to the evolution of the IABP, VADs are undergoing a revolution in design and indica-
tions for use. The current rush of devices entering clinical trials show improvements in a variety of
areas, including power transmission (transcutaneous vs. percutaneous), method of propulsion (elec-
tric centrifugal and axial flow vs. pneumatic pulsatile), and size reduction. The largest obstacle to the
widespread use of these devices on a scale commensurate with heart disease are the complications
that face these patients over the long term. The most critical future developments will focus on