Biomedical Engineering Reference
In-Depth Information
FIGURE 8-22
VADs grouped by
generation.
before the surgery, depended on his LVAD for 8 days in 1984 until a donor heart became
available (Baker, 2004).
The WorldHeart Novacor consists of an implanted, wearable pump about the size of
a human heart as well as a controller and battery pack, as shown in Figure 8-23. It has
exhibited good reliability and durability as attested to by the following statistics. Of the
more than 1700 recipients, 172 primarily BTT patients have been supported by the device
for more than 1 year, and of those 45 have been supported for more than 2 years, 24 for
more than 3 years, 11 for more than 4 years, and 1 for more than 6 years. Only 1.4% of
the pumps have needed replacement, and no patient deaths have been attributed to pump
failure.
Blood enters the Novacor pump via an inflow conduit (graft) through a large open-
ing cored into the patient's left ventricle. The low resistance of the passively filling pump
chamber presents a reduced load to the left ventricle, allowing the diseased heart to pump a
normal stroke volume with minimal effort. Once the pump chamber is full, the electrically
driven pump ejects blood through an outflow conduit into the arterial system, thereby sup-
porting the systemic circulation. The system is completely self-regulating, automatically
adjusting its beat rate and stroke volume in response to the patients changing circulatory
requirements.
The Novacor design uses two blood-sac pusher plates positioned at opposite sides
of the pump body. Electromagnetic actuators coupled to compliant linkages squeeze the
