Page 654 - Cardiac Nursing

630 P AR T IV / Pathophysiology and Management of Heart Disease

is implanted. Blood is returned to the ascending aorta through an-
other cannula. The device also uses inflow and outflow tissue
valves. Ejection is triggered by a fixed rate, changes in the velocity
of filling, or in a fill-to-empty mode. When the blood sac is filled,
or when the trigger is recognized, two electrically powered pusher
plates compress the blood sac, which is located between the two
plates. Ejection occurs when the sac is compressed. 37 The major
advantages are the implantability, which reduces infectious risk,
and the ability of the patient to be ambulatory and possibly dis-
charged from the hospital. Figure 26-9 illustrates the appearance
of the device. Patients wear a controller on either on a belt or in a
vest, and carry two batteries with them. One battery serves as a re-
serve supply when the patient switches from AC power to battery
operation, and vice versa. The other primary battery pack can sup-
ply power for up to 5 hours, allowing the patient freedom from a
tethered set-up. Figure 26-10 shows the first patient in the United
States to receive the wearable system.
The HeartMate vented electric system (Thoratec, Pleasanton,
CA) is also designed for long-term use. The HeartMate pump is
electrically driven, with a controller and battery pack system sim-
ilar to those of the Novacor pump. Ejection occurs as a result of
compression of the blood sac by a single, motor-driven pusher n Figure 26-10 A patient with the wearable Novacor left ventric-
plate. 38 Both the Novacor and HeartMate systems can support ular assist system. The patient carries a 5-hour battery pack on a spe-
cially designed belt, allowing him to be totally untethered to a heavy
operating console, as with many other types of devices. This patient
is shown at approximately 3 weeks after implantation and is waiting
for a donor heart.

patients for extended periods with a relatively low risk of throm-
boembolism or mechanical problems. They can be used to sup-
port patients awaiting heart transplantation, and because they are
portable, allow patients to be ambulatory and live in the commu-
nity. This device was evaluated in the REMATCH trial, which
randomized end-stage, NYHA class IV patients who were not el-
igible for transplantation to LVAD or optimal medical therapy. It
revealed a higher survival (23% vs. 8%) and improved quality of
life for patients randomized to LVAD. However there were ad-
verse events, such as infection, bleeding, and device malfunction
(which was 35% at 2 years). 39
The HeartMate II (Thoratec, Pleasanton, CA) device is a con-
tinuous axial flow device. Unlike the pulsatile devices, which need
a compliance chamber, the HeartMate II is much smaller but also
requires somewhat higher levels of anticoagulation. Figure 26-11
depicts the device. The inflow cannula is placed in the LV apex
and the outflow cannula is anastamosed to the ascending aorta.
The VAD pump is placed in the abdominal or peritoneal cavity,
with a percutaneous lead carrying the electrical cable to an elec-
tronic controller and battery packs, which are worn on a belt and
shoulder holster. This device was recently evaluated in 133 pa-
tients as a bridge to transplant. Survival was 75% at 6 months and
68% at 1 year. Functional status and quality of life were improved
when measured at 3 months. Bleeding, stroke, right heart failure,
and percutaneous lead infection were seen, but rates compared fa-
vorably with those reported for pulsatile flow pumps. However,
two patients sustained HeartMate II pump thrombosis. 40
n Figure 26-9 Illustration of the Novacor left ventricular assist de-
vice shows the design of the implanted system. Power is transmitted Other Continuous Flow Devices
through a percutaneous lead to the implanted pump. The patient ei-
ther wears portable batteries or can be connected to an AC power Several promising devices are under active investigation but not
source when at rest. (Courtesy of World Heart Inc. Oakland, CA.) yet FDA approved: the MicroMed-DeBakey VAD (MicroMed