HEALTH, 20 09, 1, 31-34
Published Online June 2009 in SciRes.
Connecting conduit-free and bypass circuit-less mini
LVADs eliminate the most likely sites of thrombosis
Kun-Xi Qian1
1Institute of BME, Jiangsu University, Zhenjiang, China.
Received 9 April 2009; revised 5 May 2009; accepted 7 May 2009.
All existing left ventricular assist devices
(LVADs) need inlet and outlet connecting con-
duits and the assist pumping blood flows
through the bypass circuit from left ventricle to
aorta. It will result in some most likely sites of
thrombosis and brings about physiological dis-
turbance to natural circulation, as well as addi-
tional need for anatomic occupation in chest.
The author developed a trans-apical and
cross-valvular intra-ventricular axial pump and
an aortic valvo- pump to solve these problems.
The intra-ventricular pump weighing 53g has a
length of 115mm and its largest O.D. is 13mm.
The motor is 60mm long and the pump 55mm. In
both sides of motor, specially designed needle
bearings are devised and a purge system keeps
the motor together with bearings working in sa-
line. The device is inserted into the ventricle by
trans-apex and then into the aorta by
cross-valve. It is used for recovery therapy or
bridge to transplantation. The bearing-less
valvo-pumps have an outer diameter of 21mm,
23mm or 25mm for patients with different body
weights. The weight of the devices is 27g, 31g or
40g respectively. Used for destination therapy it
can be easily sewed onto the aortic valve annu-
lus, delivers blood from ventricle to aorta di-
rectly. These two novel mini LVADs may reduce
thrombosis risk in clinical applications.
Keywords: mini lvads; physiological disturbance;
anatomic occupation; recovery or destination thera-
The clinical available LVADs both in diaphragm or ro-
tary type all have inlet and outlet connecting conduits
and the device with its conduits form a bypass circuit
(Figure 1). It has been considered that thrombus is the
most favorite to be formed in these conduits and circuit,
especially near their connecting sites; and the bypass
flow will disturb the flow patterns in ventricle as well as
in aorta which increases the danger of thrombosis.
Figure 1. Diaphragm type (upper) and rotary type (lower) of
LVADs on the patients. Their inlet and outlet connecting con-
duits together with the device form a bypass circuit, resulting in
several most likely sites of thrombosis, bringing about physio-
logical disturbance to natural circulation as well as additional
need for anatomic occupation in the chest of the patients.
32 K. X. Qian / HEALTH 1 (2009) 31-34
SciRes Copyright © 2009 HEALTH
Furthermore, this bypass circuit including connecting
conduits and the LVAD itself needs additional anatomic
occupation and that is hardly possible to be implanted in
the patients’ chest. Therefore, most available LVADs
should remain outside of the body of the patients, in-
creasing the danger of infection.
Because the difficulties in design and manufacture of
mini LVADs, other investigators have long since not suc-
ceeded in developing a fully implantable intra- ventricular
pump without inlet and outlet conduits and without by-
pass circuit [1,2,3] but their idea leads the author to de-
velop a trans-apical and cross-valvular intra-ventricular
axial pump and an aortic valvo-pump finally. These de-
vices generally solved the problems of thrombus forma-
tion outside the pump in left ventricular assist.
The device has a motor and a pump entirely contained
within one cannula (Figure 2(a)). The motor has a stator
coil with iron core and a rotor with 4-pole magnet; the
pump has an impeller and an outflow guide vane (Figure
2(b)). The motor part has 60mm length and 13mm di-
ameter; the pump part has 55mm length and 11mm di-
ameter. Therefore, the total length of the device is 115
mm. The total weight of the device is 53 g. The motor
uses rolling bearing with 8 needles on each side of the
rotor magnets. A special purge system is devised for the
infusion of saline mixed with heparin through bearing to
the pump inlet. Thus the bearing needles work in saline
and neither mechanical wear nor thrombus formation
along the bearing will occur.
In its hemo-dynamic testing, the pump can produce a
flow of 10 l/min with 80 mmHg pressure increase, at
15,000 rpm rotating speed of the pump (Figure 2(c)). At
zero flow rate corresponding to diastolic period of the
heart, the pump can maintain aortic blood pressure over
80 mmHg at 12500rpm rotating speed.
This novel pump can be inserted into the ventricle via
apex and extended into the aorta across the aortic valve.
Thus it needs no inlet and outlet connecting conduits and
no bypass circuits, delivers blood directly from ventricle
to aorta without disturbance to natural circulation, re-
quires no anatomic occupation in the chest, and can be
quickly inserted in an emergency and easily removed
after recovery of natural heart. Therefore, this device is
suitable for recovery therapy.
Aortic valvo-pump (Figure 3(a)) delivers blood flow
also directly from ventricle to aorta and needs no inlet
and outlet connecting tubes too. Similarly, it needs no
bypass circuit, will not disturb the natural circulation,
and needs no additional anatomic occupation. The device
can be sewed onto the aortic valve annulus via sewing
ring (Figure 3(b)). It has a rotor and a stator, the
guide vane
inslet port
Figure 2. Trans-apical and cross-valvular intra-ventricular axial
pump (above) delivers the blood flow directly from ventricle to
aorta, without need for inlet and outlet tubes, without bypass
circuit, without physiologic disturbance to natural circulation,
without additional need for anatomic occupation. Specially
designed purge system and needle bearing (middle) enable the
motor and the pump to work in saline and hereby to achieve
excellent antithrombogenecity and durability. Bench testing
demonstrated the pump can deliver 10l/min flow against
80mmHg pressure at 15000rpm rotating speed (below).
purge systemmotor
K. X. Qian / HEALTH 1 (2009) 31-34 33
SciRes Copyright © 2009 HEALTH
Figure 3. Aortic valvo-pump (a) and its first animal experiment
(d). The pump can be sewed onto the aortic valve annulus by
sewing ring (b) without harm to adjacent tissues, cells and or-
gan functions, delivers blood directly from ventricle to aorta,
needs no inlet and outlet tubes, needs no additional anatomic
occupation, has no physiologic disturbance to natural circula-
tion. The bearing-less design with enclosed impeller (c) ensures
the rotor suspended in blood flow and thus the mechanical wear
will not occur in the device.
former has an enclosed impeller and driven magnets, the
latter consists of a motor coil with iron core and an out-
flow guide vane (Figure 3(c)). This bearing-less design
with enclosed impeller has advantages of no existence of
stasis and dead-water area in the pump, that has been
long since acknowledged to being favorite sites of co-
agulation and thrombus formation. The rotor has a gap of
0,25mm in radius with the stator, a back-flow of about
0,8l/min flows from outlet higher pressure area to inlet
lower pressure area via this gap; thereby, wash-out of the
gap and hydraulic suspension of the rotor will be
achieved during pumping (Figure 3(c)). The devices’
outer diameters are 21mm, 23mm and 25mm respec-
tively, weighing 27gram(inc. rotor 5g), 31gram (inc. ro-
tor 7g) and 40gram(inc. rotor 11g) separately. The labo-
ratory testing demonstrated that the rotating speed for
maintaining a diastolic pressure of 80mmHg at zero flow
rate should be 17500rpm, 15000rpm and 12500rpm cor-
respondingly, the largest flow at these same speeds will
be 5l/min, 7l/min and 10l/min relatively, with ca.
50mmHg pressure increase. Therefore, these three
pumps may meet with the hemo-dynamic requirements
of 40-60kg, 60-80kg and 80-100kg body weight patients.
The first in vivo trial exhibited that the 25mm valvo-
pump could be sewed onto the aortic valve annulus of
one 80kg body weight pig easily (Figure 3(d)), without
harm to adjacent cells, tissues and organ functions. A
mentioned above, the devices have no inlet and outlet
connecting tubes and no bypass circuit, occupy no addi-
tional anatomic space and deliver the blood directly from
ventricle to the aorta, having thus less physiologic dis-
turbance to the natural circulation.
The idea of trans-apical and cross-valvular intra- ven-
tricular axial pump and aortic valvo-pump existed before.
The contribution of this paper is minimizing the motor
dimension and weight without decreasing its output
torque so as to maintain the efficient hemo-dynamic ca-
pacity of the pump. This is a result of the author’s pro-
found investigation on motor miniaturization [4].
In this paper the author deals with the thrombosis
problem outside the pump in left ventricular assist pump.
For the same problem inside the pump, the author has
much more extensive studies before [5,6,7].
These new devices have to be further investigated in
animal experiments. The author searches cooperation
with other investigators all over the world.
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Eishi, A. Kawai, O. Tagusari, H. Niinami, T. Akimoto, C.
Nojiri, K. Tsuchiya, T. Mori, H. Iiyama, and M. Endo,
(1992) A miniature intraventricular axial flow blood pump
motor coil
uide vane
34 K. X. Qian / HEALTH 1 (2009) 31-34
SciRes Copyright © 2009 HEALTH
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