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Chapter 2
•
Cardiovascular Care
65
HANDS ON
Non-IABP Percutaneous
Mechanical Circulatory
Assist Devices
•
These devices have differing
names: percutaneous ventricular
assist devices (VADs),
percutaneous ventricular
support devices, percutaneous
mechanical circulatory assist
devices, percutaneous mechanical
circulatory support devices, and
percutaneous VADs.
•
Left ventricle to aorta assist
devices—The Impella System
•
Left atrial to aorta assist
devices—The Tandem Heart
Timing IABP Counterpulsation
Arterial
pressure
(mm Hg)
100
90
80
70
60
50
KEY:
Peak systolic pressure
Dicrotic notch
Peak diastolic pressure
End-diastolic pressure
U N A S S I S T E D
A S S I S T E D ( W I T H I A B P )
Left VAD
A completely implanted left VAD is shown here.
Shoulder strap
Aorta
Left ventricle
Diaphragm
External battery
pack
Blood pump
Access device
•
IABP counterpulsation is
synchronized with either the
ECG or the arterial waveform.
Ideally, balloon inflation should
begin when the aortic valve
closes—at the dicrotic notch on
the arterial waveform. Deflation
should occur just before
diastole.
•
Timing of the counterpulsation
is crucial. Early inflation can
damage the aortic valve by
forcing it closed, whereas late
inflation permits most of the blood
emerging from the ventricle to
flow past the balloon, reducing
the pump’s effectiveness.
•
Late deflation may cause cardiac
arrest because it increases
the resistance to left ventricle
pumping. IABP counterpulsation
boosts peak diastolic pressure
and lowers peak systolic and end-
diastolic pressures.
Ventricular Assist Device
A VAD is an implantable device that
consists of a blood pump, cannulas,
and a pneumatic or electrical drive
console. The pump is synchronized
to the patient’s ECG and functions
as the heart’s ventricle. It decreases
the heart’s workload while increasing
cardiac output.
Pump Options
VADs are available as continuous flow
or pulsatile pumps. A continuous flow
pump fills continuously and returns
blood to the aorta at a constant rate.
A pulsatile pump may work in one of
two ways:
•
It may fill during systole and
pump blood into the aorta during
diastole.